Abstract
We propose a measure of nonclassical correlations in bipartite quantum states based on local unitary operations. We prove that the measure is nonzero if and only if the quantum discord is nonzero; this is achieved via a new characterization of zero discord states in terms of the state's correlation matrix. Moreover, our scheme can be extended to ensure that the same relationship holds even with a generalized version of quantum discord in which higher-rank projective measurements are allowed. We next derive a closed-form expression for our scheme in the cases of Werner states and -dimensional systems. The latter reveals that for -dimensional states, our measure reduces to the geometric discord [Dakić et al., Phys. Rev. Lett. 105, 190502 (2010)]. A connection to the Clauser-Horne-Shimony-Holt inequality is shown. We close with a characterization of all maximally nonclassical, yet separable, -dimensional states of rank at most 2 (with respect to our measure).
- Received 11 February 2012
DOI:https://doi.org/10.1103/PhysRevA.86.042106
©2012 American Physical Society