Discrimination And Estimation Of Quantum Information

This paper focuses on getting applicable information from quantum systems, discussingproblems of discriminating mixed quantum states, designing programmablediscriminators, and estimating the purity of quantum systems. To be more specific:1. We denote that the problem of unambiguously discriminating mixed quantumstates can be reduced to the problem of set discrimination. An upper bound of thesuccess probability is also provided.2. The present paper offers a necessary and sufficient condition for designingunambiguous programmable discriminators. We also offer a set of universal programmablediscriminator, which can also be utilized to unambiguously discriminatemixed states.3. Estimation of the purity of quantum systems is also studied in the presentpaper. First, we consider the problem of discriminating whether a quantum systemis in a pure state. Then, through analyzing results of discriminations, the purity ofquantum systems can be well estimated. The scheme can also be applied in estimatingthe eigenvalues of quantum states, and Schmidt number of composite systems.