We discuss the derivation of master equation when there exists an initial correlation between the system and the reservoir. The mixing property of the reservoir dynamics is crucial.
There are numerous examples in physics that can be modeled by the interaction between a small system of interest and a reservoir. The interaction typically leads to the irreversible decay of the system variables. As the system evolves into an equilibrium state, various parameters such as mean values, probabilities, and variances change until the final steady state is reached. The evolution of a system coupled to a reservoir with a short memory is often described by a master equation for the reduced density operator of the system. Master equations are important in physics because of their generality and hence wide range of applicability [1].
We consider the reduced dynamics of a small quantum system in interaction with a reservoir when the initial state is factorized. We present a rigorous derivation of a GKLS master equation in the weak-coupling limit for a generic bath, which is not assumed to have a bosonic or fermionic nature, and whose reference state is not necessarily thermal. The crucial assumption is a reservoir state endowed with a mixing property: the n-point connected correlation function of the interaction must be asymptotically bounded by the product of two-point functions (clustering property).
In this paper, the exact non-Markovian dynamics of open quantum systems in the presence of initial system-reservoir correlations is investigated for a photonic cavity system coupled to a general non-Markovian reservoir. The exact time-convolutionless master equation incorporating with initial system-reservoir correlations is obtained. The non-Markovian dynamics of the reservoir and the effects of the initial correlations are embedded into the time-dependent coefficients in the master equation. We show that the effects induced by the initial correlations play an important role in the non-Markovian dynamics of the cavity but they are washed out in the steady-state limit in the Markovian regime. Moreover, the initial two-photon correlation between the cavity and the reservoir can induce nontrivial squeezing dynamics to the cavity field.