Experimental entanglement distribution by separable states

TL;DR

This paper experimentally demonstrates that entanglement can be distributed between distant parties by exchanging a non-entangled, separable subsystem, challenging traditional notions of entanglement transmission in quantum networks.

Contribution

It provides the first experimental proof that entanglement can be distributed via a separable state, using a specific three-mode Gaussian state with thermal noise.

Findings

Successfully distributed entanglement with a separable mode

Demonstrated removal of thermal noise through quantum interference

Enhanced understanding of multipartite quantum network engineering

Abstract

The distribution of entanglement between macroscopically separated parties represents a crucial protocol for future quantum information networks. Surprisingly, it has been theoretically shown that two distant systems can be entangled by sending a third mediating system that is not entangled with either of them. Such a possibility seems to contradict the intuition that to distribute entanglement, the transmitted system always needs to be entangled with the sender. Here, we experimentally distribute entanglement by exchanging a subsystem and successfully prove that this subsystem is not entangled with either of the two parties. Our implementation relies on the preparation of a specific three-mode Gaussian state containing thermal noise that demolishes the entanglement in two of the three bipartite splittings. After transmission of a separable mode this noise can be removed by quantum interference. Our work demonstrates an unexpected variant of entanglement distribution and improves the understanding necessary to engineer multipartite quantum information networks.