Sound in a Unitary Fermi Gas

Low temperature thermodynamics and transport properties of systems ranging from solids to quantum gases are determined by phonons (sound). We measure important properties of phonons in a homogeneous unitary Fermi gas, including its dispersion relation and quantum limited attenuation. We present our measurements of the sound diffusion coefficient, a quantity which fully characterizes sound attenuation, and is closely related to viscosity and thermal conductivity of the Fermi gas.