Subradiance in dilute atomic ensembles: Role of pairs and multiple scattering

TL;DR

This paper investigates the mechanisms behind subradiant decay in dilute atomic ensembles, highlighting the roles of atomic pairs and multiple scattering, and providing a new interpretation of subradiance based on light behavior rather than collective states.

Contribution

It demonstrates that subradiance in dilute samples can be explained by multiple scattering effects, complementing the traditional collective atomic state perspective.

Findings

Close atomic pairs influence slow decay rates in dilute ensembles.

Multiple scattering dominates the dynamics at high optical depths.

Emission properties resemble radiation trapping phenomena.

Abstract

We study numerically the slow (subradiant) decay of the fluorescence of motionless atoms after a weak pulsed excitation. We show that, in the linear-optics regime and for an excitation detuned by several natural linewidths, the slow decay rate can be dominated by close pairs of atoms (dimers) forming superradiant and subradiant states. However, for a large-enough resonant optical depth and at later time, the dynamics is dominated by collective many-body effects. In this regime, we study the polarization and the spectrum of the emitted light, as well as the spatial distribution of excitation inside the sample, as a function of time during the decay dynamics. The behavior of these observables is consistent with what would be expected for radiation trapping of nearly resonant light. This finding sheds light on subradiance in dilute samples by providing an interpretation based on the light behavior of the system (multiple scattering) which is complementary to the more commonly used picture of the collective atomic Dicke state.