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On the optimal measurement for quantum discord of two-qubit states (1110.6681v1)
Published 31 Oct 2011 in quant-ph
Abstract: We present an efficient method to solve the quantum discord of two-qubit X states exactly. A geometric picture is used to clarify whether and when the general POVM measurement is superior to von Neumann measurement. We show that either the von Neumann measurement or the three-element POVM measurement is optimal, and more interestingly, in the latter case the components of the postmeasurement ensemble are invariant for a class of states.