Singular perturbation approximations for a class of linear complex quantum systems

This paper considers the use of singular perturbation approximations for a class of linear complex quantum systems arising in the area of quantum optics. The class of linear complex quantum systems under consideration arises in systems consisting of interconnections of passive optical components such as cavities, beams splitters and phase shifters. The main result of the paper shows that for a class of singular perturbations of such systems, the approximate reduced dimension quantum system and guaranteed to be physically realizable.