Physics – Quantum Physics
Scientific paper
2011-07-12
Journal of Physics A: Mathematical and Theoretical 44, 415304 (2011)
Physics
Quantum Physics
21 pages, 5 figures, revised version
Scientific paper
Among various definitions of quantum correlations, quantum discord has attracted considerable attention. To find analytical expression of quantum discord is an intractable task. In this paper, we discuss thoroughly the case of two-qubit rank-two states. An analytical expression for the quantum discord is obtained by means of Koashi-Winter relation. A geometric picture is demonstrated by means of quantum steering ellipsoid. We point out that in this case the optimal measurement is indeed the von Neumann measurement, which is usually used in the study of quantum discord. However, for some two-qubit states with the rank larger than two, we find that three-element POVM measurement is more optimal. It means that more careful attention should be paid in the discussion of quantum discord.
Du Jiangfeng
Jiang Fengjian
Shi Mingjun
Yang Wei
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