# Parametric amplification and noise-squeezing in room temperature atomic vapours

## TL;DR

This paper demonstrates room-temperature atomic vapours can be coherently manipulated using parametric excitation, leading to noise-squeezing that significantly enhances measurement sensitivity and magnetometer performance.

## Contribution

It introduces a novel application of parametric excitation in atomic vapours at room temperature, achieving noise-squeezing and improved magnetometry.

## Key findings

- Noise-squeezing enhances signal-to-noise ratio by up to 10 times.
- Magnetometer performance improves by a factor of 3.
- Resonances at parametric process frequencies observed in atomic coherences.

## Abstract

We report on the use of parametric excitation to coherently manipulate the collective spin state of an atomic vapour at room temperature. Signatures of the parametric excitation are detected in the ground-state spin evolution. These include the excitation spectrum of the atomic coherences, which contains resonances at frequencies characteristic of the parametric process. The amplitudes of the signal quadratures show amplification and attenuation, and their noise distribution is characterized by a strong asymmetry, similarly to those observed in mechanical oscillators. The parametric excitation is produced by periodic modulation of the pumping beam, exploiting a Bell-Bloom-like technique widely used in atomic magnetometry. Notably, we find that the noise-squeezing obtained by this technique enhances the signal-to-noise ratio of the measurements up to a factor of 10, and improves the performance of a Bell-Bloom magnetometer by a factor of 3.