Linear optical realization of unambiguous quantum state comparison

In this paper, we propose an experimental scheme for unambiguousquantum state comparison assisted by linear optical manipulations,twin-photons produced from parametric down-conversion, andpostselection from the coincidence measurement. In this scheme thepreparation of the general two mixed qubit states with arbitraryprior probabilities and the realization of the optimal POVMs forunambiguous quantum state comparison are presented. This proposal isfeasible by current experimental technology, and may be used insingle-qubit quantum fingerprinting.