We describe the nonequilibrium quench dynamics of the Sachdev-Ye-Kitaev models of fermions with random all-to-all interactions. These provide tractable models of the dynamics of quantum systems without quasiparticle excitations. The Kadanoff-Baym equations show that, at long times, the fermion two-point function has a thermal form at a final temperature determined by energy conservation, and the numerical analysis is consistent with a thermalization rate proportional to this temperature. We also obtain an exact analytic solution of the quench dynamics in the large
q limit of a model with
q fermion interactions: in this limit, the thermalization of the two-point function is instantaneous.
We consider the Sachdev-Ye-Kitaev (SYK) model, where interaction involves
q fermions at a time. We find the
1/q2 correction to the thermal two-point function in the large
q expansion. Using this result, we find the
1/q3 correction to the SYK free energy.