Quantum correlations in a family of bipartite separable qubit-qutrit quantum-classical correlated states are investigated by using two popular measures, i.e., the original quantum discord (OQD) method by Ollivier and Zurek [ Phys. Rev. Lett. 88 (2001) 017901 ] and the measurement-induced disturbance (MID) method by Luo [ Phys. Rev. A 77 (2008) 022301 ]. It is found that both of them are functions of a parameter partially characterizing the concerned states, however, quantum correlations evaluated via the convenient MID method are somewhat overestimated.
Measure-induced non-classicality( MINC) in a family of bipartite separable qubit-qutrit correlated states was evaluated by using the MID method proposed by the reference [Luo S L. Using measurement-induced disturbance to characterize correlations as classical or quantum[J]. Phys Rev A,2008,77: 022301]. Specifically,classical correlation in each state was derived via the spectrum resolution technique and then the MINC( i. e.,quantum correlation) was extracted. The MINC was amply analyzed so that some distinct features were exposed.
Quantum discord, a kind of quantum correlation, is defined as the difference between quantum mutual information and classical correlation in a bipartite system. In general, this correlation is different from entanglement, and quantum discord may be nonzero even for certain separable states. Even in the simple case of bipartite quantum systems, this different kind of quantum correlation has interesting and significant applications in quantum information processing. So far, quantum discord has been calculated explicitly only for a rather limited set of two-qubit quantum states and expressions for more general quantum states are not known. In this article, we derive explicit expressions for quantum discord for a larger class of two-qubit states, namely, a seven-parameter family of so called
X states that have been of interest in a variety of contexts in the field. We also study the relation between quantum discord, classical correlation, and entanglement for a number of two-qubit states to demonstrate that they are independent measures of correlation with no simple relative ordering between them.