Multipartite Entanglement versus Multiparticle Entanglement

TL;DR

This paper explores the activation of genuine multipartite entanglement (GME) from states that are initially biseparable, showing that multiple copies and entangling operations can reveal GME not apparent in single copies.

Contribution

It demonstrates that activation of GME can occur in states previously considered biseparable, highlighting the importance of physical context and entangling operations in GME detection.

Findings

Activation of GME from biseparable states is possible with multiple copies.

Entangling operations are necessary for GME activation.

Activation challenges the notion of GME as a strictly separate resource.

Abstract

Entanglement is defined as presence of quantum correlations beyond those achieved by local action and classical communication. To identify its presence in a generic state, one can, for example, check for existence of a decomposition of separable states. A natural extension is a genuine multipartite entanglement (GME), understood as nonexistenence of a decomposition into biseparable states (later called biseparable decomposition, BD). In this contribution we revisit activation of GME. We discuss few examples of states, which are decomposable into a mixture of biproduct states. However, after merging two copies of these states, we certify nonexistence of BD with witness operators. This seems to challenge our understanding of GME as a separate resource. It turns out that it requires a careful consideration of the physical context. We stress that activation of GME from multiple copies of GME-free states necessarily involves entangling operations.