Entanglement and thermalization in open fermion systems

Abstract

We numerically study two non-interacting fermion models, a quantum wire model and a Chern insulator model, governed by open system Lindblad dynamics. The physical setup consists of a unitarily evolving "bulk" coupled via its boundaries to two dissipative "leads". The open system dynamics is chosen to drive the leads to thermal equilibrium, and by choosing different temperatures and chemical potentials for the two leads we may drive the bulk into a non-equilibrium current carrying steady state. We report two main results in this context. First, we show that for an appropriate choice of dynamics of the leads, the bulk state is also driven to thermal equilibrium even though the open system dynamics does not act directly on it. Second, we show that the steady state which emerges at late time, even in the presence of currents, is lightly entangled in the sense of having small mutual information and conditional mutual information for appropriate regions. We also report some results for the rate of approach to the steady state. These results have bearing on recent attempts to formulate a numerically tractable method to compute currents in strongly interacting models; specifically, they are relevant for the problem of designing simple leads that can drive a target system into thermal equilibrium at low temperature.