Nonequilibrium dynamics of a system with quantum frustration

Abstract

Using flowequations and equilibrium and nonequilibrium dynamics of a two-level system (TLS) is investigated, which couples Ohmically via noncommuting components to two independent oscillator baths. In equilibrium, the two-level energy splitting is protected when the TLS is coupled symmetrically to both baths. A critical asymmetry angle separates the localized from the delocalized phase. Real-time decoherence of a nonequilibrium initial state is studied as well. The short-time dynamics exhibits initial slips on the scale of the cutoff frequency of the bath modes. Moreover, whereas for a single bath decay of coherence depends crucially on the chosen initial state, for a symmetric coupling to two baths this dependence vanishes.