Quantum Joule-Thomson Effect in Universal Fermi Gases

We investigate the temperature dynamics of a homogeneous Fermi gas during energy-independent losses induced by collisions with background particles. For both ideal and unitary Fermi gases, the enthalpy is proportional to the total energy of the gas and the specific enthalpy is therefore conserved in the process, making it thermodynamically equivalent to a Joule-Thomson rarefaction. We perform the thermometry by time-of-flight imaging for the ideal Fermi gas and by radio-frequency spectroscopy for the unitary Fermi gas. We observe isoenthalpic heating for both ideal and unitary Fermi gases, in contrast to cooling previously observed in excited-population-saturated uniform Bose gases.