Multiparticle entanglement as an emergent phenomenon

TL;DR

This paper introduces a method to identify global multiparticle entanglement in quantum systems using only local marginals, revealing that global entanglement can emerge even when local states appear separable.

Contribution

The authors develop a systematic approach to detect genuine multiparticle entanglement from local marginals, demonstrating that global entanglement often arises from locally separable states.

Findings

Global entanglement can be inferred from local marginals in many cases.

Global entanglement emergence is frequent and independent of particle number.

Examples show entanglement can be proven without localizing it in marginals.

Abstract

The question whether global entanglement of a multiparticle quantum system can be inferred from local properties is of great relevance for the theory of quantum correlations as well as for experimental implementations. We present a method to systematically find quantum states, for which the two- or three-body marginals do not contain any entanglement, nevertheless, the knowledge of these reduced states is sufficient to prove genuine multiparticle entanglement of the global state. With this, we show that the emergence of global entanglement from separable local quantum states occurs frequently and for an arbitrary number of particles. We discuss various extensions of the phenomenon and present examples where global entanglement can be proven from marginals, even if entanglement cannot be localized in the marginals with measurements on the other parties.