Purified discord and multipartite entanglement

TL;DR

This paper explores how bipartite quantum discord relates to multipartite entanglement in the purification system, revealing insights into quantum correlations, asymmetry, and classical-quantum correlation interplay.

Contribution

It demonstrates that quantum discord arises from both bipartite and tripartite entanglement in the purification, linking discord asymmetry to entanglement monogamy and analyzing Gaussian states.

Findings

Quantum discord requires both bipartite and tripartite entanglement.

In Gaussian states, classical correlations imply quantum correlations.

Insights into remote activation of entanglement by a third party.

Abstract

We study bipartite quantum discord as a manifestation of a multipartite entanglement structure in the tripartite purified system. In particular, we find that bipartite quantum discord necessarily manifests itself in the presence of both bipartite and tripartite entanglement in the purification. This allows one to understand the asymmetry of quantum discord (between D[A,B] and D[B,A]) in terms of entanglement monogamy. As instructive special cases, we study discord for qubits and Gaussian states in detail. As a result of this we shed new light on a counterintuitive property of Gaussian states: the presence of classical correlations necessarily requires the presence of quantum correlations. Finally, our results also shed new light on a protocol for remote activation of entanglement by a third party.