Collective resonance fluorescence in small and dense atom clouds: Comparison between theory and experiment

TL;DR

This paper investigates the collective optical response of cold, dense rubidium atom clouds, comparing experimental results with detailed simulations to understand how resonant dipole-dipole interactions influence resonance shifts and light scattering.

Contribution

It provides a comprehensive comparison between experimental data and microscopic simulations, revealing the significant role of dipole-dipole interactions in cold atom clouds' optical behavior.

Findings

Resonance line shifts differ from thermal ensembles.

Cold atom clouds show slower decay of excitations at high densities.

Strong light-induced dipole-dipole interactions are confirmed.

Abstract

We study the emergence of a collective optical response of a cold and dense $^{87}$Rb atomic cloud to a near-resonant low-intensity light when the atom number is gradually increased. Experimental observations are compared with microscopic stochastic simulations of recurrent scattering processes between the atoms that incorporate the atomic multilevel structure and the optical measurement setup. We analyze the optical response of an inhomogeneously-broadened gas and find that the experimental observations of the resonance line shifts and the total collected scattered light intensity in cold atom clouds substantially deviate from those of thermal atomic ensembles, indicating strong light-induced resonant dipole-dipole interactions between the atoms. At high densities, the simulations also predict a significantly slower decay of light-induced excitations in cold than in thermal atom clouds. The role of dipole-dipole interactions is discussed in terms of resonant coupling examples and the collective radiative excitation eigenmodes of the system.