Open Quantum Systems Initially Correlated with their Environment

Abstract

Most descriptions of open quantum system dynamics assume a product initial state between the system and its environment, as the presence of correlations causes both practical and conceptual difficulties in characterizing the evolution of the open system. In this thesis we study initially correlated states by employing an operational approach to open quantum dynamics, which resolves these problems by mapping initial preparations to future states. We apply this framework to study the dynamics of systems initially in global thermal equilibrium and we distinguish between classical and quantum correlations as classified by the notion of quantum discord. Regarding the former, we solve for the exact dynamics of the spin-boson pure dephasing model and study the effect that initial correlations have on the geometry of the decoherence in the Bloch-sphere, while also presenting an analytical treatment of a general class of pure dephasing models. We then move into the quantum domain and derive a family of weak-coupling master equations using second-order perturbation theory in the system-environment coupling. The obtained equation contains a non-negligible inhomogeneous correction term to the conventional Born-Markov master equation and is a general theoretical tool that can be applied to many physical models in the weak-coupling regime.