Thermodynamic Measurements in a Strongly Interacting Fermi Gas

TL;DR

This study measures thermodynamic properties of a strongly interacting Fermi gas, providing precise, model-independent data that calibrate temperature scales and validate theoretical predictions about superfluidity and thermodynamics.

Contribution

It offers the first experimental calibration of temperature in strongly interacting Fermi gases using model-independent thermodynamic measurements.

Findings

Good agreement with recent theoretical predictions.

Calibration shows the ideal gas temperature at pair condensation onset matches the critical temperature.

Provides estimates of chemical potential and heat capacity from thermodynamic data.

Abstract

We conduct a series of measurements on the thermodynamic properties of an optically-trapped strongly interacting Fermi gas, including the energy $E$, entropy $S$, and sound velocity $c$. Our model-independent measurements of $E$ and $S$ enable a precision study of the finite temperature thermodynamics. The $E(S)$ data are directly compared to several recent predictions. The temperature in both the superfluid and normal fluid regime is obtained from the fundamental thermodynamic relation $T=\partial E/\partial S$ by parameterizing the $E(S)$ data. Our $E(S)$ data are also used to experimentally calibrate the endpoint temperatures obtained for adiabatic sweeps of the magnetic field between the ideal and strongly interacting regimes. This enables the first experimental calibration of the temperature scale used in experiments on fermionic pair condensation. Our calibration shows that the ideal gas temperature measured for the onset of pair condensation corresponds closely to the critical temperature estimated in the strongly interacting regime from the fits to our $E(S)$ data. The results are in very good agreement with recent predictions. Finally, using universal thermodynamic relations, we estimate the chemical potential and heat capacity of the trapped gas from the $E(S)$ data.