IWQD2017 Poster Sessionposter

number Name Institution Title

P-1 Hiraku Toida NTT Basic Research Laboratories Electron paramagnetic resonance spectroscopy of NV-centers in diamond using a flux qubit

P-2 Changsuk Noh Korea Institute for Advanced Study Squeezing in ultrastrong coupling regime

P-3 Yusuke Hama RIKEN Center for Emergent Matter Science (CEMS) Relaxation to Negative Temperatures in Double Domain Systems

P-4 Wei QiuNational Institute of Information and CommunicationsTechnology

Ultra high-Q Superconducting NbN Coplanar Waveguide Resonator

P-5 Yuya Yonezu Waseda University Efficient Coupling System between optical Nanofiber and Diamond Nanowire

P-6 Rangga Budoyo NTT Basic Research Laboratories Electron Paramagnetic Resonance Spectroscopy of Er:YSO using Josephson Bifurcation Amplifier

P-7 Ayato Okada RCAST, The University of Tokyo Cavity optomechanics with surface acoustic waves

P-8 Masataka IinumaGraduate school of Advanced Sciences of Matter, HiroshimaUniveristy

Demonstration of Leggett-Garg inequality violation with finite resolution and back-action

P-9 Taewan Noh Korea Research Institute of Standards and Science (KRISS) Investigation of microwave-activated c-Phase gate in tunable 3D transmon two qubit system

P-10 Neill Lambert RIKEN Bistable Photon Emission from a Solid-State Single-Atom Laser

P-11 Mauro Cirio RIKEN Ground State Electroluminescence

P-12 Roberto Stassi RIKEN Quantum Memory in Deepstrong Coupling Regime

P-13 Vincenzo Macrì RIKEN Quantum Nonlinear Optics without Real Photons

P-14 Alessandro Ridolfo RIKEN Photon Bunching from Emission of Individual Atoms in the Ultrastrong Coupling Regime

P-15 Philipp Schneeweiss TU Wien–Atominstitut A Cold-Atom based Quantum Simulator for the full Rabi Model and its Generalizations

P-16 Emi Yukawa RIKEN Fast Generation of Macroscopic Superposition States by Coherent Driving

P-17 Shane Dooley NII Quantum metrology including state preparation and readout times

P-18 Michael Hanks NIIHigh-Fidelity Measurement of the Electronic Spin of the Nitrogen–Vacancy Center Using State-Dependent Reflection

P-19 Shojun Nakayama NII Quantum teleinteraction protocol beyond space and time

P-20 Nicolò Lo Piparo NII Toward feasible long-distance quantum communications systems

♯Odd-number posters(P-1,3,5,7,9,11,13,15,17,19) are assigned for presentation on 1st day, starting at 16:00, Monday.♯Even-number posters(P-2,4,6,8,10,12,14,16,18,20) are assigned for presentation on 2nd day, starting at 18:00, Tuesday.

Electron paramagnetic resonance spectroscopyof NV- centers in diamond using a flux qubit

H. Toida1, Y. Matsuzaki1, K. Kakuyanagi1, X. Zhu1, *,W. J. Munro1, K. Nemoto2, H. Yamaguchi1, and S. Saito1

1 NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa, 243-0198, Japan2 National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430, Japan

* Current address: The Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100190, ChinaElectron paramagnetic resonance (EPR) spectroscopy using a superconducting flux qubit is demonstrated.The electron spin ensemble is directly attached to the flux qubit to ensure large magnetic coupling betweenthem [Fig. 1 (a)]. In Fig. 1 (b), we show the results of the spectroscopy of NV- centers in diamond. Two peakswith tiny splitting are visible due to the spin resonance. From the fitting constants of these peaks, we estimatethe g-factor and the zero field splitting to be 2.05 and 2.883 GHz, respectively, which are consistent with theliterature [1] considering the calibration error of the magnet. We also estimate the sensitivity and the sensingvolume to be 500 spins/√Hz and 50 fL (5 x 10-17 m3), respectively. The sensitivity is improved for more thantwo orders of magnitude compared to the method using dc-SQUID magnetometory [2].

References[1] J. H. N. Loubser, J. A. van Wyk, Rep. Prog. Phys. 41, 1201 (1978).[2] H. Toida, et al., Appl. Phys. Lett. 108, 052601 (2016).

AcknowledgementsThis work was supported by Commissioned Research of NICT and inpart by MEXT Grant-in-Aid for Scientific Research on Innovative Areas“Science of hybrid quantum systems" (Grant No. 15H05869 and15H05870).

Fig. 1 EPR spectroscopy using a flux qubit. (a) Experimentalsetup. The spin ensemble and the flux qubit is excited throughthe same microwave line. (b) Results of the EPR spectroscopy ofNV- centers in diamond under 5.8 mT of magnetic filed along[100] direction of the crystal.

(a) (b)(a)

Squeezing in ultrastrong coupling regimeChangsuk Noh1 and Hyunchul Nha2,1

1Korea Institute for Advanced Study (KIAS), Seoul 02455, Korea2 Department of Physics, Texas A&M University at Qatar, Education City, 23874, Doha, Qatar

We present our ongoing work on quantum statistics of the photons coming out of a driven, dissipative cavity QED system in which a two-level system interacts ultra-strongly with the cavity mode. We describe such a system using a quantum master equation, with the Hamiltonian dynamics governed by the Rabi model [1,2]. Specifically, we investigate in depth the squeezing properties that can be revealed by quadrature measurements using homodyne detection [3].

References [1] A. Ridolfo, M. Leib, S. Savasta, and M.J. Hartmann, Photon

Blockade in the Ultrastrong Coupling Regime, Phys. Rev. Lett. 109, 193602 (2012).[2] A. Le Boite, M.-J. Hwang, H. Nha, and M.B. Plenio, Fate of photon

blockade in the deep strong-coupling regime, Phys. Rev. A 94, 033827 (2016).

[3] R. Stassi, S. Savasta, L. Garziano, B. Spagnolo, and F. Nori, Output field-quadrature measurements and squeezing in ultrastrong cavity-QED, New J. Phys. 18 (2016) 123005.

Relaxation to Negative Temperatures in Double Domain Systems

Yusuke Hama1,2, William J. Munro3,2, and Kae Nemoto2

1RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198 Japan2National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430, Japan

3NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa, 243-0198, Japan

References[1] Yusuke Hama, William J. Munro,

and Kae Nemoto,arXiv:1612.08963v1 [quant-ph]

AcknowledgementsThis work was supported in by the RIKEN Special Postdoctoral Researcher Program (Y. H), the JSPS KAKENHI Grant Number 25220601 and the MEXT KAKENHI Grant Number 15H05870 (K. N).

In this research, we theoretically investigate the collective phenomena in the hybrid spin systems. We studythe collective spin relaxation processes in the double spin domain system, where the spin ensemble in eachdomain equivalently couples to a single bosonic reservoir. We analyze the various relaxation processes bychanging the initial spin configuration as well as the spin size for each domain for both zero and finitetemperatures. To understand these phenomena clearly, we focus on the relaxation times and the spinaverages at the steady state. We show that these results highly depend on the initial spin configuration andthe relative spin size between the two domains. In particular, when the large spin domain is set initially intothe excited state whereas the small domain into the ground state, the novel phenomenon, the ``negativetemperature relaxation” is generated [1].

Figure 1 The collective spin relaxations. (a) The relaxation in the spin domain set initially in

the excited state with 104 spins. (b) The relaxation in the spin domain set initially

in the ground state with 102 spins. It shows the negative temperature relaxation.

This figure is adapted from Reference [1].

Ultra high-Q Superconducting NbN Coplanar Waveguide Resonator

W. Qiu, K. Makise, T. Yamashita, H. TeraiFrontier Research Laboratory, Advanced ICT Research Institute, National Institute of Information and Communications

Technology (NICT), Kobe 651-2492, Japan

The coherence time of superconducting qubit device is influenced by the two-level systems (TLSs) localized within the qubit circuit that limit the implementation of such device in quantum information and computation applications. Many TLS mechanisms can contribute to the short coherence time in superconducting qubit, such as TLS due to the high loss substrate, or at the interface of substrate and supercomputing thin film, or atthe surface of superconductor, or quasi-particle related TLS near the superconductor energy boundary [1]. Inour effort to improve the coherence time in full nitride-qubit [2,3], we developed NbN (200) oriented coplanar waveguide resonator based on Si-substrate and reduced the internal loss by one-order compare to the epi-NbN resonator developed on MgO substrate (Fig.1) [4]. In addition, recent progress of NbN resonator with ultra high-Q has been achieved (Fig.2), which make NbN a promise candidate in more complex qubit circuitry.References [1] Lara Faoro and Lev B. Ioffe, “Internal Loss of Superconducting Resonators Induced by Interacting Two-Level Systems”, Physical Review Letters 109, 157005 (2013).[2] Y. Nakamura, H. Terai, K. Inomata, T. Yamamoto, W. Qiu, and Z. Wang, “Superconducting qubits consisting epitaxially grown NbN/AlN/NbN Josephson junctions”, Applied Physics Letters, 2011. 99 (212502). [3] K. Koshino, H. Terai, K. Inomata, T. Yamamoto, W. Qiu, Z. Wang, and Y. Nakamura, and Y Nakamura, “Observation of three-state dressed states in circuit quantum electrodynamics”, Physical Review Letters, 2013.110(263601).[4] W. Qiu, K. Makise, H. Terai, “Dielectric Loss in Superconducting NbN (200) CPW Resonator Developed on Si Substrate”, IEEE Trans. Appl. Supercond. (accepted).

Acknowledgements This workshop is supported in part by JSPS KAKENHI(C) Grant Number JP25420352

10-1 100 101 102 103 104 105 106 10710-6

10-5

10-4

10-3

loss

tan

<nphoton>

NbN(100) on MgO (100) NbN(200)/TiN(200) on Si (100)

10-1 100 101 102 103 104 105 106 107 108104

105

106

107

108

Qi

<nphoton>

Fig. 1. Internal loss tanδ as a function of microwave photon number <nphoton> for NbN (200) CPWR fabricated on Si (100) and MgO (100) wafer. Black ( ): loss of NbN(200) CPWR on MgO (100), Red ( ): loss of NbN (200) CPWR on Si (100).

Fig. 2. NbN CPWR developed on Si-substrate with ultra high-Q value over 3x106 near <nphoton>~1.

Efficient Coupling System between Optical Nanofiber and Diamond Nanowire

Y. Yonezu1,2, K. Wakui2, K. Furusawa2, K. Semba2, T. Aoki11Waseda University, Shinjuku, Tokyo, Japan

2National Institute of Information and Communications Technology (NICT), Koganei, Tokyo, Japan

NV (Nitrogen-Vacancy) centers in diamond are promising candidates for various quantum technologies [1],such as quantum information and quantum metrology, utilizing interactions with light, electric fields, andmagnetic fields. In particular, for the photonic applications, efficient collection techniques of photons from NVcenters are indispensable. Recently, coupling systems between an optical nanofiber and a spherical diamondnanocrystal have been theoretically [2] and experimentally [3-5] reported. However, in the 100nm-sizedspherical nanocrystal case, the theoretical maximum coupling efficiency for the sum of both fiber ends islimited to less than 25% [2]. Here, we propose a novel coupling system between the nanofiber and a diamondnanowire (a cylindrical-structured diamond nanocrystal). The coupling efficiency as high as 75% for the sumof both fiber ends is obtained by numerical simulations.

References[1] M. W. Doherty et al., Phys. Rep. 528, 1 (2013).[2] M. Almokhtar et al., Opt. Exp. 22, 20045 (2014).[3] T. Schröder et al., Opt. Exp. 20, 10490 (2012).[4] L. Liebermeister et al. Appl. Phys. Lett. 104,

031101 (2014).[5] M. Fujiwara et al. Opt. Lett. 40, 5702 (2015).

AcknowledgementsThis work is supported in part by- JSPS KAKENHI(S) Grant Number JP25220601 - JSPS KAKENHI(A) Grant Number JP26707022- Leading Graduate Program in Science and Engineering, Waseda University from MEXT

Figure 1Schematic of the coupling system.

Figure 2Coupling efficiency as a function ofthe system geometry.

Electron Paramagnetic Resonance Spectroscopy of Er:YSO using Josephson Bifurcation Amplifier

R. P. Budoyo, K. Kakuyanagi, H. Toida, Y. Matsuzaki, W. J. Munro, H. Yamaguchi, S. Saito

NTT Basic Research Laboratories, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198 Japan

We have performed electron paramagnetic resonance spectroscopy of an Er-doped Y2SiO5 crystal using the flux induced on a superconducting quantum interference device loop of a tunable Josephson bifurcation amplifier. The observed spectra shows good agreement with the simulated spectra that include hyperfine and quadrupole interactions of 167Er. Relaxation measurements show temperature and magnetic field dependences of lifetime are consistent with phonon-bottleneck process. The inferred sensing volume and measurement sensitivity are approximately 0.15 pl and 7000 spins (for 1 s measurement), respectively.

Acknowledgements This work was supported by Commissioned Research of NICT and in part by MEXT Grant-in-Aid for Scientific Research onInnovative Areas “Science of hybrid quantum systems” (Grant No. 15H05869 and 15H05870).

Figure 1. Experiment schematic

Figure 2. Measured EPR spectra

Cavity optomechanics with surface acoustic wavesAyato Okada1

1Research Center for Advanced Science and Technology (RCAST), The University of Tokyo, Meguro-ku, Tokyo 153-8904, Japan

We are studying the optomechanical systems using surface acoustic waves (SAWs) for the prospect ofrealizing a quantum transducer. A two-dimensional SAW resonator, shown in Fig. 1, fabricated on a LiNbO3substrate incorporated with a notion of brilliant SAW focusing technique achieves the focused SAW at the center of the device (Fig. 2a). While exciting the SAW with RF, a laser beam is sent through the center hole ofthe device to probe the phase modulation imparted by the SAW induced optoelastic effect as shown in Fig. 2.Changing the polarization of the probe beam gives the completely different image of the focused SAW (Fig. 2b), owing to the tesorial nature of an optoelastic coupling between the SAW and the light, which can beutilized to compose the optomecanical system with the polarization degree of freedom.

Fig. 1 CAD images of the two-dimensional SAW resonator.

Center 1mm

240

9.6 mm Fig. 2 Spatial distribution of the laser phase modulation imparted by the SAW with the input laser polarization of (a) vertical and (b) horizontal polarization.

Next, we insert the device in a Fabry-Perot cavity and perform optical spectroscopy. [Schematic is shown in Fig. 3a.] We observe cavity enhanced Brillouin scattering and demonstrate a prototype of the SAW-based optomechanical system.

Fig. 3 (a) Frequency diagram (b) The obtained spectrum of cavity enhanced Brillouin scattering

Demonstration of Leggett-Garg inequality violation with finite resolution and back-action

Masataka Iinuma1, Yutaro Suzuki2, and Holger F. Hofmann1

1Graduate school of Advanced Sciences of Matter(ADSM), Hiroshima University, Hiroshima 739-8530, Japan2Department of Physics, Graduate school of Science, Kyoto University, Kyoto 606-8502, Japan

We are investigating fundamental problems of quantum mechanics with photon polarization[1]. Quantummechanics leads to violation of the Leggett-Garg inequalities[2], because the operator formalism predicts non-classical correlations between different spin components, which show strange statistics given by negativejoint probabilities of measurement outcomes[3]. However, a direct observation of such non-classical jointprobabilities is impossible, because the measurement uncertainties affects measurement outcomes. In asequence of measurements of spin components, the resolution and the back-action errors of the intermediatemeasurement at a measurement strength can be described by random spin flips. We have applied the spin-flip model of the measurement errors to the analysis of the experimental data obtained in the sequentialmeasurements with the setup which enables us to change the measurement strength[4]. We confirm that thereconstructed joint probabilities are independent of the measurement strength and that the obtained violationof Leggett-Garg inequality is unchanged for any combination of measurement resolution and back-action.

References[1] http://home.hiroshima-u.ac.jp/qfg/qfg/index.html/[2] A. J. Leggett and A. Garg, Phys. Rev. Lett. (1985) 54, 857[3] H. F. Hofmann, Phys. Rev. A (2015) 91, 062123, [4] Y. Suzuki, M. Iinuma, and H. F. Hofmann, New J. Phys. (2012) 103022

AcknowledgementsThis work is partially supported in part by JSPS KAKENHI(C) Grant Number JP24540428

preparation

Intermediate measurement

Final measurement

HWP( )

HWP( )

PBS

BS

Investigation of microwave-activated c-Phase gate in tunable 3D transmon two qubit system

Taewan Noh1, Gwan Yeol Park1,2, Gahyun Choi1,3, Jiman Choi1,4, Woon Song1, Soon Gul Lee2, Kibog Park3, Yonuk Chong1,4

1Korea Research Institute of Standards and Science, Daejeon, Korea2Korea University Sejong Campus, Sejong, Korea

3Ulsan National Institute of Science and Technology, Ulsan, Korea4University of Science and Technology, Daejeon, Korea

We have studied two qubit MAP (microwave-activated c-Phase) gate demonstrated earlier by J. Chow et al.[1] in our 3D transmon qubit system. Instead of using two fixed-transition frequency qubits, we replaced one of them to a tunable-frequency qubit in order to align the higher energy levels 03 and 12 in situ so that we couldmaximize the splitting of these levels. By doing so we realized the ideal condition for implementing and optimizing MAP gate, where we explored the shortest possible gate time in this scheme. We will present the estimation of the fidelity of Bell states generated by MAP gate with tomographic reconstruction of the two-qubit states.

References[1] J. Chow et al., New J. Phys. 15, 115012 (2013)

Bistable Photon Emission from a Solid-State Single-Atom Laser

CEMS, RIKEN, Saitama, Japan

Department of Physics, University of Michigan, Ann Arbor, Michigan, USA

Department of Applied Physics, Aalto University, Aalto, Finland

We predict a bistability in the photon emission from a solid-state single-atom laser comprising a microwave cavity coupled to a voltage-biased double quantum dot. To demonstrate that the single-atom laser is bistable, we evaluate the photon emission statistics and show that the distribution takes the shape of a tilted ellipse. The switching rates of the bistability can be extracted from the electrical current and the shot noise in the quantum dots. This provides a means to control the photon emission statistics by modulating the electronic transport in the quantum dots. Our prediction is robust against moderate electronic decoherence and dephasing and is important for current efforts to realize single-atom lasers with gate-defined quantum dots as the gain medium.

References

[1] Neill Lambert, Franco Nori, Christian Flindt, Phys. Rev. Lett. 115, 216803 (2015).

Ground State ElectroluminescenceM.Cirio1, S. De Liberato2, N. Lambert3, F. Nori3,4

1Interdisciplinary Theoretical Science Research Group (iTHES), RIKEN, Wako-shi, Saitama 351-0198, Japan2School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, United Kingdom

3CEMS, RIKEN, Saitama 351-0198, Japan4Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040, USA

Electroluminescence, the emission of light in the presence of an electric current, provides information on theallowed electronic transitions of a given system. It is commonly used to investigate the physics of stronglycoupled light-matter systems, whose eigenfrequencies are split by the strong coupling with the photonic fieldof a cavity. In [1] we show that, together with the usual electroluminescence, systems in the ultrastrong light-matter coupling regime emit a uniquely quantum radiation when a flow of current is driven through them.While standard electroluminescence relies on the population of excited states followed by spontaneousemission, the process we describe extracts bound photons from the dressed ground state and it has peculiarfeatures that unequivocally distinguish it from usual electroluminescence.

References

[1] M. Cirio, S. De Liberato, N. Lambert, F. Nori, Physical Review Letters 116, 113601 (2016).

Quantum Memory in Deepstrong Coupling Regime

Roberto Stassi11Center for Emergent Matter Science, RIKEN, Wako-shi, Saitama 351-0198

Quantum memories are important elements for quantum information processing applications. Here we showthat a two-level system deepstrong coupled with a cavity mode, when the parity symmetry of the RabiHamiltonian is broken, can be used to store and retrieve quantum information. We make use of an auxiliaryatomic decoupled level [1] and of the lowest two eigenstates of the symmetry broken Rabi Hamiltonian, wherewe find there is a strong suppression of decoherence in the relaxation channel T1. To preserve decoherencefrom pure dephasing channel T2, we prove it is possible to apply the dynamical decoupling procedure. Thisproposal is experimentally realizable in superconducting circuits, as the deepstrong coupling has been recentlyachieved [2] and the dynamical decoupling has been realized [3].

References[1] R. Stassi, A. Ridolfo, O. Di Stefano, M. J. Hartmann, and S. Savasta, Spontaneous Conversion from Virtual to Real Photons in the Ultrastrong-Coupling Regime, Phys. Rev. Lett.110, 243601 (2013).[2] F. Yoshihara, T. Fuse, S. Ashhab, K. Kakuyanagi, S. Saito and K. Semba, Superconducting qubit-oscillator circuit beyond the ultrastrong-coupling regime, Nature Physics 13, 44–47 (2017) .[3] J. Bylander, S. Gustavsson, F. Yan, F. Yoshihara, and K. Harrabi, G. Fitch, D. Cory, Y. Nakamura, and J.S. Tsai, W.D. Oliver, Noise spectroscopy through dynamical decoupling with a superconducting flux qubit, Nature Physics 7, 565–570 (2011).

Quantum Nonlinear Optics without Real Photons

Spontaneous parametric down-conversion is a well-known process in quantum nonlinear optics in which aphoton incident on a nonlinear crystal spontaneously splits into two photons. Here we propose an analogousphysical process where one excited atom directly transfers its excitation to a pair of spatially separated-atomswith probability approaching one. The interaction is mediated by the exchange of virtual rather than realphotons [1,2]. This nonlinear atomic process is coherent and reversible, so the pair of excited atoms cantransfer the excitation back to the first one: the atomic analogue of sum-frequency generation of light. Theparameters used to investigate this process correspond to experimentally-demonstrated values in circuitquantum electrodynamics. This approach can be expanded to realize other nonlinear inter-atomic processes,such as four-atom mixing, and is an attractive architecture for the realization of quantum devices on a chip.

Roberto Stassi1, Vincenzo Macrì1,2, Anton Frisk Kockum1, Omar Di Stefano1,2, Salvatore Savasta1,2 and Franco Nori2,3

1Center for Emergent Matter Science, RIKEN, Wako-shi, Saitama 351-01982Dipartimento di Scienze Fisiche, Università di Messina, I-98166 Messina, Italy

3Department of Physics, University of Michigan, Ann Arbor, MI 48109-1040, USA

References[1] L. Garziano, V. Macrì, R. Stassi, O. Di Stefano, F. Nori, S. Savasta, A Single Photon Can Simultaneously Excite Two or More Atoms, Phys. Rev. Lett. 117, 043601 (2016).[2] L. Garziano, R. Stassi, V. Macrì, A. Frisk Kockum, S. Savasta, F. Nori, Multiphoton quantum Rabi oscillations in ultrastrong cavity QED, Phys. Rev. A 92, 063830 (2015).

Photon Bunching from Emission of Individual Atoms in the Ultrastrong Coupling Regime

Alessandro Ridolfo1,2

1Center for Emergent Matter Science, RIKEN, Wako-shi, Saitama 351-01982Dipartimento di Scienze Fisiche, Università di Messina, I-98166 Messina, Italy

The observation of a photon emitted by a isolated two-level atom prevents the possibility to detect immediately a further photon. Some time, depending on the drive amplitude, is needed in order to excite the atom again from its ground state. Such a phenomenon can be revealed in the resonance fluorescence of single atoms and it is known as photon antibunching. Here, by using a technique based on the spectral decomposition of the field operators [1-3], we show that, when the atom is coupled to an electromagnetic resonator in the ultrastrong coupling regime, a counterintuitive scenario may arise were this well-known picture breaks down and bunched light can be observed from the emission of a single two-level atom.

References[1] A. Ridolfo et al. Phys. Rev. Lett. 109 (19), 193602 (2012) [2] A. Ridolfo et al. Phys. Rev. Lett. 110 (16), 163601 (2012) [3] R. Stassi et al. Phys. Rev. Lett. 110 (24), 243601 (2013) ωc λ

ωa Analyzer

Experimental setup for the measurement of atomic second order correlation function

A Cold-Atom based Quantum Simulator for the full Rabi Model and its Generalizations

P. SchneeweissVienna Center for Quantum Science and Technology, TU Wien–Atominstitut, Stadionallee 2, 1020 Vienna, Austria

The interaction of a two-level system (TLS) with a single bosonic mode is described by the quantum Rabimodel [1]. Here, we propose a quantum simulator for this model based on single trapped cold atoms exposedto a suitable fictitious magnetic field [2] pattern. We show that important system parameters, such as theemitter-field detuning and the coupling strength of the emitter to the mode, can be tuned over a wide range. Remarkably, assuming realistic experimental conditions [3], the simulator allows one to explore the regimes ofultra-strong coupling, deep strong coupling, and dispersive deep strong coupling. Moreover, our approachenables the implementation of important extensions, e.g., the Rabi model with a broken Z2 symmetry, manyTLS coupled to one mode (Dicke model), and direct spin-spin coupling between the TLS. The proposedquantum simulator will thus open the door towards experimental studies of the quantum Rabi model in extreme, so far unexplored physical regimes.

References[1] I. I. Rabi, Phys. Rev. 49, 324 (1936); 51, 652 (1937).[2] C. Cohen-Tannoudji and J. Dupont-Roc,

Phys. Rev. A 5, 968 (1972).[3] B. Albrecht, Y. Meng, C. Clausen, A. Dareau, P. Schneeweiss,

A. Rauschenbeutel, Phys. Rev. A 94, 061401 (2016).

AcknowledgementsAustrian Science Fund(FWF, SFB NextLite Project No. F 4908-N23)

Fig.: The plot illustrates an optical dipole trapping potential, where energycontours are shown as black lines with labels in microkelvin. A suitablefictitious magnetic field (field strength encoded by color) is spatiallyoverlapped with the trapping potential. This then gives rise to a dynamicsbetween the atomic position and the atom’s internal spin state that isdescribed by the Rabi model.

Fast Generation of Macroscopic Superposition States by Coherent Driving

E. Yukawa1,2, G. J.Milburn3, C. A. Holmes4, and K. Nemoto2

1Center of Emergent Matter Science, RIKEN, 2-1, Hirosawa, Wako-shi, Saitama, 351-0198, Japan2National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430, Japan

3Centre for Engineered Quantum Systems, School of Mathematics and Physics, The University of Queensland, St Lucia, QLD 4072, Australia

4School of Mathematics and Physics, University of Queensland, St. Lucia, QLD 4072, Australia

Macroscopic superposition states (MSSs) of spins or qubits are potentially applicable to precision measurements, quantum computation and communication technologies, besides being of fundamental interests. Such macroscopic and highly entangled states can be generated via quadratic interactions such as one-axis twisting (OAT); however, the time needed to create an MSS is often nonnegligible compared with coherence time of a spin ensemble. In this presentation, we propose a new method to create high-fidelity MSSs consisting of the OAT and a coherent driving field. In our method, the preparation time of an MSS for N 350 spins is estimated to be shorter than the coherence times of an 87Rb Bose-Einstein condensate and an ion-trapped 9Be+ observed in recent experiments. The speedup on the MSS generation time can be a significant advantage of this scheme to experimentally generate and test these states. These numbers are

AcknowledgementsMEXT Grant-in-Aid for Scientific Research on Innovative Areas KAKENHI Grant Number JP15H05870,MEXT Grant-in-Aid for Scientific Research(S) KAKENHI Grant Number JP25220601CREST, Japan Science and Technology Agency

promising for relatively large spin ensembles to form a MSS with the current technology.

Quantum Metrology Including State Preparation and Readout Times

S. Dooley1, W.J. Munro1,2, K. Nemoto1

1National Institute of Informatics (NII), 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430, Japan2NTT Basic Research Laboratories, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan

There is growing belief that the next decade will see the emergence of sensing devices based on the laws of quantum physics that outperform some of our current sensing devices. For example, in frequency estimation, using a probe prepared in an entangled state can, in principle, lead to a precision gain compared to a probe prepared in a separable state. Even in the presence of some forms of decoherence, it has been shown that the precision gain can increase with the number of probe particles N . Usually, however, the entangled and separable state preparation and readout times are assumed to be negligible. We find that a probe in a maximally entangled (GHZ) state can give an advantage over a separable state only if the entangled state preparation and readout times are lower than a certain threshold. When the probe system suffers dephasing, this threshold is much lower (and more difficult to attain) than it is for an isolated probe. Further, we find that in realistic situations the maximally entangled probe gives a precision advantage only up to some finite number of probe particles Ncutoff that is lower for a dephasing probe than it is for an isolated probe.

References[1] S. Dooley, W.J. Munro, K. Nemoto, Phys. Rev. A 94, 052320 (2016)

Acknowledgements MEXT KAKENKI Grant No. 15H05870

Toward feasible long-distance quantum communications systems

N. Lo Piparo1

1National Institute of Informatics (NII), Chiyoda-ku, Tokyo 100-0003, Japan

Memory-assisted measurement-device-independent quantum key distribution (MA-MDI-QKD) aims toimprove the rate-versus-distance behavior of QKD systems by using existing technologies [1]. While quantumrepeater systems [2], as the ultimate solution to long-distance quantum communications, are still toochallenging to be implemented, MA-MDI-QKD presents a feasible middle step toward the realization of long-distance QKD. Here, we propose two MA-MDI-QKD schemes, both relying on nitrogen-vacancy (NV) centersin diamond embedded into cavities. In the first scheme [3], we consider two NV centers in the central node.We then improved this scheme by considering only one NV center as physical memory. For both schemeswe calculate the secret key rates and compare them with conventional no-memory schemes. We show that,by using the state-of-the-art devices, we can potentially beat existing QKD schemes in reach and rate.

References[1] N. Lo Piparo and M. Razavi, IEEE Journal of Selected Topics in Quantum Electronics 21,6600508 (2015).[2] H.-J. Briegel, W. � , I. J. Cirac, and P. Zoller, Physical ReviewLetters 81, 5932 (1998).[3] Accepted in Phys. Rev. A

AcknowledgementsThis workshop is supported by JSPS