Transport is the defining property of states of matter, but often the most difficult to understand. Strongly interacting Fermi gases are especially challenging, despite their ubiquitous presence across many fields of physics.
Experiments on ultracold fermionic atoms allow the direct measurement of transport properties in ideal model systems where the hamiltonian is precisely known while transport properties are difficult to calculate theoretically.
In this talk I will present transport measurements on two strongly interacting Fermi systems, the unitary Fermi gas and the Fermi-Hubbard gas, both realized in uniform box potentials. In the unitary gas, we excite first and, for the superfluid, also second sound waves and demonstrate a quantum limited sound diffusivity given by hbar over the particle mass. For the Fermi-Hubbard gas, we measure spin diffusion and spin conductivity in the Mott insulator at half filling. Our experiments provide benchmarks for future theoretical calculations of these transport coefficients.