Entanglement distribution with separable states has recently attracted considerable attention. Recent results suggest that quantum discord - a measure for quantum correlations beyond entanglement - is responsible for this counterintuitive phenomenon. In this work we study this question from a different perspective, and find minimal requirements for a separable state to be useful for entanglement distribution. Surprisingly, we find that the presence of quantum discord is not sufficient to ensure entanglement distribution: there exist states with nonzero quantum discord which nevertheless cannot be used for entanglement distribution. As a result, we show that entanglement distribution is not possible with rank two separable states. Our work sheds new light on the task of entanglement distribution with separable states, and reveals a new classification of quantum states with respect to their usefulness for this task.
@article{arxiv.1309.0984,
title = {Limits for entanglement distribution with separable states},
author = {Alexander Streltsov and Hermann Kampermann and Dagmar Bruß},
journal= {arXiv preprint arXiv:1309.0984},
year = {2014}
}