  A hybrid approach to nonequilibrium dynamics of quantum impurity systems is
presented. The numerical renormalization group serves as a means to generate a
suitable low-energy Hamiltonian, allowing for an accurate evaluation of the
real-time dynamics of the problem up to exponentially long times using
primarily the time-adaptive density-matrix renormalization group. We extract
the decay time of the interaction-enhanced oscillations in the interacting
resonant-level model and show their quadratic divergence with the interaction
strength U. Our numerical analysis is in excellent agreement with analytic
predictions based on an expansion in 1/U.
