The classical-quantum boundary for correlations: Discord and related measures

Kavan Modi*, Aharon Brodutch, Hugo Cable, Tomasz Paterek, Vlatko Vedral

*Corresponding author for this work

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    One of the best signatures of nonclassicality in a quantum system is the existence of correlations that have no classical counterpart. Different methods for quantifying the quantum and classical parts of correlations are among the more actively studied topics of quantum-information theory over the past decade. Entanglement is the most prominent of these correlations, but in many cases unentangled states exhibit nonclassical behavior too. Thus distinguishing quantum correlations other than entanglement provides a better division between the quantum and classical worlds, especially when considering mixed states. Here different notions of classical and quantum correlations quantified by quantum discord and other related measures are reviewed. In the first half, the mathematical properties of the measures of quantum correlations are reviewed, related to each other, and the classical-quantum division that is common among them is discussed. In the second half, it is shown that the measures identify and quantify the deviation from classicality in various quantum-information- processing tasks, quantum thermodynamics, open-system dynamics, and many-body physics. It is shown that in many cases quantum correlations indicate an advantage of quantum methods over classical ones.

    Original languageEnglish
    Article number1655
    Pages (from-to)1655-1707
    Number of pages53
    JournalReviews of Modern Physics
    Issue number4
    Publication statusPublished - 26 Nov 2012

    Bibliographical note

    Modi,Kavan; Brodutch,Aharon; Cable,Hugo; Paterek,Tomasz and Vedral,Vlatko, Reviews of Modern Physics, 84(4), pp. 1655-1707, 2012. Copyright (2012) by the American Physical Society. The original article can be found at


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