Revival of Raman coherence of trapped atoms

Abstract

We perform Raman spectroscopy of optically trapped non interacting 87 Rb atoms, and observe revivals of the atomic coherence at integer multiples of the trap period. The effect of coherence control methods such as echo and dynamical decoupling is investigated experimentally, analytically and numerically, along with the effect of the anharmonicity of the trapping potential. The latter is shown to be responsible for incompleteness of the revivals. Coherent Raman control of trapped atoms can be useful in the context of free-oscillation atom intefrerometry and spatial multi-mode quantum memory.Coherent control of cold neutral atomic ensembles can be used for a variety of studies and applications in physics, such as metrology, quantum information, quantum simulators, and fundamental quantum mechanics [1][2][3][4][5][6]. Long coherence times usually imply the need to minimize perturbations on the atoms, as implemented in atomic fountain clocks and atom interferometers. However, in some cases, such as quantum memory [7][8][9][10][11][12][13], there arises also a need for long coherence times in trapped samples. This approach involves challenges such as the inhomogeneous profile of both the external potential and the atomic density [14] and elastic atomic collisions. Coherence has also been shown to revive, in the deep quantum regime, via interaction mechanisms in a Bose-Einstein condensate [15,16].Quantum control of the internal state of a trapped atom can be achieved by the use of microwave (MW) radiation, allowing extremely long coherence times [17][18][19][20][21][22] and enabling the implementation of atom-chip clocks and single-pixel quantum memories.There are, however, applications for which MW control does not suffice. In two-photon stimulated Raman control the momentum recoil is given byhk eff ≈ 2hk sin (α/2), whereh is the reduced Planck constant, k is the wave number of the Raman beams and α is the angle between them. By changing the angle α, the momentum recoilhk eff can be varied between practically zero and 2hk. This allows coupling to the external degrees of freedom of the atoms and the possibility of implementation of spatial multi-mode quantum memory [23,24].Raman atomic coherence in a trap is closely related to the fringe contrast of guided interferometers [25][26][27][28], and more specifically free-oscillation atom interferometers [26,[29][30][31][32][33][34]. These rely on the classical turning points of an underlying harmonic potential for the mirroring of the wave packets. A thermal atom free-oscillation Raman interferometer allows for Ramsey π/2 → π/2 interferometry which is completely impossible to perform in freespace, utilizing the periodicity of the trapping potential. This type of interferometer is sensitive to time-dependent * Current address: Kirchhoff-

Decoherence in a Quantum Neural Network

“…Here, we report this revival scheme of decoherence for a weakly interacting central spin system in a Markovian environment. A revival of coherence recently introduced experimentally for trapped atoms (Afek et al, 2017). We observe that also in the Heisenberg XXX-type interaction case coherence time reduces with the increase of the number of ambient spins though the revivals are present.…”

Dark-time decay of the retrieval efficiency of light stored as a Rydberg excitation in a noninteracting ultracold gas

“…This breathing mode gives rise to collapse and revival of |C(t)| 2 . This is not to be confused with the collapse and revival of |C(t)| 2 caused by the dipole mode with angular frequency ω r , also known as the sloshing mode, created even for ∆a = 0 by nonzero net photon recoil [15,26] or by creating the spin wave not in the trap center [25].…”

“…We apply this model to study several scenarios, first, photon recoil during storage combined with thermal atomic motion [13,[21][22][23], second, a harmonic differential light-shift potential [15,[23][24][25][26], and, third, release from a harmonic trap [23]. According to the model, photon recoil combined with thermal motion is one of the dominant limitations for the observed 1/e time of 30 µs.…”

Deviations from generalized equipartition in confined, laser-cooled atoms

“…reason the effect in the experiment is more pronounced is that Gaussian anharmonicity does not suffice to describe the real anharmonicity typical for dipole traps [42].…”

“…reason the effect in the experiment is more pronounced is that Gaussian anharmonicity does not suffice to describe the real anharmonicity typical for dipole traps [42]. It is still, however, very useful for simplification of calculations and qualitative analysis.…”