Numerical Renormalization-Group Approach to the Non-Equilibrium Dynamics of Quantum Impurity Problems

We present a novel approach to time dependent non-equilibrium quantum impurity problems. It is based on a combination of Feynman's concept of a reduced density matrix and Wilson's numerical renormalization group. We discuss how dissipation and decoherence arises and benchmark our algorithm using the known exact solution of the resonant-level model. Depending on the cutoff scheme, all states are needed for tracking the full time evolution, for which we show a suitable resummation procedure. As a first application, we extract the two different time scales for spin- and charge-relaxation processes in the single impurity Anderson model. An outlook for pulse-driven quantum dot problems will be given.