Interferometric Measurement of Local Spin-Fluctuations in a Quantum Gas

TL;DR

This paper demonstrates a quantum-limited interferometric technique to measure local spin-fluctuations in ultracold Fermi gases, revealing reduced spin noise and magnetic susceptibility, advancing understanding of quantum magnetism.

Contribution

It introduces a high-resolution atom-light interferometer for local spin measurements, enabling direct observation of spin-fluctuations and magnetic properties in quantum gases.

Findings

Measured spin-fluctuations reduced below shot-noise levels

Observed stronger spin-fluctuation suppression in strongly interacting gases

Deduced magnetic susceptibility as a function of temperature

Abstract

The subtle interplay between quantum statistics and interactions is at the origin of many intriguing quantum phenomena connected to superfluidity and quantum magnetism. The controlled setting of ultracold quantum gases is well suited to study such quantum correlated systems. Current efforts are directed towards the identification of their magnetic properties, as well as the creation and detection of exotic quantum phases. In this context, it has been proposed to map the spin-polarization of the atoms to the state of a single-mode light beam. Here we introduce a quantum-limited interferometer realizing such an atom-light interface with high spatial resolution. We measure the probability distribution of the local spin-polarization in a trapped Fermi gas showing a reduction of spin-fluctuations by up to 4.6(3) dB below shot-noise in weakly interacting Fermi gases and by 9.4(8) dB for strong interactions. We deduce the magnetic susceptibility as a function of temperature and discuss our measurements in terms of an entanglement witness.