Hydrodynamic Relaxation in a Strongly Interacting Fermi Gas

We report new time-domain, free evolution methods for measuring hydrodynamic transport coefficients in a strongly interacting Fermi gas. We measure the free decay of a spatially periodic density profile in a two-state mixture of ⁶Li in the normal fluid phase, confined in a box potential. This spatial profile is initially created in thermal equilibrium by a perturbing potential. After the perturbation is abruptly extinguished, the dominant spatial Fourier component exhibits an exponentially decaying (thermally diffusive) mode and a decaying oscillatory (first sound) mode, enabling independent measurement of the thermal conductivity and the shear viscosity directly.