Seminarium Optyczne

Unitary transformations are routinely modeled and implemented in thefield of quantum optics. In contrast, nonunitary transformations thatcan involve loss and gain require a different approach. In this theorytalk, a universal method to deal with nonunitary networks will beintroduced. An input to the method is an arbitrary lineartransformation matrix of optical modes that does not need to adhere tobosonic commutation relations. The method constructs a transformationthat includes the network of interest and accounts for full quantumoptical effects related to loss and gain. Furthermore, through adecomposition in terms of simple building blocks it provides astep-by-step implementation recipe, in a manner similar to thedecomposition introduced by Reck et al. in their seminal paper [Phys.Rev. Lett. 73, 58 (1994)] but applicable to nonunitarytransformations. Applications of the method include the implementationof positive-operator-valued measures and the design of probabilisticoptical quantum information protocols.