Anomalous high-density spin noise in a strongly interacting atomic vapor

TL;DR

This paper reports the discovery of anomalous spin noise spectra in dense rubidium vapor caused by resonant dipole-dipole interactions, challenging existing single-particle models and opening avenues for many-body spin noise studies.

Contribution

It demonstrates the impact of strong interactions on spin noise spectra in atomic vapors and introduces a simple two-body model to explain these effects.

Findings

Observation of spectral broadening with increasing density

Emergence of low-frequency noise component

Agreement of a two-body model with experimental data

Abstract

Spin noise spectroscopy (SNS) has become a mainstream approach to probe the dynamics of a spin ensemble in and out of equilibrium. Current models describing spin noise in interacting samples are based on an effective single particle dynamics in a bath. Here, we report the observation of a strong interaction regime which significantly affects the spin dynamics. Performing SNS in a dense Rubidium vapor, we observe anomalous distortions of the usual spin noise spectra, which we attribute to resonant dipole-dipole interaction within the ensemble. As the density of the vapor increases, we observe a dramatic broadening of the usual resonances and the emergence of an unexpected extra low-frequency noise component. We use a simple microscopic two-body numerical model to reproduce and discuss these observations. Our results suggests that the spectra cannot be described by usual models of single-atom dynamics and arise from the evolution of interacting pair of atoms. This work opens the way to the study of many-body spin noise or higher order correlators in atomic vapors using SNS.