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.
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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.
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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).
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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
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