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Observation of subradiance and superradiance in a dilute cloud of cold atoms

William Guérin

à 11h en salle C. Brot

When a photon is sent onto an atomic ensemble, it interacts collectively with the N atoms of the cloud and not simply with one of them. This can result in measurable modifications in the scattering rate, the emission diagram or the temporal dynamics of the scattering. We study these cooperative effects experimentally and theoretically. In particular, we are investigating these effects with a dilute cold-atom sample, when the very existence of these cooperative effects is somewhat counter-intuitive. I will present our recent results in this context. By studying the temporal decay of the fluorescence from a cold-atom cloud, we have directly observed superradiance and subradiance, corresponding respectively to faster and slower decay than the natural lifetime of the excited state. This is the first clear observation of many-body subradiance, 60 years after its prediction by Dicke.