Quasiequilibria in open quantum systems

In this work, the steady-state or quasiequilibrium resulting from periodically modulating the Liouvillian of an open quantum system, (t), is investigated. It is shown that differences between the quasiequilibrium and the instantaneous equilibrium occur due to nonadiabatic contributions from the gauge field connecting the instantaneous eigenstates of (t) to a fixed basis. These nonadiabatic contributions are shown to result in an additional rotation and/or depolarization for a single spin-1/2 in a time-dependent magnetic field and to affect the thermal mixing of two coupled spins interacting with a time-dependent magnetic field.