Zhi-Xi Wang

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We study the level surfaces of quantum discord for a class of two-qubit states with parallel nonzero Bloch vectors. The dynamic behavior of quantum discord under decoherence is investigated. It is shown that a class of X states has sudden transition between classical and quantum correlations under decoherence. Our results include the ones in [Phys. Rev.(More)
We present a set of inequalities for detecting quantum entanglement of 2 ⊗ d quantum states. For 2 ⊗ 2 and 2 ⊗ 3 systems, the inequalities give rise to sufficient and necessary separability conditions for both pure and mixed states. For the case of d > 3, these inequalities are necessary conditions for separability, which detect all entangled states that(More)
Explicit sufficient and necessary conditions for separability of N-dimensional rank two multiparty quantum mixed states are presented. A nonseparability inequality is also given, for the case where one of the eigenvectors corresponding to nonzero eigenvalues of the density matrix is maximally entangled. Quantum entanglement is playing an essential role in(More)
It is shown that the dissonance, a quantum correlation which is equal to quantum discord for separable state, is required for assisted optimal state discrimination. We find that only one side discord is required in the optimal process of assisted state discrimination, while another side discord and entanglement is not necessary. We show that the quantum(More)
We present a quantum secure direct communication scheme achieved by swapping quantum entanglement. In this scheme a set of ordered Einstein-Podolsky-Rosen (EPR) pairs is used as a quantum information channel for sending secret messages directly. After insuring the safety of the quantum channel, the sender Alice encodes the secret messages directly by(More)
We discuss a kind of generalized concurrence for a class of high dimensional quantum pure states such that the entanglement of formation is a monotonically increasing convex function of the generalized concur-rence. An analytical expression of the entanglement of formation for a class of high dimensional quantum mixed states is obtained. Characterized by(More)