Relaxation of an ensemble of two-level emitters in a squeezed bath

TL;DR

This paper develops a formalism to analyze how an ensemble of two-level emitters interacts with a broadband squeezed radiation reservoir, revealing different relaxation behaviors for single versus many emitters and their dependence on quantum noise sources.

Contribution

The paper introduces a unified approach to describe spin relaxation in squeezed baths, bridging single-emitter and ensemble dynamics with novel insights into noise contributions.

Findings

Single spin steady state fluctuations are independent of squeezing.

Large spin ensemble components relax independently of squeezing.

The difference is linked to vacuum fluctuations versus radiation reaction.

Abstract

We derive and evaluate equations of motion for the mean values and variances of the components of spins collectively coupled to a broadband squeezed radiation reservoir. Our formalism bridges between a single two-level emitter, represented by spin components that relax at different rates, depending on the degree of squeezing, to an ensemble of emitters represented by a large collective spin, whose components relax independently of the squeezing. For a single spin, the steady state fluctuations in the transverse components are independent of the squeezing, while the steady state of a large spin ensemble reflects the statistics of the squeezed reservoir. This follows from an analysis of the Langevin noise contributions to the equations of motion and their consequences for the first and second moments of the spin operators. We argue that the difference between a single and many spins is related to whether vacuum fluctuations or radiation reaction dominate the coupling of the spin system to the radiation environment.