Quantum Dynamics of Collective Spin States in a Thermal Gas

TL;DR

This paper develops a comprehensive quantum model to describe how atomic diffusion affects the nonclassical collective spin states in thermal gases, with implications for quantum optics and metrology.

Contribution

It introduces a stochastic, fully-quantum framework using Bloch-Heisenberg-Langevin formalism to analyze atomic diffusion effects on collective spin states.

Findings

Model accurately predicts spin noise spectra.

Describes relaxation of squeezed spin states.

Analyzes coherent coupling in hybrid spin systems.

Abstract

Ensembles of alkali or noble-gas atoms at room temperature and above are widely applied in quantum optics and metrology owing to their long-lived spins. Their collective spin states maintain nonclassical nonlocal correlations, despite the atomic thermal motion in the bulk and at the boundaries. Here we present a stochastic, fully-quantum description of the effect of atomic diffusion in these systems. We employ the Bloch-Heisenberg-Langevin formalism to account for the quantum noise originating from diffusion and from various boundary conditions corresponding to typical wall coatings, thus modeling the dynamics of nonclassical spin states with spatial inter-atomic correlations. As examples, we apply the model to calculate spin noise spectroscopy, temporal relaxation of squeezed spin states, and the coherent coupling between two spin species in a hybrid system.