A multilevel blocking approach to the sign problem in real-time quantum Monte Carlo simulations

We propose a novel approach toward the general solution of the sign problem in real-time path–integral simulations. Using a recursive multilevel blocking strategy, this method circumvents the sign problem by synthesizing the phase cancellations arising from interfering quantum paths on multiple timescales. A number of numerical examples with one or a few explicit degrees of freedom illustrate the usefulness of the method.