Subradiance and radiation trapping in cold atoms

TL;DR

This paper investigates the combined effects of subradiance and radiation trapping on the slow decay of scattered light in cold atomic clouds, revealing their distinct scaling behaviors and underlying mechanisms through experiments and simulations.

Contribution

It demonstrates that subradiance and radiation trapping can occur simultaneously with different scaling laws, clarifying their physical origins in cold atom light dynamics.

Findings

Subradiance decay rate is independent of detuning.

Radiation trapping decay depends on detuning via optical depth.

Experimental and numerical results support distinct physical mechanisms.

Abstract

We experimentally and numerically study the temporal dynamics of light scattered by large clouds of cold atoms after the exciting laser is switched off in the low intensity (linear optics) regime. Radiation trapping due to multiple scattering as well as subradiance lead to decay much slower than the single atom fluorescence decay. These two effects have already been observed separately, but the interplay between them remained to be understood. Here, we show that with well chosen parameters of the driving field, the two effects can occur at the same time, but follow different scaling behaviors. The subradiant decay is observed at late time and its rate is independent of the detuning, while the radiation trapping decay is observed at intermediate time and depends on the detuning through the optical depth of the sample. Numerical simulations based on random walk process and coupled-dipole equations support our interpretations. Our study clarifies the different interpretations and physical mechanisms at the origin of slow temporal dynamics of light in cold atoms.