Unambiguous identification of coherent states. II. Multiple resources

We analyze unambiguous identification of coherent states of an electromagnetic field. In particular, we study possible generalizations of an optical setup proposed in Sedlák et al. Phys. Rev. A 76 022326 (2007)]. We show how the unambiguous identification of coherent states can be performed in a general case when multiple copies of unknown and reference states are available. Under the condition that the experimental setup consists only of linear optical elements and photodetectors, we prove the optimality of the setup. We also investigate whether reference states after the measurement can be “recovered” and further used for subsequent unambiguous identification tasks. We show that in spite of the fact that the recovered reference states are disturbed by measurements, they can be repeatedly used for unambiguous identifications. We analyze the influence of particular type of noise in the preparation of the unknown and the reference coherent states on the performance of our unambiguous-identification setup.