Polaritonic modes in a dense cloud of atoms

TL;DR

This paper investigates resonant light scattering in dense atomic clouds, revealing that a few coherent polaritonic modes dominate the scattering process, with a correspondence between microscopic and macroscopic descriptions.

Contribution

It introduces a combined microscopic and macroscopic approach to identify and relate polaritonic modes in dense atomic clouds, highlighting their role in scattering.

Findings

Existence of a small number of superradiant polaritonic modes

Dominance of these modes in scattering processes

One-to-one correspondence between microscopic and macroscopic modes

Abstract

We analyze resonant light scattering by an atomic cloud in a regime where near-field interactions between scatterers cannot be neglected. We first use a microscopic approach and calculate numerically the eigenmodes of the cloud for many different realizations. It is found that there always exists a small number of polaritonic modes that are spatially coherent and superradiant. We show that scattering is always dominated by these modes. We then use a macroscopic approach by introducing an effective permittivity so that the atomic cloud is equivalent to a dielectric particle. We show that there is a one-to-one correspondence between the microscopic polaritonic modes and the modes of a homogeneous particle with an effective permittivity.