Observation of the Fermionic Joule-Thomson Effect

We report the observation of the quantum Joule-Thomson (JT) effect in ideal and unitary Fermi gases. We study the temperature dynamics of these systems while they undergo an energy-per-particle conserving rarefaction. For scale-invariant systems, whose equations of state satisfy the relation $U\propto PV$, this rarefaction conserves the specific enthalpy, which makes it thermodynamically equivalent to a JT throttling process. We observe JT heating in an ideal Fermi gas, stronger at higher quantum degeneracy, a result of the repulsive quantum-statistical `force' arising from Pauli blocking. In a unitary Fermi gas, we observe that the JT heating is marginal in the temperature range $0.2 \lesssim T/T_{\mathrm{F}} \lesssim 0.8$ as the repulsive quantum-statistical effect is lessened by the attractive interparticle interaction.