Comparison of equations for exact and approximate non-Markovian evolution

We consider an exactly solvable model for the multi-level system interacting with several reservoirs at low temperatures. We compare the population decay rates and decoherence rates predicted by exact solution and several approximate master equations: a second-order non-Markovian master equation (Born approximation master equation), both Markovian and non-Markovian Redfield master equations. Thus, we examine the accuracy of the widely used approximate master equations. The research was supported by Russian Science Foundation (project No. 17-71-20154).