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arXiv:1003.5925 · Physical Review Letters

Spin Self-Rephasing and Very Long Coherence Times in a Trapped Atomic Ensemble

Christian Deutsch, F. Ramírez-Martínez, Clément Lacroûte, Friedemann Reinhard, T. Schneider, Jean-Noël Fuchs, Frédéric Piéchon, Franck Laloë, Jakob Reichel, P. Rosenbusch

Published Jul 6, 2010• 185 citations
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Abstract

We perform Ramsey spectroscopy on the ground state of ultracold 87Rb atoms magnetically trapped on a chip in the Knudsen regime. Field inhomogeneities over the sample should limit the 1/e contrast decay time to about 3 s, while decay times of 58 ± 12 s are actually observed. We explain this surprising result by a spin self-rephasing mechanism induced by the identical spin rotation effect originating from particle indistinguishability. We propose a theory of this synchronization mechanism and obtain good agreement with the experimental observations. The effect is general and may appear in other physical systems.

DOI
10.1103/physrevlett.105.020401

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We perform Ramsey spectroscopy on the ground state of ultracold 87Rb atoms magnetically trapped on a chip in the Knudsen regime. Field inhomogeneities over the sample should limit the 1/e contrast decay time to about 3 s, while decay times of 58 ± 12 s are actually observed. We explain this surprising result by a spin self-rephasing mechanism induced by the identical spin rotation effect originating from particle indistinguishability. We propose a theory of this synchronization mechanism and obtain good agreement with the experimental observations. The effect is general and may appear in other physical systems.
We perform Ramsey spectroscopy on the ground state of ultra-cold 87Rb atoms magnetically trapped on a chip in the Knudsen regime. Field inhomogeneities over the sample should limit the 1/e contrast decay time to about 3 s, while decay times of 58 ± 12 s are actually observed. We explain this surprising result by a spin self-rephasing mechanism induced by the identical spin rotation effect originating from the exchange interaction. We propose a theory of this synchronization mechanism and obtain good agreement with the experimental observations. The effect is general and may appear in other physical systems.
We perform Ramsey spectroscopy on the ground state of ultracold 87 Rb atoms magnetically trapped on a chip in the Knudsen regime.Field inhomogeneities over the sample should limit the 1=e contrast decay time to about 3 s, while decay times of 58 Æ 12 s are actually observed.We explain this surprising result by a spin self-rephasing mechanism induced by the identical spin rotation effect originating from particle indistinguishability.We propose a theory of this synchronization mechanism and obtain good agreement with the experimental observations.The effect is general and may appear in other physical systems.
We perform Ramsey interferometry on an ultracold ^{87}Rb ensemble confined in an optical dipole trap. We use a π pulse set at the middle of the interferometer to restore the coherence of the spin ensemble by canceling out phase inhomogeneities and creating a spin echo in the contrast. However, for high atomic densities, we observe the opposite behavior: the π pulse accelerates the dephasing of the spin ensemble leading to a faster contrast decay of the interferometer. We understand this phenomenon as a competition between the spin-echo technique and an exchange-interaction driven spin self-rephasing mechanism based on the identical spin rotation effect. Our experimental data are well reproduced by a numerical model.
We present a compact atomic clock interrogating ultracold 87Rb magnetically trapped on an atom chip. Very long coherence times sustained by spin self-rephasing allow us to interrogate the atomic transition with 85% contrast at 5 s Ramsey time. The clock exhibits a fractional frequency stability of 5.8×10−135.8\times 10^{-13}5.8×10−13 at 1 s and is likely to integrate into the 1×10−151\times10^{-15}1×10−15 range in less than a day. A detailed analysis of 7 noise sources explains the measured frequency stability. Fluctuations in the atom temperature (0.4 nK shot-to-shot) and in the offset magnetic field (5×10−65\times10^{-6}5×10−6 relative fluctuations shot-to-shot) are the main noise sources together with the local oscillator, which is degraded by the 30% duty cycle. The analysis suggests technical improvements to be implemented in a future second generation set-up. The results demonstrate the remarkable degree of technical control that can be reached in an atom chip experiment.
We investigate the collective spin dynamics of a self-rephasing bosonic ensemble of 87Rb^{87}\mathrm{Rb}87Rb trapped in a one-dimensional vertical optical lattice. We show that the combination of the frequency shifts induced by atomic interactions and inhomogeneous dephasing, together with the spin self-rephasing mechanism, leads to the existence of a ``magic density'': i.e., a singular operating point where the clock transition is first-order insensitive to density fluctuations. This feature is very appealing for improving the stability of quantum sensors based on trapped pseudo-spin-1/2 ensembles. Ramsey spectroscopy of the $|5s{\phantom{\rule{3.33333pt}{0ex}}}^{2}{S}_{1/2},F=1,{m}_{F}=0\ensuremath{\rangle}\ensuremath{\rightarrow}|5s{\phantom{\rule{3.33333pt}{0ex}}}^{2}{S}_{1/2},F=2,{m}_{F}=0\ensuremath{\rangle}$ hyperfine transition is in qualitative agreement with a numerical model based on coupled Bloch equations of motion for energy-dependent spin vectors.