CONVERGENCE AND PATH CANCELLATION IN QUANTUM MONTE-CARLO REAL-TIME PATH INTEGRATION

We find that poor resolution of the tails of the distribution of integ rands obtained inhibits convergence in Monte Carlo calculation of real time path integrals. We show that many methods previously tried to im prove convergence neither resolve nor diminish the tails effectively. We find that large contributions to the integrand come from paths that have a large variance from the zero-path and/or that have few zero cr ossings. The results of crude dampings based on where such paths are p oorly sampled suggest that exploring cancellations of paths characteri zed by path variance and zero crossings may be effective in improving convergence. (C) 1996 American Institute of Physics.