Transport measurements of the unitary Fermi gas*

Understanding transport in strongly interacting Fermi gases is one of the most significant challenges of many-body physics. Here, we present recent measurements of the transport properties of a homogeneous, strongly interacting Fermi gas of $^6$Li atoms in the unitarity limit. We study the coupled transport of momentum and heat through the attenuation of the first-(density wave) and second-sound (entropy wave). Using a novel local thermometer, we observe the local temperature variations of second sound and measure the thermal diffusivity as well as the superfluid fraction. These results exclude a Fermi liquid description for the unitary Fermi gas and instead reveal a diffusivity attaining the Heisenberg limit, given by $\hbar/m$.