Optically Inhibited Collisional Dephasing

Physical review. A, 1985

We present the -results of an experiment designed to probe the collision-induced relaxation of excited-state Yb Zeeman coherences. Our experiment is sensitive not only to the depolarization-type relaxation mechanisms often observed in optical-pumping experiments, but also to the effects of collisionally induced velocity. changes. Our measurements were performed in the 6s 6p 3PI excited state of the even (1 =0) isotopes of gas-phase atomic Yb by means of a trilevel photon-echo technique.

Physical Review A, 2004

The decay in the hyperfine coherence of optically trapped atoms due to interactions with the environment, is only partly suppressed by "echo" spectroscopy [M. F. Andersen et al. Phys. Rev. Lett. 90, 023001 (2003)], primarily due to dynamical (time-dependent) dephasing mechanisms. We demonstrate here an improved pulse sequence, for which the decay of coherence is reduced by a factor of 2.5 beyond the reduction offered by the "echo" spectroscopy. This reduction occurs when each dark period in-between pulses is shorter than the time scale over which substantial dephasing develops. The coherence time is then limited by mixing to other vibrational levels in the trap and, to a lesser extent, the lifetime of the internal states of the atoms.

2008

We report on the control of interaction-induced dephasing of Bloch oscillations for an atomic Bose-Einstein condensate in an optical lattice under the influence of gravity. When tuning the strength of the interaction towards zero by means of a Feshbach resonance, the dephasing time is increased from a few to more than twenty thousand Bloch oscillation periods. We quantify the dephasing in terms of the width of the quasi-momentum distribution and measure its dependence on time for different values of the scattering length. Minimizing the dephasing allows us to realize a BEC-based atom interferometer in the non-interacting limit. We use it for a precise determination of a zero-crossing for the atomic scattering length and to observe collapse and revivals of Bloch oscillations when the atomic sample is subject to a spatial force gradient.

Physical Review B, 2001

The damping of quantum effects in the transport properties of electrons deposited on a surface of liquid helium is studied. It is found that due to vertical motion of the helium vapour atoms the interference of paths of duration t is damped by a factor exp −(t/τv) 3. An expression is derived for the weak-localization lineshape in the case that damping occurs by a combination of processes with this type of cubic exponential damping and processes with a simple exponential damping factor. PACS: 1 Recall that the Fourier transform of e −|t| is a Lorentzian.

Physical Review Letters, 1996

We have determined the rate of loss of atoms from a Bose-Einstein condensed gas due to binary processes in the presence of a far-detuned laser field. In this limit, the binary loss rate spectrum is markedly different from, and can greatly exceed, the basic atomic loss rate. We suggest that measurements of the loss rate spectrum can be used to determine the nature of atom interactions in a condensate. [S0031-9007(96)00919-2]

Physical Review A, 2009

We propose to implement a sub-shot-noise matter-wave interferometer via the stimulated dissociation of a molecular Bose-Einstein condensate and study the collisional loss of atom-molecule coherence during its phase-acquisition time. The obtained n-atom states are two-atom ͓SU͑1,1͔͒ coherent states with number variance ⌬n ϰ n compared to ⌬n ϰ ͱ n for the spin ͓SU͑2͔͒ coherent states formed by coherent splitting of an atomic condensate. Consequently, the Lorentzian atom-molecule phase diffusion is faster than the Gaussian phase diffusion between separated atomic condensates by a ͱ n factor.

Atomic Physics, 1987

ln intense laser beams, when perturbative treatments are no longer val id, the dressed atom approach provides a quantitative understanding of the main features of dipole or intensity gradient forces (mean value, fluctuations, velocity dependence). ln this lecture, we present such an approach and we apply it to atomic motion in an intense standing wave. New efficient laser cooling schemes taking advantage of stimulated processes are proposed. They work for a blue detuning and do not saturate at high intensity.

We present a detailed theoretical treatment of a three-level
system in a hot atomic vapor interacting with a coupling and a probe field of arbitrary strengths, leading to electromagnetically induced transparency and slow light under the two-photon resonance condition. We take into account all the relevant decoherence processes including collisions. Velocity-changing collisions
VCCs are modeled in the strong-collision limit effectively, which helps in achieving optical pumping by the coupling beam across the entire Doppler profile. The steady-state expressions for the atomic density-matrix elements are numerically evaluated to yield the experimentally measured response characteristics. The predictions, taking into account a dynamic rate of influx of atoms in the two lower levels of the
, are in excellent agreement with the reported experimental results for 4He
. The role played by the VCC parameter is seen to be distinct from that by the transit time or Raman coherence decay rate.

Chemical Physics Letters, 1979