Fidelities for transformations of unknown quantum states

Abstract

We present a general theoretical formalism to compute the fidelity of transformations of unknown quantum states. We then focus on the case of Gaussian transformations of continuous variable quantum systems, where, for the case of a Gaussian distribution of displaced coherent states, the theory is readily tractable by a covariance matrix formalism. We present analytical results for recently implemented teleportation and memory storage protocols for continuous variables.