Problem of quantifying quantum correlations with non commutative discord

A. MAJTEY; D. BUSSANDRI; T. OSÁN; P.W. LAMBERTI; A. VALDÉS HERNÁNDEZ

QUANTUM INFORMATION PROCESSING

SPRINGER

Lugar: Berlin; Año: 2017 vol. 16 p. 1 - 12

1570-0755

In this work we analyze a non-commutativity measure of quantum correlationsrecently proposed by Guo (Sci Rep 6:25241, 2016). By resorting to a systematicsurvey of a two-qubit system, we detected an undesirable behavior of such a measure related to its representation-dependence. In the case of pure states, this dependence manifests as a non-satisfactory entanglement measure whenever a representation other than the Schmidt?s is used. In order to avoid this basis-dependence feature, we argue that a minimization procedure over the set of all possible representations of the quantum state is required. In the case of pure states, this minimization can be analytically performed and the optimal basis turns out to be that of Schmidt?s. In addition, theresulting measure inherits the main properties of Guo?s measure and, unlike the latter, it reduces to a legitimate entanglement measure in the case of pure states. Some examples involving general mixed states are also analyzed considering such an optimization. The results show that, in most cases of interest, the use of Guo?s measure can result in an overestimation of quantum correlations. However, since Guo?s measure has the advantage of being easily computable, it might be used as a qualitative estimator of the presence of quantum correlations.