We will present two paradigmatic and extreme experimental studies, exploiting strongly interacting ultracold Fermi gases of 6Li atoms confined in optical potentials.
In a first experiment, we create the analogous of a Josephson junction by bisecting BEC-BCS crossover superfluids with a thin optical barrier. We observe coherent dynamics in both the population and in the relative phase between the two superfluid reservoirs, extracting the Josephson coupling energy, which appears to be maximum for unitary superfluids. For critical parameters, we see how the Josephson dynamics is strongly affected by the presence of topological defects entering the superfluid bulk.
In a second experiment, we create an artificial ferromagnetic state by segregating degenerate spin mixtures into two initially disconnected reservoirs. We study the spin dynamics for different interaction strengths and temperatures. For sufficiently high values of the inter-spin repulsive interactions and at sufficiently low temperatures, we observe a time window during which spin diffusion is zeroed, that we interpret as signature of the Stoner instability in our system.Parallel to this, we reveal the ferromagnetic behaviour of the system by observing a softening of the spin dipole mode. At long evolution times, once the ferromagnetic state has relaxed onto lower energy states of the many-body system, our measurements provide exciting new insights into the behaviour of the spin drag coefficient within temperature regimes so far not accessed in previous experiments.
