# Measuring the Hydrodynamic Linear Response of a Unitary Fermi Gas

## TL;DR

This study experimentally measures how a unitary Fermi gas responds hydrodynamically to a moving optical potential, revealing insights into its thermal conductivity and relaxation dynamics across different flow regimes.

## Contribution

It provides the first direct observation of the hydrodynamic linear response of a unitary Fermi gas in a controlled box potential environment.

## Key findings

- Density profile changes depend on thermal conductivity.
- Response varies between subsonic and supersonic speeds.
- Thermal relaxation rates are characterized by temperature gradient relaxation.

## Abstract

We directly observe the hydrodynamic linear response of a unitary Fermi gas confined in a box potential and subject to a spatially periodic optical potential that is translated into the cloud at speeds ranging from subsonic to supersonic. We show that the time-dependent change of the density profile is sensitive to the thermal conductivity, which controls the relaxation rate of the temperature gradients and hence the responses arising from adiabatic and isothermal compression.