Spin transport at non-equilibrium interfaces in the unitary Fermi gas*

Quantum gases of fermionic atoms provide a model system for studying the dynamics of strongly correlated fermions. A multi-region box trap allows exploration of transport and equilibration by enabling samples prepared in different thermodynamic states to be brought into contact. In particular, a highly spin-polarized normal-phase region and a weakly spin-polarized superfluid region provide a non-equilibrium normal-superfluid interface. The two regions can evolve towards equilibrium by exchange of particles. We implement a phenomenological mean-field model and calculate the spin and mass currents across the interface between normal and superfluid regions. We find that transport into an unpolarized superfluid from a polarized normal fluid exhibits a threshold in the normal fluid polarization, analogous to the current-voltage curve of a normal-superconductor junction. However, the threshold nearly vanishes when the superfluid reaches critical polarization. We describe progress towards experimental realization of this system using a digital micromirror device (DMD) to create programmable barriers between regions of the trap.