Due to the fundamental limitations related to the Heisenberg uncertainty principle and the non-cloning theorem, it is impossible, even in principle, to determine the quantum state of a single system without a priori knowledge of it. To discriminate nonorthogonal quantum states in some optimal way, a priori knowledge of the discriminated states has to be relied upon. In this paper, we thoroughly investigate some impact of a priori classical knowledge of two quantum states on the optimal unambiguous discrimination. It is exemplified that a priori classical knowledge of the discriminated states, incomplete or complete, can be utilized to improve the optimal success probabilities, whereas the lack of a prior classical knowledge can not be compensated even by more resources.
Unambiguous discrimination between linearly independent quantum states
