Realization And Application Of Positive-Operator-Valued Mrasure

In recent years, based on the principles of quantum mechanics, quantum in-formation theory are starting a new era of information processing, because it can handle some tasks which are not possible classically. Entanglement, as one of the most important physical resource in quantum information and computation, has been extensively used to test quantum nonlocality and design quantum informa-tion protocols. Thus more and more attentions are paid on operations of entangled states between two body or multi-body system. In especial, mutual transformation between the maximal entangled state and the non-maximally entangled state some-times may directly influence the accuracy of information processing. Unlike the nor-mal orthogonal projection measurement, positive-operator-value measure (POVM) is a generalized measurement form, which don't need to require the orthogonality among measurement operators. And it has tremendous application value in quan-tum information and computation.In this paper, we first mainly investigate a proposal for implementing all pos-sible POVM of single spin qubit, and then we propose explicit quantum circuits for implementing a POVM, by which a class of relatively general entanglement con-version can be realized determinately. In the first proposal, the POVM realization process is accomplished from the free evolution of the Heisenberg XX model by introducing another spin qubit as auxiliary and considering nearest-neighbor spin interaction. A controlled-NOT (CNOT) gate, which is a significant operator for our scheme is also constructed and the generalization to multiple-operator is considered finally. In the second proposal, we propose explicit quantum circuits for implement-ing a set of POVMs. And it has been shown that the controlled quantum logical gates in our circuits can be realized under the condition of current experimental technologies.