T. K. Chuan, J. Maillard, K. Modi, T. Paterek, M. Paternostro, M. Piani
Two distant parties can increase the amount of entanglement between them by means of quantum communication encoded in some carrier that is sent from one party to the other. It was pointed out in [T. S. Cubitt \emph{et al.}, Phys. Rev. Lett. {\bf 91}, 037902 (2003)] that this can be achieved even when the exchanged carrier is not entangled with the parties. On the other hand the carrier must be quantum, since classical communication cannot increase entanglement. We show that in general the increase in relative entropy of entanglement between the parties is bound by the amount of non-classical correlations of the carrier with the parties as quantified by the relative entropy of discord. This relation is shown to generalize subadditivity of entropy and to be naturally linked to negative conditional entropy. We also provide new examples of entanglement distribution via separable states and put further limits on this phenomenon.
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http://arxiv.org/abs/1203.1268
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