Abstracts - Centre for Quantum Technologiesqcmc.quantumlah.org/Abstracts_160701.pdf · Spectrally resolved white-light quantum interferometry for high-accuracy chromatic dispersion

Abstracts

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Scientific Programme Monday (4 July)

08:30 Registration 09:00 Carl Caves, University of New Mexico

Two Studies in Interferometry: Practical Metrology and Imperfect Boson Sampling

09:30 Klaus Molmer, University of Aarhus, Denmark Quantum trajectories and past quantum states

10:00 Mete Atature, University of Cambridge Entangling independent quantum-dot spins

10:30 Coffee/Tea Break 11:00 Alessandro Cere, Centre for Quantum Technologies, NUS

Time-resolved Scattering of a Single Photon by a Single Atom 11:20 Leonid Krivitsky, Data Storage Institute

Infrared Spectroscopy with Visible Light 11:40 Florian Kaiser, Université Nice Sophia Antipolis

Spectrally resolved white-light quantum interferometry for high-accuracy chromatic dispersion measurements

12:00 Paul Kwiat, University of Illinois at Urbana-Champaign Applications of HyperEntanglement

12:30 Lunch 14:00 Matthew Pusey, Perimeter Institute for Theoretical Physics

Direct experimental reconstruction of the Bloch sphere 14:30 Katharina Schwaiger, University of Innsbruck

Operational multipartite entanglement measures 15:00 Magdalena Zych, University of Queensland

Entanglement of temporal order from quantum theory and gravity

15:30 Coffee/Tea Break 16:00 Michael Hall, Griffith University

A Many-Interacting-Worlds Approach To Quantum Mechanics 16:30 Howard Wiseman, Griffith University

Experimental Nonlocal and Surreal Bohmian Trajectories 17:30 Poster Session 1

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Tuesday (5 July) 08:30 Registration 09:00 Andrew Doherty, University of Sydney

Quantum dot quantum computing 09:30 Michelle Simmons, University of New South Wales

Quantum Computing in Silicon with Donors 10:00 Paola Cappellaro, Massachusetts Institute of Technology

Coherent feedback of a single qubit in diamond 10:30 Coffee/Tea Break 11:00 Anirudh Narla, Department of Applied Physics, Yale

University Concurrent Remote Entanglement of Transmon Qubits using Flying Photons

11:20 Sen Yang, 3. Physikalisches Institut, Uni Stuttgart High fidelity transfer and storage of photon states in a single nuclear spin

11:40 Bill Munro, NTT Basic Research Laboratories Quantum State Engineering using Hybridization

12:00 Adam Kaufman, Harvard University Title to be advised

12:30 Lunch 14:00 Steve Flammia, The University of Sydney

Comparing Experiments to the Fault-Tolerance Threshold 14:30 Qiang Zhang, University of Science and Technology of

China, Shanghai Recent experimental progress in quantum communication

15:00 Elham Kashefi, University of Edinburgh Secure Multi-party Computing (From Classical to Quantum - From Linearity to Nonlinearity)

15:30 Coffee/Tea Break 16:00 Patrick Coles, University of Waterloo

Unstructured quantum key distribution 16:20 Paolo Villoresi, Università degli Studi di Padova

Experimental Quantum Communications in Space exploiting temporal and polarization degrees of freedom

16:40 Daniel Oblak, University of Calgary Quantum teleportation over deployed fibres and applications to quantum networks

17:00 Yi-Cong Zheng, Centre of Quantum Technologies, NUS Fault-tolerant Holonomic Quantum Computation in Surface Codes

17:30 Poster Session 2

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Wednesday (6 July) 08:30 Registration 09:00 Ronald Hanson, Delft University of Technology

From the first loophole-free Bell test to a quantum Internet 09:30 Marissa Giustina, University of Vienna

Significant-loophole-free test of local realism with entangled photons

10:00 Krister Shalm, NIST A strong loophole-free test of Local Realism

10:30 Coffee/Tea Break 11:00 Harald Weinfurter, University of Munich

Event-ready loophole free Bell test using heralded atom-atom entanglement

11:20 Roman Schmied, University of Basel Bell correlations in a Bose-Einstein condensate

11:50 Yvonne Gao, Yale University A Schrodinger Cat Living in Two Boxes

12:10 Hanna Le Jeannic, Laboratoire Kastler Brossel Large-amplitude squeezed optical Schrödinger cat states with minimized non-Gaussian operational cost

12:30 Lunch 14:00 Alex Bocharov, Microsoft

Qomputer Science at Microsoft Research 14:30 Julian Kelly, Google

Industrializing qubits through automation 15:00 Coffee/Tea Break 15:30 Bill Munro, NTT

Quantum @ NTT 16:00 Colin William, Dwave

D-Wave's Approach to Quantum Computing: 1000-qubits and Counting!

17:00 Visit to CQT

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Thursday (7 July) 08:30 Registration 09:00 Yasunobu Nakamura, University of Tokyo

Hybrid quantum systems using magnons in a ferromagnetic crystal

09:30 Hugues De Riedmatten, ICFO-The Institute of Photonic Sciences Quantum Correlation between photons and single spin-waves in a solid-state environment

10:00 Sungkun Hong, University of Vienna Towards a photon-phonon quantum interface

10:30 Coffee/Tea Break 11:00 Michael Vanner, University of Oxford

Generation of Mechanical Interference Fringes by Multi-Photon Quantum Measurement

11:20 Neil Corzo, Laboratoire Kastler Brossel Combining 1D Nanoscale Waveguides and Cold Atoms

11:50 Michal Oszmaniec, ICFO (Barcelona) Random symmetric states for robust quantum metrology

12:10 Jörg Schmiedmayer, TU-Wien Determining the essential components of a quantum many-body system from experiment

12:30 Lunch 14:00 Tim Ralph, University of Queensland

Undoing the effect of loss on entanglement 14:20 Jianwei Wang, University of Bristol

Experimental realisation of a variational ground state solver on a photonic chip

14:40 Stefanie Barz, University of Oxford Distinguishability in three-photon scattering

15:00 Sara Ducci, Paris Diderot University AlGaAs photonic devices: from quantum state generation to quantum communications

15:30 Maciej Lewenstein, ICFO Separability Revisited

Free afternoon

19:30 Conference Dinner @ Keppel Club

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Friday (8 July) 09:00 Registration

09:30 Rainer Blatt, Universtität Innsbruck Quantum Information Processing with Trapped Ions and Photons

10:30 Coffee/Tea Break

11:00 Arno Rauschenbeutel, Vienna University of Technology Programmable integrated optical circulator controlled by a single spin-polarized atom

11:30 Chao-Yang Lu, University of Science and Technology of China, Hefei Creating perfect single photons for the demonstration of quantum supremacy

12:00 David DiVincenzo, RWTH Aachen University Longitudinal Coupling: Key to Scalable Qubit Layouts?

12:30 Closing

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Poster List The poster sessions will take place on 4 and 5 July (Monday and Tuesday) at 5:30pm. There will be Poster Awards. Please use the voting card included in the Welcome Pack to vote for your favorite poster at the end of the poster session.

Poster session I – Monday (4 July)

P1-3 - Entanglement measure for composite systems of indistinguishable particles Janusz Grabowski

P1-4 - Heralded Measurement-Device-Independent Quantum Key Distribution with Vector Vortex Beams Chen Dong, Shang-Hong Zhao and Shutao Li

P1-5 - Quantum Coherence Sets The Quantum Speed Limit For Mixed States Debasis Mondal, Chandan Datta and Sk Sazim

P1-7 - Pushing single photon counting technology towards better Size, Weight and Power (SWAP) performance. Rakhitha Chandrasekara, Zhongkan Tang, Yue Chuan Tan, Kadir Durak, Cliff Cheng and Alexander Ling

P1-8 - Temporal imaging with squeezed light Mikhail Kolobov and Giuseppe Patera

P1-10 - Quantum key distribution with leaky devices Marcos Curty, Kiyoshi Tamaki and Marco Lucamarini.

P1-11 - Survivor! Analysis of a photon pair source recovered intact from a catastropic launch failure. Tang Zhongkan Xavier, Alexander Ling, Rakhitha Chandrasekara, Yue Chuan Tan and Cliff Cheng

P1-12 - Semiclassical Theory of Superresolution for Two Incoherent Optical Point Sources Mankei Tsang, Ranjith Nair and Xiao-Ming Lu

P1-13 - Quantum State Smoothing Howard Wiseman and Ivonne Guevara

P1-15 - Electronic and spin properties of Si vacancy in SiC Moein Najafi Ivaki and Mohammad Ali Vesaghi

P1-17 - Optimal two-mode attack against two-way continuous-variable quantum key distribution Yichen Zhang, Zhengyu Li, Yijia Zhao, Song Yu and Hong Guo

P1-18 - Measurement-based Formulation of Quantum Heat Engine Masahito Hayashi and Hiroyasu Tajima

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P1-19 - Development of single photon source using Silicon-Vacancy(SiV) nano-diamond Hong Kee Suk, Bae In-Ho and Lee Dong-Hoon

P1-21 - Inhibition of ground-state superradiance and light-matter decoupling in circuit QED Zeliang Xiang, Tuomas Jaako and Peter Rabl

P1-22 - Steering Bell-diagonal states Quan Quan

P1-23 - Suppression law of quantum states in a 3D photonic fast Fourier transform chip Niko Viggianiello

P1-28 - Quantum dot based simultaneous classical logic gates Ronny A. Christin and Duncan L. MacFarlane

P1-29 - Error probability in quantum-dot based quantum circuits Ronny A. Christin and Duncan L. MacFarlane

P1-30 - Measurement-dependent locality with non-i.i.d. measurements Ernest Y.-Z. Tan, Yu Cai and Valerio Scarani

P1-32 - Weiss-Weinstein Error Bounds for Quantum Parameter Estimation Xiao-Ming Lu and Mankei Tsang

P1-33 - Quantum state preparation: the untold story Holger F. Hofmann

P1-34 - Multi-photon interference explained by the action of optical phase shifts Holger F. Hofmann, Keito Hibino, Kazuya Fujiwara and Jun-Yi Wu

P1-35 - Atoms as quantum beam-splitters in waveguide QED Alexandre Roulet, Pierre-Olivier Guimond, Jibo Dai, Huy Nguyen Le and Valerio Scarani

P1-36 - Robust H∞ Estimation for Linear Uncertain Quantum Systems Shibdas Roy and Ian Petersen

P1-37 - Two qubit near-field microwave gates on 43Ca+ James Tarlton, Martin Sepiol, Jochen Wolf, Thomas Harty, Christopher Ballance, Diana Craik, Vera Schafer, Keshav Thirumalai, Laurent Stephenson, Andrew Steane and David Lucas

P1-39 - Protecting quantum discord from amplitude damping decoherence via weak measurement and its reversal Yong-Su Kim, Jiwon Yune, Kang-Hee Hong, Hyang-Tag Lim, Jong-Chan Lee, Osung Kwon, Sang-Wook Han, Sung Moon and Yoon-Ho Kim

P1-40 - Experimental demonstration of efficient superdense coding in the presence of non-Markovian noise Bi-Heng Liu, Xiao-Min Hu, Yun-Feng Huang, Chuan-Feng Li, Guang-Can Guo, Sabrina Maniscalco and Jyrki Piilo

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P1-41 - An analysis of the statistics of multi-photon interference Kazuya Fujiwara and Holger F. Hofmann

P1-43 - Phase-encoded measurement device independent quantum key distribution without a shared reference frame Ying Sun and Shang-Hong Zhao

P1-44 - Unitary Estimation with Resource Constraints Masahito Hayashi, Sai Vinjanampathy and Leong Chuan Kwek

P1-45 - Experimental Tests of Gravitational Decoherence Nathan Mcmahon and Gerard Milburn

P1-46 - Time multiplexing toward indistinguishable and deterministic single-photon generation Fumihiro Kaneda and Paul Kwiat

P1-48 - All--‐Semiconductor Quantum Repeater Device Danny Kim, Andrey Kiselev, Richard Ross, Matthew Rakher, Cody Jones and Thaddeus Ladd

P1-49 - Surface effects on the coherence of superconducting qubits Yiwen Chu, Christopher Axline, Chen Wang, Teresa Brecht, Yvonne Gao, Luigi Frunzio, Michel Devoret and Robert Schoelkopf

P1-50 - Optical properties of an atomic ensemble coupled to a band edge of a photonic crystal waveguide Ewan Munro, Leong Chuan Kwek and Darrick Chang

P1-51 - Practical Quantum Retrieval Games Juan Miguel Arrazola, Markos Karasamanis and Norbert Lutkenhaus

P1-52 - Non-local games and optimal steering at the boundary of the quantum set Yi-Zheng Zhen, Koon Tong Goh, Yu-Lin Zheng, Wen-Fei Cao, Xingyao Wu, Kai Chen and Valerio Scarani

P1-53 - Multiparty Quantum Signature Schemes Juan Miguel Arrazola, Petros Wallden and Erika Andersson

P1-54 - A scheme for estimating accidental coincidence rates between saturated single photon detectors: the effective duty cycle James Grieve, Rakhitha Chandrasekara, Zhongkan Tang, Cliff Cheng and Alexander Ling

P1-56 - Highly confining direct written waveguides for integrated quantum photonics James Grieve, Bo Xue Tan and Alexander Ling

P1-57 - Engineering high brightness and high efficiency in downconversion sources Brigitta Septriani, James Grieve, Alexander Ling and Kadir Durak

P1-58 - Multiphoton entanglement from single photon sources Jun-Yi Wu and Holger F. Hofmann

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P1-59 - Optical Resources and the Maxwell Demon Angeline Shu, Jibo Dai and Valerio Scarani

P1-60 - Full reconstruction of a 14-qubit state within 4 hours Zhibo Hou and Guo-Yong Xiang

P1-61 - Scalable quantum router architecture with code interoperability Shota Nagayama, Shigeya Suzuki, Takahiko Satoh, Takaaki Matsuo and Rodney Van Meter

P1-62 - Entanglement of quantum circular states of light Mikhail Kolobov, Dmitri Horoshko, Stephan De Bievre and Giuseppe Patera.

P1-66 - Wide-area topology of a Quantum Internet Takaaki Matsuo, Takahiko Satoh, Shota Nagayama, Shigeya Suzuki and Rodney Van Meter

P1-70 - Towards storage of single quantum dot photons in a rubidium quantum memory Janik Wolters, Lucas Beguin, Jan-Philipp Jahn, Mathieu Munsch, Andrew Horsley, Fei Ding, Aline Faber, Andreas Jöckel, Andreas Kuhlmann, Armando Rastelli, Oliver G. Schmidt, Richard J. Warburton and Philipp Treutlein

P1-71 - Quantum teleportation between multiple senders and receivers Seung-Woo Lee, Hee Su Park and Hyunseok Jeong

P1-72 - On-chip coherent conversion of photonic quantum entanglement between different degrees of freedom Lantian Feng, Ming Zhang, Zhaiyuan Zhou, Ming Li, Xiao Xiong, Le Yu, Baosen Shi, Guoping Guo, Daoxin Dai, Xifeng Ren and Guangcan Guo

P1-73 - Experimental quantum fingerprinting with weak coherent states Juan Miguel Arrazola, Feihu Xu, Keijin Wei, Wenyuan Wang, Pablo Palacios-Avila, Chen Feng, Shihan Sajeed, Hoi-Kwong Lo and Norbert Lutkenhaus

P1-74 - SpooQySats: nanosatellites to demonstrate technologies for future quantum communication networks Robert Bedington, Cliff Cheng, Yue Chuan Tan, Edward Truong-Cao, Xueliang Bai and Alexander Ling

P1-75 - Many-box locality Yu Cai, Jean-Daniel Bancal and Valerio Scarani

P1-76 - All the self-testings of the singlet for two binary measurements Yukun Wang, Xingyao Wu and Velario Scarani

P1-77 - BosonSampling with continuous variable measurements Austin Lund, Saleh Rahimi-Keshari and Timothy Ralph

P1-78 - Implementation of high-performance coincidence counting unit with a low-cost field programmable gate array Byung Kwon Park, Yong-Su Kim, Osung Kwon, Sang-Wook Han and Sung Moon

P1-79 - Quantum Noise Spectroscopy Gerardo Paz Silva, Leigh Norris and Lorenza Viola

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P1-80 - Continuous-mode analysis of a noiseless linear amplifier Yi Li, Andre Carvalho and Matthew James

P1-81 - Device-independent parallel self-testing of two singlets Xingyao Wu, Jean-Daniel Bancal, Matthew Mckague and Valerio Scarani

P1-83 - Demonstration of Quantum Permutation Algorithm with a Single Photon Ququart Pei Zhang

P1-84 - Experimental evaluation of quantum correlations between measurement errors using polarization-entangled photons as probe input Yutaro Suzuki, Masataka Iinuma, Masayuki Nakano and Holger F. Hofmann

P1-85 - Development of a readout backend for a Geiger-mode SiPM In-Ho Bae, Dong-Hoon Lee and Seongchong Park

P1-86 - The classical-quantum divergence of complexity in the Ising spin chain Whei Yeap Suen, Jayne Thompson, Andrew Garner, Vlatko Vedral and Mile Gu

P1-87 - Experimental evaluation of non-classical correlations by sequential quantum measurements Masataka Iinuma, Yutaro Suzuki, Taiki Nii, Ryuji Kinoshita and Holger F. Hofmann

P1-88 - Interferences in quantum eraser reveal geometric phases in modular and weak values Mirko Cormann, Mathilde Remy, Branko Kolaric and Yves Caudano

P1-89 - Coherent-state discrimination via non-heralded probabilistic amplification Matteo Rosati, Andrea Mari and Vittorio Giovannetti

P1-90 - Entangled photon-pairs emitted from Ag/GaN photonic crystals as sources for quantum-information processing Dalibor Javůrek and Jan Peřina Jr.

P1-91 - Conditioned quantum dynamics in a 1D lattice system Ralf Blattmann and Mølmer Klaus

P1-95 - Testing the limits of human vision with single photons Rebecca Holmes, Michelle Victora, Ranxiao Frances Wang and Paul Kwiat

P1-97 - Entanglement Restoration in Amended Entanglement Breaking Channels Álvaro Andrés Cuevas Seguel, Andrea Mari, Antonella De Pasquale, Adeline Orieux, Marcello Massaro, Fabio Sciarrino, Vittorio Giovanetti and Paolo Mataloni

P1-98 - Proper Dimension Witnessing Wan Cong, Yu Cai, Jean-Daniel Bancal and Valerio Scarani

P1-99 - Past of a photon inside an interferometer Yink Loong Len, Jibo Dai, Berge Englert and Leonid Krivitsky

P1-100 - Quantum error correction in the presence of small baths Yink Loong Len, Yicong Zheng and Hui Khoon Ng

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P1-104 - Efficient Quantum Compression for Identically Prepared Mixed States Yuxiang Yang, Giulio Chiribella and Daniel Ebler

P1-106 - When is simpler thermodynamically better? Andrew Garner, Jayne Thompson, Vlatko Vedral and Mile Gu

P1-107 - Weak Value Measurements with Pulse Recycling Courtney Krafczyk, Trent Graham, Andrew Jordan and Paul Kwiat

P1-108 - Extreme Violation of Local Realism in Quantum Hypergraph States Mariami Gachechialdze, Costantino Budroni and Otfried Guehne

P1-110 - random numbers from vacuum fluctuations Yicheng Shi, Brenda Chng and Christian Kurtsiefer

P1-111 - Rectification of light in the quantum regime Jibo Dai, Alexandre Roulet, Huy Nguyen Le and Valerio Scarani

P1-112 - Generation and measurement of four-dimensional entanglement in multi-core optical fibers Hee Jung Lee, Sang-Kyung Choi and Hee Su Park

P1-114 - Qutrit trace invariants using Bloch matrices Vinod Mishra

P1-117 - Entanglement verification with detection-efficiency mismatch Yanbao Zhang and Norbert Lutkenhaus

P1-118 - Experimental Adaptive Quantum Tomography of Two-Qubit States Stanislav Straupe, Gleb Struchalin, Konstantin Kravtsov, Igor Radchenko, Ivan Pogorelov and Sergei Kulik

P1-122 - Single-cycle squeezing of light Dmitri Horoshko and Mikhail Kolobov

P1-124 - Realization of a two-photon quantum gate based on cavity QED Bastian Hacker, Stephan Welte, Stephan Ritter and Gerhard Rempe

P1-126 - Spectrum analysis with quantum dynamical systems Shilin Ng, Shan Zheng Ang, Mankei Tsang, Wheatley Trevor, Hidehiro Yonezawa, Akira Furusawa and Elanor Huntington

P1-127 - Heisenberg’s error-disturbance relations: a joint measurement-based experimental test Yuan-Yuan Zhao, Paweł Kurzyński and Guo-Yong Xiang

P1-128 - Superradiant Emission of Ultra-Bright Photon Pairs in Doppler-Broadened Atomic Ensemble Yoon-Seok Lee, Sang Min Lee, Heonoh Kim and Han Seb Moon

P1-129 - Geometric spin echo under zero field Yuhei Sekiguchi, Yusuke Komura, Shota Mishima, Touta Tanaka, Naeko Niikura and Hideo Kosaka

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P1-130 - Heralded quantum steering with no detection loophole over a high-loss quantum channel Geoff Pryde, Morgan Weston, Sergei Slussarenko, Sabine Wollmann and Helen Chrzanowski

P1-131 - Entanglement degradation by macrorealistic modifications Stefan Nimmrichter

P1-132 - Scalable three-way quantum information tapping using parametric amplifiers with quantum correlation Nannan Liu, Xiaoying Li, Jiamin Li and Z. Y. Ou

P1-133 - Experimental demonstration of frequency-domain Hong-Ou-Mandel interference Toshiki Kobayashi, Rikizo Ikuta, Shuto Yasui, Shigehito Miki, Taro Yamashita, Hirotaka Terai, Takashi Yamamoto, Masato Koashi and Nobuyuki Imoto

P1-134 - Experimental Detection of Entanglement Polytopes via Local Filters Yuanyuan Zhao, Markus Grassl, Bei Zeng and Guoyong Xiang

P1-135 - Computing Permanents for Boson Sampling on Tianhe-2 Supercomputer Junjie Wu, Yong Liu, Baida Zhang, Xianmin Jin, Yang Wang, Huiquan Wang and Xuejun Yang

P1-136 - Universal optimal device-independent witnessing of quantum channels Michele Dall'Arno, Sarah Brandsen and Francesco Buscemi

P1-138 - Optimal communication via mixed quantum t designs Sarah Brandsen, Michele Dall'Arno and Anna Szymusiak

P1-139 - Surpassing the no-cloning limit with a heralded hybrid linear amplifier Jing Yan Haw, Jie Zhao, Josephine Dias, Syed Assad, Mark Bradshaw, Rémi Blandino, Thomas Symul, Tim Ralph and Ping Koy Lam

P1-144 - Generation and storage of multimode entangled light in a solid state, spin-wave quantum memory Kate Ferguson, Sarah Beavan, Jevon Longdell and Matthew Sellars

P1-145 - Fast-gated single-photon counting with ultra-low noise based on thermoelectrically cooled photomultiplier tube Yanhui Cai, Zhengyong Li and Xiangkong Zhan

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Poster Session II – Tuesday (5 July)

P2-146 - Kochen-Specker Theorem Proofs with Non-specific Projectors from Extended KS Value Assignment Rules Tang Weidong

P2-147 - Arbitrary Multi-Qubit Generation Farid Shahandeh, Austin P. Lund, Timothy C. Ralph and Michael R. Vanner

P2-148 - Generation of photon pairs in a nonlinear waveguide array with inhomogeneous poling pattern Francesco Lenzini, James Titchener, Sachin Kasture, Alexander N. Poddubny, Andreas Boes, Ben Haylock, Paul Fisher, Matteo Villa, Arnan Mitchell, Alexander S. Solntsev, Andrey A. Sukhorukov and Mirko Lobino

P2-149 - Geometry of system-bath coupling and gauge fields: manipulating currents and driving phase transitions Chu Guo and Dario Poletti

P2-150 - Hong-Ou-Mandel interference between two collective excitations Jun Li, Ming-Ti Zhou, Xiao-Hui Bao and Jian-Wei Pan

P2-151 - Nonlinear infrared spectrometer free from spectral selection Anna Paterova, Shaun Lung, Dmitry Kalashnikov and Leonid Krivitsky

P2-152 - Secret key agreement demonstration over 7.8 km free-space optical channel Mikio Fujiwara, Toshiyuki Ito, Mitsuo Kitamura, Hiroyuki Endo, Morio Toyoshima, Hideki Takenaka, Yoshihisa Takayama, Ryosuke Shimizu, Masahiro Takeoka, Ryutaroh Matsumoto and Masahide Sasaki

P2-153 - Interferometric Resolution of Incoherent Optical Point Sources near the Quantum Limit Ranjith Nair and Mankei Tsang

P2-155 - Efficient Large Block Codes Ancilla States Preparation for Fault-tolerant Quantum Computation Yi-Cong Zheng, Ching-Yi Lai and Todd Brun

P2-156 - Multi-photon experiments with solid-state single-photon sources Marcelo Pereira de Almeida, Juan Carlos Loredo, Tau Bernstorff Lehmann, Nor Azwa Zakaria, Paul Hiliare, Isabelle Sagnes, Aristide Lemaitre, Pascale Senellart and Andrew White

P2-157 - Violation of steering inequality with path entangled single photon Anthony Martin, Thiago Guerreiro, Fernando Monteiro, Jonatan Bohr Brask, Tamás Vertési, Boris Korzh, Felix Bussieres, Varum Verma, Adriana Lita, Richard Mirin, Saewoo Nam, Francesco Marsili, Matthew. Shaw, Nicolas Gisin, Nicolas Brunner, Hugo Zbinden and Rob Thew

P2-158 - Experimental Demonstration of Continuous Variable One Sided Device Independence

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Nathan Walk, Sara Hosseini, Jiao Geng, Oliver Thearle, Jing Yan Haw, Seiji Armstrong, Syed M. Assad, Jiri Janousek, Timothy C. Ralph, Thomas Symul, Howard Wiseman and Ping Koy Lam

P2-160 - Detector-device-independent quantum key distribution Anthony Martin, Alberto Boaron, Boris Korzh, Charles Lim, Gianluca Boso, Raphael Houlmann and Hugo Zbinden

P2-161 - Heralded hybrid noiseless linear amplifier for arbitrary coherent states Jie Zhao, Josephine Dias, Jing Yan Haw, Mark Bradshaw, Remi Blandino, Thomas Symul, Timothy Ralph, Ping Koy Lam and Syed Assad

P2-162 - Quantum teleportation by quantum walks Yun Shang

P2-163 - Characterizing ground and thermal states of few-body Hamiltonians Otfried Guehne and Felix Huber

P2-164 - Classical realization of “quantum-optical coherence tomography” by time-resolved pulse interferometry Kazuhisa Ogawa and Masao Kitano

P2-165 - Distribution of quantum coherence in multipartite systems Chandrashekar Radhakrishnan, Manikandan Parthasarathy, Segar Jambulingam and Tim Byrnes

P2-166 - Effects of measurement dependence on generalized CHSH-Bell test in the single-run and multiple-run scenarios Dan-Dan Li, Yu-Qian Zhou, Fei Gao, Xin-Hui Li and Qiao-Yan Wen

P2-167 - High fidelity entanglement swapping via a time-resolved coincidence measurement Yoshiaki Tsujimoto, Motoki Tanaka, Yukihiro Sugiura, Rikizo Ikuta, Shigehito Miki, Taro Yamashita, Hirotaka Terai, Takashi Yamamoto, Masato Koashi and Nobuyuki Imoto

P2-168 - Quantum metrology using topological quantum states. Tim Byrnes

P2-169 - Ultrafast coherent control of Bose-Einstein condensates using stimulated Raman adiabatic passage Andreas Thomasen and Tim Byrnes

P2-170 - Generation and non-destructive detection of single microwave photons Sankar Raman Sathyamoorthy

P2-171 - A correlation based entanglement criterion in bipartite multi-boson systems Wiesław Laskowski, Marcin Markiewicz, Danny Rosseau, Tim Byrnes, Kamil Kostrzewa and Adrian Kołodziejski

P2-172 - On the equivalence of separability and extendability of quantum states K. R. Parthasarathy, Ritabrata Sengupta and B. V. Rajarama Bhat

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P2-173 - Evaluation of quantum 1D repetition codes’ performance against quantum noise Takanori Sugiyama, Keisuke Fujii, Haruhisa Nagata and Fuyuhiko Tanaka

P2-174 - Monolithically integrated optics for scalable trapped-ion single-photon sources Mirko Lobino, Mojtaba Ghadimi, Valdis Blums, Benjamin G. Norton, Paul Fisher, Harley Hayden, Jason Amini, Curtis Volin, Dave Kielpinski and Erik W Streed.

P2-175 - Detection-dependent six-photon NOON state interference Rui-Bo Jin, Mikio Fujiwara, Ryosuke Shimizu, Robert Collins, Gerald Buller, Taro Yamashita, Shigehito Miki, Hirotaka Terai, Masahiro Takeoka and Masahide Sasaki

P2-176 - Stationary Light in Resonant and Far-Detuned Atom-Optic Memories Jesse Everett, Geoff Campbell, Young-Wook Cho, Pierre Vernaz-Gris, Daniel Higginbottom, Olivier Pinel, Nick Robins, Ping Koy Lam and Ben Buchler

P2-177 - Particle-Indistinguishability Signatures in Phase Space Farid Shahandeh

P2-179 - Temporal multimode storage of entangled photons Peter C. Strassmann, Alexey Tiranov, Jonathan Lavoie, Nicolas Brunner, Marcus Huber, Varun B. Verma, Sae Woo Nam, Richard P. Mirin, Adriana E. Lita, Francesco Marsili, Mikael Afzelius, Félix Bussières, Nicolas Gisin

P2-180 - Au Microdisk-Size Dependence of Quantum Dot Emission from the Hybrid Metal-Distributed Bragg Reflector Structures Employed for Single Photon Sources Baoquan Sun

P2-182 - Quantum Carburettor Effect for Photon Number Shifting Jennifer Radtke, John Jeffers and Daniel Oi

P2-183 - Noise-tolerant post-selected measurement using noise margin with GKP code state Kosuke Fukui, Akihisa Tomita and Atsushi Okamoto

P2-184 - An Optimal Design for Universal Multiport Interferometers William Clements, Peter Humphreys, Benjamin Metcalf, Steven Kolthammer and Ian Walmsley

P2-186 - Wavelength Conversion of non-classical light from rubidium atoms to the telecom band Rikizo Ikuta, Toshiki Kobayashi, Kenichiro Matsuki, Shigehito Miki, Taro Yamashita, Hirotaka Terai, Takashi Yamamoto, Masato Koashi, Tetsuya Mukai and Nobuyuki Imoto

P2-187 - Few-Photon Heterodyne Spectroscopy Gustavo Amaral, Thiago Ferreira Da Silva, Guilherme Temporão and Jean Pierre von der Weid

P2-188 - Controlling two-photon frequency entanglement using cross-Kerr effect Nobuyuki Matsuda

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P2-189 - Experimental detection of entanglement with optimal-witness families Jibo Dai, Yink Loong Len, Yong Siah Teo, Berthold-Georg Englert and Leonid A. Krivitsky

P2-190 - Irreversibility and the Arrow of Time in a Quenched Quantum System Tiago Batalhao, Alexandre Souza, Roberto Sarthour, Ivan Oliveira, Mauro Paternostro, Eric Lutz and Roberto Serra.

P2-191 - Simple and Efficient Memory-Assisted Quantum Key Distribution Nicolo Lo Piparo, Mohsen Razavi and William Munro

P2-193 - An explicit classical strategy for winning a CHSH_q game Matej Pivoluska and Martin Plesch

P2-194 - Isotropy and control of dissipative quantum dynamics Ben Dive, Daniel Burgarth and Florian Mintert

P2-195 - Quantum Theory of Two-Dimensional Resolution for Two Incoherent Optical Point Sources Shan Zheng Ang, Ranjith Nair and Mankei Tsang

P2-197 - Unified view of quantum amplification based on quantum states transformation Mengjun Hu and Yongsheng Zhang

P2-198 - Two-atom interferences in a cavity QED system Olivier Morin, Andreas Neuzner, Matthias Körber, Stephan Ritter and Gerhard Rempe

P2-199 - Exploring the limits of non-locality with pairs of photons Alessandro Cere, Hou Shun Poh, Siddarth Koduru Joshi, Adán Cabello, Marcin Markiewicz, Pawel Kurzynski, Dagomir Kaszlikowski and Christian Kurtsiefer.

P2-200 - Control and characterisation of nuclear spin memory in diamond nanocrystals Jan D. Beitner, Helena S. Knowles, Dhiren M. Kara, David-Dominik H. Jarausch and Mete Atatüre

P2-201 - Long coherence time quantum memory for polarization qubits based on a single atom in a cavity Olivier Morin, Matthias Körber, Stefan Langenfeld, Andreas Neuzner, Stephan Ritter and Gerhard Rempe

P2-202 - Quantum approaches to homomorphic encryption Joshua Kettlewell, Carlos Perez-Delgado, Yingkai Ouyang, Si-Hui Tan, Li Yu, Lin Chen and Joseph Fitzsimons

P2-204 - Silicon-vacancy: a colourful defect of diamond as solid-state single-spin for quantum information. Camille Stavrakas, Benjamin Pingault, Christian Hepp, Tina Müller, Mustafa Gündogan, Jonas Becker, Carsten Schulte, Carsten Arend, Tillman Godde, Alexander Tartakovskii, Matthew Markham, Christoph Becher, Elke Neu, Stefan Gsell, Matthias Schreck, Hadwig S

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P2-205 - Photon Antibunching and Hong-Ou-Mandel Peak Gustavo Amaral, Felipe Calliari, Thiago Ferreira Da Silva, Guilherme Temporão and Jean Pierre von der Weid

P2-207 - Quantum assisted Gaussian process regression Zhikuan Zhao, Jack Fitzsimons and Joseph Fitzsimons

P2-208 - Entanglement conditions for integrated-optics multi-port quantum interferometry experiments Junghee Ryu, Marcin Marciniak, Marcin Wiesniak and Marek Zukowski

P2-209 - Fault-tolerant Quantum Computation under non-Markovian noise Jing Hao Chai and Hui Khoon Ng

P2-210 - Quantum Phase Transition and Universal Dynamics in the Rabi Model Myung-Joong Hwang, Ricardo Puebla and Martin B. Plenio

P2-212 - Prospects for Atomic Spin-Squeezing inside Hollow-Core Photonic Crystal Fiber Zilong Chen and Shau-Yu Lan

P2-215 - Coherent manipulation of small ion Coulomb crystals in a Penning Trap Pavel Hrmo, Manoj Joshi, Vincent Jarlaud, Joseph Goodwin, Graham Stutter and Richard Thompson

P2-219 - Unifying wave-particle duality with entropic uncertainty Patrick Coles, Jedrzej Kaniewski and Stephanie Wehner

P2-222 - Generalised phase kick-back: the structure of computational algorithms from physical principles Ciaran Lee and John Selby

P2-223 - Generation of single photons with highly tunable wave shape from a cold atomic quantum memory Pau Farrera, Georg Heinze, Boris Albrecht, Melvyn Ho, Matías Chávez, Colin Teo, Nicolas Sangouard and Hugues de Riedmatten

P2-225 - High Efficiency Room-Temperature Raman Memory using Quenching Sarah Thomas, Patrick Ledingham, Benjamin Brecht, Joseph Munns, Cheng Qiu, Amir Feizpour, Ian Walmsley, Joshua Nunn and Dylan Saunders

P2-226 - Inertial Navigation using Atom Interferometry Jimmy Stammers, Xiaxi Cheng and Ed Hinds

P2-231 - A Cavity-Enhanced Room-Temperature Broadband Quantum Memory for Nanosecond Heralded Single Photons Dylan Saunders, J. H. D. Munns, T. F. M. Champion, C. Qiu, S. E. Thomas, B. Brecht, K. T. Kaczmarek, E. Poem, P. M. Ledingham, I. A. Walmsley and J. Nunn

P2-232 - Quantum parameter estimation with general dynamics Haidong Yuan and Chi-Hang Fung

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P2-233 - Modelling Atom-Filled Optical Cavities for Enhanced Light-Matter Interaction Joseph Munns, Sarah E. Thomas, Benjamin Brecht, Patrick M. Ledingham, Ian A. Walmsley, Joshua Nunn and Dylan J. Saunders

P2-234 - The Quantum-Classical Boundary for Precision Interferometric Measurements Patrick M. Birchall, Jeremy L. O'Brien, Jonathan C. F. Matthews and Hugo Cable

P2-235 - Entanglement is an inevitable feature of a non-classical universe Jonathan Richens, John Selby and Sabri Al-Safi

P2-237 - The Quantum Simulation of Quantum Chemistry Andrew Tranter, Peter Coveney, Florian Mintert and Peter Love

P2-240 - Optimal Wavelength Assignment in Hybrid Quantum-Classical DWDM Networks Sima Bahrani, Mohsen Razavi and Jawad A. Salehi

P2-241 - General method for constructing local-hidden-state (and -variable) models for multiqubit entangled states Rafael Rabelo, Daniel Cavalcanti, Leonardo Guerini and Paul Skrzypczyk

P2-242 - Towards Long Range Spin-Spin Interactions via Mechanical Resonators Arthur Safira, Jan Gieseler, Aaron Kabcenell, Shimon Kolkowitz, Alexander Zibrov, Jack Harris and Mikhail Lukin

P2-245 - Cold atom memory as a platform for quantum information Geoff Campbell, Young-Wook Cho, Jian Su, Jesse Everett, Nicholas Robins, Ping Koy Lam and Ben Buchler

P2-246 - Differential phase-time shifting protocol for QKD (DPTS) Mario A. Usuga, Davide Bacco, Jesper Bjerge Christensen, Karsten Rottwitt, Leif K. Oxenløwe and Yunhong Ding

P2-249 - Where does measurement uncertainty come from? Filip Rozpedek, Jedrzej Kaniewski, Patrick J. Coles and Stephanie Wehner

P2-250 - Fisher Information and Quantum Communication with random unitary noise Wiesław Laskowski, Marcin Markiewicz and Anna de Rosier

P2-252 - Numerical simulation of topological codes using tensor networks Andrew Darmawan and David Poulin

P2-253 - Distributing entangled states using silicon photonic chips Jianwei Wang, Damien Bonneau, Matteo Villa, Joshua Silverstone, Raffaele Santagati, Shigehito Miki, Taro Yamashita, Mikio Fujiwara, Masahide Sasaki, Hirotaka Terai, Michael Tanner, Chandra Natarajan, Robert Hadfield, Jeremy O'Brien and Mark Thompson

P2-256 - Floodlight Quantum Key Distribution Zheshen Zhang, Quntao Zhuang, Justin Dove, Franco Wong and Jeffrey Shapiro

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P2-258 - Symmetric Extendability of Quantum States and the Extreme Limits of Quantum Key Distribution Sumeet Khatri and Norbert Lutkenhaus

P2-259 - Large-Scale Simulation of the Quantum Internet Rodney Van Meter, Shigeya Suzuki, Shota Nagayama, Takahiko Satoh, Takaaki Matsuo, Amin Taherkhani, Simon Devitt and Joe Touch

P2-261 - Network-ready unconditional polarization qubit quantum memory at room temperature Eden Figueroa, Mehdi Namazi, Connor Kupchak, Bertus Jordaan and Reihaneh Shahrokhshahi

P2-262 - Compact, integrated quantum key distribution sender module for hand-held key exchange Gwen Melen, Tobias Vogl, Markus Rau, Giacomo Corrielli, Andrea Crespi, Roberto Osellame and Harald Weinfurter

P2-263 - Sub-Megahertz Single Photon Source Markus Rambach, Aleksandrina Nikolova, Till J. Weinhold and Andrew G. White

P2-265 - Device-independent demonstration that a qubit is more than a quantum coin Esteban S. Gómez, Santiago Gómez, Pablo González, Gustavo Cañas, Johanna F. Barra, Aldo Delgado, Guilherme B. Xavier, Adán Cabello, Matthias Kleinmann, Tamás Vértesi and Gustavo Lima

P2-266 - Optimal Efficiency of Heat Engines with Finite-Size Heat Baths Hiroyasu Tajima and Masahito Hayashi

P2-267 - Self-guaranteed measurement-based quantum computation Masahito Hayashi and Michal Hajdusek

P2-268 - Routing on a Quantum Internet Takahiko Satoh, Shigeya Suzuki, Shota Nagayama, Takaaki Matsuo and Rodney Van Meter

P2-269 - Architecture of software simulation of a Quantum Internet Shigeya Suzuki, Rodney Van Meter, Shota Nagayama, Takahiko Satoh and Takaaki Matsuo

P2-270 - Quantum Process Tomography of an Optically-Controlled Kerr Non-linearity Bertus Jordaan, Connor Kupchak, Sam Rind and Eden Figueroa

P2-271 - Entanglement assisted classical communication simulates “classical communication” without causal order Seiseki Akibue, Masaki Owari, Go Kato and Mio Murao

P2-273 - Quantum information applications of highly ordered stoichiometric rare earth crystals Rose Ahlefeldt, Michael Hush and Matthew Sellars

P2-274 - One-way quantum computing with arbitrarily large time-frequency continuous-variable cluster states from a single optical parametric oscillator

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Rafael Alexander, Pei Wang, Niranjan Sridhar, Moran Chen, Olivier Pfister and Nicolas Menicucci

P2-276 - Randomized benchmarking with cluster states Rafael Alexander, Peter Turner and Stephen Bartlett

P2-277 - Simple approximation of minimum error probability for pure-state signals Tsuyoshi Usuda and Shungo Asano

P2-280 - Determining the Quantum Fisher Information from Linear Response Theory Tomohiro Shitara and Masahito Ueda

P2-282 - Cooling of a one-dimensional Bose gas Bernhard Rauer, Pjotrs Grisins and Jörg Schmiedmayer

P2-283 - Concepts of non-Markovianity: a quantum hierarchy Li Li, Michael Hall and Howard Wiseman

P2-284 - Topological pumping of photons in nonlinear coupled resonator arrays Jirawat Tangpatinanon, Victor Bastidas, Dimitris Angelakis

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Abstracts - Talks Two Studies in Interferometry: Practical Metrology and Imperfect Boson Sampling Carl Caves, University of New Mexico Abstract: I will discuss two things, both briefly: quantum limits on practical quantum metrology in which photons are cheaply available from a laser and all entanglement is created at a beamsplitter and classical simulations of boson sampling in the presence of losses and imperfections. Quantum trajectories and past quantum states Klaus Molmer, University of Aarhus, Denmark Abstract: The state of a quantum system is described by a wavefunction evolving in time according to the Schroedinger equation. If measurements are carried out on the system, its wave function changes (collapses) according to the random outcome of the measurement. During a sequence of measurements on a single system, its quantum state thus follows a stochastic trajectory governed by the normal quantum mechanical time evolution, interrupted by collapses at each measurement. The trajectory quantum state successfully predicts the probabilities and mean values for the measurement of any physical observable – conditioned on the results of previous measurements. In this talk, I discuss how measurements at any moment of time do not only affect the current and the future state of the system but they also supplement our knowledge about the system at earlier times during the experiment. I shall show how such hindsight knowledge can be formally defined as a time evolving “past quantum state”, which at any time depends on all earlier and later measurement outcomes. I will show applications of this theory to experiments on atoms and superconducting qubits, and I will discuss how the concept and formalism of past quantum states relate to questions of more foundational character. Entangling independent quantum-dot spins Mete Atature, University of Cambridge Abstract: Indistinguishable single photon generation is one of the key ingredients of a photonic-based distributed quantum networks. Semiconductor quantum dots and colour centres in diamond are example solid-state systems able to generate good quality single photons and in parallel have a spin-defined ground state manifold. This opens the route to spin-photon entangled nodes and the current challenges include both efficiency and quality of spin-tagged photon generation. I will cover recent progress for efficient coupling and entangling of quantum-dot spins, as well as a brief overview of future directions.

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Time-resolved Scattering of a Single Photon by a Single Atom Alessandro Cere, Centre for Quantum Technologies, NUS Abstract: The efficiency of light-matter interfaces between single photons and single atoms depends on the bandwidth and temporal shape of the single photon, and is crucial for realistic implementations of many quantum information protocols. In particular, an exponentially rising single photon is predicted to excite a single atom with a higher efficiency compared to any other temporal shape [1]. A four-wave mixing photon pair source, in conjunction with an asymmetric cavity, generates heralded single photons of tunable bandwidth with exponentially decaying or rising shapes [2,3]. We combine the photon pair source with a trapped single atom and investigate the free space scattering for different bandwidths and temporal shapes. We study the scattering dynamics by measuring the atomic emission and the reduction in the number of transmitted photons. We observe that the atomic absorption dynamics are imprinted in the single-photon excitation mode. Infrared Spectroscopy with Visible Light Leonid Krivitsky, Data Storage Institute Abstract: We exploit the first-order interference of two Parametric Down Conversion (PDC) sources to determine real and imaginary parts of the refractive index of media in the infrared (IR) range. Frequency correlations of PDC enable determination properties of the medium at IR wavelengths using conventional visible range optics and photodetectors. Reference to: D. A. Kalashnikov, A. V. Paterova, S. P. Kulik and L. A. Krivitsky, «Infrared spectroscopy with visible light», Nature Photonics, 10, 98–101 (2016). Spectrally resolved white-light quantum interferometry for high-accuracy chromatic dispersion measurements Florian Kaiser, Université Nice Sophia Antipolis Abstract: In quantum optical metrology, exploiting an N-photon N00N-state allows performing phase sensing with better resolution compared to any classical approach exploiting N photons. Here, we introduce spectrally resolved white-light quantum interferometry which offers advantages far beyond improving phase sensitivity. As opposed to the classical scheme, our approach does not require balancing the interferometer which finds repercussions in speed, robustness, and repeatability of the related experimental procedures. Additionally, by simultaneously exploiting a N00N-state and energy-time entanglement, a simplified data fitting function can be used which improves the accuracy significantly. As an exemplary application, we exploit our scheme for measuring one of the most important parameters of today's optical telecommunication networks and mode-locked laser design, namely chromatic dispersion. We repeat both quantum and classical dispersion measurements a 100 times on a 1 m long standard single-mode fibre. Statistical data treatment shows that the quantum strategy is more than three times more accurate compared state-of-the-art results, despite detecting 2.5*10^8 times less photons, which underlines that the improved accuracy is mainly due to conceptual advantages enabled by quantum optics.

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Applications of HyperEntanglement Paul Kwiat, University of Illinois at Urbana-Champaign Abstract: Entanglement is a critical resource for many quantum communication protocols. Going further, photons that are simultaneously entangled in multiple degrees of freedom — “hyperentangled” — enable enhanced protocols that would be difficult or impossible otherwise. We will discuss our progress using hyperentangled photons from parametric downconversion in several advanced quantum communication experiments, including superdense teleportation and hyper dense coding. Direct experimental reconstruction of the Bloch sphere Matthew Pusey, Perimeter Institute for Theoretical Physics Abstract: A focus of theoretical activity in quantum foundations has been looking at quantum theory in a wide landscape of possible theories, called generalised probabilistic theories. In particular, quantum theory has been "reconstructed" by finding axioms that single the theory out from that landscape. We have taken a different approach to reconstruction, making as few theoretical assumptions as possible but inputting the raw data from a qubit experiment. I will show the resulting state space (spoiler: it's approximately a sphere) and discuss what we can conclude using it. Joint work with Mike Mazurek, Kevin Resch, and Rob Spekkens. Operational multipartite entanglement measures Katharina Schwaiger, University of Innsbruck Abstract: Entanglement is the resource to overcome the natural limitations of spatially separated parties restricted to local operations assisted by classical communication (LOCC) and hence, an entanglement measure is a function that is nonincreasing under LOCC. We recently introduced two operational entanglement measures, the source and the accessible entanglement, that are applicable for arbitrary multipartite (pure or mixed) states. Whereas the accessible entanglement characterizes the potentiality of a state to generate other states via LOCC, the source entanglement characterizes the simplicity of generating the state at hand. Furthermore, these measures can be generalized to two classes of entanglement measures. In this talk I will first introduce the two new operational entanglement measures. Then we will consider pure bipartite as well as multipartite states, show how we can derive explicit formulas for the source and accessible entanglement and use the new entanglement measures to characterize the entanglement contained in e.g. three-qubit states. Entanglement of temporal order from quantum theory and gravity Magdalena Zych, University of Queensland Abstract: Violations of Bell's theorem show that physical quantities cannot have pre-assigned values. However, the causal relations between events — e.g. operations or measurements on a system — are assumed to be fixed by the "underlying" space-time structure. Yet, according to general relativity space-time is a dynamical object and causal relations can be changed by the distribution of massive objects. Here, I will present a direct example of a non-classical causal structure arising from quantum theory and gravity: when a massive object is prepared in a specific quantum state the order between a pair of time-like events can become "entangled" with the order between another pair of time-like events. In the spirit of Bell’s theorem, I will formulate a task which can be achieved by agents exploiting “entanglement” of temporal order, and which is impossible if temporal order was predefined.

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A Many-Interacting-Worlds Approach To Quantum Mechanics Michael Hall, Griffith University Abstract: When one applies quantum mechanics to our world, we require a wave function that has support over an enormous configuration space, where each point specifies the positions of all particles and the values of all fields. In the usual many worlds picture, this wave function decomposes into many branches, all 'real' but having different statistical weights and no interactions between them. In the deBroglie-Bohm picture, just one point in the configuration space is 'real', with its evolution determined by the wave function but not vice versa. In contrast, in our recently proposed many-interacting-worlds approach [1] there is no wave function at all. Instead, there are a large but finite number of 'real' worlds, corresponding to different points in the configuration space. These worlds would each evolve classically, except for a universal interaction force acting between worlds. This force essentially acts to 'repel' nearby worlds in configuration space, and is responsible for all quantum effects. Probabilities arise as equally-weighted averages over the worlds, corresponding to ignorance as to which world a given observer occupies. Quantum predictions are recovered in the limit of an infinite number of worlds. This approach provides a new way of thinking about quantum phenomena, such as tunneling, zero-point energies and entanglement, as well as an interesting example of how to 'tweak' quantum mechanics without (apparently) breaking it. More practically, it also suggests a new method of approximating quantum evolution for large systems. [1] M.J.W. Hall, D.-A. Deckert and H.M. Wiseman, Physical Review X 4 (2014) 041013. Experimental Nonlocal and Surreal Bohmian Trajectories Howard Wiseman, Griffith University Abstract: Weak measurement allows one to empirically determine a set of average trajectories for an ensemble of quantum particles. However, when two particles are entangled, the trajectories of the first particle can depend non-locally on the position of the second particle. Moreover, the theory describing these trajectories, called Bohmian mechanics, predicts trajectories which were at first deemed ``surreal'' when the second particle is used to probe the position of the first particle. Here, we entangle two photons and measure a set of Bohmian trajectories of one of them, using weak measurements and post-selection. We show that the choice of intervention on one particle affects the trajectories of the other, and that the trajectories seem ``surreal'' only if one ignores this manifest nonlocality. Quantum dot quantum computing Andrew Doherty, University of Sydney Abstract: Gate-defined semiconductor devices are a promising avenue for implementing quantum computation. Many approaches to performing two-qubit gates have been proposed in the literature and tested in the laboratory. I will discuss our recent theoretical studies of exchange-based two-qubit gates in the context of current experimental work in GaAs. In this approach leakage errors that would typically occur are suppressed by designing the system such that they are energy non-conserving, and through the use of adiabatic control pulses. The resulting two-qubit operations can be as fast as single-qubit gates.

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Quantum Computing in Silicon with Donors Michelle Simmons, University of New South Wales Abstract: Extremely long electron and nuclear spin coherence times have recently been demonstrated in isotopically pure Si-28 [1,2] making silicon one of the most promising semiconductor materials for spin based quantum information. The two level spin state of single electrons bound to shallow phosphorus donors in silicon in particular provide well defined, reproducible qubits [3] and represent a promising system for a scalable quantum computer in silicon. An important challenge in these systems is the realisation of an architecture, where we can position donors within a crystalline environment with approx. 20-50nm separation, individually address each donor, manipulate the electron spins using ESR techniques and read-out their spin states. We have developed a unique fabrication strategy for a scalable quantum computer in silicon using scanning tunneling microscope hydrogen lithography to precisely position individual P donors in a Si crystal [4] aligned with nanoscale precision to local control gates [5] necessary to initialize, manipulate, and read-out the spin states [6]. During this talk I will focus on demonstrating spin transport [7] and single-shot spin read-out of precisely-positioned P donors in Si. I will also describe our approaches to scale up using rf reflectometry [8] and the investigation of 3D architectures for implementation of the surface code [9]. [1] K. Saeedi et al., Science 342, 130 (2013). [2] J. T. Muhonen et al., Nature Nanotechnology 9, 986 (2014). [3] B.E. Kane, Nature 393, 133 (1998). [4] M. Fuechsle et al., Nature Nanotechnology 7, 242 (2012). [5] B. Weber et al., Science 335, 6064 (2012). [6] H. Buch et al., Nature Communications 4, 2017 (2013). [7] B. Weber et al., Nature Nanotechnology 9, 430 (2014). [8] M.G. House et al., Nature Communications 6, 8848 (2015) [9] C. Hill et al., Science Advances 1, e1500707 (2015). Coherent feedback of a single qubit in diamond Paola Cappellaro, Massachusetts Institute of Technology Abstract: The most common approach to engineering desired operations on qubits subjected to the deleterious effects of their environment relies on open-loop quantum control techniques. Feedback control, an alternative strategy inspired by the success of classical control, is less pervasive in the quantum setting because of the complications introduced by quantum measurement. I will present the experimental implementation of a feedback-control algorithm with a solid-state spin qubit associated with the nitrogen vacancy centre in diamond. The algorithm exploits coherent feedback to overcome the limitations of measurement-based feedback. The feedback algorithm can protect the qubit against intrinsic dephasing noise for milliseconds (orders of magnitude larger than the qubit dephasing time) by exploiting a long-lived ancillary qubit. In addition, it can protect the qubit coherence, while performing two essential qubit gates—NOOP and NOT gates—during the protection time.

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Concurrent Remote Entanglement of Transmon Qubits using Flying Photons Anirudh Narla, Department of Applied Physics, Yale University Abstract: Concurrent remote entanglement is an essential primitive in quantum information science. It consists of entangling on demand two arbitrary, distant quantum systems which never directly interact. In quantum optics, concurrent remote entanglement experiments have recently provided loophole-free tests of quantum non-locality and form the basis for the modular architecture of quantum computing. In these experiments, the Alice and Bob qubits are each first entangled with their respective traveling photons. Subsequently, the two photon paths interfere on a beam-splitter, which acts as a which-path eraser, and are then directed to single-photon detectors. A key feature of this concurrent remote entanglement protocol is its robustness to photon losses, unlike schemes that rely on continuous variable states. This robustness arises from heralding the entanglement on the detection of events which can be selected for their unambiguity and are uniquely linked to the production of a pure entangled state. Here we demonstrate this protocol in the domain of superconducting quantum circuits where the natural carriers of information between modules are traveling microwave photons. Our demonstration exploits, in a single experiment, a set of tools that had been previously the exclusive privilege of quantum optics experiments, namely microwave single-photon sources and detectors together with the spatial and temporal control of these photons to make them indistinguishable. With these tools, we have realized the which-path erasure of microwave photons and thus the generation of loss-tolerant entanglement between distant superconducting qubits by concurrent measurements. The protocol speed and prospects for improving fidelity make this a very promising implementation for the distribution of quantum information with microwave flying photons. Our experiment opens for superconducting qubits the new prospect of modular quantum information. High fidelity transfer and storage of photon states in a single nuclear spin Sen Yang, 3. Physikalisches Institut, Uni Stuttgart Abstract: Photons are natural carriers of quantum information over long distances. Matter systems have good storage capabilities and processing qubits. However, it is challenging to integrate all these capabilities into one system. The nitrogen-vacancy (NV) defect center in diamond does show significant potential for realizing solid-state quantum networks. The NV center provides a hybrid spin system in which electron spins are used for fast, high-fidelity control and readout, and nuclear spins are well-isolated from their environment yielding ultra-long coherence time. Electron and nuclear spins could form a small-scale quantum register. A so far missing link is to store quantum information from a light field into the defects spins in such a way that scalable quantum repeater networks is possible. Here we demonstrate a new scheme based on the interaction of an optical photon and a hybrid electron-nuclear spin system. The storage process is achieved by coherently transferring a single photon to an entangled electron-nuclear spin state of a nitrogen vacancy center in diamond. The process resembles a photon-nuclear spin. We demonstrate this scheme by storage of a photon qubit in a single solid-state nuclear spin qubit with average fidelity ~98% and storage time of 10 seconds. By choosing a particular optically excited state, the nuclear spin storage is made robust against over 1000 rounds repetitive excitation of the electron spin, a key requirement for a versatile quantum node. The photon-nuclear spin interface and the nuclear spin storage demonstrated here constitutes a further step towards a practical solid-state quantum network comprising diamond spins and photons. Reference: Yang, et al, arXiv:1511.04939 (2015)

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Quantum State Engineering using Hybridization William Munro, NTT Basic Research Laboratories Abstract: The development of quantum information enabled technologies has reached an interesting stage where we can now in principle engineer composite systems to exploit the best properties of these individual systems. Hybridisation allows us to undertake operations and tasks that may otherwise prove difficult. In this presentation we show how by strongly coupling an ensemble of electron spins hosted by nitrogen-vacancy centers in diamond to a superconducting circuit, the coherence properties of the composite system can be significantly increased, even beyond those of the ensemble or the superconducting circuit. Our research opens up a path towards long lived quantum memories, solid-state microwave frequency combs and points to a new route to cavity QED experiments with dense spin ensembles where the direct dipole-dipole interaction between spins becomes important and many-body phenomena will be directly accessible. Atomic to generalized Hong-Ou-Mandel interference: probing entanglement in the dynamics of many-body systems Adam Kaufman, Harvard University Abstract: Entanglement within a many-body system is a defining feature of strongly correlated quantum systems. Recent theoretical developments point to the entropy of entanglement as a means to classify unusual quantum phases, such as spin liquids and topological phases. In this talk I will present an experimental scheme to probe entanglement in itinerant systems of bosons. By employing techniques used to observe atomic Hong-Ou-Mandel interference, it is possible to perform many-body interference that probes the indistinguishability of quantum states. I will discuss how this interference allows us to measure quantum purity, second order Rényi (entanglement) entropy and mutual information within finite Bose-Hubbard chains. In the context of these techniques, I will focus on our investigation of the dynamics of quenched, isolated Bose-Hubbard chains. Here we observe that thermal ensembles appear to emerge from a pure quantum state, while the entanglement entropy quantitatively approaches the thermal entropy. Our observations experimentally illustrate the role of entanglement in facilitating thermalization of pure systems undergoing unitary dynamics. Comparing Experiments to the Fault-Tolerance Threshold Steve Flammia, The University of Sydney Abstract: Achieving error rates that meet or exceed the fault-tolerance threshold is a central goal for quantum computing experiments, and measuring these error rates using randomized benchmarking is now routine. However, direct comparison between measured error rates and thresholds is complicated by the fact that benchmarking estimates average error rates while thresholds reflect worst-case behavior. These two can differ by orders of magnitude in the regime of interest. I will discuss how to facilitate comparison between the experimentally accessible average error rates and the worst-case quantities that arise in current threshold theorems by describing relations between the two for a variety of physical noise sources, including dephasing, thermal relaxation, coherent and incoherent leakage, as well as coherent unitary over and under rotation. The results indicate that it is coherent errors that lead to an enormous mismatch between average and worst case, and we quantify how well these errors must be controlled to ensure fair comparison between average error probabilities and fault-tolerance thresholds. Finally, I will describe how a recently introduced measure of coherent errors called the unitarity can sometimes be used to directly quantify the distance to the threshold based on data collected from randomized benchmarking experiments.

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Recent experimental progress in quantum communication Qiang Zhang, University of Science and Technology of China, Shanghai Abstract: Quantum-communication network is believed to be the next-generation platform for remote information processing tasks, including unconditional secure communication, communication complexity reduction and etc. In this talk, I shall review the recent experiment progress in measurement device independent quantum key distribution. Also, we shall talk about a recent experiment, which implements quantum finger printing beating the classical limit. Secure Multi-party Computing (From Classical to Quantum - From Linearity to Nonlinearity) Elham Kashefi, University of Edinburgh Abstract: to be updated Unstructured quantum key distribution Patrick Coles, University of Waterloo Abstract: Quantum key distribution (QKD) allows for communication with security guaranteed by quantum theory. The main theoretical problem in QKD is to calculate the secret key rate for a given protocol. Analytical formulas are known for protocols with symmetries, since symmetry simplifies the analysis. However, experimental imperfections break symmetries, hence the effect of imperfections on key rates is difficult to estimate. Furthermore, it is an interesting question whether (intentionally) asymmetric protocols could outperform symmetric ones. In this work, we develop a robust numerical approach for calculating the key rate for arbitrary discrete-variable QKD protocols. Ultimately this will allow researchers to study ``unstructured'' protocols, i.e., those that lack symmetry. Our approach relies on transforming the key rate calculation to the dual optimization problem, which dramatically reduces the number of parameters and hence the calculation time. We illustrate our method by investigating some unstructured protocols for which the key rate was previously unknown.

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Experimental Quantum Communications in Space exploiting temporal and polarization degrees of freedom Paolo Villoresi, Università degli Studi di Padova Abstract: Quantum Communications (QC) in Space are gaining a strong momentum for both providing the way to realize tests on the interplay of Quantum Physics and Gravity on very long scale and for terminals in relative motion as well as to provide a network of secure communications on planetary scale. In the perspective to extend the realm of QC toward larger distances, we would like to present the extension of the single photons exchange, initially demonstrated for LEO orbits to a source in MEO orbit. Moreover, we would like to report on the experiment using the temporal modes of light as the physical degree of freedom used for the encoding of the qubit [6]. This represent an evolution with respect to the polarization of the photon, used in the first demonstration of QC in Space. These QC experiments were realized at MLRO - Matera Laser Ranging Observatory of the ASI Italian Space Agency, in Matera, Italy. Quantum teleportation over deployed fibres and applications to quantum networks Daniel Oblak, University of Calgary Abstract: Quantum teleportation allows the disembodied transfer of a quantum state between two distant objects. For instance a photon interacting with one member of an entangled photon pair, by means of a so-called Bell-state measurement, will have its state transferred onto the second member of the pair. Starting in 1998, this puzzling prediction of quantum mechanics has been demonstrated by many groups around the world; however, with one very recent exception by Hensen et al., only the photon that received the teleported state, if any, traveled over a long distance while the photons partaking in the Bell-state measurement were always measured closely to where they had been created. Here, taking advantage of the Calgary metropolitan fibre network, we report the teleportation of a quantum state from a telecommunication-wavelength photon, interacting with another telecommunication photon after both have travelled in bee-line over several kilometres, onto a photon at 795 nm wavelength. This improves the state-of-the-art in terms of teleportation distance - which we define in the arguably most natural way to be the spatial separation between the locations of the Bell-state measurement and that of the photon, at the time of this measurement, that receives the teleported state - by almost one order of magnitude from 818 m to 6.2 km, thereby establishing an important requirement for quantum repeater-based communications. Our demonstration, which is compatible with quantum memory for light (another key component of a quantum repeater), verifies quantum teleportation over a truly macroscopic distance, and constitutes an important milestone towards the creation of a global quantum internet.

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Fault-tolerant Holonomic Quantum Computation in Surface Codes Yi-Cong Zheng, Centre of Quantum Techonlogy Abstract: We show that universal holonomic quantum computation (HQC) can be achieved fault-tolerantly by adiabatically deforming the gapped stabilizer Hamiltonian of the surface code, where quantum information is encoded in the degenerate ground space of the system Hamiltonian. We explicitly propose procedures to perform each logical operation, including logical state initialization, logical state measurement, logical CNOT, state injection and distillation,etc. In particular, adiabatic braiding of different types of holes on the surface leads to a topologically protected, non-Abelian geometric logical CNOT. Throughout the computation, quantum information is protected from both small perturbations and low weight thermal excitations by a constant energy gap, and is independent of the system size. Also the Hamiltonian terms have weight at most four during the whole process. The effect of thermal error propagation is considered during the adiabatic code deformation. With the help of active error correction, this scheme is fault-tolerant, in the sense that the computation time can be arbitrarily long for large enough lattice size. It is shown that the frequency of error correction and the physical resources needed can be greatly reduced by the constant energy gap. From the first loophole-free Bell test to a quantum Internet Ronald Hanson, QuTech and Kavli Institute of Nanoscience, Delft University of Technology Abstract: The realization of a highly connected network of qubit registers is a central challenge for quantum information processing and long-distance quantum communication. Diamond spins associated with NV centers are promising building blocks for such a network as they combine a coherent optical interface [1] (similar to that of trapped atomic qubits) with a local register of robust and well-controlled nuclear spin qubits [2]. Here we present our latest progress towards scalable quantum networks, including the first loophole-free violation of Bell’s inequalities [3,4] and the realization of a robust quantum network memory with nuclear spin qubits using decoherence-protected subspaces [5]. [1] W. Pfaff et al., Science 345, 532 (2014). [2] J. Cramer et al., Nature Comm. 7, 11526 (2016). [3] B. Hensen et al., Nature 526, 682 (2015). [4] B. Hensen et al., arXiv:1603.05705 (2016). [5] A. Reiserer et al., Phys. Rev. X 6, 021040 (2016). Significant-loophole-free test of local realism with entangled photons Marissa Giustina, University of Vienna Abstract: Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bell’s theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bell’s inequalities. Previous experiments convincingly supported the quantum predictions. Yet, every experiment requires assumptions that provide loopholes for a local realist explanation. Here, we report a Bell test that closes the most significant of these loopholes simultaneously. Using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors, we observe a violation of a Bell inequality with high statistical significance.

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A strong loophole-free test of Local Realism Krister Shalm, NIST Abstract: We present a loophole-free violation of local realism using entangled photon pairs. All relevant events in our Bell test are spacelike separated, and we use a high-quality polarization-entangled source of photons, combined with high-efficiency single-photon detectors to observe a statistically strong violation of a Bell inequality. Event-ready loophole free Bell test using heralded atom-atom entanglement Harald Weinfurter, University of Munich Abstract: Atom-photon entanglement together with entanglement swapping forms the basis for an event-ready Bell experiment closing the detection as well as the locality loophole. Entanglement between atoms separated by 400 m and fast state-dependent ionisation of the atoms enables space-like separated observers. We observe an S-value of S=2.54+/-0.24 disvalidating local realistic theories with high confidence. Bell correlations in a Bose-Einstein condensate Roman Schmied, University of Basel Abstract: The results of measurements by different observers can show correlations that are stronger than any classical theory allows. These Bell correlations (or nonlocal correlations) can be confirmed by violating a Bell inequality, for which quantum entanglement is necessary but insufficient. Tremendous progress has been made recently in characterizing many-body systems through the entanglement of their constituent bodies. However, even though multi-partite Bell inequalities are known, the detection of Bell correlations in large systems has remained elusive, due to the lack of suitable measurement schemes that can be implemented with limited detection resolution and acquisition time. We have experimentally demonstrated Bell correlations between the particles of a spin-squeezed Bose-Einstein condensate of about 480 rubidium-87 atoms [1]. This means that Bell correlations are present in moderately entangled and experimentally accessible many-body systems, and that they can be revealed by collective and coarse-grained measurements. Consequently, a locally causal description of the world does not necessarily become more adequate as the system size increases. We derive our Bell correlation witness from a recent Bell inequality involving only one- and two-body correlation functions [2], which gives it a natural scalability to large systems. While it does not provide a loophole-free and device-independent Bell test, it is a powerful tool for characterizing correlations in many-body systems state-independently. Our witness and its application to spin-squeezed states open the way for using many-body systems as probes into the epistemic nature of our world, as well as for quantum information tasks such as certified randomness generation with high rates. [1] R. Schmied, J.-D. Bancal, B. Allard, M. Fadel, V. Scarani, P. Treutlein, N. Sangouard: Science 352, 441 (2016). [2] J. Tura, R. Augusiak, A. B. Sainz, T. Vértesi, M. Lewenstein, A. Acín: Science 344, 1256 (2014).

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A Schrodinger Cat Living in Two Boxes Yvonne Gao, Yale University Abstract: Quantum superpositions of distinct coherent states in a single-mode harmonic oscillator, known as “cat states”, have been an elegant demonstration of Schr¨odinger’s famous cat paradox. Here, we realize a two-mode cat state of electromagnetic fields in two microwave cavities bridged by a superconducting artificial atom, which can also be viewed as an entangled pair of single-cavity cat states. We present full quantum state tomography of this complex cat state over a Hilbert space exceeding 100 dimensions via quantum non-demolition measurements of the joint photon number parity. The ability to manipulate such multi-cavity quantum states paves the way for logical operations between redundantly encoded qubits for fault-tolerant quantum computation and communication. Large-amplitude squeezed optical Schrödinger cat states with minimized non-Gaussian operational cost Hanna Le Jeannic, Laboratoire Kastler Brossel Abstract: The generation of freely-propagating large coherent-state superposition (CSS) is a critical capability in the context of the optical hybrid quantum information approach. However, their generation at a reasonable preparation rate remains challenging. We recently proposed and implemented a novel optical scheme enabling their heralded generation. Based on two-mode squeezed vacuum, linear mixing, and a n-photon detection performed on one of the modes, the process allowed to optimize the formation of the CSS in a versatile way, focusing all the non-Gaussian resources to prepare only the non-Gaussian part of the state. Using such a strategy, we demonstrated the experimental realization of large-amplitude squeezed CSS with a size |α|²=3 and a fidelity of 80%. The developed protocol and the achieved preparation rate make these states suitable as initial resources for subsequent quantum information protocols. Qomputer Science at Microsoft Research Alex Bocharov, Microsoft Abstract: Over the course of three decades, quantum algorithms have been developed that offer fast solutions to problems in a variety of fields including cryptography, number theory, optimization, chemistry, physics, and materials science. The parallel advance of quantum devices necessitates the development of software tools and platforms for programming, harnessing, and controlling a quantum computer. I will give a brief overview of Microsoft’s directions in quantum computation, focusing on recent work of the Quantum Architectures and Computation (QuArC) group. I will discuss promising applications of quantum computers, as well as Computer science methods and software techniques required to implement such applications in simulation and in real hardware.

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Industrializing qubits through automation Julian Kelly, Google Abstract: Recent advances in fidelity of digital superconducting qubits have enabled complex demonstrations of error correction and quantum simulation, highlighting their potential as a useful computational resource. However, scaling these experiments to numbers of qubits that are classically intractable will require significant advances in quantum control. In particular, operating systems of qubits with high fidelity requires some level of human intervention, hindering scalability. Although components of qubit control are typically automated, a full system solution is needed. Here, we present a framework for bootstrapping and diagnosing qubits fully autonomously by relating control calibrations as a directed graph. We demonstrate how this system can be used to scale control of many qubits, as well as assist in industrializing qubit manufacturing and characterization. Quantum @ NTT William Munro, NTT Abstract: The mission of NTT's Basic Research Laboratory is the promotion of advances in science and its contribution to our future business. To achieve these missions, we conduct basic research in the fields of Materials Science, Physical Science and Optical Science. Quantum Science is one such area where we have significant expertise in photonics, solid-state, superconducting and hybrid systems. In this presentation, we will highlight our recent developments in these area and discuss our future direction, indicating why fundamental research is so important. D-Wave's Approach to Quantum Computing: 1000-qubits and Counting! Colin William, Dwave Abstract: In this talk I will describe D-Wave's approach to quantum computing, including the system architecture of our 1000-qubit D-Wave 2X, its programming model, and performance benchmarks. Furthermore, I will describe how the native optimization and sampling capabilities of the quantum processor can be exploited to tackle problems in a variety of fields including medicine, machine learning, and computational finance.

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Hybrid quantum systems using magnons in a ferromagnetic crystal Yasunobu Nakamura, University of Tokyo Abstract: Collective excitations in solids sometime have long coherence times useful for quantum information processing. Superconducting qubits are the most advanced and successful example among them. In addition to long-lived harmonic oscillator modes found in superconducting resonators and cavities, nonlinearity brought by Josephson junctions plays a crucial role in quantum state control and measurement in superconducting quantum circuits. Now it is natural to apply the excellent quantum tools to other quantum systems. We are particularly interested in controlling other collective excitations in solids. It will expand the territory of our quantum technologies and give rise to quantum interfaces and transducers between various physical systems with different energy scales, which could be useful for quantum communication and sensing. In this talk, I will review our recent activities on quantum magnonics using a millimeter-scale ferromagnetic sphere as an example of such hybrid quantum systems. The collective spin excitations in the sphere, in particular the uniform spin precession, are strongly coupled with a microwave cavity mode [1] and then indirectly with a superconducting qubit [2]. The magnon-induced vacuum Rabi splitting observed in the system indicates that we can readily apply the well-established schemes of cavity (circuit) QED to magnons and manipulate and measure their quantum states. I will also discuss interaction between the collective spin excitations and infrared light and present experimental results on optomagnonics [3,4]. [1] Y. Tabuchi et al., Phys. Rev. Lett. 113, 083603 (2014). [2] Y. Tabuchi et al., Science 349, 405 (2015); arXiv:1508.05290. [3] R. Hisatomi et al., Phys. Rev. B. 93, 174427 (2016). [4] A. Osada et al., Phys. Rev. Lett. 116, 223601 (2016). Quantum Correlation between photons and single spin-waves in a solid-state environment Hugues De Riedmatten, ICFO-The Institute of Photonic Sciences Abstract: Quantum correlations between photons (ideally at telecom wavelengths) and long-lived spin-waves in quantum memories is an important resource for the distribution of quantum information to remote locations, using quantum repeater architectures. In this talk, I will focus on single spin-waves in a solid-state environment. Rare-earth (RE) doped crystals are promising candidates as quantum memories for light as they offer coherence properties comparable to those of atomic systems, but free of the drawbacks deriving from atomic motion. The research on RE based quantum memories has been so far mostly focused on the mapping of photonic quantum bits to optical collective excitations, but this leads to short lived and mostly pre-determined storage. However, some RE ions, as Praseodymium and Europium, exhibit the suitable energy level scheme, with three long-lived hyperfine ground states, to enable the spin-wave storage by transferring the collective optical excitations into collective spin excitations [1,2]. I will present our recent and current efforts towards the realization of quantum correlation between photons and long-lived single spin-waves in a Praseodymium doped crystal, following two different approaches. One approach consists in storing a single photon from a non-degenerate correlated pair generated by cavity enhanced spontaneous down conversion [3] in a solid state spin-wave quantum memory, leading to strong quantum correlation between a telecom photon and a solid-state spin wave. The other approach consists in using the quantum memory as a source of correlated photon pair

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with embedded memory. Finally, I will present a new approach towards the demonstration of solid-state integrated quantum memories, using laser-written waveguides [4]. [1] M. Gündoğan, P. M. Ledingham, K. Kutluer, M. Mazzera and H. de Riedmatten , A solid state spin-wave quantum memory for time-bin qubits, Phys. Rev. Lett. 114, 230501 (2015) [2] P. Jobez, C. Laplane, N. Timoney, N. Gisin, A. Ferrier, P. Goldner, and M. Afzelius, Coherent Spin Control at the Quantum Level in an Ensemble-Based Optical Memory, Phys. Rev. Lett. 114, 230502 (2015) [3] J. Fekete, D. Rieländer, M. Cristiani, and H. de Riedmatten, Ultranarrow-Band Photon-Pair Source Compatible with Solid State Quantum Memories and Telecommunication Networks Phys. Rev. Lett. 110, 220502 (2013) [4] G. Corrielli, A. Seri, M. Mazzera, R. Osellame and H. de Riedmatten, “An integrated optical memory based on laser written waveguides”, Phys. Rev. Applied 5, 054013 (2016) Towards a photon-phonon quantum interface Sungkun Hong, University of Vienna Abstract: Interfacing a single photon with various quantum degrees of freedom is an outstanding problem in modern quantum information science. For instance, it allows for manipulation and long-distance communication of remote quantum systems such as spin states of atoms, atomic ensembles or solid-state qubits. Recently, micro-fabricated mechanical devices have been considered as possible building blocks for quantum information architectures. They combine an engineerable solid-state platform on the nanoscale with the possibility to coherently interact with a variety of physical systems, which allows for mechanics-based hybrid quantum systems that interconnect different qubits through mechanical modes. I will discuss the implementation of a protocol (based on the probabilistic DLCZ scheme) to realize quantum interface between single phonons of a nano-mechanical device and single optical photons. In particular, I will present our recent demonstration of non-classical correlations between single photons and phonons in a micro-fabricated optomechanical resonator, which is the first step towards photon-phonon quantum interface. Generation of Mechanical Interference Fringes by Multi-Photon Quantum Measurement Michael Vanner, University of Oxford Abstract: One of the cornerstones of quantum mechanics is that matter can possess both particle- and wave-like properties. Since the inception of quantum mechanics, such wavelike behaviour has been observed in ever more massive systems - ranging from electrons, neutrons, ultracold atoms, and even large molecules comprising many hundreds of atoms. An exciting route to further extend the exploration of quantum phenomena to a macroscopic regime is through the study of quantum optomechanics where optical fields are used to manipulate the motion of mechanical resonators using radiation pressure. In contrast to a two-slit experiment, a mechanical oscillator can exhibit interference fringes in a quadrature of motion (analogous to the pattern on a distant screen) where the superposition is in the conjugate quadrature (analogous to the wavefunction at the slits). Thus far, mechanical interference fringes have only been observed in microscopic mechanical resonators - single trapped ions. Here we report the observation of mechanical interference fringes in the motion of a macroscopic membrane comprising 10^16 atoms [1]. Our experiment to generate and observe mechanical interference fringes consists of a SiN membrane forming part of two optical interferometers. One of the interferometers uses single photon detection to generate non-Gaussian mechanical states and the other uses an independent optical field to reconstruct the mechanical phase-space distribution. By counting

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a single photon in the output of the state preparation interferometer the optical field is projected into a path entangled number state. When the mechanical resonator interacts with this optical state it will then experience a superposition of a momentum transfer (single photon present) and the identity operation (no photon present), and interference fringes will be generated in the mechanical position distribution. The size of the superposition that can be generated, and indeed the frequency of the mechanical interference fringes, can be enhanced by projecting the optical field onto a N00N state, where the momentum transfer to the mechanical oscillator is enhanced by a factor of N. We have experimentally observed a factor of two increase in the mechanical interference fringe frequency by projection onto a two-photon N00N state, where the phase super-resolution of the measurement is mapped to the mechanical motion. We would like to highlight that our approach can generate non-classical mechanical states, which exhibit Wigner negativity, independent of the mechanical thermal occupation and the optomechanical coupling strength. Moreover, the scheme is resilient to loss, and can be readily applied to other optomechanical and bosonic systems more broadly. This observation of interference fringes in a macroscopic mechanical resonator opens an avenue for several further studies including the exploration of potential quantum gravitational phenomena, and the development of quantum metrology and sensing applications. [1] M. Ringbauer, T. J. Weinhold, A. G. White, M. R. Vanner arXiv:1602.05955 (2016). Combining 1D Nanoscale Waveguides and Cold Atoms Neil Corzo, Laboratoire Kastler Brossel Abstract: Reversible light-matter interfaces are crucial elements in quantum optics and quantum information networks. In this context, our group focuses on the manipulation of light at the single-photon level using ensembles of cold neutral atoms. In a free-space implementation, we reported for instance the quantum storage of qubits encoded in the orbital angular momentum degree of freedom [1] and a multiple-degree-of-freedom quantum memory for structured light [2]. Recently, our group has also developed an interface where light, tightly guided by a subwavelength-diameter optical fiber, strongly interacts with free or trapped atoms near its vicinity. Here, I will describe two of our more recent results using this interface: a) the demonstration of slow light and optical storage at the single-photon level in this all-fibered setting [3]; and b) the observation of a large Bragg reflection off a 1D optical lattice [4]. Our atom-fiber interface, with its enhanced atom-photon interactions, constitutes a promising alternative to free-space focusing, which limits the interaction one can obtain, and provides a novel platform for developing all-fibered quantum networks. [1] A. Nicolas et al., A quantum memory for orbital angular momentum photonic qubits, Nature Photon. 8, 234 (2014). [2] V. Parigi et al., Storage and retrieval of vector beams of light in a multiple-degree-of-freedom quantum memory, Nature Commun. 6, 7706 (2015). [3] B. Gouraud et al., Demonstration of a memory for tightly guided light in an optical nanofiber, Phys. Rev. Lett. 114, 180503 (2015). [4] N. Corzo et al., Large Bragg reflection from a 1D chains of trapped atoms near a nanoscale waveguide, in preparation.

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Random symmetric states for robust quantum metrology Michal Oszmaniec, ICFO (Barcelona) Abstract: We study how useful random states are for quantum metrology, i.e., surpass the classical limits imposed on precision in the canonical phase estimation scenario. First, we prove that random pure states drawn from the Hilbert space of distinguishable particles typically do not lead to super-classical scaling of precision even when allowing for local unitary optimization. Conversely, we show that random states from the symmetric subspace typically achieve the optimal Heisenberg scaling without the need for local unitary optimization. Surprisingly, the Heisenberg scaling is observed for states of arbitrarily low purity and preserved under finite particle losses. Moreover, we prove that for such states a standard photon-counting interferometric measurement suffices to typically achieve the Heisenberg scaling of precision for all possible values of the phase at the same time. Finally, we demonstrate that metrologically useful states can be prepared with short random optical circuits generated from three types of beam-splitters and a non-linear (Kerr-like) transformation. The full version of the work can be found on arXiv:1602.05407 Determining the essential components of a quantum many-body system from experiment Jörg Schmiedmayer, TU-Wien Abstract: A central objective of quantum simulators is to capture the essential physics of complex quantum many-body systems from experimental observations. We experimentally study a pair of tunnel-coupled one-dimensional atomic superfluids, which realise the quantum sine-Gordon model. From measured interference patterns we extract phase correlation functions and analyse if, and under which conditions, the higher-order correlation functions factorise into lower ones. This allows us to characterise the essential features of the model solely from our experimental measurements, detecting the relevant quasiparticles, their interactions and the topologically distinct vacua. Our method provides comprehensive insights into a non-trivial quantum field theory and establishes a general method to analyse quantum many-body systems through experiments. Undoing the effect of loss on entanglement Tim Ralph, University of Queensland Abstract: We present experimental results in which a two-mode squeezed state that has been corrupted by a large amount of loss on one mode is recovered via distillation. The level of entanglement in our distilled state is higher than that achievable by direct transmission of any state through a similar loss channel. This is a key bench-marking step towards the realisation of a practical continuous-variable quantum repeater and other CV quantum protocols.

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Experimental realisation of a variational ground state solver on a photonic chip Jianwei Wang, University of Bristol Abstract: We report an experimental implementation of a new hybrid protocol for solving eigenproblems using a quantum photonic processor and a classical searching algorithm. This protocol estimates the ground state energy of a quantum system by combining ideas from phase estimation and variational eigensolvers. Specifically, it learns this energy via direct measurement of only one qubit and then applies a variational optimisation of the trial state to estimate the minimal energy. We use this protocol to infer the ground state for the exciton transfer Hamiltonian in chlorophyll on a reconfigurable silicon quantum photonic device that can implement non-compiled controlled unitary operations. Distinguishability in three-photon scattering Stefanie Barz, University of Oxford Abstract: When more than two particles are involved, interference takes on a surprisingly rich character, which extends beyond the pairwise distinguishabilities. In fact, the output statistics from three interfering photons depends on four real parameters. Here, we show how the full parameter space can be probed experimentally by generating heralded single photons in three independent photon sources and interfering them in a fibre tritter. The full coincidence landscape is accessed by exploiting multiple degrees of freedom: time delays and polarisation. AlGaAs photonic devices: from quantum state generation to quantum communications Sara Ducci, Paris Diderot University Abstract: Nonclassical states of light are key components in quantum information science; in this domain, the maturity of semiconductor technology offers a huge potential in terms of ultra-compact devices including the generation, manipulation and detection of many quantum bits. Here we present our last achievements on AlGaAs quantum photonic devices emitting non-classical states of light at room temperature via spontaneaous parametric down conversion; the choice of this platform combines the advantages of a mature fabrication technology, photon pair emission in the C-telecom band, a direct band-gap and a high electro-optics effect. Here we show how microcavities based on a transverse pump configuration generating counterpropagating photons display an exterme versatility to engineer frequency correlations between the two photons of the pair. A toolbox to engineer and measure continuous variable entanglement leading to the production of Schrodinger cats and compass states will be presented. On the other hand, devices based on modal phase matching allow to achieve an extreme compactness, having already led to electrically injected photon pair sources working at room temperature. The quality of the quantum state generated by our devices will be caracterized in terms of indistinguishability and level of entanglement between the photons. In the last part of the talk, we will present our last results on a simple and complete system based on our source and on standard telecom components to perform a multi-user distribution of quantum keys based on polarization entangled photons.

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Separability Revisited Maciej Lewenstein, ICFO Abstract: Although assessing entanglement for generic multipartite states is recognized to be a very difficult task there might be tractable ways when the states under scrutiny fulfill some symmetries. Here we revisited the separability problem of general Diagonal Symmetric states, showing that they display a non trivial and rich structure, linked to their non-locality properties. Quantum Information Processing with Trapped Ions and Photons Rainer Blatt, Universatität Innsbruck Abstract: In this talk, the basic toolbox of the Innsbruck quantum information processor based on a string of trapped Ca+ ions will be reviewed. For quantum information processing, the toolbox operations are employed for quantum computations [1], for quantum simulations [2], and with optical cavities and photons they are used for the implementation of quantum interfaces [3] for the realization of quantum networks. For quantum computation, a scalable Shor algorithm was realized [1] with a string of trapped Ca+ ions. Towards scaling the trapped ion quantum computer, we encode one logical qubit in entangled states distributed over seven trapped-ion qubits. We demonstrate the capability of the code to detect one bit flip, phase flip or a combined error of both, regardless on which of the qubits they occur. Furthermore, we apply combinations of the entire set of logical single-qubit Clifford gates on the encoded qubit to explore its computational capabilities [4]. The quantum toolbox is further applied to carry out both analog and digital quantum simulations. The basic simulation procedure will be presented and its application will be discussed for a variety of spin Hamiltonians. Moreover, a spectroscopic technique is presented to study artificial quantum matter and use it for characterizing quasiparticles in a many-body system of trapped atomic ions [5]. For the realization of a quantum interface, trapped Ca+ ions in a cavity QED setup allow entanglement of a qubit with a photon and quantum state mapping [3]. [1] T. Monz et al., Science 351, 1068 (2016). [2] P. Jurcevic et al., Nature 511, 202 (2014). [3] T. Northup and R. Blatt, Nature Photonics 8, 356 (2014). [4] D. Nigg et al., Science 345, 302 (2014). [5] P. Jurcevic et al., Phys. Rev. Lett. 115, 100501 (2015). Programmable integrated optical circulator controlled by a single spin-polarized atom Arno Rauschenbeutel, TU Wien - Atominstitut, Vienna, Austria Abstract: We realize an integrated optical circulator which is based on the chiral interaction of a single atom with a pair of whispering-gallery-modes in a silica bottle microresonator. The strong transverse confinement of these modes leads to an inherent link between the local polarization of the light and its sense of propagation in the resonator, clockwise or counter-clockwise. In conjunction with the strongly polarization-dependent transition strengths of spin-polarized rubidium 85 atoms, this allows us to implement a direction-dependent atom-light interaction: For the clockwise propagating mode, we reach the strong coupling regime, while the coupling between the counter-clockwise mode and the atom is negligible. Interfacing this nonreciprocal atom-cavity system with two tapered fiber couplers in add-drop configuration thus implements an optical circulator. We study the device performance and

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show that the spin state of the atom controls to which output ports the light is routed. The demonstrated circulator is compatible with ultra-low light levels down to single photons and can, in principle, be operated in a quantum superposition of different routing directions. It thereby constitutes a first example of a new class of nonreciprocal quantum devices with many potential applications in integrated optical quantum networks and circuits. Creating perfect single photons for the demonstration of quantum supremacy Chao-Yang Lu, University of Science and Technology of China, Hefei Abstract: In this talk, I will report two routes towards experimental boson sampling with many photons. One is based on spontaneous parametric down-converted (SPDC) photon pairs that are generated probabilistically. Exploiting scattershot boson sampling scheme, the probabilistic nature of SPDC can be overcome by using ~n^2 SPDC sources. The other, more direct, route is employing deterministically generated single photons from solid-state quantum emitters. To reach boson sampling to a scale of 20-30 photons, both approaches would need single photons (heralded or deterministically generated) with simultaneously high purity, efficiency, and indistinguishability. This criteria was, however, not fulfilled previously, and thus, boson sampling with SPDC was limited to 3 photons for arbitrary input configuration and quantum dot (QD) single photons was limited to 2-photon experiments in the past 15 years since the first observation of antibunching. We developed SPDC two-photon source with simultaneously a brightness of ~12 MHz/W, a collection efficiency of ~70% and an indistinguishability of ~91% between independent photons. With this, we demonstrate genuine and distillable entanglement of ten photons under different pump power [1]. Such a state-of-the-art multi-photon platform will provide enabling technologies for challenging optical quantum information tasks such as teleportation of three degrees of freedom of photons [2] and scattershot boson sampling. Self-assembled InGaAs QDs are promising solid-state emitters with near-unity quantum efficiency and fast decay rate. Using a QD coupled to a micropillar, we produced single photons with high purity, near-unity indistinguishability [3], and high extraction efficiency, compatibly and simultaneously [4]. Long streams of >1000 single photons separated by tens of microseconds maintain a >92% indistinguishability, which are shown to be near transform limit [5]. The single photons are time-bin encoded and interfered in an electrically programmable loop-based network [6]. With further refinement, the two approaches may be feasible to be scaled up to ≳ 20-boson sampling to outperform classical computers, and thus provide experimental evidence against the Extended Church-Turing Thesis. References: [1] X.-L. Wang et al. Experimental ten-photon entanglement, arXiv:1605.08547. [2] X.-L. Wang et al. Quantum teleportation of multiple degrees of freedom of a single photon, Nature 518, 516 (2015). [3] Y.-M. He et al. On-demand semiconductor single-photon source with near-unity indistinguishability Nature Nanotechnology 8, 213 (2013). [4] X. Ding et al. On-demand single photons with high extraction efficiency and near-unity indistinguishability from a resonantly driven quantum dot in a micropillar, Phys. Rev. Lett. 116, 020401 (2016). [5] H. Wang et al. Near transform-limited single photons from an efficient solid-state quantum emitter, Phys. Rev. Lett. 116, 213601 (2016). [6] Y. He et al. Boson sampling with a single-photon device, arXiv:1603.04127

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Longitudinal Coupling: Key to Scalable Qubit Layouts? David DiVincenzo, RWTH Aachen University Abstract: Many labs presently plan to scale up to the next generation of quantum computing systems (10-100 qubits) usings arrays of coupled qubit-cavity systems, with the coupling being described by the Jaynes-Cummings Hamiltonian. But this coupling is not ideal for scaleup; we have worked out constructions, feasible within circuit QED, for a new fixed-frequency superconducting qubit and show how it can be scaled up to a grid with strictly local interactions, where interactions involve longitudinal rather than transverse (Jaynes-Cummings) couplings. This longitudinal coupling is inherently different from the usual σx-type \textit{transverse coupling}even with always-on interactions; couplings produce dressed qubits, but the range of dressing extends strictly to the nearest-neighbor resonator and no further. We note that just four distinct resonator frequencies, and only a single unique qubit frequency, suffice for the scalability of this scheme. Details of this work are found in arxiv:1511.06138.

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Abstracts – Posters (Monday) P1-3 Entanglement measure for composite systems of indistinguishable particles Janusz Grabowski Abstract: We analyze the concept of entanglement for multipartite system with bosonic and fermionic constituents and its generalization to systems with arbitrary parastatistics. We use the representation theory of symmetric groups to formulate a unified approach to this problem in terms of simple tensors with appropriate symmetry which turn out to be highest weight vectors of the natural representation of the symmetric group. For an arbitrary parastatistics, we define the S-rank generalizing the notion of the Schmidt rank. The S-rank, defined for all types of tensors, serves for distinguishing entanglement of pure states and constructing an entanglement measure on mixed states, satisfying all standard requirements. P1-4 Heralded Measurement-Device-Independent Quantum Key Distribution with Vector Vortex Beams Chen Dong, Shang-Hong Zhao and Shutao Li Abstract: The vector vortex(VV) beam, originally introduced to exhibit a form of single particle quantum entanglement between different degrees of freedom, has specific applications for quantum-information protocols. In this paper, by combining measurement-device-independent quantum key distribution (MDI-QKD) with spontaneous parametric-down-conversion source(SPDCS), we present a modified MDI-QKD scheme with pairs of VV beams, which shows a structure of hybrid entangled entanglement corresponding to intrasystem entanglement and intersystem entanglement. The former entanglement, which is entangled between polarization and orbit angular momentum within each VV beam, is adopted to overcome the polarization misalignment associated with random rotations in quantum key distribution. The latter entanglement, which is entangled between the two VV beams, is used to perform MDI-QKD protocol with SPDCS to inherit the merit of heralded process. The numerical simulations show that our modified scheme has apparent advances both in transmission distance and key generation rate compared to the original MDI-QKD. Furthermore, our modified protocol only needs to insert q-plates in practical experiment. P1-5 Quantum Coherence Sets The Quantum Speed Limit For Mixed States Debasis Mondal, Chandan Datta and Sk Sazim Abstract: We cast observable measure of quantum coherence or asymmetry as a resource to control the quantum speed limit (QSL) for unitary evolutions. For non-unitary evolutions, QSL depends on that of the state of the system and environment together. We show that the product of the time bound and the coherence (asymmetry) or the quantum part of the uncertainty behaves in a geometric way under partial elimination and classical mixing of states. These relations give a new insight to the quantum speed limit. We also show that our bound is experimentally measurable and is tighter than various existing bounds in the literature. http://www.sciencedirect.com/science/article/pii/S0375960115010518

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P1-7 Pushing single photon counting technology towards better Size, Weight and Power (SWAP) performance. Rakhitha Chandrasekara, Zhongkan Tang, Yue Chuan Tan, Kadir Durak, Cliff Cheng and Alexander Ling Abstract: Single photon counting is widely used in low-light sensing and communications experiments. However, the development of detector technology often does not keep pace with the development of new optical sources or protocols, restricting the deployment of quantum communication infrastructure. Our team is working on a number of quantum experiments where the Size, Weight and Power (SWAP) requirements are too challenging for commercial-off-the-shelf detector modules and necessitate the development of fast, compact and efficient detector circuits. In this poster, we present a novel in-situ measurement method that extracts the pulse height from silicon Geiger-mode avalanche photodiodes (GM-APDs) while it is performing photon counting. This technique will enable fine control of the GM-APD when it is actively quenched, and enable a compact and efficient detector circuit that is capable of detecting millions of photon events per second. We also consider the interplay of photon statistics (from a single photon source) and detector circuit response in order to develop a model that predicts the performance of a quantum communication system based on entangled photons from Spontaneous Parametric Downconversion sources. P1-8 Temporal imaging with squeezed light Mikhail Kolobov and Giuseppe Patera Abstract: We generalize the scheme of conventional temporal imaging to quantum temporal imaging viable for nonclassical states of light. As an example, we apply our scheme to temporally broadband squeezed light and demonstrate a possibility of its noiseless magnification. In particular, we show that on can magnify by a given factor the coherence time of squeezed light and match it to the response time of the photodetector. This feature opens new possibilities for practical applications of temporally broadband squeezed light in quantum optics and quantum information. P1-10 Quantum key distribution with leaky devices Marcos Curty, Kiyoshi Tamaki and Marco Lucamarini. Abstract: In recent years, there has been a great effort to prove the security of quantum key distribution (QKD) with a minimum number of assumptions. Besides its intrinsic theoretical interest, this would allow for larger tolerance against device imperfections in the actual implementations. However, even in this device-independent scenario, one assumption seems unavoidable, that is, the presence of a protected space devoid of any unwanted information leakage in which the legitimate parties can privately generate, process and store their classical data. Here we relax this unrealistic and hardly feasible assumption and introduce a general formalism to tackle the information leakage problem in QKD systems. We apply our security proof to cases of practical interest and show key rates similar to those obtained in a perfectly shielded environment. Our work constitutes a fundamental step forward in guaranteeing implementation security of quantum communication systems.

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P1-11 Survivor! Analysis of a photon pair source recovered intact from a catastropic launch failure. Tang Zhongkan Xavier, Alexander Ling, Rakhitha Chandrasekara, Yue Chuan Tan and Cliff Cheng Abstract: Secure generation of symmetric key material at distant sites using quantum signals, known as quantum key distribution (QKD), is one of the most technologically mature outcomes of research into quantum communication. Several efforts are ongoing to utilize satellites as receivers or transmitters for QKD demonstrations in order to overcome the distance limit due to the fiber losses and the lack of quantum repeaters. Motivated by the vision of a global quantum communication network, we present a compact and rugged photon pair source that can be embedded into small cost-effective satellites called CubeSats. One of the driving requirements to utilize CubeSats for this purpose is to build a photon pair source that is compatible with the size, weight and power (SWaP) requirements of a nanosatellite. The complete package (photon pair source and the electronics) was compact (9.5 × 9.6 x 3.8 cm^3) with a mass of about 250 g and was designed to fit a standard CubeSat spacecraft. The package was installed into GomX-2 CubeSat to be deployed from International Space Station. Unfortunately the mission failed when the launch vehicle was destroyed shortly after launch but GomX-2 was successfully recovered from the debris. The science package within was found to be completely operational, continuing to produce high quality polarization correlations. Post-recovery data is compared to baseline measurements collected before the launch attempt and no degradation in brightness or polarization correlation was observed. In this talk, we will discuss the steps taken in assembling the source, discuss how possible points of failure can be addressed in future designs, and describe future missions that are in the pipeline. The ability of the source to survive very dramatic conditions yields lessons for designers of practical quantum technology. It demonstrates that with adequate engineering quantum devices need not be delicate instruments confined to laboratory environments. Our work leverages the on-going revolution in small satellite systems and demonstrates that the financial and technical barriers to quantum experiments in space are rapidly falling. P1-12 Semiclassical Theory of Superresolution for Two Incoherent Optical Point Sources Mankei Tsang, Ranjith Nair and Xiao-Ming Lu Abstract: Using a semiclassical model of photodetection with Poissonian noise and insights from quantum metrology, we prove that linear optics and photon counting can optimally estimate the separation between two incoherent point sources without regard to Rayleigh's criterion. The model is applicable to weak thermal or fluorescent sources as well as lasers.

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P1-13 Quantum State Smoothing Howard Wiseman and Ivonne Guevara Abstract: Smoothing is an estimation method whereby a classical state (probability distribution for classical variables) at a given time is conditioned on all-time (both earlier and later) observations. Here we define a smoothed quantum state for a partially monitored open quantum system, conditioned on an all-time monitoring-derived record. We calculate the smoothed distribution for a hypothetical unobserved record which, when added to the real record, would complete the monitoring, yielding a pure-state ``quantum trajectory''. Averaging the pure state over this smoothed distribution yields the smoothed quantum state. This is a mixed state, but, we show, less mixed than the conventional (filtered) state conditioned only on the past record. We distinguish our quantum smoothed state from other concepts that have been studied recently, and show how the choice of actual unravelling affects the purity increase over that of the filtered state. P1-15 Electronic and spin properties of Si vacancy in SiC Moein Najafi Ivaki and Mohammad Ali Vesaghi Abstract: The silicon vacancy in silicon carbide is a strong emergent candidate for applications in quantum information processing and sensing. Alongside research focusing on nitrogen vacancy centers in diamond, an alternative strategy seeks to identify new spin systems with an expanded set of technological capabilities. 4H, 6H and 3C polytypes of SiC all host coherent and optically addressable defect spin states, including states in all three with room-temperature quantum coherence. Electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) investigations suggest that silicon vacancy related point defects in SiC possess properties the similar to those of the NV center in diamond, which in turn makes the silicon vacancy in silicon carbide a strong emergent candidate for applications in quantum information processing and sensing. We are seeking to provide a new theoretical frame to explain a wider range of experimental results. Employing a proposed generalized Hubbard model, with the help of electronic structure programs, DFT, second quantization, and various computational approaches, we are bring about new insight on this special vacancy. Our central point of attention is folding in two main approaches for finding Hubbard parameters as well as wave functions: SP3 orbitals and DFT. To obtain electronic and spin properties of the system, we combine these two, taking into account all the governing interactions and possibilities for the system to relax itself. The properties may include: spatial symmetries, ground and excited states spin, Spin densities, entanglement, and transition energy of optical transition. P1-17 Optimal two-mode attack against two-way continuous-variable quantum key distribution

Yichen Zhang, Zhengyu Li, Yijia Zhao, Song Yu and Hong Guo Abstract: We report the optimal eavesdropping strategy against two-way continuous-variable quantum key distribution at fixed channel parameters, which is given by a two-mode attack with symmetric and appropriate separable correlations.

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P1-18 Measurement-based Formulation of Quantum Heat Engine Masahito Hayashi and Hiroyasu Tajima Abstract: There exist two formulations for quantum heat engine. One is semi-classical scenario, and the other is full quantum scenario. The former is formulated as a unitary evolution for the internal system, and is adopted by the community of statistical mechanics. In the latter, the whole process is formulated as unitary. It was adopted by the community of quantum information. However, their formulation does not consider measurement process. In particular, the former formulation does not work when the amount of extracted work is observed. In this paper, we formulate the quantum heat engine as the measurement process because the amount of extracted work should be observed in a practical situation. Then, we clarify the contradiction of the former formulation by using a novel trade-off relation. The trade-off relation clarifies the impossibility of proper work extraction by an internal unitary process. P1-19 Development of single photon source using Silicon-Vacancy(SiV) nano-diamond Hong Kee Suk, Bae In-Ho and Lee Dong-Hoon Abstract: The single photon source(SPS) using impurity centers in nano-diamonds, in specific nitrogen-vacancy(NV) and silicon-vacancy (SiV) centers is becoming a promising qubit for quantum metrology and communications. As the single emitter, impurity center of silicon-vacancy (SiV) in a nano-diamond is investigated. In this conference, we present the current status and results of the development of the single photon source at KRISS. P1-21 Inhibition of ground-state superradiance and light-matter decoupling in circuit QED Zeliang Xiang, Tuomas Jaako and Peter Rabl Abstract: We study effective light-matter interactions in a circuit QED system consisting of a single LC resonator, which is coupled symmetrically to multiple superconducting qubits. Starting from a minimal circuit model, we demonstrate that in addition to the usual collective qubit-photon coupling the resulting Hamiltonian contains direct qubit-qubit interactions, which prevent the otherwise expected superradiant phase transition in the ground state of this system. Moreover, these qubit-qubit interactions are responsible for an opposite mechanism, which at very strong couplings completely decouples the photon mode and projects the qubits into a highly entangled ground state. These findings shed new light on the controversy over the existence of superradiant phase transitions in cavity and circuit QED systems, and show that the physics of ultrastrong light-matter interactions in two- or multi-qubit settings differ drastically from the more familiar one qubit case.

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P1-22 Steering Bell-diagonal states (Ref. www.nature.com/articles/srep22025) Quan Quan Abstract: We investigate the steerability of two-qubit Bell-diagonal states under projective measurements by the steering party. In the simplest nontrivial scenario of two projective measurements, we solve this problem completely by virtue of the connection between the steering problem and the joint-measurement problem. A necessary and sufficient criterion is derived together with a simple geometrical interpretation. Our study shows that a Bell-diagonal state is steerable by two projective measurements iff it violates the Clauser-Horne-Shimony-Holt (CHSH) inequality, in sharp contrast with the strict hierarchy expected between steering and Bell nonlocality. We also introduce a steering measure and clarify its connections with concurrence and the volume of the steering ellipsoid. In particular, we determine the maximal concurrence and ellipsoid volume of Bell-diagonal states that are not steerable by two projective measurements. Finally, we explore the steerability of Bell-diagonal states under three projective measurements. A simple sufficient criterion is derived, which can detect the steerability of many states that are not steerable by two projective measurements. Our study provided a number of instructive analytical results on steering, which are quite rare in the literature. These results not only furnish a simple geometric picture about steering of Bell-diagonal states, but also offer valuable insight on the relations between entanglement, steering, and Bell nonlocality. They may serve as a starting point for exploring more complicated steering scenarios. P1-23 Suppression law of quantum states in a 3D photonic fast Fourier transform chip Niko Viggianiello Abstract: During the last three decades, photonic platforms have been demonstrated to be in principle capable to perform universal quantum computing. Recently, multi-particle interference effects of many photons in large interferometers are attracting a strong interest, as they should be able to show unprecedented evidences of the superior quantum computational power compared with that of classical devices. The main example is given by the boson sampling computational problem, which consists in sampling from the probability distribution given by the permanents of the nxn submatrices of a given Haar random unitary. The problem is computationally hard (in n) for a classical computer, since calculating the permanent of a complex-valued matrix is a #P hard problem. However, sampling from the output distribution can be efficiently achieved by letting n indistinguishable photons evolve through an optical interferometer implementing the unitary transformation in the Fock space, and by detecting output states. The chance to provide evidences of a post-classical computation with this relatively simple set-up has triggered a large experimental effort, leading to small-scale implementations, as well as theoretical analyses on the effects of experimental imperfections and on possible implementations including alternative schemes. In the context of searching for experimental evidences, a boson sampling experiment poses a problem of certification of the result’s correctness in the computationally hard regime. The very complexity of the boson-sampling computational problem precludes the use of a brute-force approach, that is, calculating the expected probability distribution at the output and comparing it with the collected data. Efficient statistical techniques able to rule out trivial alternative distributions have been proposed and tested, but the need for more stringent tests able to rule out less trivial distributions has led, and continues to encourage, additional research efforts in this direction. In particular, an efficient test able to confirm true n-photon interference in a multimode device has been recently proposed. The protocol is based on the use of an interferometer implementing the Fourier matrix. When feeding this device with multi-photon states of a specific symmetry, suppression of many output configurations is

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observed, due to granular many-particle interference. The implications of this effect go well beyond the certification of boson sampling devices. As a generalization of the two-photon/two-modes Hong–Ou–Mandel (HOM) effect, the suppression law, also named Zero-Transmission law, is important at a fundamental level, while at the practical level it could be used as a diagnostic tool for a wide range of photonic platforms. We report the experimental observation of the recent theoretically proposed suppression law for Fourier matrices, and its use to validate quantum many-body interference against alternative non-trivial hypotheses resulting in similar output probability distributions. The Fourier matrices have been implemented with an efficient and reliable approach by exploiting the quantum version of the fast Fourier Transfprm. The unitariy is implemented in integrated interferometers by exploiting the three-dimensional (3D) capabilities of femtosecond laser writing, so adopting an architecture scalable to a larger number of modes. The peculiar behaviour of Fock states compared with other kinds of states is investigated, showing in principle the validity of the certification protocol for the identification of true granular n-particle interference, which is the source of a rich landscape of quantum effects such as the computational complexity of boson sampling and can be a building block for a well tested source for quantum simulation platforms. P1-28 Quantum dot based simultaneous classical logic gates Ronny A. Christin and Duncan L. MacFarlane Abstract: The interaction with a “flying” photon traveling through a waveguide and a quantum dot has been previously proposed as a way to create quantum photonic logic gates. We propose a hybrid logic gate based on the interaction between a path encoded photon and quantum dots coupled to the waveguides. In this work, the stimulated emission characteristics of quantum dots are leveraged to enable logical operations such as the NAND gate. P1-29 Error probability in quantum-dot based quantum circuits Ronny A. Christin and Duncan L. MacFarlane Abstract: Quantum Dots have been investigated for various roles in quantum computing. However, spontaneous emission results in the loss of quantum information. The lifetime, τ21, and the speed of light in the waveguides determine the maximum physical dimensions of the circuit for a given number of quantum dots and probability of information loss. Control, therefore, over τ21 is critical to the realization of these circuits. This work details the Purcell factors necessary to realize a circuit of any reasonable size.

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P1-30 Measurement-dependent locality with non-i.i.d. measurements Ernest Y.-Z. Tan, Yu Cai and Valerio Scarani Abstract: For tests or applications of Bell inequalities, an important assumption is that the measurements are chosen freely, or more specifically, that the choice of measurements is independent of the source [1]. This can also be viewed in terms of randomness amplification, where partially free random bits are used as inputs for the measurements and the measurement outcomes are taken as output bits [2]. The consequences of relaxing the assumption of measurement independence have been investigated in previous works [1,3], indicating for instance that a relatively small amount of measurement dependence is sufficient to model a violation of the CHSH inequality. On the other hand, Pütz and co-workers [3] showed that the set of correlations that can be modelled in this manner is restricted to a set referred to as the measurement-dependent local (MDL) polytope. In particular, they provided an MDL inequality for i.i.d. measurements that can be violated by quantum correlations for arbitrarily small amounts of measurement independence. In this work, we study the case of non-i.i.d. measurements, which may be correlated across multiple runs of a Bell test. We focus mainly on the case of block-i.i.d. measurements with blocks of size 2. We have found that the inequality developed for the i.i.d. case is substantially less robust in this scenario, but also that there exist inequalities more suitable for the block-i.i.d. case. However, we have found a nontrivial level of measurement dependence beyond which the no-signalling polytope becomes a subset of the MDL block-i.i.d. polytope, and thus there can be no quantum violations of MDL block-i.i.d. inequalities beyond this level. Therefore, this shows that the result for the i.i.d. scenario does not generalise to the non-i.i.d. scenario. [1] Hall, M. Relaxed Bell inequalities and Kochen-Specker theorems. Phys. Rev. A 84, 022102 (2011). [2] Colbeck, R. and Renner, R. Free randomness can be amplified. Nature Physics 8, 450–453 (2012). [3] Pütz, G., Rosset, D., Barnea, T. J., Liang, Y.-C., and Gisin, N. Arbitrarily Small Amount of Measurement Independence Is Sufficient to Manifest Quantum Nonlocality. Phys. Rev. Lett. 113, 190402 (2014). P1-32 Weiss-Weinstein Error Bounds for Quantum Parameter Estimation Xiao-Ming Lu and Mankei Tsang Abstract: We propose a quantum version of the Weiss-Weinstein lower bounds on the estimation error of random parameters. The quantum Weiss-Weinstein bounds (QWWB) is a superior alternative to the popular quantum Cramer-Rao bound (QCRB), in the sense that it includes the QCRB as a special case and does not require the differentiability of prior distributions and conditional quantum states as the QCRB does.

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P1-33 Quantum state preparation: the untold story Holger F. Hofmann Abstract: Quantum mechanics usually starts with the assumption that physical systems are described by quantum states. However, the preparation of a system in a specific quantum state is itself an actual physical process in the laboratory, and no discussion of quantum measurement can be complete without a look at the actual physics of quantum state preparation. Here, I present a general analysis of the state preparation process that identifies dynamical randomizations as the central characteristics of all quantum state preparation processes. I point out that this result provides a physical explanation for the mathematical formalism that may resolve many of the mysteries of quantum mechanics. P1-34 Multi-photon interference explained by the action of optical phase shifts Holger F. Hofmann, Keito Hibino, Kazuya Fujiwara and Jun-Yi Wu Abstract: Multi-photon interferences are described by superpositions of different photon numbers in the paths of the interferometer. But what determines the periodicity of a specific interference fringe when the input state and the detected state are superpositions of a wide range of path states? Here, we show that the periodicity of a multi-photon fringe is a function of the input and output photon numbers that corresponds to the classical relation between intensity differences in the interferometer. P1-35 Atoms as quantum beam-splitters in waveguide QED Alexandre Roulet, Pierre-Olivier Guimond, Jibo Dai, Huy Nguyen Le and Valerio Scarani Abstract: Rapid experimental progress is being made in the field of waveguide QED. This provides an interesting playground for studying what happens when devices that are usually considered classical are replaced by quantum objects allegedly performing the same functionality. In this paper we present the following three devices:

• an atomic beam-splitter; • a cavity made of atomic Bragg mirrors; • a diode based on two non-identical atoms.

Please refer to the attached abstract for further details on our submission. P1-36 Robust H∞ Estimation for Linear Uncertain Quantum Systems Shibdas Roy and Ian Petersen Abstract: We consider classical estimators for a class of physically realizable linear quantum systems. Optimal estimation using a complex Kalman filter for this problem has been previously explored. Here, we study robust H∞ estimation for uncertain linear quantum systems. The estimation problem is solved by converting it to a suitably scaled H∞ control problem. The solution is obtained in the form of two complex algebraic Riccati equations. A relevant example involving dynamic optical squeezers is presented to illustrate the efficacy of our method.

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P1-37 Two qubit near-field microwave gates on 43Ca+ James Tarlton, Martin Sepiol, Jochen Wolf, Thomas Harty, Christopher Ballance, Diana Craik, Vera Schafer, Keshav Thirumalai, Laurent Stephenson, Andrew Steane and David Lucas Abstract: Quantum logic with trapped atomic ions relies on coupling the ions via their shared motional modes. This coupling is provided by the gradient of a driving field over the extent of the ions’ motion. This driving field has traditionally been produced by lasers because of the favorable short wavelengths that can be used. However, when ions are confined tens of microns above a waveguide, strong magnetic field gradients can be generated at microwave frequencies despite their long free-space wavelength [1]. Compared with lasers, this approach promises a higher level of control and integration, along with a reduction of technical complexity thanks to the relative ease of generating and manipulating microwave fields. So far, this method has only been applied at the National Institute of Standards and Technology, resulting in a two qubit gate fidelity of 76% [2]. We present our research on this technique using an in-house designed and micro-fabricated surface ion trap at room temperature. We have been able to implement a two qubit Mølmer-Sørensen gate on two 43Ca+ ions in a static field of 146G with 99.3% fidelity, above the fault-tolerant threshold. We also present our work towards developing a new trap with two major technical improvements. The first of these is to produce a microwave field gradient at an approximate field null with a single "meander" electrode, as proposed by the Hannover group [3]. The second improvement is to cryogenically cool the trap, which should reduce the ion heating rate [4,5], one of the main sources of gate error in our current system. References [1] C. Ospelkaus et al., Physical Review Letters 101, 090502 (2008) [2] C. Ospelkaus et al., Nature 476, 181-184 (2011) [3] M. Carsjens et al., Applied Physics B 114, 243-250 (2014) [4] J. Labaziewicz et al., Physical Review Letters 101, 180602 (2008) [5] J. Chiaverini et al., Physical Review A 89, 012318 (2014) P1-39 Protecting quantum discord from amplitude damping decoherence via weak measurement and its reversal Yong-Su Kim, Jiwon Yune, Kang-Hee Hong, Hyang-Tag Lim, Jong-Chan Lee, Osung Kwon, Sang-Wook Han, Sung Moon and Yoon-Ho Kim Abstract: We show that a protocol deploying weak measurement and quantum measurement reversal can effectively protect quantum discord from amplitude damping decoherence, and thus enabling to distribute quantum correlation between two remote parties in a noisy environment. We theoretically and experimentally evaluate the effectiveness of quantum measurement reversal in protecting the amount of quantum discord. Our results ultimately verifies that general quantum correlations can be protected by the protocol.

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P1-40 Experimental demonstration of efficient superdense coding in the presence of non-Markovian noise Bi-Heng Liu, Xiao-Min Hu, Yun-Feng Huang, Chuan-Feng Li, Guang-Can Guo, Sabrina Maniscalco and Jyrki Piilo Abstract: Many quantum information tasks rely on entanglement, which is used as a resource, for example, to enable efficient and secure communication. Typically, noise, accompanied by loss of entanglement, reduces the efficiency of quantum protocols. We demonstrate experimentally a superdense coding scheme with noise, where the decrease of entanglement in Alice’s encoding state does not reduce the efficiency of the information transmission. Having almost fully dephased classical two-photon polarization state at the time of encoding, we reach values of mutual information close to 1.43 (1.73) with 3-state (4-state) encoding. This high efficiency relies both on non-Markovian features, that Bob exploits just before his Bell-state measurement, and on very high visibility (99.6%) of the Hong-Ou-Mandel interference within the experimental set-up. Our proof-of-principle results pave the way for exploiting non-Markovianity to improve the efficiency of quantum information processing tasks. P1-41 An analysis of the statistics of multi-photon interference Kazuya Fujiwara and Holger F. Hofmann Abstract: As total photon number increases, the interference of photon number states at a 50:50 beam splitter results in increasingly complex quantum interference patterns in the probability distribution over possible output photon numbers. In this presentation, we analyze the quantum interference patterns of the output for arbitrary photon numbers and derive a simple relation that explains the appearance of periodic oscillations of probability in the output photon number difference. P1-43 Phase-encoded measurement device independent quantum key distribution without a shared reference frame Ying Sun and Shang-Hong Zhao Abstract: In this paper, a phase-encoded measurement device independent quantum key distribution (MDI-QKD) without a shared reference frame, which can generate secure keys between two parties while the quantum channel or interferometer introduces an unknown and slowly time-varying phase, is presented. Taking finite-key analysis into account, the asymptotic secret key rate and error rate, respectively, with single photons source (SPS) and weak coherent source (WCS), is analyzed. The numerical simulation show that the improved phase-encoded MDI-QKD has apparent superiority both in transmission distance and key generation rate, and the robustness and practical security will be greatly improved in the high-speed MDI-QKD system, while the fluctuations of the secure key rate are primarily due to the low systematic repetition rate. Moreover, the rejection of the frame-calibrating part will intrinsically reduce the consumption of resources as well as the potential security flaws of practical MDI systems. The analysis results indicate the feasibility of our scheme and its value for QKD network scenarios.

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P1-44 Unitary Estimation with Resource Constraints Masahito Hayashi, Sai Vinjanampathy and Leong Chuan Kwek Abstract: This paper addresses the estimation of the unknown phase parameter. Our problem is composed of the optimization of the input state and the measurement. We impose the energy constraint to the input state when the Hamiltonian is given as the number operator in the Boson-Fock space. Then, we show that quadratic enhancement in the mean squared error of the estimated parameter when the energy is sufficiently large. We propose an experimental setup to generate an input state achieving for enhanced metrology using squeezing transformations.

P1-45 Experimental Tests of Gravitational Decoherence Nathan Mcmahon and Gerard Milburn Abstract: Quantum mechanics and general relativity are two major achievements in physics, both tested to high levels of accuracy. However as the theory currently stands these two ideas are fundmentally incompatible. While understanding the full theory is a significant project, taking the Newtonian limit we can begin to test gravitional interactions within the quantum regime. There has been some interest in a class of models, such as the Penrose and Diosi models [1,2], where gravitional interactions cause spontaneous collapse. More recently the approach taken by Kefri, Taylor and Milburn predicts the same amount of decoherence from gravitational sources as the Diosi model, but is built off the initial assumption that gravity can only interact via a classical channel[3]. This kind of model leads to other interesting results such as in their initial and subsequent papers where the KTM model appears to indicate that interactions via gravity can never generate entanglement[3,4]. If such a statement is true in general it would place a limit on what kind of quantum technologies could be constructed. Such as in the recent proposal by Johnsson, Brennen, and Twamley [5] for a the measurement of the gravitational field using superconducting qubits. In this style of technology the entanglement used is generated by gravitational interactions. If the KTM model is indeed the correct description of Newtonian quantum gravity then this proposal would not be a feasible approach to emergent quantum technologies This leads to significant testable differences between the original quantum theory and these spontaneous collapse via gravitational interactions models. Considering optomechanical systems, we find that gravitational decoherence appears as a pure temperature shift in the bath modes. Therefore any signitures of decoherence would simply appear as a external source of heating in any prior experiments not testing for gravitational decoherence. We have considered methods to distinguish the signiture of gravitaitional decoherence from other sources of heating and will discuss proposals for experimental tests of gravitational decoherence. In particular we will discuss a proposal for an experimental test for gravitational decoherence, which appears to be feasible with current technologies. [1] On gravity's role in quantum state reduction, Roger Penrose, General relativity and Gravitation 28 (5):581-600, (1996). [2] The gravity-related decoherence master equation from hybrid mechanics, Lajos Diosi, J.Phys.Conf.Ser. 306 012006 -(9), (2011) [3] A classical channel model for gravitational decoherence, D. Kafri, J.M. Taylor and G. J. Milburn, New J. Physics 16, 065020, (2014). [4] Bounds on quantum communication via Newtonian gravity, D. Kafri, G. J. Milburn, J. M. Taylor, New J. Physics 17, 015006, (2015). [5] Macroscopic superpositions and gravimetry with quantum magnetomechanics, MT Johnsson, GK Brennen, J Twamley, arXiv:1412.6864, (2014).

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P1-46 Time multiplexing toward indistinguishable and deterministic single-photon generation Fumihiro Kaneda and Paul Kwiat Abstract: Photon-pair generation by spontaneous parametric downconversion (SPDC) or spontaneous four-wave mixing (SFWM) has been widely used for creating two- and multi-partite entangled states and heralded single-photon states. However, the probabilistic nature of the photon-pair generation process is a key obstacle to scaling up QIP systems beyond proof-of-principle experiments. We report on our recent efforts toward a periodic and deterministic single-photon source by use of time multiplexing of a heralded single-photon source pumped by periodic laser pulses. Our preliminary implementation of a multiplexed source demonstrated substantially enhanced single-photon probabilities. P1-48 All--‐Semiconductor Quantum Repeater Device Danny Kim, Andrey Kiselev, Richard Ross, Matthew Rakher, Cody Jones and Thaddeus Ladd Abstract: Long distance quantum communication requires the ability to transmit, buffer, and process quantum information via nodes called quantum repeaters. Proposals for quantum repeaters exist in many media including trapped ions, atomic gases, and superconducting optomechanics. An all solid-state approach would be desirable for manufacturability, scalability, and potentially superior performance. Here, we propose an all semiconductor quantum optoelectronic device (see Fig 1) that interfaces an optically-active self-assembled quantum dot molecule (QDM) and a gated-dot array (GDA). The QDM provides an optical interface and the GDA provides the storage of the quantum bits. The device emits a spin-entangled photon, where the spin entanglement is subsequently transferred from the QDM to the GDA through capacitive coupling. The resulting resource is an emitted photon whose polarization is entangled to the electron spins in the GDA. This device can potentially operate at a clock cycle in excess of 100MHz, orders of magnitude faster than current quantum repeater schemes. In this poster I will present an analysis of the device, its operation, and also preliminary experimental data that supports the feasibility of this device. Topics include the proposed device heterostructure, Poisson-Schrödinger simulations of the device, and the entanglement transfer scheme. Experiments towards extending T2 times with pulse shaping and exploring other material systems in which this device may be realized will also be presented.

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P1-49 Surface effects on the coherence of superconducting qubits Yiwen Chu, Christopher Axline, Chen Wang, Teresa Brecht, Yvonne Gao, Luigi Frunzio, Michel Devoret and Robert Schoelkopf Abstract: Solid-state qubits that act as artificial atoms have many advantages over real atoms or ions, such as engineerability, scalability, and the lack of need for trapping or cooling schemes. However, their quantum coherence is generally degraded due to the complex environment in which they reside. In particular, while high-quality, nearly flawless bulk materials can be used in these qubits, the presence of surfaces inevitably introduces imperfections. These surface effects are an important limiting factor in the performance of solid state qubits ranging from nitrogen-vacancy centers in diamond to superconducting Josephson-junction based devices. We study the decoherence of 3D transmon superconducting qubits on sapphire and silicon and find that the lifetimes of these qubits are limited by loss due to material interfaces. In the case of silicon, we demonstrate the use of micromachining techniques to replace lossy substrate material with a perfect dielectric – vacuum. In addition to improving the decay lifetimes of the qubits, our technique modifies their magnetic noise environment. This could provide insight into the origin of the yet unexplained excess flux noise that affects the performance of tunable qubits and other SQUID-based devices. P1-50 Optical properties of an atomic ensemble coupled to a band edge of a photonic crystal waveguide Ewan Munro, Leong Chuan Kwek and Darrick Chang Abstract: Photonic crystal waveguides (PCWs) have attracted significant interest in recent years as a platform for realizing novel quantum light-matter interfaces. The ability to engineer their dispersive and modal properties via design and fabrication permits control of the electromagnetic environment experienced by nearby atoms, which may be leveraged to achieve strongly-enhanced atom-photon coupling efficiencies, as well as for the exploration of new regimes of quantum optics. An exciting example of the latter is the ability to engineer long-range coherent interactions between atoms, which occurs when the atomic transition frequency is inside a band gap of the PCW. Here we investigate the fundamental optical properties of an ensemble of such atoms, finding rich features that differ markedly from standard atomic ensembles. The linear spectrum exhibits a range of resonant features, some of which may be used for characterization of the ensemble, and which moreover display strong optical nonlinearities that yield strong photon anti-bunching in the scattered light. Our results are of direct relevance to atom-PCW experiments that should soon be realizable.

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P1-51 Practical Quantum Retrieval Games Juan Miguel Arrazola, Markos Karasamanis and Norbert Lutkenhaus Abstract: Complex cryptographic protocols are often constructed from simpler building-blocks. In order to advance quantum cryptography, it is important to study practical building-blocks that can be used to develop new protocols. An example is quantum retrieval games (QRGs) which have broad applicability and have already been used to construct quantum money schemes. In this work, we introduce a general construction of quantum retrieval games based on the hidden matching problem and show how they can be implemented in practice using available technology. More precisely, we provide a general method to construct (1-out-of-k) QRGs, proving that their cheating probabilities decrease exponentially in k. Additionally, we show how they can be implemented using sequences of phase-encoded coherent states and linear optics, even in the presence of experimental imperfections. Our results are a new tool in the arsenal of the practical quantum cryptographer. P1-52 Non-local games and optimal steering at the boundary of the quantum set Yi-Zheng Zhen, Koon Tong Goh, Yu-Lin Zheng, Wen-Fei Cao, Xingyao Wu, Kai Chen and Valerio Scarani Abstract: The boundary between classical and quantum correlations is well characterised by linear constraints called Bell inequalities. It is much harder to characterise the boundary of the quantum set itself in the space of no-signaling correlations. By looking at the question from the perspective of non-local games based on steering, Oppenheim and Wehner (OW) found an intriguing property of specific points of the quantum boundary: the local state of Bob is steered to one that saturates a local fine-grained uncertainty relation. Our work brings to the fore the question of whether the OW condition characterises the whole of the quantum boundary, in any scenario. P1-53 Multiparty Quantum Signature Schemes Juan Miguel Arrazola, Petros Wallden and Erika Andersson Abstract: Digital signatures are widely used in electronic communications to secure important tasks such as financial transactions, software updates, and legal contracts. The signature schemes that are in use today are based on public-key cryptography and derive their security from computational assumptions. However, it is possible to construct unconditionally secure signature protocols. In particular, using quantum communication, it is possible to construct signature schemes with information-theoretic security based on fundamental principles of quantum mechanics. Several quantum signature protocols have been proposed, but none of them has been explicitly generalised to more than three participants, and their security goals have not been formally defined. Here, we first extend the security definitions of Swanson and Stinson so that they can apply also to the quantum case, and introduce a formal definition of transferability based on different verification levels. We then prove several properties that multiparty signature protocols with information-theoretic security -- quantum or classical -- must satisfy in order to achieve their security goals. We also express two existing quantum signature protocols with three parties in the security framework we have introduced. Finally, we generalize a quantum signature protocol by Dunjko et al. to the multiparty case, proving its security against forging, repudiation and non-transferability. Notably, this protocol can be implemented using any point-to-point quantum key distribution network and therefore is ready to be experimentally demonstrated.

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P1-54 A scheme for estimating accidental coincidence rates between saturated single photon detectors: the effective duty cycle James Grieve, Rakhitha Chandrasekara, Zhongkan Tang, Cliff Cheng and Alexander Ling Abstract: In the field of quantum photonics, the correlated detection of single photons is a routine task, with applications in experiments as diverse as metrology and quantum key distribution. In any such experiment, two or more single photon detectors are operated in parallel, with their signals combined via hardware or post-processing to produce a coincidence signal. Since two uncorrelated streams of photons will occasionally produce coincidences by chance, care must be taken to minimise the contribution of such “accidental” coincidences, typically by operating the entire experiment at a very low throughput. In many cases however, it is sufficient to simply subtract these spurious events in post-processing, for which a good estimation of their rate is essential. Unfortunately, such estimations typically require assumptions which are only valid at low rates, where the detector count rates respond in an approximately linear fashion to the incoming event stream. At higher rates, so-called “saturation” behaviour of the single photon detector results in markedly non-linear behaviour, reducing the useful range of event rates which can be detected. In this presentation we discuss a general method for estimating rates of accidental coincidence at rates commonly associated with these saturation effects and non-linear behaviour. By combining the effects of the recovery time of both detector circuits and the waiting-time statistics of the light source into an “effective duty cycle” we are able to accommodate arbitrarily complex recovery behaviour at high event rates. In our discussion, we provide a detailed high-level model for the recovery process of passively quenched avalanche photodiodes, and demonstrate effective accidental coincidence subtraction at rates commonly considered outside of the range of these detectors. By post-processing experimental data using our model, we observe an improvement in the visibility of polarization correlation fringes from 88.7% to 96.9% over a large dataset with highly varying flux. We belive this technique will be useful in improving the signal-to-noise ratio in applications which depend on coincidence measurements, especially in situations where rapid changes in flux may make a rate-limiting strategy impossible. Although we will present a detailed treatment for passively quenched APDs, we emphasise the very general nature of this estimation strategy, and will provide explicit protocols for its application to arbitrary detector technologies and incoming event statistics. This work recently appeared in Optics Express: http://dx.doi.org/10.1364/OE.24.003592

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P1-56 Highly confining direct written waveguides for integrated quantum photonics James Grieve, Bo Xue Tan and Alexander Ling Abstract: Compact waveguide chips fabricated by femtosecond direct write in glass have become a powerful and mature tool for the realisation of large scale quantum photonics experiments, with a number of implementations discussed extensively in the literature. To date, most work in this area has utilized a femtosecond oscillator with an external amplifier, with the resulting few-kilohertz pulse train providing the high pulse energies needed to achieve permanent modification of the substrate material. These pulses are brought to a focus with relatively low numerical aperture optics, and the resulting waveguides exhibit a pronounced asymmetric cross-section due to the point spread function of the lens. This may be problematic in quantum optics experiments which make use of the polarization of photons to encode quantum information, as shape-induced birefringence may cause degradation of the guided photon state. We have developed a femtosecond laser direct write waveguide platform that employs a minimally modified commercial oscillator without amplification and a high numerical aperture objective to fabricate waveguides in the flint glass SF11. With high repetition rates and pulse energies only slightly above the threshold for modification, multiple pulses contribute to the waveguide morphology which is no longer dominated by the point spread function. The resulting waveguides exhibit markedly reduced aspect ratio when compared to those produced by amplified systems, and also feature a small mode cross-section (around 1.6um FWHM), which we attribute to an unusually high peak modification of the refractive index. This increased mode confinement may enable reduced bending radius, and allow for a further reduction in the scale of large photonic circuits. In this contribution, we will discuss the fabrication process, as well as present data on the performance of bus waveguides and optical components such as directional couplers. It is our belief that this novel fabrication scheme will provide an attractive alternative to conventional, high pulse energy systems. The reduced cost associated with our oscillator-only approach will also help to lower the barriers to participation in this promising area of research. P1-57 Engineering high brightness and high efficiency in downconversion sources Brigitta Septriani, James Grieve, Alexander Ling and Kadir Durak Abstract: The workhorse technique for generating correlated pairs of photons is based on spontaneous parametric downconversion in nonlinear crystals. These photon pair sources are usually designed with relatively short crystal lengths, in the belief that this is necessary to attain good performance. We show, contrary to common practice, that concurrent high brightness and efficiency is also available to longer crystals. We present comprehensive measurement data on the pump and collection beam parameters necessary to achieve high collection efficiency (89.01.7% and 81.93.7% for signal and idler) together with high brightness when a single thick b-Barium Borate crystal (15.76mm) is pumped with a narrow linewidth laser. We observe a linewidth broadening in the spectrum of the downconverted light when compared to numerical simulation, which we associate with an effective interaction length defined only by the overlap of the pump and collection modes within the crystal volume. This contrasts with commonly used “thin-crystal” geometries, in which the interaction length is defined by the length of the crystal. We note that this reduction in the effective interaction length is the result of spatial walk-off of the pump beam. We also conduct a systematic mapping of brightness and efficiency by varying the pump and collection mode sizes. Our data convincingly demonstrates high brightness and efficiency over a range of focusing conditions, highlighting the robust nature of this source design.

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The surprising results from this work will be of interest to optical designers and those involved in the construction and operation of photon pair sources, particularly where both high brightness and efficiency are required. Field deployment of these devices often imposes strict limits on size, weight and power (SWAP), and we belive the adoption of a thick-crystal BBO strategy may open up new opportunities for correlated photon sources in real-world scenarios. This work has just been accepted for publication by Optica (http://arxiv.org/abs/1511.04159). P1-58 Multiphoton entanglement from single photon sources Jun-Yi Wu and Holger F. Hofmann Abstract: We study the experimentally accessible properties of multi-photon entanglement generated by single photon sources and beam splitters. As the photon number increases, it is possible to observe a rich variety of structures in the photon distributions obtained after linear optics transformations. In this presentation, we focus on the patterns obtained from the unbiased interference of all modes that is described by a discrete Fourier transformation of the light field amplitudes and show how the entanglement can be characterized using the correlations of photon statistics observed in the two multi-mode outputs. P1-59 Optical Resources and the Maxwell Demon Angeline Shu, Jibo Dai and Valerio Scarani Abstract: A recent experimental study explored the power of an optical Maxwell demon to extract work from thermal states at the same temperature [Vidrighin et al., Phys. Rev. Lett. \textbf{116}, 050401 (2016)]. We present a study of the effect of the demon when one uses resource states that are easy to implement. P1-60 Full reconstruction of a 14-qubit state within 4 hours Zhibo Hou and Guo-Yong Xiang Abstract: Full quantum state tomography (FQST) plays a unique role in the estimation of the state of a quantum system without a priori knowledge or assumptions. Unfortunately, since FQST requires informationally (over)complete measurements, both the number of measurement bases and the computational complexity of data processing suffer an exponential growth with the size of the quantum system. A 14-qubit entangled state has already been experimentally prepared in ion trap, and the data processing capability for FQST of a 14-qubit state seems to be far away from practical applications. In this paper, the computational capability of FQST is pushed forward to reconstruct a 14-qubit state with a run time of only 3.35 hours using the linear regression estimation (LRE) algorithm, even when informationally overcomplete Pauli measurements are employed. The computational complexity of LRE algorithm is first reduced from O(10^19) to O(10^15) for a 14-qubit state by dropping all the zero elements and its computational efficiency is further sped up by fully exploiting the parallelism of LRE algorithm with parallel Graphic Processing Unit (GPU) programming. Our result can play an important role in quantum information technologies with large quantum systems.

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P1-61 Scalable quantum router architecture with code interoperability Shota Nagayama, Shigeya Suzuki, Takahiko Satoh, Takaaki Matsuo and Rodney Van Meter Abstract: The future Quantum Internet will require scalable quantum routers, modied quantum repeaters that are capable of three or more long distance connections and of routing among the connections, and that support error correcting code conversion for interoperability. We suggest a quantum router architecture which satisfies the requirements above and analyze the error probability of a generalized procedure for creating Bell pairs with each qubit encoded in a different error correcting code mentioned often in quantum repeater research. Based on our analysis, the combination of purification before encoding and purification after encoding with post-selection may result in lower residual error rate, therefore this combination and our router architecture may be preferred for practical quantum routers for the world wide Quantum Internet. P1-62 Entanglement of quantum circular states of light Mikhail Kolobov, Dmitri Horoshko, Stephan De Bievre and Giuseppe Patera. Abstract: We consider a class of quantum macroscopic superposition of coherent states equidistant on a circle in phase space. Such states generalize well-known even and odd coherent states to N-component quantum superposition. We derive analytical expression for entanglement and discuss the measure of non-classicality for these states. Our results demonstrate a peculiar behavior of entanglement and non-classicality due to N-component quantum interference in phase space. P1-66 Wide-area topology of a Quantum Internet Takaaki Matsuo, Takahiko Satoh, Shota Nagayama, Shigeya Suzuki and Rodney Van Meter Abstract: The purpose of this research is to generate reasonable quantum topologies for a reliable Quantum Internet simulation. As Quantum Internet is expected to be complementary to the classical Internet, we extracted sub-topologies from existing classical Internet, and modified them into quantum topologies. In order to assess the accuracy of our generation method, we used statistical comparison between generated topologies and classical raw topologies. As a result, generated topologies showed statistically similar characteristics to the existing real world topologies. Therefore, topologies generated by our method can be considered reasonable for a Quantum Internet simulation.

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P1-70 Towards storage of single quantum dot photons in a rubidium quantum memory Janik Wolters, Lucas Beguin, Jan-Philipp Jahn, Mathieu Munsch, Andrew Horsley, Fei Ding, Aline Faber, Andreas Jöckel, Andreas Kuhlmann, Armando Rastelli, Oliver G. Schmidt, Richard J. Warburton and Philipp Treutlein Abstract: The availability of quantum networks promises a plethora of radically new applications and novel insights. However, establishing the hardware for a quantum network is a challenging task. A source of indistinguishable single photons is required along with means to store the single photons at each network node. For single photon generation, semiconductor quantum dots have emerged as a prime resource, as they provide triggered single-photon emission at a high rate and with high spectral purity. Independently, atomic ensembles have emerged as one of the best quantum memories for single photons, providing high efficiency storage and long memory lifetimes. We report on our efforts to combine these two disparate physical systems to exploit the best features from both worlds. On the one hand, we have developed a novel type of GaAs/AlGaAs quantum dot single photon source that emits narrow-band single-photons (∆ν ∼ 1 GHz) at Rb wavelengths. On the other hand, we are pushing forward an EIT-based quantum memory to store these photons in a dense ensemble of Rb87 atoms. P1-71 Quantum teleportation between multiple senders and receivers Seung-Woo Lee, Hee Su Park and Hyunseok Jeong Abstract: Quantum teleportation is a core protocol to realize quantum communication and quantum computation. In order to realize quantum communication in network, it may be essential to realize an efficient way to transfer unknown quantum states among multiple participants. A teleportation protocol from one sender to many receivers was proposed previously and demonstrated experimentally, but any protocol to transfer quantum states possesed by multiple senders, possibly separated spatially or temporally in communication network, directly to the others has been missing so far. Here we propose a scheme for teleportation between arbitrary number of senders and receivers, and report its experimental demonstration with linear optics and multi-photon entanglement as a proof-of-principle test. The main achievements of our work are not only to propose a protocol for quantum teleportation between arbitrary participants with its experimental demonstration, but also to realize the near-deterministic Bell state measurement with linear optics proposed recently in [Phys. Rev. Lett. 114, 113603 (2015)]. We expect our work to pave the way to realization of multiparty quantum teleportation in network. P1-72 On-chip coherent conversion of photonic quantum entanglement between different degrees of freedom Lantian Feng, Ming Zhang, Zhaiyuan Zhou, Ming Li, Xiao Xiong, Le Yu, Baosen Shi, Guoping Guo, Daoxin Dai, Xifeng Ren and Guangcan Guo Abstract: In the quantum world, a single particle can have various degrees of freedom to encode the quantum information. Therefore, efficiently and fully controlling of those degrees of freedom simultaneously is on demanding. For example, path or polarization degree of freedom of single photons has been used in the recent investigations of quantum photonic integrated circuits (QPICs), while usually only one of them was used. Here, we introduce the transverse waveguide mode degree of freedom to QPICs, and demonstrate the coherent conversion of photonic quantum entangled state (NOON state) between different degrees of freedom on a single chip for the first time. By using mode multiplexers and mode converters, single photons in different optical paths or different polarizations can be converted to/back to different transverse waveguide modes in a single multi-mode waveguide, with the latter

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being an ideal platform for higher dimensional quantum information processes. The preservation of quantum coherence in these conversion processes is proven by single photon and two photon quantum interference using a fiber beam-splitter (BS) or on-chip BSs. These results provide us with the ability to control and convert multiple degrees of freedom of photons for the QPIC-based quantum information process. P1-73 Experimental quantum fingerprinting with weak coherent states Juan Miguel Arrazola, Feihu Xu, Keijin Wei, Wenyuan Wang, Pablo Palacios-Avila, Chen Feng, Shihan Sajeed, Hoi-Kwong Lo and Norbert Lutkenhaus Abstract: Quantum communication holds the promise of creating disruptive technologies that will play an essential role in future communication networks. For example, the study of quantum communication complexity has shown that quantum communication allows exponential reductions in the information that must be transmitted to solve distributed computational tasks. Recently, protocols that realize this advantage using optical implementations have been proposed. Here we report a proof-of-concept experimental demonstration of a quantum fingerprinting system that is capable of transmitting less information than the best-known classical protocol. Our implementation is based on a modified version of a commercial quantum key distribution system using off-the-shelf optical components over telecom wavelengths, and is practical for messages as large as 100 Mbits, even in the presence of experimental imperfections. Our results provide a first step in the development of experimental quantum communication complexity. P1-74 SpooQySats: nanosatellites to demonstrate technologies for future quantum communication networks Robert Bedington, Cliff Cheng, Yue Chuan Tan, Edward Truong-Cao, Xueliang Bai and Alexander Ling Abstract: SpooQySats are 10x10x30cm CubeSat nanosatellites that will be assembled and operated from the Centre For Quantum Technologies (CQT) to test and validate our upcoming SPEQS (Small Photon Entangling Quantum System) entangled photon sources, in preparation for future space-to-ground QKD (Quantum Key Distribution) demonstration missions. CubeSat is the industry standard specification for nanosatellites and has spawned a rapidly growing industry of compatible subsystems and services. Our SpooQySats are being based around the latest platform produced by the Danish company GomSpace which they demonstrated aboard GomX-3: an advanced CubeSat deployed into orbit from the International Space Station (ISS) in October 2015. Key components include the AX100 digital UHF radio transceiver and A3200 onboard computer which are highly miniaturised so that they can both be mounted onto a single PC104 board. The platform allows for a significant amount of flexibility and a range of SpooQySat designs have been researched, including SpooQy-lite (a 10x10x20cm design) and SpooQy-Max (which contains redundant spares of key sub-systems). Our preferred launch option for SpooQySats is deployment from the ISS as this represents a suitable compromise between ease of access, flyover frequency, regular launches, cost, mission lifetime and proven effectiveness with GomX-3. Communications with SpooQySats will be made over UHF with a new ground station we are building at NUS and with the ground stations of collaborating partners around the world. Future missions may additionally use S-band radios to allow for increased data rates. To ensure that the satellites will survive the rocket launch and operate effectively in the space environment, various tests need to be performed. These include vibration and shock

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tests (to simulate the launch) and thermal cycling tests performed under vacuum (the combination often referred to as “shake and bake”). Particular attention must be paid to testing the CQT payload as the GomSpace product lines are already qualified to be space compatible. An additional concern of the space environment is ionising radiation. While traditional space-compatible parts are thoroughly tested and optimised for such environments, many cheaper commercial parts are not requiring us to perform our own tests to determine suitability and expected lifetimes. Early versions of the SPEQS payload have already been demonstrated to survive these tests. The objective of the initial SpooQySats will be to perform Bell's inequality violations in-situ using the SPEQS source and to investigate how its performance is affected by regular operation in space. No photons will be beamed outside of the satellite. In later missions we hope to collaborate with other groups specialising in transmission optics, high performance attitude determination/control systems, and space-to-ground laser communications to take additional steps towards space-to-ground QKD demonstration using nanosatellites. P1-75 Many-box locality Yu Cai, Jean-Daniel Bancal and Valerio Scarani Abstract: It has been a long standing question to search for physical principles that defines quantum physics. Within the framework of no-signalling theories, several principles have been proposed to single out the quantum set of distributions. However, all previous proposed principles are satisfied by the "almost quantum" set, a set of distributions provably larger than the quantum set. By modifying the assumptions of one of these principles, namely Macroscopic Locality (ML), we propose the principle of Many-Box Locality (MBL). Here we will present the tools we developed to study the MBL_N sets as well as some preliminary results on the characterization of MBL_N sets. P1-76 All the self-testings of the singlet for two binary measurements Yukun Wang, Xingyao Wu and Velario Scarani Abstract: Self-testing refers to the possibility of characterizing uniquely (up to local isometries) the state and measurements contained in quantum devices, based only on the observed input-output statistics. Already in the basic case of the two-qubit singlet, self-testing is not unique: the two known criteria (the maximal violation of the CHSH inequality and the Mayers–Yao correlations) are not equivalent. It is unknown how many criteria there are. In this paper, we find the whole set of criteria for the ideal self-testing of a singlet with two measurements and two outcomes on each side; it coincides with all the extremal points of the quantum set that can be obtained by measuring the singlet.

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P1-77 BosonSampling with continuous variable measurements Austin Lund, Saleh Rahimi-Keshari and Timothy Ralph Abstract: We show that the classical hardness argument of Aaronson and Arkipov can be extended to a scheme involving only continuous variable measurements on the output of a BosonSampling device. Our argument is presented for exact BosonSampling using matrices whose permanent is not near zero. We discuss the impediments to extending this result to approximate sampling. P1-78 Implementation of high-performance coincidence counting unit with a low-cost field programmable gate array Byung Kwon Park, Yong-Su Kim, Osung Kwon, Sang-Wook Han and Sung Moon Abstract: We present a CCU with high speed and a short coincidence time window using a low-cost FPGA (Altera DE0-Nano Development and Education Board with a Cyclone IV FPGA chip, less than $100). The CCU was programmed with Verilog hardware description language (Verilog HDL). It has 8 logic inputs, and the internal delays of each input can be tuned independently with the resolution of 0.7 ns using buffers embedded in the FPGA. The maximum input frequency and the minimum coincidence time window are 163 MHz and 0.47 ns, respectively. It has 12 outputs including 8 single-input counts and 4 coincidence counts, however the number of inputs and outputs can be easily increased if necessary. The coincidence configurations up to 8 inputs, i.e., eight-fold coincidences, can be chosen by the user. The CCU is connected with a USB-to-serial board (ROVITECK, I-FT232H) to communicate with a personal computer via a universal serial bus (USB). All the parameters, including the size of the coincidence time window, the internal delays of the input channels, and the coincidence configurations, are easily defined and adjusted with the graphic user interface (GUI) programmed with LabView or C]. We remark that the total component price of this high performance CCU costs under $200. With its excellent performance at a low-cost implementation, our CCU is ready to be employed in quantum optics and quantum information laboratories. P1-79 Quantum Noise Spectroscopy Gerardo Paz Silva, Leigh Norris and Lorenza Viola Abstract: We present spectroscopy protocols capable of characterizing an environment coupling to multiple qubits. Concretely, we are able to reconstruct the correlation functions of the bath in frequency space, i.e., the power spectra of the environment. This is achieved by measuring the response of the qubits under control pulses with particular symmetries and in the presence of the bath of interest. We discuss implications of these protocols to quantum control, metrology, and fault-tolerant quantum computing.

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P1-80 Continuous-mode analysis of a noiseless linear amplifier Yi Li, Andre Carvalho and Matthew James Abstract: We develop a dynamical model to describe the operation of the non-deterministic noiseless linear amplifier (NLA) proposed by Ralph and Lund in the regime of continuous modes inputs. We analyse the dynamics conditioned on the detection of photons and show that the amplification gain depends on detection times and on the temporal profile of the input state and the auxiliary single photon state required by the NLA. We also show that the output amplified state inherits the pulse shape of the ancilla photon. P1-81 Device-independent parallel self-testing of two singlets Xingyao Wu, Jean-Daniel Bancal, Matthew Mckague and Valerio Scarani Abstract: Device-independent self-testing is the possibility of certifying the quantum state and the measurements, up to local isometries, using only the statistics observed by querying uncharacterized local devices. In this paper, we study parallel self-testing of two maximally entangled pairs of qubits: in particular, the local tensor product structure is not assumed but derived. We prove two criteria that achieve the desired result: a double use of the Clauser-Horne-Shimony-Holt inequality and the $3\times 3$ Magic Square game. This demonstrate that the magic square game can only be perfectly won by measureing a two-singlets state. The tolerance to noise is well within reach of state-of-the-art experiments. P1-83 Demonstration of Quantum Permutation Algorithm with a Single Photon Ququart Pei Zhang Abstract: We report an experiment to demonstrate a quantum permutation determining algorithm by employing photon polarization and spatial modes. The quantum permutation determining algorithm displays the speedup of quantum algorithm by determining the parity of the permutation in only one step of evaluation compared with two for classical algorithm. This experiment is accomplished in single photon level and the method exhibits universality in high-dimensional quantum computation. P1-84 Experimental evaluation of quantum correlations between measurement errors using polarization-entangled photons as probe input Yutaro Suzuki, Masataka Iinuma, Masayuki Nakano and Holger F. Hofmann Abstract: We investigate the correlations between measurement errors when two non-commuting polarization components are jointly measured using a polarization filter set to an intermediate angle between the two target polarizations. Using entangled photon pairs as input, we can distinguish the rates of individual errors from the rates at which errors happen jointly by comparing the known correlations of the input with the experimentally observed correlations between the measurement outcomes. The results show that the correlations between the errors are consistent with the non-classical correlations between the operator observables expressed by the commutation relations.

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P1-85 Development of a readout backend for a Geiger-mode SiPM In-Ho Bae, Dong-Hoon Lee and Seongchong Park Abstract: Photon counting detectors such as avalanche photodiodes (APDs) and photomultiplier tubes (PMTs) are widely used in a variety of applications such as quantum optics experiment, remote sensing, nuclear physics, astrophysics, and fluorescence spectroscopy [1]. Silicon photomultiplier (SiPM), another Geiger Mode photodetector, is based on Si technology having a similar operation principle with PMT [2]. Since it has many promising advantages such as low magnetic susceptibility, structural robustness, compact size, and low device cost compared to PMT of similar performance, SiPM comes into focus for medical application [3]. In this work, we developed a readout backend for a SiPM operating in a Geiger-mode. There are a couple of differences between conventional APDs and SiPMs in operation although they have the same principle of light sensing mechanism. For example, Fig. 1(a) and (b) show output current pulses from an APD (Hamamatsu C0902) and a SiPM (SensL 3020) at breakdown voltage, respectively. Note that the figures were obtained in the persistent mode of an oscilloscope. When the APD operated at the breakdown voltage, there were a lot of avalanche pulses in random timing sequence. After appearance of the central avalanche pulse, retriggering of avalanche pulses occurs randomly with subsequently arriving photons. The amplitudes of retriggered avalanche pulses are lower than the central pulse because the diode voltage is gradually recovered to the initial bias voltage during recovery time. On the contrary with the APD, the SiPM does not show any recovery time as shown in Fig 1(b). It is because output pulses from individual pixels are superimposed as the SiPM is composed of thousands of APD pixels. Due to such differences of the SiPM, its readout backend has to be approached differently with that of the APD. We have developed a readout backend for a Geiger-mode SiPM and will apply it to evaluate dark count characteristics of a SiPM in order to demonstrate its feasibility. P1-86 The classical-quantum divergence of complexity in the Ising spin chain Whei Yeap Suen, Jayne Thompson, Andrew Garner, Vlatko Vedral and Mile Gu Abstract: Can quantum information fundamentally change the way we perceive what is complex? Here, we study statistical complexity, a popular quantifier of complexity that captures the minimal memory required to classically model a process. We construct a quantum variant of this measure, and evaluate it analytically for a classical Ising spin chain. The resulting complexity measure - quantum statistical complexity - exhibits drastically different qualitative behaviour. Whereas the classical statistical complexity of the spin chain grows monotonically with temperature, its quantum complexity rises to a maximum at some finite temperature then tends back towards zero for higher temperatures. This demonstrates that our notion of what is complex depends fundamentally on which information theory we employ.

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P1-87 Experimental evaluation of non-classical correlations by sequential quantum measurements Masataka Iinuma, Yutaro Suzuki, Taiki Nii, Ryuji Kinoshita and Holger F. Hofmann Abstract: Ozawa's argument on the measurement uncertainty relation implies the possibility of exploring the relations between the measurement outcomes and the target observable. Here, we experimentally investigate this relation and its role to the measurement errors by performing a sequence of two non-commuting observables on the polarization components of a single photon. The initial measurement commutes with the target observable and the second one is only sensitive to a complimentary observable. By controlling the strength of the initial measurement, we can change the balance between the classical and the non-classical correlations in the quantum measurement. The experimental results show that quantum correlation between the initial and the final measurement outcomes significantly reduces the measurement error, even though the polarization component detected in the final measurement is orthogonal to the target polarization. P1-88 Interferences in quantum eraser reveal geometric phases in modular and weak values Mirko Cormann, Mathilde Remy, Branko Kolaric and Yves Caudano Abstract: In this letter, we present a new procedure to determine completely the complex modular values of arbitrary observables of pre- and post-selected ensembles, which works experimentally for all measurement strengths and all post-selected states. This procedure allows us to discuss the physics of modular and weak values in interferometric experiments involving a qubit meter. We determine both the modulus and the argument of the modular value for any measurement strength in a single step, by controlling simultaneously the visibility and the phase in a quantum eraser interference experiment. Modular and weak values are closely related. Using entangled qubits for the probed and meter systems, we show that the phase of the modular and weak values has a topological origin. This phase is completely defined by the intrinsic physical properties of the probed system and its time evolution. The physical significance of this phase can thus be used to evaluate the quantumness of weak values. P1-89 Coherent-state discrimination via non-heralded probabilistic amplification Matteo Rosati, Andrea Mari and Vittorio Giovannetti Abstract: A scheme for the detection of low-intensity optical coherent signals is presented based on non-linear operations which rely on the probabilistic amplifier by Ralph and Lund and/or on a partial dephasing transformation of the received signals, preserving the zero and one photon-number subspace while destroying any further coherence. The success probability gains up to 1.85% with respect to the optimized Kennedy receiver and, when employed in an adaptive strategy, approaches the Helstrom bound appreciably faster than the Dolinar receiver. An optical cavity implementation of the partial dephaser is proposed and its performances are analyzed.

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P1-90 Entangled photon-pairs emitted from Ag/GaN photonic crystals as sources for quantum-information processing Dalibor Javůrek and Jan Peřina Jr. Abstract: Metallo-dielectric photonic crystals are highly efficient sources of photon pairs. The photon pairs are emitted in the process of spontaneous parametric down-conversion. A perturbative quantum-mechanical model of SPDC in layered media has been developed. The one-dimensional metallo-dielectric photonic crystal consisting of eleven GaN/Ag layers has been designed in order to achieve the highest photon-pair emission rate. In the designed crystal, the quantities characterizing a photon pair such as signal photon number density, correlated areas or number of emitted noise photon pairs have been investigated. The emission of photon pairs has showed up to be high due to strong resonance of down-converted TM polarized photons inside the structure. The resonance caused the emission of the photon pairs to be highly localized both in radial emission angle and in wavelength. P1-91 Conditioned quantum dynamics in a 1D lattice system Ralf Blattmann and Mølmer Klaus Abstract: We consider a quantum particle on a one dimensional lattice subject to weak local measurements and study its stochastic dynamics conditioned on the measurement outcomes. Depending on the measurement strength our analysis of the quantum trajectories reveals dynamical regimes reaching from quasi-coherent wave packet oscillations to a Zeno-type dynamics. We analyse how these dynamical regimes are directly reflected in the spectral properties of the noisy measurement records. P1-95 Testing the limits of human vision with single photons Rebecca Holmes, Michelle Victora, Ranxiao Frances Wang and Paul Kwiat Abstract: The rod photoreceptor cells in the retina respond to single photons, but it is not yet known whether this leads to perception of the light. We discuss techniques using a heralded single-photon source to study the lower limit of human vision, and report some recent improvements, including the use of EEG-contingent stimulus presentation. P1-97 Entanglement Restoration in Amended Entanglement Breaking Channels

Álvaro Andrés Cuevas Seguel, Andrea Mari, Antonella De Pasquale, Adeline Orieux, Marcello Massaro, Fabio Sciarrino, Vittorio Giovanetti and Paolo Mataloni Abstract: Let’s consider two entangled photons, with one of them representing our testing system S and the other photon playing the role of an ancilla A. Then, apply a quantum channel acting on S, such that, when applied twice, the result is an entanglement loss. These channels are said to be Entanglement Breaking Channels of order 2 (EBC-2). Here we show the behavior of such entanglement breaking channels, realized by a proper sequence of local Amplitude Damping Maps, in which a system S belonging to a polarization-entangled photon state is injected. In these conditions, we demonstrate how to restore the entanglement in presence of these channels. This is demonstrated by a sequence of two similar channel pairs, giving a four-channel transmission line M+M+N+N, a structure that destroys the entanglement more efficiently than only two EBC-2. In this case, we prove both theoretically and experimentally that it is possible to reconstruct the line by reordering its four parts as M+N+M+N. Then, by a counterintuitive mechanism this sequence allows to restore the entanglement, giving a new channel that is no more entanglement

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breaking. We conclude that, by using suitable techniques as the one used in our experiment, it is possible to amend entanglement losses in different kinds of noisy channels.

P1-98 Proper Dimension Witnessing Wan Cong, Yu Cai, Jean-Daniel Bancal and Valerio Scarani Abstract: Dimension witnessing, first introduced by Brunner et al in [1], is a device independent technique to obtain a lower bound on the quantum dimension of a system. Dimension witnesses can be obtained as linear inequalities on the observed statistics $sum_{cz}s_{cz}P(c|z)\leq S_d$: a violation of the inequality guarantees that the measured systems are of a dimension higher than d. Dimension can be witnessed for single systems [2] or for composite ones. In the latter case, if the dimension witness is based on a Bell inequality [1, 3], it also rules out a classical origin for the correlations. Specifically, Ref [1] proved that a sufficiently high violation of the CGLMP3 inequality [4] excludes the possibility that a pair of qubits is being measured. We have proved that CGLMP4 has a similar property: it has a bound for qubits and a bound for qutrits; a violation above the latter certifies that two ququarts or larger systems are being measured. However, we have also noticed that the qutrit bound for CGLMP4 can be violated with sequential measurements on two pairs of qubits. This observation begs the question of what one is actually testing. On the one hand, two pairs of qubits do form a system of two ququarts: as such, the dimension witnessing is not flawed. On the other hand, just by grouping together two emissions of a two-qubit source, one would not claim to have the freedom to perform all ququart measurements, which seems to be the real motivation of using a dimension witness. We have proved that sequential measurements on two-qubit sources can also lead to a violation of the qubit bound of CGLMP3 and to an almost maximal violation of CGLMP8. It may ultimately be the case that the CGLMP family does not give dimension witnesses with all the desired properties, and one will have to find others. Therefore, we propose a device-independent certification of a Bell-state measurement (BSM) as a proper dimension witness. This certification is a modification of the method used in [5]. We show that in satisfying this criteria, the measurements needed cannot be done sequentially on two qubits, hence demonstrating the ability to perform a non-trivial ququart measurement. References [1] N. Brunner, S. Pironio, A. Acin, N. Gisin, A. A. Methot, and V. Scarani. “Testing the Dimension of Hilbert Spaces”. Phys. Rev. Lett. 100.21 (2008), p. 210503. [2] N. Brunner, M. Navascués, and T. Vértesi. “Dimension Witnesses and Quantum State Discrimination”. Phys. Rev. Lett. 110.15 (2013), p. 150501. [3] K.F. Pal, T.Vertesi. “Bounding the Dimension of Bipartite Quantum Systems”. Phys. Rev. A 79 (2009), 042106. [4] D. Collins, N. Gisin, N. Linden, S. Massar, and S. Popescu. “Bell Inequalities for Arbitrarily High-Dimensional Systems”. Phys, Rev. Lett. 88.4 (2002), p. 040404. [5] R. Rabelo, M. Ho, D. Cavalcanti, N. Brunner, and V. Scarani. “Device-Independent Certification of Entangled Measurements”. Phys. Rev. Lett. 107.5 (2011), p. 050502.

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P1-99 Past of a photon inside an interferometer Yink Loong Len, Jibo Dai, Berge Englert and Leonid Krivitsky Abstract: In 2013, A. Danan et. al. [1] reported an experiment that aims to answer "where were the photons passing through an interferometer?". They concluded that "the photons do not always follow continuous trajectories", and "only the description with both forward and backward evolving quantum states provides a simple and intuitive picture of pre- and post-selected quantum particles". The experiment, however, used classical light and statistics, and no conclusion about single photons can be made. In this work, we set up a similar but simplified experiment. Using entangled down-conversion photons, we were able to study the past of single photons, where the path information of the (signal) photons that entered the interferometer are encoded in the polarizations of their down-conversion partner (idler) photons. The path information is extracted by performing measurement of unambiguous discrimination (MUD) on the idler photons. Our results show that the standard formalism of quantum mechanics, and concepts of path knowledge and interference visibility, do sufficiently provide simple and straightforward explanation of the observed results. There is no ambiguity that leads us to conclude discontinuous trajectories. We stress that one could only speak of trajectory only when path knowledge is available, and it will always be continuous. When no path information is available, corresponding to inconclusive result in MUD, the concept of trajectory is simply undefined. [1] A. Danan, D. Farfurnik, S. Bar-Ad, and L. Vaidman, Phys. Rev. Lett., 111, 240402 (2013). P1-100 Quantum error correction in the presence of small baths Yink Loong Len, Yicong Zheng and Hui Khoon Ng Abstract: For the implementation of a realistic quantum computer, an important element is quantum error correction (QEC), in which one actively detects and corrects errors that occurs in the physical system. In the standard QEC analysis, the error or noise model usually falls under two categories.

1. Memoryless noise, in which one describes the noise by using completely positive, trace-preserving (CPTP) maps (or Lindblad master equation for continuous time) that acts on the system only. Since any effect from its coupling with the environment or bath is disregarded, the bath carries no information or memory about the system at all.

2. Memory-full noise or Hamiltonian noise, in which one studies the joint unitary

evolution of the full system and bath. With the full bath included, one has a closed-system unitary dynamics, such that any initial information encoded in the system is always preserved within the system+bath.

Depending on which error models, one can get very different results for the fault-tolerance threshold, i.e. a theoretical bound below which efficient quantum computer is not possible. However, in reality, we expect the experimental situation to fall somewhere in between the two extremes, with a small number of degrees of freedom providing some memory capacity for information to how to and from the system, but also couple to a dissipative bath that limits the memory. These few strongly-coupled degrees of freedom are identified as small baths. In this poster, we show some initial steps towards a more realistic analysis of the effective error on the system with QEC, taking into account the presence of small baths. In particular, we derived the necessary and sufficient condition for perfect QEC with the baths included. Using a spin model and 5-qubit code, we also studied how is the performance of QEC affected due to the presence of small baths. From our simulations, we find that there is an optimal rate for high quality QEC, and frequent applications of QEC is not necessarily the better.

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P1-104 Efficient Quantum Compression for Identically Prepared Mixed States Yuxiang Yang, Giulio Chiribella and Daniel Ebler Abstract: We present one-shot compression protocols that optimally encode ensembles of N identically prepared mixed states into O(log N) qubits. In contrast to the case of pure-state ensembles, we find that the number of encoding qubits drops down discontinuously as soon as a nonzero error is tolerated and the spectrum of the states is known with sufficient precision. For qubit ensembles, this feature leads to a 25% saving of memory space. Our compression protocols can be implemented efficiently on a quantum computer. P1-106 When is simpler thermodynamically better? Andrew Garner, Jayne Thompson, Vlatko Vedral and Mile Gu Abstract: Living organisms capitalize on their ability to predict their environment to maximize their available free energy,and invest this energy in turn to create new complex structures. Is there a preferred method by which this manipulation of structure should be done? Our intuition is "simpler is better," but this is only a guiding principal. Here we substantiate this claim by thermodynamic reasoning. We present a framework for the manipulation of patterns - ordered sequences of data - by predictive devices. We identify the dissipative costs and how they can be minimized by the choice of memory in the predictive devices. For pattern generation, we see that simpler is indeed better. However, contrary to intuition, when it comes to extracting work from a pattern, any device capable of making statistically accurate predictions can recover the entire free energy. P1-107 Weak Value Measurements with Pulse Recycling Courtney Krafczyk, Trent Graham, Andrew Jordan and Paul Kwiat Abstract: Recycling undetected photons in a weak measurement can substantially improve the signal-to-noise ratio for a given number of input photons. We demonstrate a preliminary improvement by a factor of 1.36 over a system with no recycling, potentially reaching a factor of 3.2 over that of a conventional measurement. P1-108 Extreme Violation of Local Realism in Quantum Hypergraph States Mariami Gachechialdze, Costantino Budroni and Otfried Guehne Abstract: We study nonlocal properties of hypergraph states, or nonlocal stabilizer states, which are generalisations of well-known graph states. We find that some families of hypergraph states violate local realism exponentially like GHZ states but are more robust than their graph-state analogues. In the end, we give applications in quantum metrology and measurement-based quantum computation.

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P1-110 random numbers from vacuum fluctuations Yicheng Shi, Brenda Chng and Christian Kurtsiefer Abstract: We implement a quantum random number generator based on a balanced homodyne measurement of vacuum fluctuations of the electromagnetic field. The digitized signal is directly processed with a fast randomness extraction scheme based on a linear feedback shift register. The random bit stream is continuously read in a computer at a rate of about 480 Mbit/s and passes an extended test suite for random numbers. P1-111 Rectification of light in the quantum regime Jibo Dai, Alexandre Roulet, Huy Nguyen Le and Valerio Scarani Abstract: One of the missing elements for realising an integrated optical circuit is a rectifying device playing the role of an optical diode. A proposal based on a pair of two-level atoms strongly coupled to a one-dimensional waveguide showed a promising behavior based on a semi-classical study [Fratini et al., Phys. Rev. Lett. 113, 243601 (2014)]. Our study in the full quantum regime shows that, in such a device, rectification is a purely multi-photon effect. For an input field in a coherent state, rectification reaches up to 70% for the range of power in which one of the two atoms is excited, but not both. P1-112 Generation and measurement of four-dimensional entanglement in multi-core optical fibers Hee Jung Lee, Sang-Kyung Choi and Hee Su Park Abstract: Photons with high-dimensional entanglement are of interest due to a greater information capacity and a better error resilience compared to conventional two-dimensional qubits. Most of high-dimensional experiments so far have been carried out using spatial modes of photons such as orbital angular momentum (OAM) in free space. This work focuses on generation and measurement of spatially entangled state in multi-core fibers (MCFs) that contain four almost identical cores. Such an MCF has recently been a topic of intensive research for application to space-division multiplexing optical communication that overcomes the capacity limit of a single-mode fiber (SMF). We realize the high-dimensional spatially entangled state between different MCFs by combining spontaneous parametric down conversion (SPDC) as a photon source and a technique to measure arbitrary supepositions of the core modes using a spatial light modulator (SLM). P1-114 Qutrit trace invariants using Bloch matrices Vinod Mishra Abstract: Recently, a new approach to the representation of a qutrit [1] was presented using spin-1 matrices. The starting point of this approach is the spin-1 sector of the 2-qubit states represented as the Hilbert space spanned by 2 sets of Pauli matrices. Finally these 4 by 4 spin-1 matrices were replaced by 3 by 3 spin-1 matrices as they obey the same commutation rules. At the same time another approach using 4-dimensional Bloch matrices [2] have been used to represent 2-qubit states but with different parametrization of matrix elements. The author has also derived the trace invariants implied by the positivity constraints of the 2-qubit reduced density matrix. In the current work, qutrit trace invariants have been derived and their implications for the geometrical representation as in [1] has also been worked out. [1] Pawel Kurzynski et al. “Three-dimensional visualization of a qutrit”, arXiv:1601.07361v1 [2] Omar Gamel, “Entangled Bloch Spheres: Bloch Matrix and two qubit state space”, arXiv:1602.01548v1

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P1-117 Entanglement verification with detection-efficiency mismatch Yanbao Zhang and Norbert Lutkenhaus Abstract: Entanglement is a necessary condition for secure quantum key distribution (QKD). When there is an efficiency mismatch between various detectors used in a QKD system, it is still an open problem how to verify entanglement. Here we present a method to address this problem, given that the detection-efficiency mismatch is characterized and known. The method does not assume an upper bound on the number of photons arriving at each threshold detector, and it works even if the efficiency mismatch can be controlled by an adversary. Our results suggest that, the larger the efficiency mismatch is, the smaller the set of entangled states that can be verified becomes. When there is no mismatch, our method can verify entanglement even if the method based on squashing models [N. J. Beaudry, T. Moroder, and N. Lutkenhaus, Phys. Rev. Lett. 101, 093601 (2008)] fails. P1-118 Experimental Adaptive Quantum Tomography of Two-Qubit States Stanislav Straupe, Gleb Struchalin, Konstantin Kravtsov, Igor Radchenko, Ivan Pogorelov and Sergei Kulik Abstract: We report an experimental realization of an adaptive quantum state tomography for two-qubit states. A Bayesian inference is utilized to estimate the state and its properties of interest (eg. purity, concurrence) and to infer the accuracy of estimation. We compare our adaptive approach with random measurements which are known to be optimal in a non-adaptive case. We observe a qualitative enhancement in the estimation accuracy. The scaling of the Bures distance to the true state (which is used as a figure of merit) with overall number of registered events N is close to N^{-1} for pure states, while the non-adaptive measurements gives close to N^{-1/2} scaling. Experiments are performed with polarization states of photons produced in a spontaneous parametric down-conversion process. The setup was designed to allow the preparation of states with variable degree of entanglement and purity. Only factorized measurements were realized in the experiment. The performance of entangling measurements was studied by numerical simulations. Experimental and numerical results clearly demonstrate an advantage of the adaptive strategy over the random measurements. Importantly, adaptive tomography, even restricted to factorized measurements, still outperforms non-adaptive one with no restrictions on measurements. Another important point is that adaptive tomography is less sensitive to instrumental errors. We have studied the tomography performance in the case of artificially introduced instrumental errors and have observed that the 'noise floor' for the adaptive protocol is lower. This work extends adaptive state tomography to the case of multi-qubit states. We have demonstrated the experimental feasibility of a fully adaptive Bayesian state estimation protocol for two-qubit states, and the proposed algorithm is versatile and can be applied to systems of arbitrary dimensions. The results discussed here were recently published in G. Struchalin, et al. Phys. Rev. A 93, 012103 (2016). P1-122 Single-cycle squeezing of light Dmitri Horoshko and Mikhail Kolobov Abstract: We describe a method for generating ultrabroadband squeezed light by parametric downconversion in an aperiodically poled nonlinear crystal. We obtain the exact solution in special functions for the wave equation in such a crystal with undepleted pump and linear chirp of the spatial frequency of poling. We obtain also an approximate solution of the same equation in elementary functions and show its good agreement with the exact solution within the squeezing band.

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P1-124 Realization of a two-photon quantum gate based on cavity QED Bastian Hacker, Stephan Welte, Stephan Ritter and Gerhard Rempe Abstract: All-optical quantum technologies require a strong interaction between photons. Despite considerable efforts across several areas of research, a deterministic interaction between photonic quantum bits has so far not been reached, because the required nonlinearities are hard to achieve. We have now employed one rubidium atom strongly coupled to the light field of an optical cavity to realize the long-standing goal of a photon-photon quantum logic gate based on the deterministic Duan-Kimble protocol [1]. Two distinct, flying photonic qubits enter our setup and emerge in a well-defined processed state. The gate was characterized via quantum tomography and shows faithful operation with an average fidelity well above the quantum threshold. Such a universal two-photon gate enables a plethora of applications in quantum communication and quantum computing and may therefore open a new era in the field of optical quantum information processing. [1] L.-M. Duan, H. J. Kimble, Phys. Rev. Lett. 92, 127902 (2004) P1-126 Spectrum analysis with quantum dynamical systems Shilin Ng, Shan Zheng Ang, Mankei Tsang, Wheatley Trevor, Hidehiro Yonezawa, Akira Furusawa and Elanor Huntington Abstract: In this work, we proposed a theoretical framework of spectrum-parameter estimation with quantum dynamical systems, found simple analytical results for the quantum limits of estimating the parameters of stochastic processes, and studied measurement and data analysis techniques that approach our limits. As an illustration to our theory, we analyzed an experiment of continuous optical phase estimation to demonstrate the proximity of experimental performance and our limits. P1-127 Heisenberg’s error-disturbance relations: a joint measurement-based experimental test Yuan-Yuan Zhao, Paweł Kurzyński and Guo-Yong Xiang Abstract: The Heisenberg’s error-disturbance relation is a cornerstone of quantum physics. It was recently shown to be not universally valid and two different approaches to reformulate it were proposed. The first one focuses on how error and disturbance of two observables, A and B, depend on a particular quantum state. The second one asks how a joint measurement of A and B affects their eigenstates. Previous experiments focused on the first approach. Here, we focus on the second one. Firstly, we propose and implement an extendible method for quantum walk-based joint measurements of noisy Pauli operators to test the error-disturbance relation for qubits introduced in Phys. Rev. A 89, 012129 (2014). Then, we formulate and experimentally test a new universally valid relation for the three mutually unbiased observables. We therefore establish a fundamentally new method of testing error-disturbance relations. P1-128 Superradiant Emission of Ultra-Bright Photon Pairs in Doppler-Broadened Atomic Ensemble Yoon-Seok Lee, Sang Min Lee, Heonoh Kim and Han Seb Moon Abstract: Photon pair source with high generation rate and narrow bandwidth is one of the most desirable quantum devices for many researchers to realize long-distance quantum communication, where quantum entanglement swapping between completely autonomous sources and the capability of interaction with quantum memory are essentially required. Spontaneous parametric down-conversion (SPDC) has been widely used and constantly

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developed as a major resource for quantum optics due to high generation rate and scalability, such as waveguide nonlinear crystal. However, short coherence time of paired photon limits coupling with another quantum device and causes synchronizing problem for entanglement swapping. In the last decade, a variety of sophisticated methods have been suggested and experimentally demonstrated for generation of the narrowband photon pairs. One of the ingenious approaches is spontaneous four-wave mixing (SFWM), which is based on collective excitation of atomic ensemble and successfully exploited to generation of narrowband photon pairs using highly dense ultracold atoms. However, the need for ultracold temperatures still limits their applicability and thus recent efforts have been made toward replacing ultracold atoms with thermal vapor. Furthermore, the pair generation rate is too low to be used for practical application. Here, we experimentally demonstrate the robust and ultra-bright photon pair source with a coincidence counting rate per input pump power of 64,600 cps/mW and relatively narrow bandwidth using thermal vapor cell. The remarkable generation rate is achieved by superradiant emission of photon pairs, which is attributed to coherent contribution of almost velocity groups in Doppler-broadened ladder-type atomic ensemble. The strong time-correlation of the paired photons exhibited the violation of the Cauchy-Schwartz inequality by a factor of 2370 ± 150. The quadratic proportionality of the probability of detecting a heralded single photon as a function of the optical depth clarifies that the ultra-brightness results from the superradiance in the Doppler-broadened atomic ensemble. In addition, superradiant beating of a single photon at a high optical depth is observed for the first time, to the best of our knowledge; this implies coherent superposition of two-photon amplitudes from different velocity classes. This scalable and highly bright paired photon source is ideal for quantum entanglement swapping between completely autonomous sources and practically applicable for room temperature quantum device in micrometer-scale vapor cell. P1-129 Geometric spin echo under zero field Yuhei Sekiguchi, Yusuke Komura, Shota Mishima, Touta Tanaka, Naeko Niikura and Hideo Kosaka Abstract: Spin echo is a fundamental tool for quantum registers and biomedical imaging. It is believed that a strong magnetic field is needed for the spin echo to provide long memory and high resolution since a degenerate spin cannot be controlled or addressed under a zero magnetic field. While a degenerate spin is never subject to dynamic control, it is still subject to geometric control. We here show the spin echo of a degenerate spin subsystem, which is geometrically controlled via a mediating state split by the crystal field, in a nitrogen vacancy center in diamond. The demonstration revealed that the degenerate spin is protected by inherent symmetry breaking called zero-field splitting. The geometric spin echo under zero field provides an ideal way to maintain the coherence without any dynamics, thus opening the way to pseudo-static quantum RAM and non-invasive biosensors. P1-130 Heralded quantum steering with no detection loophole over a high-loss quantum channel Geoff Pryde, Morgan Weston, Sergei Slussarenko, Sabine Wollmann and Helen Chrzanowski Abstract: Entanglement shared between remote parties is important both for fundamental explorations of quantum physics and for a range of tasks in secure quantum communications, remote information processing, metrology and more. Optics provides an obvious and powerful method for sharing entangled states over long distances, but loss through optical fibres, atmospheric transmission or diffraction effects makes it difficult or impossible to close a Bell inequality detection loophole for far-away parties, limiting the ability to verify that entanglement really has been shared.

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Quantum steering (also called EPR steering) tests provide a more loss-tolerant method of verifying entanglement. However, for losses corresponding to long-range transmission over tens or hundreds of kilometres, the detection loophole is opened for these tests as well. Here we consider the case where channel loss is so high that even a loss-tolerant quantum steering protocol cannot be completed directly. We design and experimentally demonstrate a protocol that allows quantum steering to be completed even in this case. We use entanglement swapping to herald the presence of half of an entangled pair, after a lossy channel, and then complete the steering protocol with the detection loophole closed. The key experimental tools that enabled this advance were two high-performance (high heralding efficiency and purity) entangled-photon sources which we developed, coupled with superconducting nanowire single photon detectors (NIST). P1-131 Entanglement degradation by macrorealistic modifications Stefan Nimmrichter Abstract: The steady experimental progress towards observing quantum phenomena in nanoscopic systems has brought new attention to a controversial but intriguing idea: The concept of macroscopic realism, i.e. the objective modification of quantum mechanics to eliminate superpositions in the macro-world and to resolve the 'measurement problem'. Not only will experiments soon enter a stage where the most prominent macrorealistic proposals become testable, but the idea can also be exploited to systematically assess the degree of macroscopicity achieved in arbitrary mechanical quantum experiments. One experiment can be rated more macroscopic than another when it rules out a larger class of macrorealistic modifications. So far, the assessment of experiments with large mechanical systems has focused on single-particle interference and coherent oscillations of nanomechanical oscillators. Here, we study how mechanical entanglement is affected by macrorealistic modifications and what potential degree of macroscopicity can be achieved by establishing quantum correlations between mechanical systems. P1-132 Scalable three-way quantum information tapping using parametric amplifiers with quantum correlation Nannan Liu, Xiaoying Li, Jiamin Li and Z. Y. Ou Abstract: We demonstrate that a phase-insensitive parametric amplifier, coupled to a quantum correlated source, can be used as a quantum information tap for noiseless three-way signal splitting. We find that the output signals are amplified noiselessly in two of the three output ports while the other can more or less keep its original input size without adding noise. This scheme is able to cascade and scales up for efficient information distribution in an optical network. Furthermore, we find this scheme satisfies the criteria for a non-ideal quantum non-demolition (QND) measurement and thus can serve as a QND measurement device. With two readouts correlated to the input, we find this scheme also satisfies the criterion for sequential QND measurement.

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P1-133 Experimental demonstration of frequency-domain Hong-Ou-Mandel interference Toshiki Kobayashi, Rikizo Ikuta, Shuto Yasui, Shigehito Miki, Taro Yamashita, Hirotaka Terai, Takashi Yamamoto, Masato Koashi and Nobuyuki Imoto Abstract: We observed the Hong-Ou-Mandel(HOM) interference between two photons with different frequencies. In the experiment, we input a 780 nm photon and a 1522 nm photon to a frequency converter that partially exchanges the wavelengths of the photons between 780 nm and 1522 nm. We measured coincidence counts between the output photons at 780 nm and those at 1522 nm from the frequency converter. The observed visibility of the HOM interference was 0.71±0.04, which clearly exceeds the maximum value of 0.5 in the classical wave theory. P1-134 Experimental Detection of Entanglement Polytopes via Local Filters Yuanyuan Zhao, Markus Grassl, Bei Zeng and Guoyong Xiang Abstract: Entanglement polytopes result in finitely many types of entanglement that can be detected by only measuring single-particle spectra. With high probability, however, the local spectra lie in more than one polytope, hence providing no information about the entanglement type. To overcome this problem, we propose to additionally use local filters. We experimentally demonstrate the detection of entanglement polytopes in a four-qubit system. Using local filters we can distinguish the entanglement type of states with the same single particle spectra, but which belong to different polytopes. P1-135 Computing Permanents for Boson Sampling on Tianhe-2 Supercomputer Junjie Wu, Yong Liu, Baida Zhang, Xianmin Jin, Yang Wang, Huiquan Wang and Xuejun Yang Abstract: Boson sampling [1], a specific quantum computation problem, is widely regarded to be one of the most achievable fields in which quantum machine will outperform the most powerful classical computer in the near term, although up to now no upper-bound of how fast the classical computers can compute matrix permanents, the core problem of Boson sampling, has been reported. Here we test the computing of the matrix permanent on Tianhe-2 [2], a supercomputer retaining its position as the world's No. 1 system for six times since June 2013. We arrived at the time (about 77.41~112.44 minutes) to compute the permanent of a 50×50 matrix in an acceptable precision. In addition, we have found that Ryser's algorithm will produce an unacceptable error with the increase of problem scale, compared to Balasubramanian-Bax/Franklin-Glynn's algorithm in the same complexity. The precision issue suggests carefully check in future research of Boson sampling, and comprehensive comparison between quantum computer and classical computer. More details: arXiv1606.05836. [1] Aaronson, S. and Arkhipov, A. The computational complexity of linear optics. In Proceedings of the Forty-third Annual ACM Symposium on Theory of Computing, STOC '11, 333-342 (ACM, New York, NY, USA, 2011). [2] Liao, X et al., MilkyWay-2 supercomputer: system and application. Front. Comput. Sci. 8(3), 345-356, June (2014).

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P1-136 Universal optimal device-independent witnessing of quantum channels Michele Dall'Arno, Sarah Brandsen and Francesco Buscemi Abstract: Quantum process tomography, the standard procedure to characterize any quantum channel in nature, is affected by a circular argument: in order to characterize the channel, the tomographic preparation and measurement need in turn to be already characterized. We break this loop by designing an operational framework able to optimally characterize any given unknown quantum channel in a device-independent fashion, namely, by only looking at its input-output statistics, under the sole assumption that quantum theory is valid. We provide explicit solutions, in closed form, for practically relevant cases such as the erasure, depolarizing, and amplitude-damping channels. P1-138 Optimal communication via mixed quantum t designs Sarah Brandsen, Michele Dall'Arno and Anna Szymusiak Abstract: We operationally introduce mixed quantum t designs as the most general arbitrary-rank extension of projective quantum t designs which preserves indistinguishability from the uniform distribution for t copies. First, we derive upper bounds on the classical communication capacity of any mixed t design measurement, for t in [1,5]. Second, we explicitly compute the classical communication capacity of several mixed t design measurements, including the depolarized version of: any qubit and qutrit symmetric, informationally complete (SIC) measurement and complete mutually unbiased bases (MUB), the qubit icosahedral measurement, the Hoggar SIC measurement, any anti-SIC (where each element is proportional to the projector on the subspace orthogonal to one of the elements of the original SIC), and the uniform distribution over pure effects. P1-139 Surpassing the no-cloning limit with a heralded hybrid linear amplifier Jing Yan Haw, Jie Zhao, Josephine Dias, Syed Assad, Mark Bradshaw, Rémi Blandino, Thomas Symul, Tim Ralph and Ping Koy Lam Abstract: The linearity of quantum mechanics dictates that it is impossible to generate perfect clones of arbitrary quantum states. Associated with this restriction is the quantitative `no-cloning limit' that sets an upper bound to the quality of the generated clones. Recently it was suggested that by abandoning determinism, probabilistic methods could offer a way of circumventing the no-cloning limit, enabling clones to have fidelity surpassing the no-cloning limit. We report the first experimental demonstration of a probabilistic scheme of cloning arbitrary quantum states that clearly surpasses the no-cloning limit. Our scheme is based on a hybrid amplifier that combines an ideal deterministic linear amplifier with a heralded measurement-based noiseless amplifier. We demonstrate the production of up to five clones with the fidelity of each clone clearly exceeding the corresponding no-cloning limit. Because successful cloning events are heralded, our scheme has the potential to be adopted in quantum repeater, teleportation and computing applications.

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P1-144 Generation and storage of multimode entangled light in a solid state, spin-wave quantum memory Kate Ferguson, Sarah Beavan, Jevon Longdell and Matthew Sellars Abstract: Here we demonstrate generating and storing entanglement in a solid state, spin-wave quantum memory with on-demand recall using the process of rephased amplified spontaneous emission (RASE). Amplified spontaneous emission (ASE), resulting from an inverted ensemble of Pr3+ ions doped into a Y2SiO5 crystal, generated entanglement between the collective atomic state of the ensemble and the output optical field. The ensemble was then rephased using a four-level echo technique. By violating the inseparability criterion for continuous variables entanglement between the ASE and its echo was confirmed when the RASE was stored as a spin-wave for up to 5 µs. In addition, RASE was used to generate temporally multimode entanglement with almost perfect distinguishability between two temporal modes demonstrated. P1-145 Fast-gated single-photon counting with ultra-low noise based on thermoelectrically cooled photomultiplier tube Yanhui Cai, Zhengyong Li and Xiangkong Zhan Abstract: Single-photon detecting (SPD) and counting is a crucial technique in a large number of areas such as quantum key distribution (QKD)[1,2], fluorescence laser scanning microscopy[3], high-resolution light detection and ranging (LIDAR)[4]. Although many schemes have been proposed to detect single photons up till now[2,5], it is a long way to develop an ideal single-photon detector with both high efficiency and low noise which always restrict each other. Recently, we establish a photon counting system using an ultra-low-noise photomultiplier tube (PMT), and realize the SPD with high detection efficiency of 35% at 405 nm assisted with fast-gating technology. Removing the noise due to leakage, we have discriminated the photonic signal at much smaller level with short interval of ~9 ns. Furthermore, we develop a ultra-stable thermoelectric cooling system to reduce the dark counts (DCs) generated in the PMT. Results show that the total DCs become smaller and smaller as the temperature decreasing. At -20 degree and below, the net dark count will be pretty close to zero, which is be on a par with the superconducting nanowire detectors. This work is supported by the National Natural Science Foundation of China (Grant Nos. 11274037 and 11574026), the Program for New Century Excellent Talents in University, MOE of China (Grant No. NCET-12-0765), and the Foundation for the Author of National Excellent Doctoral Dissertation, China (Grant No. 201236). References [1] Peng CZ, Zhang J, Yang DC et al., Phys. Rev. Lett. 98, 010505 (2007) [2] Scarani V, Bechmann-Pasquinucci H, Cerf N J, et al., Rev. Mod. Phys. 81, 1301–1350 (2009) [3] Benninger R, Ashby W, Ring E and Piston D, Opt. Lett. 33, 2895–2897 (2008) [4] Howland G, Lum D, Ware M and Howell J, Opt. Express 21, 23822–23837 (2013) [5] Xu L L, Wu E, Gu X R, Jian Y, Wu G and Zeng H P, Appl. Phys. Lett. 94, 161106 (2009)

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Abstracts – Posters (Tuesday) P2-146 Kochen-Specker Theorem Proofs with Non-specific Projectors from Extended KS Value Assignment Rules Tang Weidong Abstract: Since the enlightening proofs of quantum contextuality first established by Kochen and Specker, and also by Bell --- known as Bell-KS theorem or simply KS theorem --- more than half a century ago, various simplified and ingenious proofs have been presented to terminate the non-contextual hidden variable(NCHV) arguments of our nature at a microscopic scale. To show the conflict between the NCHV theory and quantum mechanics, using Kochen-Specker(KS) sets of yes-no tests is a common way. Whereas, amid most of the published proofs of KS theorem, the projectors in a KS set to form a direct logical contradiction are specifically chosen. Here a method for mass production of the proofs, from projectors in non-specific directions as the core part of the KS set to extract the contradiction in a statistical manner, is proposed. It provides a more distinct understanding of KS theorem from a geometric view. P2-147 Arbitrary Multi-Qubit Generation Farid Shahandeh, Austin P. Lund, Timothy C. Ralph and Michael R. Vanner Abstract: An active field of research in quantum optics and quantum information is the development of techniques for producing arbitrary quantum states of different physical systems. This is by virtue of the broad range of applications including quantum computation and communication, quantum simulation, and quantum metrology, that each need specific quantum states as a resource. Here, we propose and analyse a scheme for single-rail-encoded arbitrary multi-qubit quantum state generation to provide a versatile tool for quantum optics and quantum information applications. Our scheme can be realized, for small numbers of qubits, with current technologies using single photon inputs, passive linear optics, and heralding measurements. The particular examples of two- and three-qubit cluster states are studied in detail. We show that such states can be prepared with a high probability of success. Our analysis quantifies the effects of experimentally relevant imperfections and inefficiencies. The general case of arbitrary $N$-qubit preparation is discussed and some interesting connections to the boson sampling problem are given. P2-148 Generation of photon pairs in a nonlinear waveguide array with inhomogeneous poling pattern Francesco Lenzini, James Titchener, Sachin Kasture, Alexander N. Poddubny, Andreas Boes, Ben Haylock, Paul Fisher, Matteo Villa, Arnan Mitchell, Alexander S. Solntsev, Andrey A. Sukhorukov and Mirko Lobino Abstract: We propose and experimentally demonstrate a nonlinear waveguide array with inhomogeneous poling pattern designed for the generation of photon pairs. This device deterministically separates the generated photon pair in two different spatial modes while keeping the pump in a separate waveguide. The biphoton wavefunction produced from the device is characterized by employing a novel method based on reversed sum-frequency generation measurements.

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P2-149 Geometry of system-bath coupling and gauge fields: manipulating currents and driving phase transitions Chu Guo and Dario Poletti Abstract: Quantum systems in contact with an environment display a rich physics emerging from the interplay between dissipative and Hamiltonian terms. We consider a dissipative boundary driven ladder in presence of a gauge field which can be implemented with ion microtraps arrays. The dissipation stimulates currents while the gauge field tends to steer the flow. We show that depending on the geometry of coupling to the baths and of the strength of the gauge field, non-equilibrium phase transitions emerge strongly modifying the currents both in magnitude and spatial distribution. This work shows how quantum simulations can be used to pave the way towards new ways of controlling energy and heat flow in nano and quantum systems. An extended abstract is attached. P2-150 Hong-Ou-Mandel interference between two collective excitations Jun Li, Ming-Ti Zhou, Xiao-Hui Bao and Jian-Wei Pan Abstract: Single collective excitations in one atomic ensemble have been widely used to store single photons, harnessing the enhanced atom-light coupling. By creating and manipulating more distinct excitations, one atomic ensemble may encode many qubits and become a promising platform for quantum computing and quantum simulation. Here we generate two distinct collective excitations in a deterministic fashion via Rydberg blockade and realize the Hong-Ou-Mandel interference between them. These two excitations occupy different Zeeman levels, and a beam-splitter operation is performed via stimulated Raman transitions. By converting the excitations into single photons and performing coincidence detection, a high two-excitation interference visibility is measured. Moreover, the interference results in an entangled NOON state for two excitations, which is two times more sensitive to the magnetic field, compared with a single excitation. A straight-forward extension of our experiment may realize Bose sampling with multiple excitations in a collective fashion. P2-151 Nonlinear infrared spectrometer free from spectral selection Anna Paterova, Shaun Lung, Dmitry Kalashnikov and Leonid Krivitsky Abstract: Nonlinear interference of parametric down conversion (PDC) allows simultaneous measurements of real and imaginary parts of the refractive index in the infrared (IR) range using visible range optics and detectors [1]. However, the method still requires spectral and spatial selection. Here we present a special arrangement of the interferometer, which allows eliminating this requirement and results in the increased sensitivity and throughput. P2-152 Secret key agreement demonstration over 7.8 km free-space optical channel Mikio Fujiwara, Toshiyuki Ito, Mitsuo Kitamura, Hiroyuki Endo, Morio Toyoshima, Hideki Takenaka, Yoshihisa Takayama, Ryosuke Shimizu, Masahiro Takeoka, Ryutaroh Matsumoto and Masahide Sasaki Abstract: Security in free-space (wireless) communication is an important issue in modern communication networks. Recently, secret key agreement between two terminals by exploiting the physical properties of a channel has attracted much attention. This includes quantum key distribution (QKD) as an extremely secure case in which an eavesdropper’s power is only limited by law of physics. In these scenarios, a sender (Alice), a legitimate receiver (Bob), and an eavesdropper (Eve) share correlated information through a broadcast

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channel (called a wiretap channel) from Alice to Bob and Eve, and then exchange messages over a public channel to establish a key between Alice and Bob which is secure against Eve. While QKD provides the ultimate security, its operation distance and capacity are limited. One of the natural direction is thus to compromise Eve’s power with practically reasonable assumptions. The reasonability may highly depend on a real condition of each communication scenario. To explore such an issue from an experimental side in the free-space optical link scenario, we construct a line-of-sight free-space optical link system in which two receiver terminals are installed on Tokyo Free-space optical link shown in Fig.1. One of the receiver terminals works as Eve’s terminal to estimate the maximum information leakage ratio in a practical situation. By using this system, we succeed in demonstrating the secret key agreement protocol over 7.8 km free-space optical channel with eye safe wavelength region. The secure key rate depends on a weather condition, however, 7 M bit/s is obtained. Our experimental result can contribute for further feasibility discussions on implementing a physical layer secret key agreement in free-space optical link as well as for free-space QKD since while our experiment is operated in classical region, the experimental observation of the free-space channel properties in weak laser power regime could be useful for estimating the feasibility of future free-space QKD links. P2-153 Interferometric Resolution of Incoherent Optical Point Sources near the Quantum Limit Ranjith Nair and Mankei Tsang Abstract: We propose and analyze an interferometric system for estimating the separation between thermal point sources well below the Rayleigh limit. Monte-Carlo simulations demonstrating the superresolution effect are also presented. P2-155 Efficient Large Block Codes Ancilla States Preparation for Fault-tolerant Quantum Computation Yi-Cong Zheng, Ching-Yi Lai and Todd Brun Abstract: Fault-tolerant quantum computation (FTQC) schemes using multi-qubit large block codes require a huge amount of clean ancilla states of different types with weak error correlation inside each block. These ancilla states are usually logical stabilizer states of the data code blocks, which are generally difficult to prepare if code size is large. Meanwhile, the yield rate of preparation process are typically extremely low when the distance of block code is large. Here, we propose a protocol to distill various of ancilla states necessarily for FTQC fault-tolerantly using classical codes. Analytical analysis shows that correlated errors can be largely removed. At the same time, the yield rate can be high for general large block code with arbitrary size, using proper classical codes. Numerical Monte-Carlo simulation based on [[23,1,7]] quantum Golay code and quantum [[127, 57, 11]] support this conclusion with reasonably low gate error rates. P2-156 Multi-photon experiments with solid-state single-photon sources Marcelo Pereira de Almeida, Juan Carlos Loredo, Tau Bernstorff Lehmann, Nor Azwa Zakaria, Paul Hiliare, Isabelle Sagnes, Aristide Lemaitre, Pascale Senellart and Andrew White Abstract: Multi-photon experiment with solid-state single-photon sources Solid-state emitters, such as semiconductor quantum dots, are a promising platform for single-photon sources. Recent breakthroughs in material syntheses and fabrication

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processes have enabled a new generation of devices, which combine high emission brightness with a near unity indistinguishable pure single-photon output. We will present our work towards developing and employing quantum dot single-photon sources to realise quantum-based technologies. We will focus on devices consisting of a single quantum dot deterministically coupled to a micro-pillar cavity. The enhanced spontaneous emission due to Purcell factors available in these devices, result in a bright single-photon output [1,2]. Here we demonstrate solid-state photon sources with an absolute brightness at the output of a single-mode finer of 14% and purities up to 99% [3]. We also consider the temporal behaviour of the single-photon indistiguishability. We show that photons emitted with temporal separation as high as 400s display two-photon quantum interference [3]. We will discuss how this property can be used in experiments requiring multiple indistinguishable single-photons. Finally we present our preliminary results employing 2, 3 and 4 single-photons to realise optical entangling circuits [4] and qubit fusion operations, as well as to demonstrate quantum algorithms, in particular the Boson Sampling. [1] O. Gazzano et al., Nat. Comm. 4, 1425 (2013). [2] Somaschi, N., Giesz, V., Santis, L. De, Loredo, J. C., Almeida, M. P., et al., arXiv:1510.06499 (2015). [3] Loredo, J. C., Zakaria, N. A., Somaschi, N., Anton, C., Santis, L. De, Giesz, V., Grange, T., Broome, M. A., Gazzano, O., Coppola, G., Sagnes, I., Lemaitre, A., Auffeves, A., Senellart, P., Almeida, M. P., White, A. G., arXiv:1601.00654 (2016). [4] Gazzano, O., Almeida M. P., et al., Phys. Rev. Lett. 110, 250501 (2013). P2-157 Violation of steering inequality with path entangled single photon Anthony Martin, Thiago Guerreiro, Fernando Monteiro, Jonatan Bohr Brask, Tamás Vertési, Boris Korzh, Felix Bussieres, Varum Verma, Adriana Lita, Richard Mirin, Saewoo Nam, Francesco Marsili, Matthew. Shaw, Nicolas Gisin, Nicolas Brunner, Hugo Zbinden and Abstract: Here we report the violation of quantum steering inequality by a single-photon entanglement via displacement-based measurements. P2-158 Experimental Demonstration of Continuous Variable One Sided Device Independence Nathan Walk, Sara Hosseini, Jiao Geng, Oliver Thearle, Jing Yan Haw, Seiji Armstrong, Syed M. Assad, Jiri Janousek, Timothy C. Ralph, Thomas Symul, Howard Wiseman and Ping Koy Lam Abstract: For continuous variable quantum key distribution (CV QKD) a new key rate that is one sided device independent (1sDI) has been found based on the Gaussian family of protocols. The new key rate has been derived from a recently found entropic uncertainty relation. The new key rate shows a close relationship with steering. With the new key rate we have attempted to demonstrate five of a possible six 1sDI protocols. Three of these yielded a positive key. The first two were Entanglement based protocols and the third was a prepare and measure scheme.

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P2-160 Detector-device-independent quantum key distribution Anthony Martin, Alberto Boaron, Boris Korzh, Charles Lim, Gianluca Boso, Raphael Houlmann and Hugo Zbinden Abstract: To prevent all known and yet-to-be-discovered detector side-channel attacks, a measurement-device-independent QKD (mdi- QKD) protocol was proposed [2]. In this scheme, Alice and Bob each randomly prepare one of the four Bennett & Brassard (BB84) states and send it to a third party, Charlie, whose role is to introduce entanglement between Alice and Bob via a Bell- state measurement (BSM). Alice and Bob do not have to trust Charlie since any other non-entangling measurement would necessarily introduce some noise between them. Unfortunately, mdiQKD possesses many drawbacks. Firstly, the achievable secure key rates (SKR) are significantly lower compared to conventional prepare and measure (P&M) QKD systems [3, 4]. This is mainly because a two-photon BSM relies on coincidence detections, which sets stringent requirements on the detector efficiency. Another factor is that a two-photon BSM implemented with linear optics is at most 50% efficient and, when using WCSs, the results from one of the bases cannot be used for the raw-key generation due to an inherent 25% error rate [5, 6]. Furthermore, the resource overhead in the finite-key scenario [7] is significantly larger compared to common P&M schemes [4, 8]. Finally, the technological complexity of mdiQKD is greater due to the use of two-photon interference, requiring both photons to be indistinguishable in all degrees of freedom (DOFs) : temporal, polarization and frequency. We have recently proposed a QKD scheme that overcomes the aforementioned limitations but is still secure against all detector side-channel attacks [9]. This bridges the gap between the superior performance and practicality of P&M QKD schemes and the enhanced security offered by mdiQKD. Our scheme, referred to as detector- device-independent QKD (ddiQKD), essentially follows the idea of mdiQKD, however, instead of encoding separate qubits into two independent photons, we exploit the concept of a two-qubit single-photon (TQSP). P2-161 Heralded hybrid noiseless linear amplifier for arbitrary coherent states Jie Zhao, Josephine Dias, Jing Yan Haw, Mark Bradshaw, Remi Blandino, Thomas Symul, Timothy Ralph, Ping Koy Lam and Syed Assad Abstract: As a direct consequence of the linearity and unitarity of quantum mechanics, phase-insensitive linear amplifiers inevitably suffer some amount of signal-to-noise (SNR) degradation. Recently, it was conceived theoretically and demonstrated experimentally that by forgoing determinism, benefits of noiseless linear amplification could be extracted, though at the detriment of success probability. Here we report a heralded hybrid linear amplifier (HLA) for arbitrary coherent states that overcomes the noise penalty with only linear optical elements. Such HLA, comprising of the ideal linear amplifier and the measurement-based noiseless linear amplifier, allows one to trade off between the SNR and the success probability flexibly. Given an arbitrary input coherent state, both amplification gains and truncations are freely tunable to optimise the success probability while preserving the input Gaussianity. We report an output SNR up to 1.53 times that of the input, which provides a clear demonstration of a noiseless linear amplifier working nondeterministically.

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P2-162 Quantum teleportation by quantum walks Yun Shang Abstract: It is well-known that the preparation of entangled pairs and joint measurement necessary for quantum teleportation are very difficult to realize in experiments. Is it possible to avoid the above two hurdles in quantum teleportation? Based on quantum walks, a novel scheme of quantum teleportation is developed to relax these hurdles. This scheme does not require the preparation of an entangled state as a source beforehand, and the main resources are only two shift operators. For the case of an unknown qubit state, two steps of quantum walks can be enough for teleportation. However, completely unlike complex joint measurement in original teleportation scheme, the proposed scheme just needs local measurement. For the case of $n$-dimensional states, quantum walks on graphs can be used to teleport. However, comparing the cost of measurement basis with Bennet \emph{et al.}'s scheme, only two $n$ dimensional measurement bases are needed, rather than one $n^{2}$ dimension measurement basis. These factors can help effectively decrease the error problem and potentially lead to faster, more reliable quantum computation.

P2-163 Characterizing ground and thermal states of few-body Hamiltonians

Otfried Guehne and Felix Huber Abstract: We provide methods to characterize the states generated by two- and, more generally, k-body Hamiltonians as well as the convex hull of these sets. This leads to new insights into the question which states are uniquely determined by their marginals and to a generalization of the concept of entanglement. Finally, certification methods for quantum simulation can be derived. P2-164 Classical realization of “quantum-optical coherence tomography” by time-resolved pulse interferometry Kazuhisa Ogawa and Masao Kitano Abstract: Quantum-optical coherence tomography (Q-OCT) provides a dispersion-canceled axial-imaging method, but its practical use is limited by the weakness of the light source and by artifacts in the images. A recent study using chirped-pulse interferometry (CPI) has demonstrated dispersion-canceled and artifact-free OCT with a classical system; however, unwanted background signals still remain after removing the artifacts. Here, we propose a classical optical method that realizes dispersion-canceled, artifact-free, and background-free OCT. This OCT method uses time-resolved pulse interferometry (TRPI), which we proposed to achieve dispersion-canceled OCT with a classical system. We have also introduced a subtraction method to remove artifacts and background signals. With these methods, we experimentally demonstrated dispersion-canceled, artifact-free, and background-free axial imaging of a coverglass and cross-sectional imaging of the surface of a coin. P2-165 Distribution of quantum coherence in multipartite systems Chandrashekar Radhakrishnan, Manikandan Parthasarathy, Segar Jambulingam and Tim Byrnes Abstract: The distribution of coherence in multipartite systems is examined. We use a new coherence measure with entropic nature and metric properties, based on the quantum Jensen-Shannon divergence. The metric property allows for the coherence to be decomposed into various contributions, which arise from local and intrinsic coherences. We

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find that there are trade-off relations between the various contributions of coherence, as a function of parameters of the quantum state. In bipartite systems the coherence resides on individual sites or distributed among the sites, which contribute in a complementary way. In more complex systems the characteristics of the coherence can display more subtle changes with respect to the parameters of the quantum state. In the case of the XXZ Heisenberg model, the coherence changes from a monogamous to a polygamous nature. This allows us to define the shareability of coherence, leading to monogamy relations for coherence.

P2-166 Effects of measurement dependence on generalized CHSH-Bell test in the single-run and multiple-run scenarios Dan-Dan Li, Yu-Qian Zhou, Fei Gao, Xin-Hui Li and Qiao-Yan Wen Abstract: Bell tests, as primitive tools to detect nonlocality in bipartite systems, rely on the major assumption — measurement independence. Since ensuring measurement independence in a practical Bell test is extremely difficult, it is crucial to explore effects of relaxing the assumption. Recently, in the simplest CHSH-Bell test, D. E. Koh et al. [Phys. Rev. Lett. 109, 160404 (2012)] builded the relation between measurement dependence and the maximum value of CHSH-Bell correlation function that an adversary (Eve) can fake. As well, J. E. Pope et al. [Phys. Rev. A 8, 032110 (2013)] and X. Yuan et al. [Phys. Rev. A 91, 032111 (2015)] settled the same problem in the multiple-run scenario with the general input distribution and the factorizable one, respectively. While, pertinent results in generalized CHSH-Bell test is still missing. Here, we study this problem and establish the relation among measurement dependence, guessing probability and the maximum value of generalized CHSH-Bell correlation function. Furthermore, we also consider the multiple-run scenario and show the relations in both input distributions. Interestingly, compared with the simplest CHSH-Bell test, we find that it is more difficult for Eve to fake a violation in generalized CHSH-Bell test under some special cases. P2-167 High fidelity entanglement swapping via a time-resolved coincidence measurement Yoshiaki Tsujimoto, Motoki Tanaka, Yukihiro Sugiura, Rikizo Ikuta, Shigehito Miki, Taro Yamashita, Hirotaka Terai, Takashi Yamamoto, Masato Koashi and Nobuyuki Imoto Abstract: We experimentally demonstrated high fidelity entanglement swapping using two polarization-entangled photon pairs generated by spontaneous parametric down conversion (SPDC) pumped by continuous-wave (cw) light via a time-resolved coincidence measurement. The two entangled photon pairs are generated by cw-pumped SPDC through a periodically poled lithium niobate waveguide in a Sagnac configuration and they were sufficiently narrowed by interference filters with the central wavelengths 1541 nm and 1580 nm. The time-resolved photon detection is achieved by superconducting nanowire single-photon detectors with low timing jitter. After performing the Bell-state measurement on the two photons at 1541 nm, we performed the quantum state tomography on the remaining two photons at 1580 nm. The observed fidelity of the two photons to the maximally entangled state was 0.84 $\pm$ 0.04.

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P2-168 Quantum metrology using topological quantum states. Tim Byrnes Abstract: One of the standard ways to obtain a quantum enhancement for precision measurements is to use entanglement in the system to reduce quantum noise. This allows for obtaining a square root enhancement approaching the Heisenberg limit going beyond the standard quantum limit. Here we discuss a different approach for obtaining a quantum enhancement using topological states. As is well known, the electrical quantum Hall effect can measure the unit of conductance extremely precisely, to a level in the region of 10^-10 in relative error. This is due to the Hall resistance being a topological quantity, and is robust to imperfections. We apply this same idea to measuring the mass of atoms in Bose-Einstein condensates (BEC) using vortices. By displacing a vortex in a BEC, this gives rise to a Magnus force, which in turn creates a current in the BEC. The current is related to the transverse population difference as a topological quantity. This gives rise to an analogue quantum Hall effect in BECs, which should be readily observable using existing experimental techniques. Instead of quantization in units of e/h, this gives quantization in units of m/h, where m is the mass of the atoms. Measuring the mass of atoms very precisely gives the possibility of a novel definition of the standard of the kilogram in terms of a fixed number of atoms. The kilogram is the last SI unit that is still defined in terms of a material artifact (the IPK). Currently only the relative mass of an atom can be precisely measured, and not the absolute mass. If a precise measurement of an atom can be made this potentially could contribute to a way of defining the standard of mass quantum mechanically. This is in contrast to other methods which are based primarily on classical techniques. P2-169 Ultrafast coherent control of Bose-Einstein condensates using stimulated Raman adiabatic passage Andreas Thomasen and Tim Byrnes Abstract: Bose-Einstein condensates have been proposed for a variety of quantum information tasks including quantum simulation, metrology and information processing. Their attractiveness in these applications is partly due to the fact that physical interactions are boosted by the occupation number of a BEC. For instance, dipole transition matrix elements exhibit an order of N dependence, which is a good reason to expect that speedups in coherent control are possible. Furthermore, cold atoms are well known to coherently store quantum memories with long lifetimes. If both these aspects of cold atomic BECs can be harnessed for quantum computing, one may bridge a gap in between platforms that are useful for storage purposes and those that perform very fast operations (e.g. superconducting circuits, etc.) However, using BECs for these tasks is not without difficulties. Spontaneous emission terms appear in the equations of motion of a BEC proportional to the number of particles squared. Thus, even slight leakage into the excited states of a BEC has serious consequences for the fidelity of any operations performed on it. We propose a novel scheme for performing arbitrary unitary operations on two-component rubidium 87 BECs using stimulated Raman adiabatic passage (STIRAP). STIRAP is a technique for population transfer in quantum systems that avoids excitation of bright states. It does so by effecting a transfer exclusively through adiabatic evolution of the dark eigenstate manifold of a slowly evolving Hamiltonian. In this way it becomes possible to completely avoid spontaneous emission as long as the adiabatic condition is adhered to. Our scheme assumes that BECs have been magnetically trapped with a preference for first-order Zeeman insensitive hyperfine ground levels. It is thus readily implementable by experimenters. Through simulations we obtain fidelities greater than 99.9% when the operation is applied for 27.7 ns on a BEC containing 1000 atoms.

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P2-170 Generation and non-destructive detection of single microwave photons Sankar Raman Sathyamoorthy Abstract: In this poster, we show how to use superconducting qubits at the end of a semi-infinite transmission line, analogous to atoms in front of a mirror, to generate and detect microwave photons. We present two simple and efficient schemes to generate a single photon on demand from a coherent pi pulse using the atom in front of a mirror, along with either a beam splitter or by using tunable coupling [1]. The frequency of the emitted photon can be tuned by tuning the level splitting of the qubit and the single photon wave-packets can be shaped in time. The presented schemes are relatively insensitive to dephasing and can be extended to generate correlated and entangled photons. They can also be used to generate photonic superposition states between 0 and 1 in arbitrary wave packets. We also present a scheme to non-destructively detect a propagating microwave photon by using the strong effective photon-photon interaction mediated by the artificial atom. We show that by cascading atoms, we can increase the measurable signal beyond the vacuum noise, leading to signal to noise ratio for photon detection above 1 [2]. The single photon to be detected survives the interactions making the scheme QND in photon number. References: [1] S. R. Sathyamoorthy, A. Bengtsson, S. Bens, M. Simoen, P. Delsing, G. Johansson, arXiv:1511.03038 (2015) [2] S. R. Sathyamoorthy, L. Tornberg, A. F. Kockum, B. Q. Baragiola, J. Combes, C. M. Wilson, T. M. Stace, and G.Johansson, Phys. Rev. Lett. 112, 093601 (2014). P2-171 A correlation based entanglement criterion in bipartite multi-boson systems Wiesław Laskowski, Marcin Markiewicz, Danny Rosseau, Tim Byrnes, Kamil Kostrzewa and Adrian Kołodziejski Abstract: We describe a criterion for the detection of entanglement between two multi-boson systems. The criterion is based on calculating correlations of Gell-Mann matrices with a fixed boson number on each subsystem. This applies naturally to systems such as two entangled spinor Bose-Einstein condensates. We apply our criterion to several experimentally motivated examples, such as an SzSz entangled BECs, ac Stark shift induced two-mode squeezed BECs, and photons under parametric down conversion. We find that entanglement can be detected for all parameter regions for the most general criterion. Alternative criteria based on a similar formalism are also discussed together with their merits.

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P2-172 On the equivalence of separability and extendability of quantum states K. R. Parthasarathy, Ritabrata Sengupta and B. V. Rajarama Bhat Abstract: Motivated by the notions of k-extendability and complete extendability of the state of a finite level quantum system as described by Doherty et al (Phys. Rev. A, 69:022308), we introduce parallel definitions in the context of Gaussian states and using only properties of their covariance matrices derive necessary and sufficient conditions for their complete extendability. It turns out that the complete extendability property is equivalent to the separability property of a bipartite Gaussian state. Following the proof of quantum de Finetti theorem as outlined in Hudson and Moody (Z.Wahrscheinlichkeitstheorie und Verw. Gebiete, 33(4):343--351), we show that separability is equivalent to complete extendability for a state in a bipartite Hilbert space where at least one of which is of dimension greater than 2. This, in particular, extends the result of Fannes, Lewis, and Verbeure (Lett. Math. Phys. 15(3): 255--260) to the case of an infinite dimensional Hilbert space whose C* algebra of all bounded operators is not separable. Latest version of this paper can be seen in arXiv: http://arxiv.org/abs/1601.02365 P2-173 Evaluation of quantum 1D repetition codes’ performance against quantum noise Takanori Sugiyama, Keisuke Fujii, Haruhisa Nagata and Fuyuhiko Tanaka Abstract: As error rates of quantum gates implemented in recent experiments approach a fault-tolerant threshold for a depolarizing noise model, it becomes more important to investigate performance of quantum error correction codes against more general and realistic noise models. The standard approach assuming depolarizing noise models is not realistic and can overestimate the performance. On the other hand, a rigorous approach with the diamond norm is applicable to realistic noise models but greatly underestimates the performance. Here we propose a new theoretical framework for evaluating performances of quantum error correction codes, which is applicable to any local noise models. We apply the method to a quantum 1D repetition code, and numerically evaluate the performance with 9 to 61 physical qubits. Our numerical results clarify the effect of quantum coherence in noise on the performance of quantum 1D repetition codes. P2-174 Monolithically integrated optics for scalable trapped-ion single-photon sources Mirko Lobino, Mojtaba Ghadimi, Valdis Blums, Benjamin G. Norton, Paul Fisher, Harley Hayden, Jason Amini, Curtis Volin, Dave Kielpinski and Erik W Streed. Abstract: We demonstrate the first ion chip trap with fully integrated and scalable diffractive mirrors. We realize high efficiency collection, gathering 5.81(0.84)% total ion light collection and coupling 2.41 (0.89)% of total ion light into a single mode fiber.

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P2-175 Detection-dependent six-photon NOON state interference Rui-Bo Jin, Mikio Fujiwara, Ryosuke Shimizu, Robert Collins, Gerald Buller, Taro Yamashita, Shigehito Miki, Hirotaka Terai, Masahiro Takeoka and Masahide Sasaki Abstract: We have experimentally demonstrated and analyzed theoretically six-, four- and two-photon interference from a NOON state emitted by a spontaneous parametric down conversion source detected using six superconducting nanowire single-photon detectors. It was found that the coherence time, visibility and shape of the interference patterns are strongly dependent on the detection schemes. This is the first experimental observation of detection dependency of NOON state interferometry with up to six photons at telecom wavelengths. The results of this experiment and the theoretical analysis will find applications in analytical approaches which are based on the envelope of the NOON state interference pattern. P2-176 Stationary Light in Resonant and Far-Detuned Atom-Optic Memories Jesse Everett, Geoff Campbell, Young-Wook Cho, Pierre Vernaz-Gris, Daniel Higginbottom, Olivier Pinel, Nick Robins, Ping Koy Lam and Ben Buchler Abstract: Stationary light (SL) describes light that has been stopped but not entirely absorbed into an atomic ensemble. SL is one possible method for enhancing incredibly weak nonlinear interactions between single photons. Stationary light has previously been demonstrated with electromagnetically-induced transparency (EIT). In EIT, light resonant with an atomic transition passes slowly through an atomic ensemble with the assistance of a separate optical field – a control field. The control field couples the excited state to a second ground state, preventing spontaneous emission and generating a coherent atomic polarisation, or spinwave. The light propagates along with the spinwave, and by sending two counter-propagating control fields, the spinwave is pushed in both directions, and the light is effectively trapped in the atoms. Using an optically dense, elongated MOT of 87Rb, we observe directly the behaviour of EIT-SL. Due to a large optical depth, we are able to confine a pulse in a small region of the MOT. We image the spinwave from the side, perpendicular to the direction of propagation, and are even able to push it back and forth by changing the ratio of the control field intensities. We demonstrate that the propagation of EIT-SL can be described by a simple equation. We also present a novel form of stationary light. Operating in the Raman regime, where the light is far detuned from the atomic transition, the light travels quickly through the memory. The control field causes the light to be coherently absorbed into and re-emitted from the atoms. Because the light is not confined to the spinwave, a different mechanism leads to the creation of stationary light. By using counter-propagating control fields with carefully chosen angles and frequencies and a specific shape of spinwave, the light generated destructively interferes at each end of the atomic ensemble. The system does not evolve, due to a destructive interference between light travelling in opposite directions coupling into the spinwave. Thus, a strong stationary optical field is generated. The condition for Raman-SL behaviour is that the spinwave integrates to zero over the length of the ensemble. A spinwave that does not satisfy this condition rapidly evolves to one that does. To experimentally test this theory, we write the spinwaves in a gradient echo memory and send the counter-propagating control fields. Imaging the spinwave gives additional information about the evolution of the spinwave, confirming the stationary light and the rapid evolution of non-stationary spinwaves. We show that the possible enhancement of nonlinear interaction scales in the same way for EIT-SL and Raman-SL. we propose an experimentally realisable scheme by which useful nonlinear interactions can be generated in the far-detuned system. The optical field of SL is used to AC-Stark shift the energy of an atomic level on which another pulse is stored, generating a

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measurable phase shift of the second pulse. We are currently pursuing experimental evidence of these interactions. P2-177 Particle-Indistinguishability Signatures in Phase Space Farid Shahandeh Abstract: Particle indistinguishability imposes entanglement on the states of identical particles via the (anti)symmetrisation postulate. Such a fluffy bunny entanglement, however, is considered to be unphysical and inaccessible. In Peres words "no quantum prediction, referring to an atom located in our laboratory, is affected by the it mere presence of similar atoms in remote parts of the universe." Here, we consider the possibility of any observable effects due to particle indistinguishability on the quantum phase-space representation of bosonic particles. We order the amount of nonclassicality of the Wigner function and particle indistinguishability in a bipartite system of n identical boson particles and prove that, regardless of the known classical and quantum correlation contents of the state, redistributing particles between the two modes always changes both quantities in an equivalent way, unambiguously representing the connection between phase-space nonclassicality and quantum particle indistinguishability.

P2-179 Temporal multimode storage of entangled photons Peter C. Strassmann, Alexey Tiranov, Jonathan Lavoie, Nicolas Brunner, Marcus Huber, Varun B. Verma, Sae Woo Nam, Richard P. Mirin, Adriana E. Lita, Francesco Marsili, Mikael Afzelius, Félix Bussières, Nicolas Gisin Abstract: For practical optical quantum communication and computation based on the quantum repeater scheme, time-division multiplexing significantly increases the probability of success. An approach based on atomic ensembles and linear optics requires the ability to store multiple temporal modes inside the quantum memory. [1] Here we demonstrate the storage and release of at least 8 temporal modes in an atomic frequency comb (AFC) [2] solid-state quantum memory, where at least two of the modes contain a single photon. Each of the two stored photons (at 883 nm) is polarization-entangled with a partner photon at a telecom wavelength, i.e. two entanglement bits (ebits) are stored simultaneously. To certify the entanglement of the two pairs we develop and apply a new entanglement witness. The novel entanglement witness is compatible for the experiments with the limited number of detectors and is more efficient than the general quantum tomographic approach. Our work is the first direct demonstration of storage of multiple pairs of entangled photons using different temporal modes. This experiment proves that the temporal multiplexing in the same spatial mode of quantum memories can be achieved for the entangled photon pairs and opens a way for further developments to build a quantum repeater. [1] Sangouard, N. et al. Quantum repeaters based on atomic ensembles and linear optics, Rev. Mod. Phys. 83, 33-80 (2011). [2] Afzelius, M. et al. Multimode quantum memory based on atomic frequency combs, Phys. Rev. A 79, 052329 (2009).

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P2-180 Au Microdisk-Size Dependence of Quantum Dot Emission from the Hybrid Metal-Distributed Bragg Reflector Structures Employed for Single Photon Sources Baoquan Sun Abstract: We investigate metallic microdisk-size dependence of quantum dot (QD) spontaneous emission rate and microantenna directional emission effect for the hybrid metal-distributed Bragg reflector structures based on a particular single QD emission. It is found that the measured photoluminescence (PL) intensity is very sensitive to the size of metallic disk, showing an enhancement factor of 11 when the optimal disk diameter is 2 micrometer and the numerical aperture of microscope objective NA=0.5. It is found that for large metal disks, the Purcell effect is dominant for enhanced PL intensity, whereas for small size disks the main contribution comes from plasmon scattering at the disk edge within the light cone collected by the microscope objective. P2-182 Quantum Carburettor Effect for Photon Number Shiftin Jennifer Radtke, John Jeffers and Daniel Oi

Abstract: The quantum carburettor effect is an elegant, experimentally feasible demonstration of the bosonic nature of light. Here we use this effect with conditional measurement to implement the Susskind-Glogower photon number shifting operator, a non-Gaussian operation with potential applications in continuous variable quantum information processing. P2-183 Noise-tolerant post-selected measurement using noise margin with GKP code state Kosuke Fukui, Akihisa Tomita and Atsushi Okamoto Abstract: We propose a method for highly reliable measurement with GKP code states by introducing noise margin. We use a hybrid quantum information processing where qubit degrees of freedom for logical level are combined with quantum continuous variables for enhancing noise resistance. As a simple example to show the validity of our proposal, we applied for entanglement distribution and the results of numerical calculations confirm the improvement of error rate using reasonable resources. This newly discovered property which is different from discrete variables opens up potential for quantum information processing in a continuous variable.

P2-184 An Optimal Design for Universal Multiport Interferometers William Clements, Peter Humphreys, Benjamin Metcalf, Steven Kolthammer and Ian Walmsley Abstract: Linear optical quantum interferometry is a general framework that encompasses any experiment that produces quantum states of light in several modes, interferes these modes, and performs quantum measurements on them. It has been extremely successful as a platform to study the foundations of quantum mechanics [1], perform quantum-enhanced optical metrology [2], and demonstrate the principles of quantum simulation and universal quantum computation [3]. However, building large optical interferometers that provide high-fidelity interference is a challenge. Recently, reconfigurable universal photonic circuits, that can implement any unitary transformation between several optical spatial modes, have emerged as a powerful tool to provide this interference in chip-scale devices. They have already been used to demonstrate a wide range of experiments, with interference between up to six modes [4]. Their design is based on the seminal work by Reck et al [5], who

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showed that such universal circuits can be implemented by a specific planar triangular array of 2x2 beam splitters and phase shifters, which are programmed using a simple analytical method. However, this 20-year old design does not make use of the minimum possible space on a planar substrate, nor does it have the most robust performance with respect to component imperfections. In this sense, the design by Reck et al is not optimal. We present a new design for universal photonic circuits, based on an alternative arrangement of beam splitters and phase shifters, which outperforms the Reck design in several respects. This design occupies half the physical footprint of the Reck design, which will allow larger and lower-loss circuits to be built on integrated chips. I will also show that the optical transformation implemented by devices built according to our design is much more robust to imperfections such as unbalanced loss within the circuit. I will present a new decomposition of a unitary matrix into 2x2 elements representing beam splitters, which we use to straightforwardly program all the optical elements in the circuit to achieve the intended transformation. We will also introduce our own recent experimental efforts to realise the construction of this optimal device using a silica-based waveguide circuit. This compact and loss tolerant design for fully programmable universal photonic devices will be of great interest to anyone interested in building experimental reconfigurable linear optical circuits. The new unitary matrix decomposition method that is used to program these circuits will also be useful for other quantum systems, for example for ion traps [6] and superconducting circuits [7]. More details about this work will be made available in a forthcoming ArXiv preprint, named “An Optimal Design for Universal Photonic Circuits”. The authors of this preprint have also jointly filed a patent for this work. P2-186 Wavelength Conversion of non-classical light from rubidium atoms to the telecom band Rikizo Ikuta, Toshiki Kobayashi, Kenichiro Matsuki, Shigehito Miki, Taro Yamashita, Hirotaka Terai, Takashi Yamamoto, Masato Koashi, Tetsuya Mukai and Nobuyuki Imoto Abstract: We Observed non-classical telecom light which has a correlation with cold rubidium atoms. In the experiment, the light at 780 nm was prepared from the rubidium atomic ensemble. The wavelength of the light was converted to the telecom one at 1522 nm by using a second-order nonlinearlity in a periodically-poled lithium niobate. By the Hanbury-Brown and Twiss experiment, we measured the autocorrelation function of the telecom light. The observed value was clearly below 1, which shows the non-classical photon statistics of the light after the wavelength conversion. P2-187 Few-Photon Heterodyne Spectroscopy Gustavo Amaral, Thiago Ferreira Da Silva, Guilherme Temporão and Jean Pierre von der Weid Abstract: We perform a high resolution Fourier Transform Spectroscopy of optical sources in the few-photon regime based on the phenomenon of two-photon interference in a beam splitter. From the heterodyne interferogram between test and reference sources it is possible to obtain the spectrum of the test source relative to that of the reference. The method proves to be a useful asset for spectral characterization of faint optical sources below the range covered by classical heterodyne beating techniques.

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P2-188 Controlling two-photon frequency entanglement using cross-Kerr effect Nobuyuki Matsuda Abstract: The frequency conversion of quantum light is a crucial technology for quantum networking. We have recently developed a scheme for realizing spectral and temporal reshaping of single photon wave packets using cross phase modulation (XPM). Here we demonstrate that quantum entanglement of correlated photons remains throughout XPM using a two-photon interference experiment. P2-189 Experimental detection of entanglement with optimal-witness families Jibo Dai, Yink Loong Len, Yong Siah Teo, Berthold-Georg Englert and Leonid A. Krivitsky Abstract: We report an experiment in which one determines, with least tomographic effort, whether an unknown two-photon polarization state is entangled or separable. The method measures whole families of optimal entanglement witnesses. We introduce adaptive measurement schemes that greatly speed up the entanglement detection. The experiments are performed on states of different ranks, and we find good agreement with results from computer simulations. P2-190 Irreversibility and the Arrow of Time in a Quenched Quantum System Tiago Batalhao, Alexandre Souza, Roberto Sarthour, Ivan Oliveira, Mauro Paternostro, Eric Lutz and Roberto Serra. Abstract: Irreversibility is one of the most intriguing concepts in physics. While microscopic physical laws are perfectly reversible, macroscopic average behavior has a preferred direction of time. According to the second law of thermodynamics, this arrow of time is associated with a positive mean entropy production. Using a nuclear magnetic resonance setup, we measure the nonequilibrium entropy produced in an isolated spin-1/2 system following fast quenches of an external magnetic field. We experimentally demonstrate that it is equal to the entropic distance, expressed by the Kullback-Leibler divergence, between a microscopic process and its time reversal. Our result addresses the concept of irreversibility from a microscopic quantum standpoint. Paper is available at http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.115.190601, and comments are available at http://physics.aps.org/articles/v8/106 P2-191 Simple and Efficient Memory-Assisted Quantum Key Distribution Nicolo Lo Piparo, Mohsen Razavi and William Munro Abstract: Memory-assisted quantum key distribution (MA-QKD) aims to use current quantum-device technologies to offer better rate-versus-distance behavior than that of conventional QKD systems. Here, we present a novel system that relies on only one physical memory: a nitrogen-vacancy (NV) center embedded into a cavity. We calculate the secret key rate of such a system by considering all major sources of error and we show that, in certain regimes of operation, our system leads to a key rate enhancement compared to the no-memory QKD systems for distances larger than 200 km.

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P2-193 An explicit classical strategy for winning a CHSH_q game Matej Pivoluska and Martin Plesch Abstract: A CHSH_q game is a generalization of the standard two player CHSH game, having q different input and output options. In contrast to the binary game, the best classical and quantum winning strategies are not known exactly. In our work we provide a constructive classical strategy for winning a CHSH_q game, with q being a prime. Our construction achieves a winning probability better than 1/22*q^(-2/3), which is in contrast with the previously known constructive strategies achieving only the winning probability of O(q^-1). P2-194 Isotropy and control of dissipative quantum dynamics Ben Dive, Daniel Burgarth and Florian Mintert Abstract: We investigate the problem of what evolutions an open quantum system with Hamiltonian controls can undergo. A series of no-go theorems, primarily based on the anisotropy of spectral properties, are given which exclude channels from being reachable for any unitary controls. As well as studying examples of the use and strength of these criteria, we explore their relation with existing approaches on the controllability of open quantum systems and links with quantum thermodynamics. P2-195 Quantum Theory of Two-Dimensional Resolution for Two Incoherent Optical Point Sources Shan Zheng Ang, Ranjith Nair and Mankei Tsang Abstract: We obtain the quantum Cramer-Rao (QCR) bound for estimating the 2-D separation of two incoherent optical point sources. The bound is independent of the x- and y-separations. We also propose a linear-optics-based measurement scheme that attains the quantum bound for sub-Rayleigh separations.

P2-197 Unified view of quantum amplification based on quantum states transformation Mengjun Hu and Yongsheng Zhang Abstract: A general framework of quantum state amplification using the language of quantum state transformation is given systematically. The concept of amplification of quantum states is defined specifically and the amplification of a set of quantum states is formulated generally as the transformation of quantum states. Three different kinds of important quantum amplifications, i.e., deterministic noisy quantum amplification, probabilistic noiseless quantum amplification, and deterministic noiseless quantum amplification are identified and discussed. For deterministic quantum amplification, the linearity of amplification is proven to be incompatible with the noiseless amplification while it is not true for probabilistic quantum amplification. However, deterministic noiseless quantum amplification is shown physically attainable if the requirement of linearity of amplification is relaxed. The relation between the gain of amplification and the success probability is discussed for probabilistic quantum amplification. Assuming that success probability is the same for all quantum states to be amplified, we obtain a generally valid relation between the gain of amplification and the success probability. Particular interest is given to phase-preserving quantum amplification of Gaussian states which has been shown of theoretical interest and of practical importance in quantum information and quantum communication recently. Our results of quantum state

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amplification not only enrich the research of quantum amplification but also can be helpful for further practical applications. P2-198 Two-atom interferences in a cavity QED system Olivier Morin, Andreas Neuzner, Matthias Körber, Stephan Ritter and Gerhard Rempe Abstract: A single-atom in a cavity is the most simple system of cavity quantum electrodynamics and constitutes a tremendous platform for quantum information. Increasing the system up to two atoms offers new possibilities in terms of amount of information that one can process, presents new physical effects and remains highly non-linear, in contrast to large atomic ensembles. Here, we show the experimental study of such a system by trapping two atoms in a high-finesse cavity combined with a single-site-resolved imaging technique. As for the paradigmatic double-slit experiment, we observe the fundamental role of the relative phase between possible optical paths determined by the atoms' relative positions. Indeed, this new degree of freedom introduces non-trivial effects based on the cavity-mediated long-range interaction between the atoms. Furthermore, those results witness the high level of control achieved in our experimental setup and its suitability for two-atom based quantum information protocols.

P2-199 Exploring the limits of non-locality with pairs of photons Alessandro Cere, Hou Shun Poh, Siddarth Koduru Joshi, Adán Cabello, Marcin Markiewicz, Pawel Kurzynski, Dagomir Kaszlikowski and Christian Kurtsiefer. Abstract: Bell inequalities are a powerful tool in discriminating whether Nature is better described by classical theories or non-local ones. I will present our efforts in experimentally test Bell inequalities and the predictions of standard quantum mechanics using a source of polarization entangled photon pairs, in particular our most recent two works. In the first, we attempt to saturate the Tsirelson bound, the well known 2sqrt(2) predicted by standard quantum mechanics. This attempt allowed us to exclude some of the alternative, non-local theories [1]. In the second, I present an approach to discriminate between classical and non-classical system based on the computational complexity of the output, as opposed to the statistical nature of the standard Bell tests [2]. [1] Poh, H. S., et al., "Approaching Tsirelson's bound in a photon pair experiment," PRL 115, 180408 (2015) [2] Poh, H. S., et al., "Probing quantum-classical boundary with compression software," http://arxiv.org/abs/1504.03126 (2015) P2-200 Control and characterisation of nuclear spin memory in diamond nanocrystals Jan D. Beitner, Helena S. Knowles, Dhiren M. Kara, David-Dominik H. Jarausch and Mete Atatüre Abstract: Nitrogen-vacancy (NV) centres in diamond are excellent sensors for magnetic and electric fields, and temperature. Embedded in nanodiamonds they allow in vivo sensing. However, measurements are restricted by the short electron spin coherence time typically seen in nanocrystals. Sensitivity can be increased by taking advantage of the NV host nuclear nitrogen spin. Here, we demonstrate initialisation of the nuclear spin and, measure a lifetime exceeding 15 milliseconds and a coherence time of 241 microseconds, limited by the lifetime of the NV electron spin. This result enhances the potential sensitivities and spectral resolution of nano-MRI measurements achievable with such NV centres.

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P2-201 Long coherence time quantum memory for polarization qubits based on a single atom in a cavity Olivier Morin, Matthias Körber, Stefan Langenfeld, Andreas Neuzner, Stephan Ritter and Gerhard Rempe Abstract: Extended storage of quantum information is a long standing goal since decades. It is particularly motivated by the fact that quantum network implementations strongly rely on quantum memories for light. Long storage time and high efficiency are the main two figures of merit for a quantum memory. However, it remains challenging to fulfill both criteria at a level that is sufficient to beat classical systems. The use of single atoms as a light-matter interface offers the advantage of reducing the number of external and internal degrees of freedom. This is particularly relevant for the realization of quantum information tasks where decoherence mechanisms mostly come from a lack of control on the system. Here, we present a single-atom-based quantum memory with a read-write efficiency of about 10\% and a storage time on the order of 10ms. Mainly, decoherence induced by magnetic field fluctuations is overcome by coherent manipulation of the atomic state after writing the qubit, to move the information into a pseudo-clock state that is less sensitive to magnetic field fluctuations. This paves the way for the implementation of long distance quantum communication protocols e.g. quantum repeaters. P2-202 Quantum approaches to homomorphic encryption Joshua Kettlewell, Carlos Perez-Delgado, Yingkai Ouyang, Si-Hui Tan, Li Yu, Lin Chen and Joseph Fitzsimons Abstract: The advent of computationally secure fully homomorphic encryption schemes has had a dramatic impact on the field of cryptography. Such encryption schemes allow for information processing to be performed on encrypted data without decryption and in a purely non-interactive way. By necessity, however, classical approaches are limited to security only under certain assumptions about the computational power of the adversary. Here we explore the question of whether a quantum approach might offer stronger security guarantees. We prove both a no-go theorem, showing that fully homomorphic encryption is impossible if the mutual information between ciphertext and plaintext is required to be exactly zero. When this restriction on the mutual information is relaxed, however, non-trivial privacy homomorphisms become possible. We introduce two explicit protocols which admit non-trivial computational models, models which cannot be simulated classically, while still placing strong limits on the information content of cipher texts. Based on arXiv:1406.2456, arXiv:1411.5254 and arXiv:1508.00938 P2-204 Silicon-vacancy: a colourful defect of diamond as solid-state single-spin for quantum information. Camille Stavrakas, Benjamin Pingault, Christian Hepp, Tina Müller, Mustafa Gündogan, Jonas Becker, Carsten Schulte, Carsten Arend, Tillman Godde, Alexander Tartakovskii, Matthew Markham, Christoph Becher, Elke Neu, Stefan Gsell, Matthias Schreck, Hadwig S Abstract: While pure diamond transmits visible light and appears as a clear colourless crystal, the implantation of defects such as impurities or vacancies in the diamond lattice during or after the gemstone's formation can lead to changes in its electronic band structure

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and therefore a change in colour - this is how boron made the famous Hope Diamond so remarkably blue. The local electronic perturbation caused by such defects, called 'colour-centres', creates discrete electronic states within the insulator's bandgap similar to those of an atom, whose spin states can be addressed individually and manipulated with light. We study a silicon-based colour-centre, the negatively charged silicon-vacancy (SiV-). Within the crystal lattice, an implanted silicon atom does not exactly sit in place of the carbon atom that it replaced. Instead, there is a split-vacancy configuration between the unoccupied lattice sites and the nearest neighbour carbon atoms [1]. It differs from the more abundant and extensively-studied nitrogen-vacancy (NV-) in that 80 percent of its emission [2] (where it is 4 percent for NV-) is in a narrow zero-phonon-line (ZPL) at 737 nm at cryogenic temperatures [3]. Our experimental and theoretical work, particularly over the last three years, has unravelled the electronic structure of 28Si SiV centres [1,3]. This contributed to a profound understanding of its internal level structure which made optically accessible the electronic spin of these defects. Due to the split vacancy, the extra electron of the SiV centre sees a double-well potential, giving it two possible orbital configurations with the same energy. Besides, the electron possesses intrinsically another degree of freedom: its spin state which can be up or down. Since there are four possible arrangements (combinations) of orbital and spin degrees of freedom (spin up and spin down for each of the two orbitals), both the ground and excited states are four-fold degenerate. Spin-orbit coupling lifts the orbital degeneracy and therefore the total degeneracy becomes a two-fold (spin only). By exposing single SiVs to a magnetic field where the Zeeman effect lifts the remaining spin degeneracy, we were able to test our model successfully and show that SiVs possess a spin one-half [1,3]. Using resonant laser excitation at cryogenic temperatures, we were able to report spin-tagged resonance fluorescence and reveal a spin-state purity approaching unity in the excited state, highlighting the potential of the centre as an efficient spin-photon quantum interface. Preparing coherent superposition states of the electronic spin that could be used as quantum bits enabled us to achieve coherent population trapping (CPT) and measure a spin coherence time of the ground state [5] over 45 ns. Our efforts are now directed towards the realisation of the all-optical control of the electronic spin and the identification of the main sources of spin decoherence. The combination of ultrafast coherent control of individual spins and the high quality and reproducibility of the optical spectrum across multiple SiV- centers can serve to realise the basic components of a distributed quantum network. [1] Muller, T et al. Optical signatures of silicon-vacancy spins in diamond. Nature communications, 5, 3328, 2014. [2] Aharonovich, I et al. Diamond photonics. Nature Photonics, 5, 397–405, 2011. [3] Feng, T et al. Characteristics and origin of the 1.681 eV luminescence center in chemical-vapor-deposited diamond films. Journal of Applied Physics, 73, 1415, 1993. [4] Hepp, C et al. Electronic Structure of the Silicon Vacancy Color Center in Diamond. Physical Review Letters, 112, 036405, 2014. [5] Pingault, B, Becker, J et al. All-Optical Formation of Coherent Dark States of Silicon-Vacancy Spins in Diamond. Physical Review Letters, 113, 263601, 2014. P2-205 Photon Antibunching and Hong-Ou-Mandel Peak Gustavo Amaral, Felipe Calliari, Thiago Ferreira Da Silva, Guilherme Temporão and Jean Pierre von der Weid Abstract: Photon antibunching was observed in a modified Hong-Ou-Mandel interferometer as a peak in the coincidence count events between detectors. The inversion of the interference pattern is equally observed when the wave packets are frequency displaced. The mathematical description agrees with the experimental results when the correction for weak coherent states in included. The second order autocorrelation function at zero time

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was experimentally determined by means of the Hanburry-Brown and Twiss experiment when a photon at one arm of the interferometer's output heralds the presence of the other. P2-207 Quantum assisted Gaussian process regression

Zhikuan Zhao, Jack Fitzsimons and Joseph Fitzsimons Abstract: Gaussian Process Regression is widely considered as a powerful model for regression problems in the field of supervised machine learning. However its practicality is limited by the slow runtime on a classical computer when applying to problems involving inference from large sets of data. In this work, we present a novel application of an extended version of the quantum algorithm for linear systems [Harrow et al., Phys. Rev. Lett. 103, 150502 (2009)] to speedup the computation of Gaussian Processes. A preprint of this work appears as arXiv:1512.03929. P2-208 Entanglement conditions for integrated-optics multi-port quantum interferometry experiments Junghee Ryu, Marcin Marciniak, Marcin Wiesniak and Marek Zukowski Abstract: Integrated optics allows one to perform interferometric experiments based upon multi-port beam-splitter. To observe entanglement effects one can use multi-mode parametric down-conversion emissions. When the structure of the Hamiltonian governing the emissions has (infinitely) many equivalent Schmidt decompositions into modes (beams), one can have perfect EPR-like correlations of numbers of photons emitted into “conjugate modes” which can be monitored at spatially separated detection stations. We provide series of entanglement conditions for all prime numbers of modes, and show their violations by bright multi-mode squeezed vacuum states. One family of such conditions is given in terms of the usual intensity-related variables. Moreover, we show that an alternative series of conditions expressed in terms averages of observed rates, which is a generalization of the ones given in arXiv:1508.02368, is a much better entanglement indicator. Thus the rates seem to emerge as a powerful concept in quantum optics. P2-209 Fault-tolerant Quantum Computation under non-Markovian noise Jing Hao Chai and Hui Khoon Ng Abstract: In the control of quantum systems, noise is a major hurdle to overcome. For a sequence of operations on an input quantum state, noise causes the output quantum state to deviate from the ideal situation. Encoding the qubit as multi-qubit physical systems, applying error correction and using fault-tolerant design for quantum operations are some of the methods that can be used to protect quantum information from noise. However, these schemes increase the complexity of the system, which increases the error rate of the system. The error rate of such systems under these schemes for a given noise model gives us a gauge of the usefulness of these schemes. However the complexity of the overall schemes makes it difficult to calculate this number. A certain class of such systems and operations is simulable numerically in an efficient manner, via the stabilizer formalism and Gottesman-Knill theorem. In such schemes, it is usually assumed for analysis that errors are non-correlated between physical qubits and different times. Moreover, a noise map is usually derived from a master equation of Lindblad form, or equivalently taken as a completely positive, trace-preserving map. Such a treatment for noise assumes that the environment contains no memory or that the memory time is much shorter that the timescale of intended

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quantum operations. Though such an assumption is usually reasonable, the concept of fault tolerance involves the question of whether such schemes are robust to different types of noise. Prior study have shown a wide disparity between the feasibility of such schemes under non-Markovian noise than compared to Markovian ones. To investigate if this were really the case, we propose to consider a situation where controlled quantum systems possess small but uncontrollable quantum degrees of freedom, which we call the “small bath”. The small bath is capable of holding a limited amount of memory of past interactions with the system. We are therefore interested in the effect of such a small bath has on the error rates of the system, and how this changes when the dimension of the small bath changes. Using the stabilizer formalism, we are able to capture some simple dynamics of the non-Markovian noise with a toy model of a system that has applied operations and error correction cycles. A direct simulation of the dynamics of this kind of system therefore allow for observation of patterns and provide estimations of error rates which would otherwise be too complicated to solve analytically. In order to verify that the simulation functions as intended, we first used it to verify the threshold derived by others for different schemes. In so doing, we were able to locate the assumptions used to derive the threshold, and identify their impact on the threshold. It is ultimately hoped that the numerical results provided by this toy model of non-Markovian noise can aid more rigorous analyses for such noise in quantum systems. P2-210 Quantum Phase Transition and Universal Dynamics in the Rabi Model Myung-Joong Hwang, Ricardo Puebla and Martin B. Plenio Abstract: We show that the Rabi model undergoes a second-order superradiant quantum phase transition [1]. Given that the Rabi model consists only of a single atom and a single-mode cavity field, this finding is surprising, as it is commonly assumed that a quantum phase transition occurs in infinitely extended systems, in terms of a number of system components. We prove the QPT by deriving an exact solution in the limit where the atomic transition frequency in unit of the cavity frequency tends to infinity. The effect of a finite transition frequency is studied by analytically calculating finite-frequency scaling exponents as well as performing a numerically exact diagonalization. Going beyond this equilibrium QPT setting, we prove that the dynamics under slow quenches in the vicinity of the critical point is universal, that is, the dynamics is completely characterized by critical exponents. Our analysis demonstrates that the Kibble-Zurek mechanism can precisely predict the universal scaling of residual energy for a model without spatial degrees of freedom. Moreover, we find that the onset of the universal dynamics can be observed even with a finite transition frequency. References: [1] M.-J. Hwang, R. Puebla, and M. B. Plenio, Physical Review Letters 115, 180404 (2015); selected as Editors' suggestion. P2-212 Prospects for Atomic Spin-Squeezing inside Hollow-Core Photonic Crystal Fiber Zilong Chen and Shau-Yu Lan Abstract: Hollow-core photonic crystal fibers have matured to a point where laser-cooled atomic ensembles have been loaded into these fibers, forming a high optical density medium naturally suited for nonlinear optics applications. Increasingly, researchers are utilizing the same platform for quantum metrology applications, for example as optical lattice clock, or as atom interferometer in our group at NTU, Singapore, with advantages in compactness and potentially better control over systematics over conventional atomic sensors. However, the typically small ensemble size, N, implies the precision of the sensor is limited by the standard quantum limit to the poor absolute precision of 1/sqrt(N) when using un-entangled

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atoms. The standard quantum limit can be overcome by using atomic spin-squeezed states, which are entangled. Spin-squeezing is an extremely promising approach, with ~18-20dB metrological improvement already demonstrated in cavity-based systems and ~3dB in free space setups. In this presentation, I will explore the prospects of generating spin-squeezed states on the clock states of Rb-87 atoms inside a hollow-core photonic crystal fiber setup using quantum non-demolition measurements. P2-215 Coherent manipulation of small ion Coulomb crystals in a Penning Trap Pavel Hrmo, Manoj Joshi, Vincent Jarlaud, Joseph Goodwin, Graham Stutter and Richard Thompson Abstract: Trapped ions in a Penning trap provide a fruitful environment for quantum simulation. We investigated the preparation of small, laser cooled Coulomb crystals for potential for use in such simulations. Our previous work demonstrated the ground state cooling of a single 40Ca+ ion using resolved sideband laser cooling. We extend this technique to cooling two ions both in an axial chain and in the radial plane of the trap. We cool the centre of mass modes for both configurations and the breathing and tilt modes for the axial and planar crystal respectively. To check the coherence time of our qubits we performed Ramsey spectroscopy and applied dynamical decoupling techniques to extend this time by more than a factor of 5. Furthermore, we present our efforts to realise a two qubit gate on the two ion crystal. P2-219 Unifying wave-particle duality with entropic uncertainty Patrick Coles, Jedrzej Kaniewski and Stephanie Wehner Abstract: An interferometer - no matter how clever the design - cannot reveal both the wave and particle behavior of a quantum system. This fundamental idea has been captured by inequalities, so-called wave-particle duality relations (WPDRs), that upper bound the sum of the fringe visibility (wave behavior) and path distinguishability (particle behavior). Another fundamental idea is Heisenberg's uncertainty principle, stating that some pairs of observables cannot be known simultaneously. The distinction between these two concepts has been debated in the literature. Here we provide closure to the debate by showing that WPDRs correspond to a modern formulation of the uncertainty principle, namely, the uncertainty relation for the min- and max-entropies, which is used in quantum cryptography. Furthermore, our unification provides a framework for solving an outstanding problem of how to formulate universally valid WPDRs for interferometers with more than two paths, and we employ this framework to derive some novel WPDRs. P2-222 Generalised phase kick-back: the structure of computational algorithms from physical principles Ciaran Lee and John Selby Abstract: The advent of quantum computing has challenged classical conceptions of which problems are efficiently solvable in our physical world. This motivates the general study of how physical principles bound computational power. In this paper we show that some of the essential machinery of quantum computation – namely reversible controlled transformations and the phase kick-back mechanism – exist in any operational-defined theory with a consistent notion of information. These results provide the tools for an exploration of the physics underpinning the structure of computational algorithms. We investigate the relationship between interference behaviour and computational power, demonstrating that

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non-trivial interference behaviour is a general resource for post-classical computation. In proving the above, we connect higher-order interference to the existence of post-quantum particle types, potentially providing a novel experimental test for higher-order interference. Finally, we conjecture that theories with post-quantum interference – the higher-order interference of Sorkin – can solve problems intractable even on a quantum computer. P2-223 Generation of single photons with highly tunable wave shape from a cold atomic quantum memory Pau Farrera, Georg Heinze, Boris Albrecht, Melvyn Ho, Matías Chávez, Colin Teo, Nicolas Sangouard and Hugues de Riedmatten Abstract: We report on a single photon source with highly tunable photon shape based on cold ensemble of Rubidium atoms. We follow the DLCZ scheme to implement an emissive quantum memory, which can be operated as a photon pair source with controllable delay. We find that the temporal wave shape of the emitted read photon can be precisely controlled by changing the shape of the driving read pulse. We generate photons with temporal durations varying over three orders of magnitude up to 10 μs without a significant change of the read-out efficiency. We prove the non-classicality of the emitted photons by measuring their antibunching, showing near single photon behavior at low excitation probabilities. We also show that the photons are emitted in a pure state by measuring unconditional autocorrelation functions. Finally, to demonstrate the usability of the source for realistic applications, we create ultra-long single photons with a rising exponential or doubly peaked wave shape which are important for several quantum information tasks. P2-225 High Efficiency Room-Temperature Raman Memory using Quenching Sarah Thomas, Patrick Ledingham, Benjamin Brecht, Joseph Munns, Cheng Qiu, Amir Feizpour, Ian Walmsley, Joshua Nunn and Dylan Saunders Abstract: Optical quantum information processing offers a very promising platform for quantum technologies because photons are essentially noise-free at room temperature and have many degrees of freedom in which information can be encoded. However, the generation of deterministic single photons remains an unsolved problem. Quantum memories could be used to synchronise probabilistic single photon sources and significantly reduce the waiting time for many-photons states [1]. For temporal multiplexing it is critical to have both a high memory efficiency η and a large time-bandwidth product B. This product, B=τδ, quantifies the maximum number of multiplexing operations, determined by the memory bandwidth δ, within the storage lifetime of the memory, τ. Warm broadband Raman memories are a strong candidate for temporal-multiplexing as time-bandwidth products of B~1000 have been demonstrated [2]. However, to date broadband Raman memories have been limited in efficiency to η~30% [2]. Here we improve the state-of-the-art for broadband Raman memories and improve the memory efficiency to η=57±5%, without any adverse effects to the time-bandwidth product. The Raman memory protocol uses a Λ-level scheme to adiabatically transfer population between ground states via an off-resonant Raman transition. We implement the Raman protocol using the D2 transition in caesium. The total memory efficiency η is proportional to the square of the optical depth of the Cs vapour which increases exponentially with temperature. However, above 70°C, our ability to prepare the memory in the initial state, via optical pumping, with high fidelity decreases rapidly due to radiation trapping: photons

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emitted by spontaneous decay in the optical pumping process can depolarise other atoms if the vapour is optically thick [3]. To fully polarise the ensemble at higher temperatures we reduce the effect of radiation trapping by quenching: atoms collide with a molecular buffer gas and transfer their energy to the vibrational modes of the molecule. By introducing 10 Torr of N2 as a buffer gas we suppress radiation trapping and can polarise the Cs ensemble up to 90°C (Fig. 1(a)). This allows us to operate the Raman memory at much higher optical depths, significantly increasing the Raman coupling constant. We observe a memory efficiency of 57±5%; almost double previous results (Fig. 1(b)). We expect the addition of quenching to warm alkali quantum memories to play a significant role in next generation light-matter interactions at room-temperature. [1] Nunn, J. et al. "Enhancing multiphoton rates with quantum memories." Phys. Rev. Lett. 110, 133601 (2013). [2] Michelberger, P. S. et al. "Interfacing GHz-bandwidth heralded single photons with a warm vapour Raman memory." New Journal of Physics (2015). [3] Molisch, A. F. & Oehry, B. P. "Radiation Trapping in Atomic Vapours" (Oxford Science Publications, 1998). P2-226 Inertial Navigation using Atom Interferometry Jimmy Stammers, Xiaxi Cheng and Ed Hinds Abstract: In recent years, atom interferometry has been used to measure inertial forces, such as acceleration due to Earth's gravity, to remarkable precision. Developments into robust and compact laser sources has also enabled atomic gravimeters to be operated outside of typical laboratory environments. This raises the prospect of inertial navigation using atom interferometry as an additional practical application. Conventional inertial navigation systems employ extremely precise measurements of acceleration and rotation to determine position over time, but are prone to bias drifts that limit their long-term accuracy. This can be improved using the intrinsic stabilty of atoms to correct for measurement errors of a mechanical accelerometer. In turn, the high bandwidth accelerometer signal eliminates the problem of measurement dead time of the interferometer, associated with trapping and cooling an atomic ensemble. We present work on the design and operation of a hybrid atom interferometer and mechanical accelerometer system to measure a range of linear acceleration. P2-231 A Cavity-Enhanced Room-Temperature Broadband Quantum Memory for Nanosecond Heralded Single Photons Dylan Saunders, J. H. D. Munns, T. F. M. Champion, C. Qiu, S. E. Thomas, B. Brecht, K. T. Kaczmarek, E. Poem, P. M. Ledingham, I. A. Walmsley and J. Nunn Abstract: Broadband quantum memories hold great promise as multiplexing elements in future photonic quantum information protocols. Alkali vapour Raman memories combine high-bandwidth storage, on-demand read-out, and operation at room temperature without collisional fluorescence noise. However, previous implementations have required large control pulse energies and suffered from four-wave mixing noise. Here we present a Raman memory where the storage interaction is enhanced by a low-finesse birefringent cavity tuned into simultaneous resonance with the signal and control fields, dramatically reducing the energy required to drive the memory. By engineering anti-resonance for the anti-Stokes field,

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we also suppress the four-wave mixing noise and report the lowest unconditional noise floor yet achieved in a Raman-type warm vapour memory, $(15\pm2)\times10^{-3}$ photons per pulse, with a total efficiency of $(9.5\pm0.5)$\%. P2-232 Quantum parameter estimation with general dynamics Haidong Yuan and Chi-Hang Fung Abstract: One of the main quests in quantum metrology, and quantum parameter estimation in general, is to find out the highest achievable precision with given resources and design schemes to attain it. In this article we present a general framework for quantum parameter estimation which relates the ultimate precision limit directly to the geometrical properties of underlying dynamics. With this framework we present systematic methods for computing the ultimate precision limit and optimal probe states. We further demonstrate the power of the framework by deriving a sufficient condition on when ancillary systems are not useful for improving the precision limit. P2-233 Modelling Atom-Filled Optical Cavities for Enhanced Light-Matter Interaction Joseph Munns, Sarah E. Thomas, Benjamin Brecht, Patrick M. Ledingham, Ian A. Walmsley, Joshua Nunn and Dylan J. Saunders Abstract: A means for precise experimental characterization of the dielectric susceptibility of an atomic ensemble inside an optical cavity is important for design and operation of quantum light matter interfaces, particularly in the context of quantum information processing. Here we present a numerically optimised theoretical model to predict the spectral response of an atom-filled cavity, including both homogeneous and inhomogeneous broadening at high optical densities. We investigate the regime where the two broadening mechanisms are of similar magnitude, which makes the use of common approximations invalid. Our model agrees with an experimental implementation with warm caesium vapour in a ring cavity. P2-234 The Quantum-Classical Boundary for Precision Interferometric Measurements Patrick M. Birchall, Jeremy L. O'Brien, Jonathan C. F. Matthews and Hugo Cable Abstract: Precise measurements of optical phase underlie many technological and scientific investigative techniques, therefore understanding how to maximize the precision of these measurements is of key interest. We consider the task of measuring an optical phase, which has an associated loss, whilst minimizing the number of photons incident upon the phase. It is often argued that an important quantum advantage can be obtained for this task in the measurement of delicate or photosensitive samples. We study the achievable precision one can obtain whilst utilizing only classical techniques and compare these strategies to fundamental limitations on the attainable precision imposed by quantum mechanics found in previous studies. We devise an optical setup which is able to measure a phase with a root-mean-square error of only ~4% larger than an optimal non-classical strategy. We also present provide potentially practical strategies using either classical or non-classical techniques which provide a precision close to the optimal non-classical strategy. These results are presented in arXiv:1602.07561.

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P2-235 Entanglement is an inevitable feature of a non-classical universe Jonathan Richens, John Selby and Sabri Al-Safi Abstract: One of the most striking features of quantum theory is the existence of entangled states, responsible for Einstein's so called ``spooky action at a distance''. These states emerge as part of the mathematical formalism of quantum theory, but to date there exists no set of simple physical axioms that predict their existence. For example, existing reconstructions of quantum theory in the framework of generalised probabilistic theories can be see as derivations of entanglement from physical or informational principles, but can hardly be viewed as a minimal set of physical properties from which the existence of entangled states can be derived. In the presented work I will show that all physical theories that can be represented as generalised probabilistic theories must have dynamics that generate entangled states, making only the very minimal assumption of reversible transitivity. Reversible transitivity is a feature shared by both quantum and classical theory. I states that the state space of a closed system is preserved and can be fully explored by the dynamics permitted by the theory. Reversibility is an essential property of quantum theory as it ensures that information cannot be destroyed or cloned, and is thus believed to be an essential feature of any likely / reasonable theory of nature. For example, without reversibility the second law of thermodynamics could be routinely and systematically broken. Transitivity is the requirement that all states in the state space can be reached under the allowed dynamics from all others. With reversibility, this can be absorbed into the definition of a state space - i.e. the set of all states that can be generated. We consider all reversibly transitive interacting theories and find that all, with the exception of classical probability theory, must have dynamics that generate entangled states. By relaxing the postulate of transitivity we find that reversibility and information gain implies disturbance are sufficient to imply the existence of entangled states. These postulates derive the phenomenon of entanglement from purely physical principles, and establish entanglement as an inevitable feature of any natural non-classical probabilistic theory of nature. The ramifications of these results are surprising. For example, one could in principle (without any knowledge of quantum theory) observe any non-classical phenomena (such as interference) and imply that existence of entangled states. P2-237 The Quantum Simulation of Quantum Chemistry Andrew Tranter, Peter Coveney, Florian Mintert and Peter Love Abstract: Fundamental to quantum chemistry is the determination of ground state energies of molecular systems. It is known that a quantum device would allow for an exponential speedup of the exact calculation of such energies, allowing for more accurate computational analysis of chemical reactions. In this poster, we aim to give a broad overview as to some of the techniques involved in implementing electronic structure calculations on a quantum device. In particular we consider the Bravyi-Kitaev mapping - an alternative to the traditional Jordan-Wigner mapping of electronic operators to qubit operators. We also consider the impact of ordering schemes in a Trotterized Hamiltonian. Finally, we discuss the consequences of these techniques with regards to quantum resource requirements, and the implications of this for near-future experimental work demonstrating these techniques.

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P2-240 Optimal Wavelength Assignment in Hybrid Quantum-Classical DWDM Networks Sima Bahrani, Mohsen Razavi and Jawad A. Salehi Abstract: An efficient algorithm for optimal allocation of wavelengths in a hybrid dense-wavelength-division-multiplexing (DWDM) system, carrying both quantum and classical data, is proposed. The transmission of quantum bits alongside intense classical signals on the same fiber faces major challenges arising from the background noise generated by classical channels. Raman scattering, in particular, is shown to have detrimental effects on the performance of quantum key distribution systems. Here, by using an optimal wavelength allocation technique, we minimize the Raman induced background noise on quantum channels, hence maximize the achievable secret key generation rate for quantum channels. We show that the conventional solution that involves splitting the spectrum into only two bands, one for quantum and one for classical channels, is not necessarily optimum, and, in fact, could generate a key rate considerably lower then that of the optimal assignment. We show that, in the latter optimal case, we might need several quantum and classical bands interspersed among each other. P2-241 General method for constructing local-hidden-state (and -variable) models for multiqubit entangled states Rafael Rabelo, Daniel Cavalcanti, Leonardo Guerini and Paul Skrzypczyk Abstract: We propose a numerical method for constructing local-hidden-state (LHS) models – and consequently local-hidden-variable (LHV) models – for multiqubit states based on semidefinite programming. This method can be applied to arbitrary states and general (POVM) measurements and can also be adapted to generate random states with LHS models. As applications we present new families of states with LHS models, including Bell-diagonal states, noisy GHZ and noisy W states, and generate a list of over 400000 new entangled two-qubit states with LHS model for projective measurements and 1400 for POVM measurements. P2-242 Towards Long Range Spin-Spin Interactions via Mechanical Resonators Arthur Safira, Jan Gieseler, Aaron Kabcenell, Shimon Kolkowitz, Alexander Zibrov, Jack Harris and Mikhail Lukin Abstract: Nitrogen vacancy centers (NVs) are promising candidates for quantum computation, with room temperature optical spin read-out and initialization, microwave manipulability, and weak coupling to the environment resulting in long spin coherence times. The major outstanding challenge involves engineering coherent interactions between the spin states of spatially separated NV centers. To address this challenge, we are working towards the experimental realization of mechanical spin transducers. We have successfully fabricated magnetized high quality factor (Q>105), doubly-clamped silicon nitride mechanical resonators integrated close to a diamond surface, and report on experimental progress towards achieving the coherent coupling of the motion of these resonators with the electronic spin states of individual NV centers under cryogenic conditions. Such a system is expected to provide a scalable platform for mediating effective interactions between isolated spin qubits.

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P2-245 Cold atom memory as a platform for quantum information Geoff Campbell, Young-Wook Cho, Jian Su, Jesse Everett, Nicholas Robins, Ping Koy Lam and Ben Buchler Abstract: Numerous physical implementations of optical quantum memories exist, or have been proposed, each offering its own merits and drawbacks. Here, we present the technical details and characterisation of an implementation that is based on a collection of cold rubidium 87 atoms. The atoms are trapped and cooled in an elongated magneto optical trap (MOT) that provides an optical depth of approximately 600 on the F = 1 to F'=2 transition. The coherence time of the hyperfine ground state transition is 1 ms, limited by the atomic temperature of 100 micro-kelvin. The atomic population is optically pumped into a single Zeeman sub-level to increase the optical depth and eliminate unwanted transitions. We characterise the ensemble using imaging techniques and by analysing the performance as a quantum memory. The racetrack-shaped magnetic fields coils provide open optical access for absorption imaging of the cloud. The technique also allows us to directly monitor the propagation of slow or stored light in the atoms. This provides direct feedback to optimally align a probe field to the spatial profile of the atoms. We use both the electromagnetically induced transparency (EIT) and Gradient Echo Memory (GEM) techniques to examine the quantum performance of the MOT as a memory. EIT is used to demonstrate that the dynamics of the light-atom interaction and unwanted four-wave-mixing (4WM) processes can be effectively modelled and controlled. Using optical pumping, the 4WM process can be eliminated. We use GEM to demonstrate that the memory adds little excess noise and reproduces input states with a high fidelity (0.997 for a single-photon level coherent state). The memory is shown to out-perform an ideal fibre loop and operates in the no-cloning regime. We illustrate the flexibility of the cold-atom platform by presenting extensions to the basic memory. We demonstrate temporally multi-mode storage for 20 pulses, all with an efficiency of over 5%, and a frequency-domain dual-rail memory with an efficiency of 35%. We also discuss using the cold-atom memory to implement arbitrary linear operations on optical modes and how it may be used as an effective high-finesse optical resonator. P2-246 Differential phase-time shifting protocol for QKD (DPTS) Mario A. Usuga, Davide Bacco, Jesper Bjerge Christensen, Karsten Rottwitt, Leif K. Oxenløwe and Yunhong Ding Abstract: We explore the implementation of a novel protocol for fiber-based high-dimensional quantum key distribution (QKD) which improves over the traditional DPS-QKD and COW protocols. P2-249 Where does measurement uncertainty come from? Filip Rozpedek, Jedrzej Kaniewski, Patrick J. Coles and Stephanie Wehner Abstract: Quantum correlations and measurement uncertainty are inherently linked. In this context we are interested in the question whether measurement uncertainty is an inherent property of the measured quantum system or whether it is a consequence of the lack of knowledge about the measurement process. Specifically, let us consider the perspective of entropic uncertainty relations, so that we are interested in the ability of some observer to predict the measurement outcome. Then, assuming that the guessing party has access to the quantum correlations between the measurement apparatus and the system measured, is it possible for him to better predict the measurement outcome than in the classical scenario where those correlations are inaccessible to the observer? To answer these questions we use the model of the simple uncertainty games in which one performs one out of two

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incompatible measurements chosen uniformly at random and the uncertainty of the outcome conditional on the basis choice is evaluated. In such games there will always be some uncertainty of the measurement outcome independently of the input state. Since the basis choice is probabilistic, it can be represented by a fully mixed register of dimension two. Here we consider a more complex scenario, where the "basis" register is in a coherent superposition state. We find that introducing coherence facilitates guessing and hence we show that it leads to a qualitatively new class of problems. P2-250 Fisher Information and Quantum Communication with random unitary noise

Wiesław Laskowski, Marcin Markiewicz and Anna de Rosier Abstract: The effect of the collective random unitary noise on an input state, described by the fidelity of the final state to the initial one, is difficult to assess, since it demands optimization over O(d^2) parameters of a unitary transformation. We utilize the relation between Bures fidelity and Quantum Fisher Information (QFI) in order to provide analytically tractable bound on fidelity of a multipartite quantum state undergoing such collective unitary noise. This new property of QFI enabling one to certify robustness against noise for different classes of states. In order to get deeper insight into the problem of collective unitary noise we checked statistical properties of fidelity by means of Monte Carlo simulations. P2-252 Numerical simulation of topological codes using tensor networks Andrew Darmawan and David Poulin Abstract: The surface code is a promising candidate for quantum error correction in many architectures, requiring only nearest-neighbour interactions on a two-dimensional square lattice. Our understanding of the performance of the surface code is mostly based on numerical simulations which have found a high threshold relative to other error correction schemes. These simulations usually assume Pauli noise, which has the advantage that it allows efficient simulation within the stabilizer formalism. However most realistic noise processes (e.g. amplitude damping and systematic over rotation), are non-Pauli. In this work we present an improved simulation scheme for the surface code under local non-Pauli noise. Our schemes are based on the tensor network description of the surface code as a projected entangled pair state (PEPS). Syndrome sampling, computation of the process matrix and logical error rates can all be performed by contracting an appropriate tensor network. P2-253 Distributing entangled states using silicon photonic chips Jianwei Wang, Damien Bonneau, Matteo Villa, Joshua Silverstone, Raffaele Santagati, Shigehito Miki, Taro Yamashita, Mikio Fujiwara, Masahide Sasaki, Hirotaka Terai, Michael Tanner, Chandra Natarajan, Robert Hadfield, Jeremy O'Brien and Mark Thompson Abstract: We demonstrate high-fidelity distribution of entanglement across two integrated silicon photonic chips. Path-entangled Bell states are generated and manipulated on chip, and coherently distributed between the two separate chips using a path-polarization interconversion on each chip. The two-qubit states are analyzed on chips using reconfigurable quantum circuits, and we observe a violation of the Bell-type inequality of 2.638±0.039, confirming the distribution of entanglement

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P2-256 Floodlight Quantum Key Distribution Zheshen Zhang, Quntao Zhuang, Justin Dove, Franco Wong and Jeffrey Shapiro Abstract: We introduce floodlight quantum key distribution (FL-QKD), which exploits multi-mode encoding to greatly boost secret-key efficiency (SKE) and secret-key rate (SKR). With a coincidence-based channel-monitoring unit, FL-QKD is secure against collective attacks. In our proof-of-principle experiment, we achieve 0.55 bits/channel-use SKE and 55 Mb/s SKR over a channel with 10-dB propagation loss. The demonstrated SKE and SKR represent more than 100-fold and 50-fold improvements, respectively, over state-of-the-art QKD systems for the same channel attenuation. P2-258 Symmetric Extendability of Quantum States and the Extreme Limits of Quantum Key Distribution Sumeet Khatri and Norbert Lutkenhaus Abstract: We investigate QKD protocols with two-way communication that are based on the quantum phase of the well-known BB84 and six-state protocols. The quantum phase consists of the source sending quantum signals to the receiver, who measures them, leaving only classical data on both sides. Our goal is to find the highest value of the quantum bit error rate Q for which two-way classical post-processing protocols on the data can create secret keys. Using the BB84 quantum phase, such protocols currently exist for Q ≤ 1

5 . On

the other hand, for Q ≥ 14 no such protocol can exist as the observed data is compatible with

an intercept-resend channel. This leaves the interesting question of whether successful protocols exist in the gap 1

5 ≤ Q ≤ 1

4 . For the six-state protocol, the corresponding gap is

known to be 5− √510

≤ Q ≤ 13.

The current lower bounds have previously been shown to come from the symmetric extendability of the underlying quantum state shared between Alice and Bob after a two-way protocol called advantage distillation. Our work looks more generally at two-way post-processing protocols within the gap and asks the question of symmetric extendability of the states after them, for if they are symmetrically extendable then no secret key is possible. We have analyticallyconstructed a symmetric extension throughout the gap for a particular class of protocols using a two-step procedure. Numerical analysis shows that for other arbitrary protocols the states are also symmetrically extendable throughout the gap. Moreover, for a very large percentage of protocols tested, our two-step construction works. We thus have very strong evidence to believe that there does not exist a two-way classical post-processing protocol to create a secret key beyond the current bounds, so that there is a point beyond which classical correlations of quantum origin are no longer useful in creating a secret key. P2-259 Large-Scale Simulation of the Quantum Internet Rodney Van Meter, Shigeya Suzuki, Shota Nagayama, Takahiko Satoh, Takaaki Matsuo, Amin Taherkhani, Simon Devitt and Joe Touch Abstract: The Quantum Internet (QI) will be a worldwide network of quantum repeater networks, enabling quantum information services including entanglement-based cryptographic functions such as quantum key distribution, secure distributed quantum computation, and high-precision sensors. We are developing a large-scale simulator to study

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the expected behavior and quantitatively evaluate solutions to the numerous design problems. Our engineering methodology is to apply solutions developed in the Internet community where possible. Our ultimate goal is simulation of ten thousand quantum repeater nodes, organized into one hundred networks each comprising about hundred nodes. At this scale, we expect to be able to study the macroscopic behavior of a Quantum Internet and potentially see and examine emergent behavior that otherwise would not occur until networks are deployed. P2-261 Network-ready unconditional polarization qubit quantum memory at room temperature Eden Figueroa, Mehdi Namazi, Connor Kupchak, Bertus Jordaan and Reihaneh Shahrokhshahi Abstract: Here we study how the optical response of cold atomic environments is transformed by the motion of atoms at room temperature and consequently characterize the optimal performance of room temperature quantum light-matter interfaces. Our findings enable us to attain complete quantum memory operation for polarization qubits in a warm 87Rb atomic vapor with an average fidelity of 86.6%, thereby defeating any classical strategy exploiting the non-unitary character of the memory efficiency. Our system significantly decreases the technological overhead required to achieve quantum memory operation and will serve as a building block for scalable and technologically simpler many-memory quantum machines P2-262 Compact, integrated quantum key distribution sender module for hand-held key exchange Gwen Melen, Tobias Vogl, Markus Rau, Giacomo Corrielli, Andrea Crespi, Roberto Osellame and Harald Weinfurter Abstract: We report on the implementation of an integrated optics module (35x20x8mm3) enabling to implement secure free-space key exchange in all optical communication terminals. We demonstrate its maturity in the first key exchange with a hand-held Alice system. P2-263 Sub-Megahertz Single Photon Source Markus Rambach, Aleksandrina Nikolova, Till J. Weinhold and Andrew G. White Abstract: Hybrid quantum technologies seek to combine the advantages of two individual quantum architectures by transferring the information between the two systems. We want to benefit from the high mobility and ease of transmission of photons for quantum communication and exploit the excellent readout and storage capabilities of atomic qubits as a quantum memory, which is essential to build up quantum repeater networks for quantum data processing. Efficient interaction of photons with atoms requires a match of the photons’ spectral properties to those of the resonances of the atomic species. The atomic transition usually has a much narrower bandwidth than single photons generated by spontaneous parametric down-conversion (SPDC), the current gold standard of producing high-purity heralded single photons at flexible wavelengths. To develop hybrid quantum technologies therefore requires significantly reducing the single photon emission spectra to fulfill these requirements. The way we try to achieve this is by using an optical cavity to enhance the probability of creating the photons in the spectral and spatial resonator mode.

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Previous cavity-based SPDC sources have achieved bandwidths comparable to atomic linewidths, but divide their operation time into stabilisation and photon production phases, resulting in typical duty cycles < 50%. The so far narrowest photons from SPDC [1] have bandwidths still well above a MHz and only one source has demonstrated 100% duty cycle [2]. We report 100 % duty cycle generation of sub-MHz single photon pairs at the Rubidium D1 line using cavity-enhanced spontaneous parametric downconversion [3]. The double exponential decay of the temporal intensity cross-correlation function exhibits a bandwidth of 66616 kHz for the single photons, an order of magnitude below the natural linewidth of the target transition. This is, to our knowledge, the narrowest bandwidth of single photons from SPDC to date. A new method of placing half-wave plate inside the cavity helps to achieve triple resonance between pump, signal and idler photon, reducing the bandwidth and simplifying the locking scheme. Additionally, stabilisation of the cavity to the pump frequency enables the 100 % duty cycle. The narrow bandwidth in combination with the tunability makes our system the perfect source for the future integration in gradient echo memories, one of the most promising candidates for quantum memories to date, or hollow-core glass fibers filled with rubidium gas to allow the construction of novel quantum logic gates. We believe our new method of generating extremely narrow-band photons has the potential to become a standard technique in the field of hybrid quantum technologies and will therefore be of great interest to the field. [1] J. Fekete, D. Rieländer, M. Cristiani, and H. de Riedmatten, Phys. Rev. Lett. 110, 220502 (2013). [2] M. Scholz, L. Koch, and O. Benson, Phys. Rev. Lett. 102, 063603 (2009). [3] M. Rambach, A. Nikolova, T. J. Weinhold, and A. G. White, arxiv: 1601.06173 (2016). P2-265 Device-independent demonstration that a qubit is more than a quantum coin Esteban S. Gómez, Santiago Gómez, Pablo González, Gustavo Cañas, Johanna F. Barra, Aldo Delgado, Guilherme B. Xavier, Adán Cabello, Matthias Kleinmann, Tamás Vértesi and Gustavo Lima Abstract: Qubits are the simplest quantum systems and as such they have a pronounced binary structure. Therefore, the qubit is sometimes compared to a »quantum coin« having infinitely many sets of two sides which can only be tossed when specifying the desired set. However, this picture fails to capture the richness of the quantum world and we here present an experiment on pairs of polarization-entangled photonic qubits which cannot be explained by two-outcome measurements. We combine this with device-independent evidence that the system is best described by two qubits thus showing that quantum measurements on a qubit are fundamentally non-binary and that the binary picture of the qubit thus cannot be uphold. Since such measurements cannot be sharp, in addition this constitutes the first device-independent certification of a genuine generalized quantum measurement. P2-266 Optimal Efficiency of Heat Engines with Finite-Size Heat Baths Hiroyasu Tajima and Masahito Hayashi Abstract: The optimal efficiency of quantum (or classical) heat engines whose heat baths are $n$-particle systems is given by the information geometry and the strong large deviation. We give the optimal work extraction process as a concrete energy-preserving unitary time evolution among the heat baths and the work storage.

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We show that our optimal work extraction turns the disordered energy of the heat baths to the ordered energy of the work storage, by evaluating the ratio of the entropy difference to the energy difference in the heat baths and the work storage, respectively. By comparing the statistical machanical optimal efficiency with the macroscopic thermodynamical bound, we evaluate the accuracy of the macroscopic thermodynamics with finite-size heat baths from the statistical mechanical viewpoint. We also evaluate the quantum coherence effect on the optimal efficiency of the cycle processes without restricting their cycle time, by comparing the classical and quantum optimal efficiencies. P2-267 Self-guaranteed measurement-based quantum computation Masahito Hayashi and Michal Hajdusek Abstract: We introduce a new verification protocol for measurement-only blind quantum computation where the client can only perform single-qubit measurements and the server has sufficient ability to prepare a multi-qubit entangled states. Previous such protocols were limited by strong assumptions about the client's quantum devices. We remove these assumptions by performing self-testing procedure to certify the initial entangled state prepared by the server as well as the operation of the client's quantum devices. In the case of an honest server and client's devices, the protocol produces the correct outcome of the quantum computation. Given a cheating server or malicious quantum devices, our protocol bounds the probability of the client accepting an incorrect outcome while introducing only modest overhead in terms of the number of copies of the initial state needed that scales as $O(n^4\log n)$, where $n$ is the size of the initial universal resource. P2-268 Routing on a Quantum Internet Takahiko Satoh, Shigeya Suzuki, Shota Nagayama, Takaaki Matsuo and Rodney Van Meter Abstract: A routing algorithm is required in order to communicate across a multi-hop network. As with the Internet, in our design a Quantum Internet has a two-tier routing system: internal routing within a homogeneous network known as a Quantum AS (QAS), and external routingbetween heterogeneous networks, in an internetwork of QASes. As the number of nodes grows, the traffic and computational cost of a routing protocol grow quickly. Thus, to manage network heterogeneity, achieve scalability, and allow operational autonomy, a two-tier system is needed. We are evaluating two options: a fully recursive structure and quantum adapted BGP. To verify this scheme, we are progressing with the simulation of the Quantum Internet that contains ten thousand quantum repeaters. P2-269 Architecture of software simulation of a Quantum Internet Shigeya Suzuki, Rodney Van Meter, Shota Nagayama, Takahiko Satoh and Takaaki Matsuo Abstract: We have started development of a quantum repeater network simulator -- QUISP. The goal of a quantum repeater network is to create a pair of entangled qubits between two nodes specified by application initiated by a user somewhere on the network. To build such a quantum repeater network system, we want to estimate the cost to build it. In this abstract, we discuss the key assumptions, the key design decisions of the simulator.

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P2-270 Quantum Process Tomography of an Optically-Controlled Kerr Non-linearity Bertus Jordaan, Connor Kupchak, Sam Rind and Eden Figueroa Abstract: Any optical quantum information processing machine would be comprised of fully-characterized constituent devices for both single state manipulations and tasks involving the interaction between multiple quantum optical states. Ideally for the latter, would be an apparatus capable of deterministic optical phase shifts that operate on input quantum states with the action mediated solely by auxiliary signal fields. Here we present the complete experimental characterization of a system designed for optically controlled phase shifts acting on single-photon level probe coherent states. Our setup is based on a warm vapor of rubidium atoms under the conditions of electromagnetically induced transparency with its dispersion properties modified through the use of an optically triggered N-type Kerr non-linearity. We fully characterize the performance of our device by sending in a set of input probe states and measuring the corresponding output via time-domain homodyne tomography and subsequently performing the technique of coherent state quantum process tomography. This method provides us with the precise knowledge of how our optical phase shift will modify any arbitrary input quantum state engineered in the mode of the reconstruction. P2-271 Entanglement assisted classical communication simulates “classical communication” without causal order Seiseki Akibue, Masaki Owari, Go Kato and Mio Murao Abstract: Phenomena induced by the existence of entanglement, such as nonlocal correlations, exhibit characteristic properties of quantum mechanics distinguishing from classical theories. When entanglement is accompanied by classical communication, it enhances the power of quantum operations jointly performed by two spatially separated parties. Such a power has been analyzed by the gap between the performances of joint quantum operations implementable by local operations at each party connected by classical communication with and without the assistance of entanglement. In this work, we present a new formulation for joint quantum operations connected by classical communication beyond special relativistic causal order but without entanglement and still within quantum mechanics. Using the formulation, we show that entanglement assisting classical communication necessary for implementing a class of joint quantum operations called separable maps can be interpreted to simulate "classical communication" not respecting causal order. Our results reveal a new counter-intuitive aspect of entanglement related to spacetime. P2-273 Quantum information applications of highly ordered stoichiometric rare earth crystals Rose Ahlefeldt, Michael Hush and Matthew Sellars Abstract: We propose the use of stoichiometric rare earth crystals for quantum information applications. In addition to the long coherence times characteristic of rare earth ions, these materials have high spatial and spectral densities of ions, and a highly ordered rare earth lattice. These properties allow improvements in quantum memory performance, and new applications that have not previously been considered for rare earth lattice. In particular, when the optical inhomogeneous broadening is smaller than both the hyperfine structure and the ion-ion interaction strength, quantum many body effects will be visible, including excitation blockade, which has never before been seen in a the solid state. We show that this regime is reachable in current materials by using isotopic purification to reduce the crystalline disorder, and demonstrate this method for EuCl3.6H2O, achieving a linewidth of

114

25 MHz, well below both the hyperfine structure and dominant interaction strength. We discuss the use of this material for quantum memory implementations and many body studies. P2-274 One-way quantum computing with arbitrarily large time-frequency continuous-variable cluster states from a single optical parametric oscillator Rafael Alexander, Pei Wang, Niranjan Sridhar, Moran Chen, Olivier Pfister and Nicolas Menicucci Abstract: One-way quantum computing is experimentally appealing because it requires only local measurements on an entangled resource called a cluster state. Record-size, but non-universal, continuous-variable cluster states were recently demonstrated separately in the time and frequency domains. We propose to combine these approaches into a scalable architecture in which a single optical parametric oscillator and simple interferometer entangle up to (3 x 10^3 frequencies) x (unlimited number of temporal modes) into a computationally universal continuous-variable cluster state. P2-276 Randomized benchmarking with cluster states Rafael Alexander, Peter Turner and Stephen Bartlett Abstract: In measurement-based quantum computation, once a universal resource state can be generated then in principle computation can proceed via single-site measurements only. However, unless the errors in elementary gate operations are sufficiently low, the computation will not be fault-tolerant. Here we generalize the randomized benchmarking protocol for a single-qubit to a linear cluster state computation, which provides partial, yet efficient characterization of the noise associated with the target gate set. We consider two different approaches: the first makes uses the single-qubit Clifford group (the standard 2-design for randomized benchmarking). The second approach uses recently introduced measurement-based 2-designs, which relies on the intrinsic randomness of measurement-based quantum computation in order to generate random elements. P2-277 Simple approximation of minimum error probability for pure-state signals Tsuyoshi Usuda and Shungo Asano Abstract: To compute the minimum error probability is indispensable for estimating performance of a quantum communication system and security of a quantum cryptographic protocol. However, even if the optimum measurement and the analytical expression of the minimum error probability are known, computation is hard when the number of quantum signals is extremely large. In the previous study, we proposed a simple and easily computable approximation of the minimum error probability. In this presentation, we demonstrate the approximation and show extended versions. The extended versions of approximation is shown to be more accurate than the original version. We also give numerical results of the approximation for various signals, e.g. binary signals coded by linear codes.

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P2-280 Determining the Quantum Fisher Information from Linear Response Theory Tomohiro Shitara and Masahito Ueda Abstract: The quantum Fisher information is characterized as a metric on the space of quantum states that monotonically decreases under quantum operations, and gives an upper bound on the accuracy of state estimation. Due to the noncommutative nature of quantum theory, there exist infinitely many types of the quantum Fisher information. The operational meanings of each quantum Fisher information beyond the monotonicity have been investigated individually, and even how it is related to observable quantities has not been revealed yet. We propose a method of determining a general quantum Fisher information using the linear response theory in statistical mechanics. We generalize the fluctuation-dissipation theorem, which connects the linear response function with the generalized covariance in the frequency domain. Based on this theorem, we can determine the generalized covariance from the admittance, which is an experimentally measurable quantity. Since the generalized covariance is an equivalent description of the quantum Fisher information, we can also experimentally determine the quantum Fisher information by measuring the admittance. P2-282 Cooling of a one-dimensional Bose gas Bernhard Rauer, Pjotrs Grisins and Jörg Schmiedmayer Abstract: We experimentally study the dynamics of a degenerate one-dimensional Bose gas that is subject to a continuous outcoupling of atoms. Although standard evaporative cooling is rendered ineffective by the absence of thermalizing collisions in this system, we observe substantial cooling. This cooling proceeds through homogeneous particle dissipation and many-body dephasing, enabling the preparation of otherwise unexpectedly low temperatures. Our observations establish a scaling relation between temperature and particle number, and provide insights into equilibration in the quantum world. P2-283 Concepts of non-Markovianity: a quantum hierarchy Li Li, Michael Hall and Howard Wiseman Abstract: The evolution of a closed quantum system is completely determined by the Schrodinger equation. In contrast, the dynamics of an open quantum system are influenced by its environment. As no physical system is truly isolated, this is a situation which applies very widely, and is an important consideration as diverse as atomic physics, optics and quantum information. There has been significant recent interest in characterizing non-Markovian processes for open quantum systems. These have primarily centred on two new, closely-related formal approaches: distinguishability and divisibility. The first approach defines non-Markovianity as an increase in the distinguishability of system states, relative to some measure such as trace distance or relative entropy. The second approach is again solely formulated in terms of the system dynamical map, and requires this map to be “divisible” into completely positive maps connecting the system states at different times. However, more broadly, a general consensus as to the `correct' approach to quantum Markovianity is still very much missing, and it remains a controversial issue. The main aim of our work is to significantly clarify and bring order to the debate, by reviewing a large number of physical concepts that either have been, or could reasonably be, used to define quantum Markovianity, and proving a number of hierarchical relations between them.

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P2-284 Topological pumping of photons in nonlinear coupled resonator arrays Jirawat Tangpatinanon, Victor Bastidas, Dimitris Angelakis Abstract: Topological pumping allows the robust transport of quantum particles in a 1D periodic lattices. The pumping is implemented by adiabatic and cyclic deformation of the Hamiltonian. In contrast to conventional 2D topological materials, the 1D material can be thought of as having (1+1) dimensions, where time acts as an extra dimension with periodic boundary conditions. Hence, the topology of the effective 2D system can be associated with the Chern number, resulting in transport properties which are robust against small perturbations. In this work, we propose a realization of such pump using photons in nonlinear coupled resonator arrays, where the frequency of the resonator is periodically modulated in space and time. In contrast to the linear regime, inherent nonlinearity in our model enables the robust transport of Fock state with few photons per site. We show that signatures of such topological pumping can be observed in a lossy array, as small as nine sites. This brings such signatures into the realm of observability in existing circuit QED technologies.

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Program at a Glance

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Abstracts - Centre for Quantum Technologiesqcmc.quantumlah.org/Abstracts_160701.pdf · Spectrally resolved white-light quantum interferometry for high-accuracy chromatic dispersion