A general approach to physical realization of unambiguous quantum-state   discrimination
  We present a general scheme to realize the POVMs for the unambiguous discrimination of quantum states. For any set of pure states it enables us to set up a feasible linear optical circuit to perform their optimal discrimination, if they are prepared as single-photon states. An example of unknown states discrimination is discussed as the illustration of the general scheme. 
Bing He, J\'anos A. Bergou