摘要

With the quantum state filtering as a known example, it has been shown that the unambiguous discrimination between subsets of nonorthogonal quantum states is possible with a certain possibility of success. In present work, besides reconsidering the known case of quantum state filtering, we also ask what happens if parts of the states are shared by both the subsets or if there are more than two subsets. The procedure, which is designed to find the optimal way for quantum set discrimination, contains two steps. For each case, we at first construct a one-photon interferometer (OPI) to realize the unambiguous discrimination in an enlarged Hilbert space according to the Neumark's theorem. The awards from the OPI are double: an optical experiment and the operators in terms of positive operator-valued measures. Then, with the operators from its corresponding OPI and the given a priori probability for each state, we are able to find out the optimal operators which can discriminate the subsets in an optimal way. It is shown that the OPIs, which have been discussed in present work, can be constructed by taking the quantum state filtering as their elementary process. This fact indicates that the problem of quantum set discrimination can be reduced to the known problem of quantum state filtering.