Cooperativity in light scattering by cold atoms

TL;DR

This paper presents a quantum theoretical analysis of cooperative light scattering effects in cold atomic clouds, revealing superradiant and subradiant phenomena, and deriving analytical expressions for scattered light and radiation pressure.

Contribution

It introduces a quantum master equation approach in the single-excitation limit to describe cooperative scattering in cold atoms, including analytical results and validity conditions.

Findings

Identification of superradiant and subradiant scattering features

Analytical expressions for scattered intensity and radiation pressure

Demonstration of collective suppression of atomic excitation

Abstract

A cloud of cold N two-level atoms driven by a resonant laser beam shows cooperative effects both in the scattered radiation field and in the radiation pressure force acting on the cloud center-of-mass. The induced dipoles synchronize and the scattered light presents superradiant and/or subradiant features. We present a quantum description of the process in terms of a master equation for the atomic density matrix in the scalar, Born-Markov approximations, reduced to the single-excitation limit. From a perturbative approach for weak incident field, we derive from the master equation the effective Hamiltonian, valid in the linear regime. We discuss the validity of the driven timed Dicke ansatz and of a partial wave expansion for different optical thicknesses and we give analytical expressions for the scattered intensity and the radiation pressure force on the center of mass. We also derive an expression for collective suppression of the atomic excitation and the scattered light by these correlated dipoles.