Correlated steady states and Raman lasing in continuously pumped and probed atomic ensembles

TL;DR

This paper investigates the steady states of continuously pumped atomic ensembles, revealing correlated states and Raman lasing phenomena, with implications for quantum metrology and information processing.

Contribution

It introduces a self-consistent method to include pair correlations in the steady state analysis of multilevel atomic ensembles under continuous pumping.

Findings

Identification of regimes of Raman lasing in atomic ensembles

Characterization of the photon spectrum and coherence times

Demonstration of correlated steady states beyond uncorrelated assumptions

Abstract

Spin-polarised atomic ensembles probed by light based on the Faraday interaction are a versatile platform for numerous applications in quantum metrology and quantum information processing. Here we consider an ensemble of Alkali atoms that are continuously optically pumped and probed. Due to the collective scattering of photons at large optical depth, the steady state of atoms does not correspond to an uncorrelated tensor-product state, as is usually assumed. We introduce a self-consistent method to approximate the steady state including the pair correlations, taking into account the multilevel structure of atoms. We find and characterize regimes of Raman lasing, akin to the model of a superradiant laser. We determine the spectrum of the collectively scattered photons, which also characterises the coherence time of the collective spin excitations on top of the stationary correlated mean-field state, as relevant for applications in metrology and quantum information.