Entropy production of a qubit out of the perturbative regime

The calculation of Rényi and von Neumann entropy production rates in open quantum systems has been explored by our group for simple systems in the weak coupling limit. However, there have been questions regarding the validity of certain results in higher perturbative order. We therefore investigate entropy flows in an environment that disturbs the quantum system so that perturbation theory is no longer applicable. In this case, our formalism of evaluating powers of density matrices has to be generalized for analogous quasi-density matrices and is thus different from the previous approach. We present the obtained results and discuss differences to the weak coupling case.