Spin noise spectroscopy of a noise-squeezed atomic state

TL;DR

This paper demonstrates how spin noise spectroscopy can detect and analyze noise squeezing in atomic systems, revealing detailed spin dynamics and enhancing measurement sensitivity even without macroscopic coherence.

Contribution

It provides new insights into noise squeezing mechanisms in atomic spin systems and showcases the technique's potential for improving magnetic sensor performance.

Findings

Identification of noise asymmetry at magnetic resonance

Spectrum structure reveals noise process timescales

Enhanced sensitivity in regimes without atomic coherence

Abstract

Spin noise spectroscopy is emerging as a powerful technique for studying the dynamics of various spin systems also beyond their thermal equilibrium and linear response. Here, we study spin fluctuations of room-temperature neutral atoms in a Bell-Bloom type magnetometer. Driven by indirect pumping and undergoing a parametric excitation, this system is known to produce noise-squeezing. Our measurements not only reveal a strong asymmetry in the noise distribution of the atomic signal quadratures at the magnetic resonance, but also provide insight into the mechanism behind its generation and evolution. In particular, a structure in the spectrum is identified which allows to investigate the main dependencies and the characteristic timescales of the noise process. The results obtained are compatible with parametrically induced noise squeezing. Notably, the noise spectrum provides information on the spin dynamics even in regimes where the macroscopic atomic coherence is lost, effectively enhancing the sensitivity of the measurements. Our work promotes spin noise spectroscopy as a versatile technique for the study of noise squeezing in a wide range of spin based magnetic sensors.