Cooling of Atoms due to Momentum Diffusion

Eugeny Korsunsky, A. Snegiriov, Vyacheslav M Gordienko +2 more

Eugeny Korsunsky, Boris G. Matisov, Laurentius Windholz

Laurent Sanchez-Palencia, G. Grynberg

Sigurd Dyrting

We study the dynamics of laser-cooled two-level atoms in a time-dependent standing wave. In the absence of spontaneous emission, our model reduces to the much studied quantum standard mapping. For a sample of atoms initially cooled to the Doppler limit, the momentum variance increases linearly with interaction time. A sample of atoms initially cooled to the recoil limit will display momentum diffusion at a rate that is determined by two numbers: the classical chaos parameter and a dimensionless Planck parameter. This diffusion ceases after the quantum-mechanical break time. Spontaneous emission will modify the diffusion rate of both Doppler- and recoil-cooled atoms. We show that one component of the new diffusion constant is due to spontaneous recoil and that there is a correction to the deterministic diffusion rate due to the destruction of correlations in the stroboscopic position. Spontaneous emission will destroy the dynamic localization of atoms cooled to the recoil limit. The new momentum diffusion constant can be related to the quasistationary state-decoherence rate. \textcopyright{} 1996 The American Physical Society.

G. S. Agarwal, Klaus Mølmer

We consider the momentum diffusion of atoms moving in a standing-wave laser field. We show how the correlation-function approach as originally applied to atoms at rest can be generalized to derive the velocity dependence of the momentum diffusion coefficient in standing waves, and that it gives results in agreement with the transport-equation approach to laser cooling. As an example we apply our calculations to determine the achievements of laser cooling in intense fields where cooling may occur around a nonvanishing velocity. Here we obtain temperatures which are 30% lower than the corresponding minimum obtained around zero velocity. Our explicit calculations involve usage of the optical Bloch equations, the quantum regression theorem, and the matrix continued-fraction method.

William D. Phillips, Harold J. Metcalf