title: Quantum Discord for d⊗2 Systems.
abstract: We present an analytical solution for classical correlation, defined in terms of linear entropy, in an arbitrary system when the second subsystem is measured. We show that the optimal measurements used in the maximization of the classical correlation in terms of linear entropy, when used to calculate the quantum discord in terms of von Neumann entropy, result in a tight upper bound for arbitrary d⊗2 systems. This bound agrees with all known analytical results about quantum discord in terms of von Neumann entropy and, when comparing it with the numerical results for 10(6) two-qubit random density matrices, we obtain an average deviation of order 10(-4). Furthermore, our results give a way to calculate the quantum discord for arbitrary n-qubit GHZ and W states evolving under the action of the amplitude damping noisy channel.
authors.affiliation: 1] Department of Mathematics, Shanghai Jiaotong University, Shanghai 200240, China [2] Department of Physics and Astronomy, University College London, WC1E 6BT London, United Kingdom.
authors.forename: Zhihao
authors.initials: Z
authors.lastname: Ma
authors.affiliation: 1] Department of Mathematics, College of Science, Zhejiang University of Technology, Hangzhou 310023, China [2] Centre for Quantum Technologies, National University of Singapore, 117543 Singapore.
authors.forename: Zhihua
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Departamento de Física, Faculdade de Ciências, Universidade Estadual Paulista.
authors.forename: Felipe Fernandes
authors.initials: FF
authors.lastname: Fanchini
authors.affiliation: 1] School of Mathematical Sciences, Capital Normal University, Beijing 100048, China [2] Max-Planck-Institute for Mathematics in the Sciences, 04103 Leipzig, Germany.
authors.forename: Shao-Ming
authors.initials: SM
authors.lastname: Fei