Thermalization dynamics of a dissipative two-level system in a Fermi bath with contact interactions*

We study the dynamics of a quasi-homogeneous Fermi gas under a strong internal-state drive. A highly spin-imbalanced weakly-interacting mixture is created in two internal states in a box trap. The minority is then driven to a third internal state with a radio-frequency field, where this third state interacts via unitary limited interactions with the majority. We investigate the dynamics of the minority under a strong drive with a Rabi frequency much larger than the Fermi energy of the host atoms. We extract the Rabi frequency renormalized by interactions and the relaxation of the effective magnetization (the relative population difference). We observe that after a few cycles, the system reaches a non-trivial steady state characterized by a detuning-dependent magnetization. This system is understood as dissipative two-level systems, which evolve to their thermal equilibrium state via interactions with the fermionic bath. We extract the effective T1 and T2 times characterizing the decay to the steady-state as well as the mean-field shift of the resonance frequency of the two-level systems. Our study paves the way to studying equilibrium states of unitary Fermi gases in the presence of strong driving fields.