On the upper bound of classical correlations in a bipartite quantum system

Abstract For a bipartite quantum system consisting of subsystems A and B it was shown by Zhang et al (2012 Phys. Lett . A 376 3588–92) that the amount of classical correlations, which is used to define the quantum discord, is known to be bounded from above by the minimum of the von Neumann entropies of the subsystems A and B . We provide an alternative proof that is shorter and more transparent as it works without defining correlation matrices.