  We study in a nonperturbative fashion the thermodynamics of a unitary Fermi
gas over a wide range of temperatures and spin polarizations. To this end, we
use the complex Langevin method, a first principles approach for strongly
coupled systems. Specifically, we show results for the density equation of
state, the magnetization, and the magnetic susceptibility. At zero
polarization, our results agree well with state-of-the art results for the
density equation of state and with experimental data. At finite polarization
and low fugacity, our results are in excellent agreement with the third-order
virial expansion. In the fully quantum mechanical regime close to the balanced
limit, the critical temperature for superfluidity appears to depend only weakly
on the spin polarization.
