Flow equation calculation of transient and steady-state currents in the Anderson impurity model

Transient and steady-state currents through dc-biased quantum impurity models beyond the linear-response regime are of considerable interest, both from an experimental and a theoretical point of view. Here we present an analytical approach for the calculation of such currents based on the flow equation method (method of infinitesimal unitary transformations). Specifically, we analyze the Anderson impurity model in its mixed valence regime where the coupling to the leads is switched on suddenly at time t=0. We observe the real time buildup of the current until it reaches its steady-state limit.