| The discrimination of completely unknown quantum states is a difficult problem in quantum state discrimination. We study the general case of unknown qubit discrimination, where the input states are constructed with arbitrary number of the unknown qubits as the reference. The optimal measurements for the unknown qubit discrimination are derived in two different approaches. Implementation of unknown state discrimination is realized by unitary transformation in the extended space of inputs. To study the discrimination of unknown single photon states and unknown coherent states, we present the methods for linear optical realization of the general transformations on single photon states and coherent state products. Finally, we describe two physical systems for unknown optical qubit discrimination and unknown coherent state discrimination. One application of unknown coherent state discrimination is efficient and non-destructive quantum database searching. |
