REDFIELD THEORY IS QUANTITATIVE FOR COUPLED HARMONIC-OSCILLATORS

We investigate the accuracy of Redfield theory predictions for the dynamics of a fully quantum-mechanical system-bath problem. Both the system and the bath in this model are harmonic oscillators, and the system is coupled linearly to the bath. This model can be solved exactly using well-known numerical techniques. We compare exact numerical calculations to the predictions of Redfield theory for a variety of coupling strengths. The expectation value of the system number operator and the system position autocorrelation function are the dynamical quantities we use in our comparisons. For those extreme cases in which Redfield theory does not exhibit good quantitative agreement, assumptions of Redfield theory are relaxed to obtain better approximations to the exact result.