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arXiv:1606.00218 · Physical Review Letters

Competition between Spin Echo and Spin Self-Rephasing in a Trapped Atom Interferometer

Cyrille Solaro, Alexis Bonnin, Frédéric Combes, M. Lopez, Xavier Alauze, Jean-Noël Fuchs, Frédéric Piéchon, Franck Pereira dos Santos

Published Oct 14, 2016• 18 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1103/physrevlett.117.163003

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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 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 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.
Abstract We evaluate the performance and phase diffusion of trapped 87 Rb atoms in an atom chip sensor with Ramsey interferometry and Hahn’s spin echo in the time and phase domains. We trace out how the phase uncertainty of interference fringes grows with time. The phase-domain spin echo enables us to measure many-second-long phase diffusion with a low-cost local oscillator that otherwise seems unrealistic to obtain with such an oscillator. In the Ramsey experiment we record interference fringes with contrast decaying in 12 s, and with a frequency uncertainty of 80 mHz corresponding to the dephasing time of 2.8 s. A clear distinction is drawn between the decoherence of the atomic ensemble, and the dephasing originating from the local oscillator. Spin echo cancels most of the perturbations affecting the Ramsey experiments, and leaves the residual phase noise of only 19 mHz mostly attributed to the local oscillator frequency instability, yielding the increased coherence time of 11.9 s which coincides with the contrast decay time in the Ramsey sequence. A number of perturbation sources leading to homogeneous and inhomogeneous dephasing is discussed. Our atom chip sensor is useful in probing fundamental interactions, atomtronics, microcantilever, and resonant cavity profiling in situ .
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 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.
We observe the coherence of an interacting two-component Bose-Einstein condensate (BEC) surviving for seconds in a trapped Ramsey interferometer. Mean-field-driven collective oscillations of two components lead to periodic dephasing and rephasing of condensate wave functions with a slow decay of the interference fringe visibility. We apply spin echo synchronous with the self-rephasing of the condensate to reduce the influence of state-dependent atom losses, significantly enhancing the visibility up to 0.750.750.75 at the evolution time of 1.51.51.5 s. Mean-field theory consistently predicts higher visibility than experimentally observed values. We quantify the effects of classical and quantum noise and infer a coherence time of 2.82.82.8 s for a trapped condensate of $5.5\ifmmode\times\else\texttimes\fi{}{10}^{4}$ interacting atoms.