Quantum discord bounds the amount of distributed entanglement

TL;DR

This paper establishes a fundamental limit on how much entanglement can be distributed between two parties, showing it is bounded by the quantum correlations (discord) of the carrier, with implications for quantum communication protocols.

Contribution

It introduces a bound linking entanglement distribution to quantum discord, providing new insights and examples of entanglement transfer using unentangled states.

Findings

Entanglement increase is bounded by quantum discord of the carrier.

Examples of entanglement distribution via unentangled states are provided.

Limits on entanglement distribution phenomena are established.

Abstract

The ability to distribute quantum entanglement is a prerequisite for many fundamental tests of quantum theory and numerous quantum information protocols. Two distant parties can increase the amount of entanglement between them by means of quantum communication encoded in a carrier that is sent from one party to the other. Intriguingly, entanglement can be increased even when the exchanged carrier is not entangled with the parties. However, in light of the defining property of entanglement stating that it cannot increase under classical communication, the carrier must be quantum. Here we show that, in general, the increase of relative entropy of entanglement between two remote parties is bounded by the amount of non-classical correlations of the carrier with the parties as quantified by the relative entropy of discord. We study implications of this bound, provide new examples of entanglement distribution via unentangled states and put further limits on this phenomenon.