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

D. Moretti, D. Felinto, J. W. R. Tabosa, A. Lezama

Published Jan 1, 2010• 24 citations
OpenAlex

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 and reading laser pulses 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 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.

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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 and reading laser pulses 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 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.
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 and reading laser pulses 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 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.
We report on a detailed investigation of the dynamics and the saturation of a light grating stored in a sample of cold cesium atoms. We employ Bragg diffraction to retrieve the stored optical information impressed into the atomic coherence by the incident light fields. The diffracted efficiency is studied as a function of the intensities of both writing and reading laser beams. A theoretical model is developed to predict the temporal pulse shape of the retrieved signal and compares reasonably well with the observed results.
We report the storage of a spatial light grating in a sample of cold caesium atoms. The grating is stored in the atomic medium using a backward four-wave-mixing laser beam configuration with two counterpropagating control fields and a noncollinear probe field. The grating was stored during a controllable dark interval after which turning on the control fields alone resulted in a light pulse emission in the forward and backward probe beam directions. Grating storage times up to 4 µs were observed.
We have developed a theoretical description of the evolution of ground state coherences between magnetic sublevels in Rb vapor in the presence of a magnetic field along an arbitrary direction. This formalism uses a rotation matrix approach to describe the evolution of coherences created by two traveling wave laser pulses with orthogonal polarizations. The effect of a magnetic field can be described as a time-dependent rotation of the atomic system about the quantization axis. Predictions based on this theoretical formalism for the functional form of Larmor oscillations in a magnetic field are studied using a coherent transient effect known as magnetic grating free induction decay (MGFID) using room temperature vapor and laser cooled atoms. We find the theoretical predictions to be in excellent agreement with data. The velocity distribution of the cold sample measured from the dephasing time of the MGFID in the absence of magnetic fields is in agreement with the sample temperature obtained by imaging the ballistic expansion of the trapped cloud. By using rate equations to model atomic coherences, it is also possible to predict the evolution of magnetic grating echoes (MGE) in a magnetic field. We compare these predictions with experiments from cold atoms and discuss applications of the MGFID and MGE that relate to a precision measurement of the atomic ggg factor ratio using 85Rb^{85}\mathrm{Rb}85Rb and 87Rb^{87}\mathrm{Rb}87Rb isotopes.
We consider retrieving of a light pulse stored in a medium of atoms with Λ-configuration of levels under conditions of electromagnetically induced transparency when a pulse of the external magnetic field inhomogeneous over the medium length is applied to the medium during the absence of the control field. It is shown that the coherence of lower levels of medium atoms acquires a phase depending on the coordinate along the medium and that the temporal shape of the retrieved pulse, if it is recorded interferometrically, reflects the coordinate dependence of the magnetic field.