The dynamics of spin-boson systems at very low temperatures has been studied using a real-time path-integral simulation technique, which combines a stochastic Monte Carlo sampling over the quantum fluctuations with an exact treatment of the quasiclassical degrees of freedom. To a large degree, this special technique circumvents the dynamical sign problem and allows the dynamics to be studied directly up to long real times in a numerically exact manner. This method has been applied to two important problems: (1) crossover from nonadiabatic to adiabatic behavior in electron-transfer reactions, (2) the zero-temperature dynamics in the antiferromagnetic Kondo region 1/2<K<1, where K is Kondo’s parameter.

• Received 1 June 1994

DOI:https://doi.org/10.1103/PhysRevB.50.15210