A new stochastic method for the direct computation of real-time Green’s functions is proposed. The inherent sign problem is circumvented by partitioning the path integration into two parts, one of which involves conventional stochastic sampling, and the other explicit or analytical summation. Using this method, the dynamics of the spin-boson model may be computed up to several tunneling periods. The results reveal surprisingly complex relaxation behaviors near the coherent-incoherent boundary at low temperatures.

• Received 23 October 1991

DOI:https://doi.org/10.1103/PhysRevLett.68.899