期刊
PHYSICAL REVIEW A
卷 84, 期 4, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevA.84.042313
关键词
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资金
- National Research Foundation
- Ministry of Education, Singapore [WBS: R-710-000-008-271]
- NNSF of China [11075227, 10935010]
Quantum discord provides a measure for quantifying quantum correlations beyond entanglement and is very hard to compute even for two-qubit states because of the minimization over all possible measurements. Recently a simple algorithm to evaluate the quantum discord for two-qubit X states was proposed by Ali, Rau, and Alber [Phys. Rev. A 81, 042105 (2010)] with minimization taken over only a few cases. Here we shall at first identify a class of X states, whose quantum discord can be evaluated analytically without any minimization, for which their algorithm is valid, and also identify a family of X states for which their algorithm fails. And then we demonstrate that this special family of X states provides furthermore an explicit example for the inequivalence between the minimization over positive operator-valued measures and that over von Neumann measurements.
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