Quantum transport in strongly interacting, ultracold fermi gases in box potentials

Abstract

Transport of strongly interacting fermions is crucial for systems as varied as high-𝑇 subscript 𝑐 superconductors, twisted bi-layer graphene, nuclear fission, and neutron stars. In this thesis, I will describe the experiments we performed to measure the transport properties of a strongly-interacting atomic Fermi gas. This system features interactions as strong as allowed by quantum mechanics and features one of the highest pairing strength, with a superfluid transition temperature on the order of the Fermi temperature. Moreover, it is also scale-invariant, making its properties directly relevant for systems with many order of magnitude higher densities. We trap these atoms in a uniform box potential made from repulsive laser light, the key experimental advancement that makes the transport experiment presented here possible. Here, we observe a very low, universal, Heisenberg-uncertainty limited diffusion of both sound and heat by studying the propagation of sound waves and conduction of heat in a uniform gas. Similar to a growing number of high-𝑇 subscript 𝑐 superconductors, we observe anomalous transport properties, like the viscosity and thermal conductivity, that cannot be explained by a Fermi-liquid theory. We show the temperature dependence of all non-zero transport properties, which constitutes a complete characterization of transport phenomena in the spin-balanced, strongly-interacting Fermi gas. Our findings inform theories of fermion transport, with relevance for hydrodynamic flow of electrons, neutrons, and quarks.