Spatial Coherence of Light in Collective Spontaneous Emission

TL;DR

This paper demonstrates that an optically-thin ensemble of 11,000 atoms can spontaneously produce spatially coherent light through collective effects like superradiance, challenging the assumption that coherence requires stimulated emission.

Contribution

It reveals that collective coupling in atomic ensembles can generate spatial coherence without population inversion or stimulated emission.

Findings

Spatial coherence observed in a 11,000-atom ensemble

Coherence arises from Dicke superradiance and subradiance

Challenging the notion that stimulated emission is necessary for coherence

Abstract

When a quantum system is put into an excited state, it will decay back to the ground state through a process termed spontaneous emission. It is generally assumed that spontaneous emission between different individual emitters would not be coherent with each other; to produce coherent light one would need population inversion and stimulated emission. In this work, we show that an optically-thin ensemble of 11,000 radiating atoms spontaneously organize to produce spatially coherent light. The reason for this coherence is collective-coupling of the individual emitters via Dicke superradiance and subradiance (as opposed to amplification through stimulated emission).