A quantum cryptographic receiver, a method of achieving unambiguous state discrimination measurement of a coherent light state and a quantum cryptographic system incorporating the quantum cryptographic receiver or the method. In one embodiment, the quantum cryptographic receiver includes: (1) a beamsplitter that receives an incoming coherent state from a sender and splits the incoming coherent state into at least first and second separate coherent states and (2) at least one photodetector, associated with the beamsplitter, that is positionable with respect to the first and second separate coherent states to detect a presence of a photon therein at a particular phase, the presence revealing information originated by the sender.