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Correlation Distance and Bounds for Mutual Information
Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, QLD 4111, Australia
Received: 21 June 2013; in revised form: 21 August 2013 / Accepted: 3 September 2013 / Published: 6 September 2013
Abstract: The correlation distance quantifies the statistical independence of two classical or quantum systems, via the distance from their joint state to the product of the marginal states. Tight lower bounds are given for the mutual information between pairs of two-valued classical variables and quantum qubits, in terms of the corresponding classical and quantum correlation distances. These bounds are stronger than the Pinsker inequality (and refinements thereof) for relative entropy. The classical lower bound may be used to quantify properties of statistical models that violate Bell inequalities. Partially entangled qubits can have lower mutual information than can any two-valued classical variables having the same correlation distance. The qubit correlation distance also provides a direct entanglement criterion, related to the spin covariance matrix. Connections of results with classically-correlated quantum states are briefly discussed.
Keywords: mutual information; variational distance; trace distance; Pinsker inequality; quantum entanglement
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MDPI and ACS Style
Hall, M.J.W. Correlation Distance and Bounds for Mutual Information. Entropy 2013, 15, 3698-3713.
Hall MJW. Correlation Distance and Bounds for Mutual Information. Entropy. 2013; 15(9):3698-3713.
Hall, Michael J.W. 2013. "Correlation Distance and Bounds for Mutual Information." Entropy 15, no. 9: 3698-3713.