Superradiance in a Large and Dilute Cloud of Cold Atoms in the Linear-Optics Regime

TL;DR

This paper experimentally demonstrates superradiant decay in a large, dilute cloud of cold atoms in the linear-optics regime, showing increased decay rates at large detuning and suppression near resonance.

Contribution

It provides the first direct measurement of off-axis superradiant decay in a dilute atomic cloud under linear-optics conditions, confirming theoretical predictions.

Findings

Decay rate increases with optical depth at large detuning

Superradiant decay is suppressed near resonance due to multiple scattering

Off-axis superradiance observed in dilute cold atom clouds

Abstract

Superradiance has been extensively studied in the 1970s and 1980s in the regime of superfluores-cence, where a large number of atoms are initially excited. Cooperative scattering in the linear-optics regime, or "single-photon superradiance" , has been investigated much more recently, and superra-diant decay has also been predicted, even for a spherical sample of large extent and low density, where the distance between atoms is much larger than the wavelength. Here, we demonstrate this effect experimentally by directly measuring the decay rate of the off-axis fluorescence of a large and dilute cloud of cold rubidium atoms after the sudden switch-off of a low-intensity laser driving the atomic transition. We show that, at large detuning, the decay rate increases with the on-resonance optical depth. In contrast to forward scattering, the superradiant decay of off-axis fluorescence is suppressed near resonance due to attenuation and multiple-scattering effects.