Limits for entanglement distribution with separable states

TL;DR

This paper investigates the conditions under which separable quantum states can be used for entanglement distribution, revealing that quantum discord alone is insufficient and that rank constraints limit this capability.

Contribution

It establishes that nonzero quantum discord does not guarantee usefulness for entanglement distribution and shows that rank two separable states cannot facilitate this process.

Findings

Quantum discord is not sufficient for entanglement distribution.

Rank two separable states cannot be used for entanglement distribution.

The work introduces a new classification of quantum states based on their usefulness for entanglement distribution.

Abstract

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.