Accurate modeling of single quantum system dynamics under the truncated Wigner approximation

Theoretical modeling of the dynamics of open quantum systems remains a notoriously challenging endeavor. Existing dynamical methods typically treat interactions between quantum systems and their environment at the ensemble level and/or implicitly project out environmental degrees-of-freedom. Here, we present a nonadiabatic quantum dynamics formulation that relaxes these assumptions and, in contrast to the aforementioned class of methods, provides access to the dynamical interaction of single quantum systems with their environment. This formulation is based on the truncated Wigner approximation combined with a perturbative series describing transitions between quantum states. Whereas other approaches capable of describing single ensemble members exist, this method uniquely allows for a systematic improvement of accuracy up to the exact answer. We show that, even for challenging test cases, this method converges rapidly, making for an efficient simulation tool for studying single quantum system phenomena.