This thesis summarizes experimental work investigating strongly interacting Fermi gases in two and three dimensions. Radio-frequency spin manipulation is used to initialize and probe strongly interacting Fermi gases dynamically to measure relaxation to a steady-state. Time-resolved spectroscopy is used to discover the p-wave contacts by observing how correlations in the system develop after quenching the atoms into an interacting state. By combining quasi-steady state measurements with new contact relations, an attractive p-wave interaction energy as large as half the Fermi energy is inferred. Spin echo measurements of the magnetization dynamics are used to observe spin transport in two and three dimensions in the presence of strong interactions. The bare spin diffusivity is distinguished from the Leggett-Rice effect, in which demagnetization is slowed by precession of a spin current around the local magnetization. Observations of the demagnetization dynamics support the conjecture that a general quantum bound on spin transport is obeyed where the diffusivity D greater than or similar to ħ/m, where m is the particle mass.
We revisit early suggestions to observe spin-charge separation (SCS) in cold-atom settings in the time domain by studying one-dimensional repulsive Fermi gases in a harmonic potential, where pulse perturbations are initially created at the center of the trap. We analyze the subsequent evolution using generalized hydrodynamics (GHD), which provide an exact description, at large space-time scales, for arbitrary temperature
T, particle density, and interactions. At
T=0 and vanishing magnetic field, we find that, after a nontrivial transient regime, spin and charge dynamically decouple up to perturbatively small corrections which we quantify. In this limit, our results can be understood based on a simple phase-space hydrodynamic picture. At finite temperature, we solve numerically the GHD equations, showing that for low
T>0 effects of SCS survive and characterize explicitly the value of
T for which the two distinguishable excitations melt.
The concept of indistinguishability is the key element in quantum statistics. But, are particles really either indistinguishable or distinguishable? Most works begin with the premise that all the particles, for example, in a quantum gas, are indistinguishable. Can we vary the degree of distinguishability in some controlled, continuous manner and see how it affects the behavior of the quantum gas, such as Bose-Einstein condensation (BEC)? We have found a complex parameter with a definite phase that does just that. As it deviates from zero, a gas mixture of originally indistinguishable bosons would divide into several distinct species that undergo BEC individually. Each species is found to be in a new type of atomic state whose spin structure adapts itself to the prevailing densities of the gases in the mixture.