Dynamics of a stored Zeeman coherence grating in an external magnetic field

TL;DR

This study explores how external magnetic fields influence the evolution and coherence of Zeeman gratings in cold cesium atoms, revealing conditions that significantly extend coherence times and demonstrating the effects of magnetic inhomogeneities.

Contribution

It provides new insights into controlling Zeeman coherence in cold atoms using magnetic fields, including a simplified model explaining the observed phenomena.

Findings

Magnetic fields cause collapses and revivals in atomic coherence.

Optimal magnetic field orientation extends coherence decay time fivefold.

Magnetic inhomogeneities contribute to coherence decay.

Abstract

We investigate the evolution of a Zeeman coherence grating induced in a cold atomic cesium sample in the presence of an external magnetic field. The gratings are created in a three-beam light storage configuration using two quasi-collinear writing laser pulses and reading with a counterpropagating pulse after a variable time delay. The phase conjugated pulse arising from the atomic sample is monitored. Collapses and revivals of the retrieved pulse are observed for different polarizations of the laser beams and for different directions of the applied magnetic field. While magnetic field inhomogeneities are responsible for the decay of the coherent atomic response, a five-fold increase in the coherence decay time, with respect to no applied magnetic field, is obtained for an appropriate choice of the direction of the applied magnetic field. A simplified theoretical model illustrates the role of the magnetic field mean and its inhomogeneity on the collective atomic response.