Revisiting Quantum Discord for Two-Qubit X States: The Error Bound to an Analytical Formula
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In this article, we investigate the error bound of quantum discord, obtained from the analytic formula of Ali et al. (Phys. Rev. A 81, 042105, 2010) for the case of general X states and from the analytic formula of Fanchini et al. (Phys. Rev. A 81, 052107, 2010) for the case of symmetric X states. For this purpose we consider 3-element POVM. We find that the results of Ali et al. and Fanchini et al. may have the worst-case errors of 0.004565 and 0.0009, respectively.
KeywordsQuantum discord Quantum correlation
This work is supported by the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (NRF-2010-0025620).