Open hybrid quantum systems

The recent technological and scientific advances has allowed for the fabrication and ever-progressing characterization of interacting quantum mechanical systems. I focus on the theoretical description of such hybrid quantum systems. Specifically, I discuss two prototypical classes of light-matter systems: polaritonic and optomechanical systems. They are characterized by linear and nonlinear quantum mechanical interactions, respectively. I introduce possible physical realizations, discuss light-matter interaction giving rise to polaritons, and derive optomechanical interaction for a ferromagnetic system. The experimental reality also requires an understanding of dissipation and decoherence. I therefore describe how input-output formalism can be employed to model the optical response of open hybrid quantum systems. In addition, I discuss the possibility of the electromagnetic vacuum modifying chemistry by the formation of hybridized light-matter states, polaritons. These theoretical approaches to open hybrid quantum systems have wider applicability than their physical realizations and further elucidates the possibilities of light-matter interaction. This dissertation is composed of an introductory text and five publications — three of which have been published while two are under peer review at the time of writing.