Broadband Optical Cooling of AlH+ to the Rotational Ground State

Christopher M. Seck, Chien-Yu Lien, Brian C. OdomPhysics & Astronomy, Northwestern University

RH10ISMS, UIUCJune 19, 2014

ISMS, UIUC, June 19, 2014

Motivation• Quantum control of atomics revolutionary.• Extend quantum control toolbox to molecules.• State manipulation requires rotational control.

�̇�= 𝑑𝑑𝑡 (𝑚𝑝

𝑚𝑒)

Time-varying constantsNJP 11, 055049

(2009)

Quantum computing

Coherent control,ultracold & quantum

chemistry, etc.

Alignment

Orientation

ISMS, UIUC, June 19, 2014

e-

?p+ 2

Difficulty of Molecules

• State manipulation in atomics easy.• No closed cycling transitions in molecules.• Electronic relaxation generally excites vibrations.

• Large thermal distribution at room temperature.• Each populated state requires unique laser frequency.

ISMS, UIUC, June 19, 2014

Ba+

3

Difficulty of Molecules

• AlH+ advantages:• ∽30 electronic excitation-relaxation cycles.• 99.9% in v = 0, 96% among N = 0 – 9 at 300 K.• P- well separated from Q-, R-branches.

• 14 cm-1 (420 GHz) between P-/Q-branches.

ISMS, UIUC, June 19, 2014

360 nm

1600 cm-1 = 2400 K

4

BROC

• Broadband Rotational Optical Cooling.• Selectively drive P-branch.• Parity barrier between N = 0, 1.• Timescale of ∽μs via 10 electronic excitation-relaxations.∽• < scatters before vibrational excitation.

ISMS, UIUC, June 19, 2014

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BROC

• Drive P-branch, avoiding P(1).• Spectral cutoff width < 2 cm-1.

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SFPL for AlH+

• Spectrally-filtered Pulsed Laser.• 4-f configuration common to fs pulse-shaping.• SHG Spectra-Physics Mai Tai HP.• Vibrational cooling of Cs2 by Orsay group [Viteau et al, Science 321, 5886 (2008)].

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Apparatus and Experiment

r0 = 3 mmz0 = 15 mmΩRF = 2π · 2.35 MHz, 300 VPPEC’s = 850 VDC

ISMS, UIUC, June 19, 2014

• Ablation-load, laser cool Ba+. Ablation-load 50 Al∽ +.• Translational motion sympathetically cooled.

• AlH+ formed from background gas 1 minute.∽ 8

Apparatus and Experiment

• Ablation-load, laser cool Ba+. Ablation-load 50 Al∽ +.• Translational motion sympathetically cooled.

• AlH+ formed from background gas 1 minute.∽• Apply rotational cooling, state-selective (1+1’) REMPD.• TOFMS using analog-mode Hamamatsu MCP.

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Apparatus and Experiment

• TOF resolves Al+ (27 u) and AlH+ (28 u).• Ion numbers calculated by integrated signal in each bin.• Al+ fraction is molecule population in targeted rotational state.

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Results and Discussion

• Initial (red diamonds) and BROC (green circles) distributions.

ISMS, UIUC, June 19, 2014

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Results and Discussion

• Initial (red diamonds) and BROC (green circles) distributions.

ISMS, UIUC, June 19, 2014

• 300 K thermal distribution.

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Results and Discussion

• Initial (red diamonds) and BROC (green circles) distributions.• Toy Monte Carlo method used for statistical analysis.

ISMS, UIUC, June 19, 2014

• 94(5)% in N = 0, 1.• T (+ parity) < 13 K.• T (- parity) < 19 K.

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VA-BROC

• Vibrationally-Assisted Broadband Rotational Optical Cooling.• Drive P(1) until v’’ = 1 decay. Relaxation to v’’ = 0 provides 3rd photon.• Cooling light then pumps to single-parity rotational ground state.• Timescale set by vibrational decay of 100 ms.∽

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VA-BROC

• Shift mask position to drive P(1).

ISMS, UIUC, June 19, 2014

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Results and Discussion

• VA-BROC (blue triangles) results.

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Results and Discussion

• VA-BROC (blue triangles) results.• Toy Monte Carlo method used for statistical analysis.

ISMS, UIUC, June 19, 2014

• in N = 0.• in N = 1.• .

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Results and Discussion

• VA-BROC timing results.• 127 ms expected from theory.

ISMS, UIUC, June 19, 2014

𝜏=140 (20 )ms

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Summary

• BROC: Broadband Rotational Optical Cooling.• Rotationally cooled AlH+ to ground state of each parity.• < 13 (< 19) K for the positive (negative) parity.

• VA-BROC: Vibrationally-Assisted Broadband Rotational Optical Cooling.• Rotationally cooled AlH+ to single-parity ground state.• N = 0 population increase from to .• to in 140(20) ms.

• Cooling technique applicable to molecules separated P-branches with diagonal vibrational decays.• Complex masks, broadband vibrational repumps extend technique to

larger class of molecules.

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Next Steps and Outlook

• More reliable/faster AlH+ production via REMPI.• Currently exploring AlH & AlH3 UHV-compatible chemistry.• Expertise/advice is greatly needed!

• Improve single-parity preparation from 100 ms to ∽ ∽μs.• 2-photon A2Π1/2 X2Σ+ excitation via (1+1) or (1+1’) process.• Laser sources commercially available.

• Hyperfine state cooling as preliminary to full molecular coherent control.

• Positioned to perform first molecular spectroscopy in the Lamb-Dicke regime.

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The Odom GroupGrad Students and PostdocsMatthew Dietrich (postdoc)Mark KokishChien-Yu LienYen-Wei LinChris SeckPatrick StollenwerkMing-Feng Tu

UndergradsXiaowen Chen

Group AlumniJoan Marler (postdoc)Jason Nguyen (postdoc)Vaishnavi Rajagopal (grad)David Tabor (grad)Marc Bourgeois (ugrad)Fillan Grady (ugrad)Scott Williams (ugrad)

… and The People Paying for It

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Michael Schmitt

Additional details:(1+1’) REMPD: arXiv:1402:0123Rotational cooling: arXiv:1402.3918

BROC & VA-BROC Timescales

ISMS, UIUC, June 19, 2014

• Parity-preserving BROC timescale via simulation at 1% of Isat.• Parity-cooling VA-BROC timescale via v’ = 1 lifetime. 22

Toy Monte Carlo Method

ISMS, UIUC, June 19, 2014

• n-tuple array generated by binomial random number generation using experimental ion numbers.

• Avoids binomial confidence intervals far from central limit approximation.

1.3σ

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Time-dependent Fit Function

𝑃0𝑑=𝑃0

𝑓 −𝑃1𝑖 𝐵2𝑒

− 𝑇𝜏

ISMS, UIUC, June 19, 2014

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