Distributing Entanglement with Separable States

TL;DR

This paper demonstrates that quantum entanglement can be distributed using only separable states, highlighting the quantum correlations present even without entanglement, and emphasizing the role of classical information in quantum communication.

Contribution

It presents an experimental method to distribute entanglement via separable states, revealing the quantumness of correlations beyond entanglement itself.

Findings

Entanglement can be distributed with separable states.

Separable states can serve as a resource for quantum communication.

Classical information plays a crucial role in the process.

Abstract

Like a silver thread, quantum entanglement [1] runs through the foundations and breakthrough applications of quantum information theory. It cannot arise from local operations and classical communication (LOCC) and therefore represents a more intimate relationship among physical systems than we may encounter in the classical world. The `nonlocal' character of entanglement manifests itself through a number of counterintuitive phenomena encompassing Einstein-Podolsky-Rosen paradox [2,3], steering [4], Bell nonlocality [5] or negativity of entropy [6,7]. Furthermore, it extends our abilities to process information. Here, entanglement is used as a resource which needs to be shared between several parties, eventually placed at remote locations. However entanglement is not the only manifestation of quantum correlations. Notably, also separable quantum states can be used as a shared resource for quantum communication. The experiment presented in this paper highlights the quantumness of correlations in separable mixed states and the role of classical information in quantum communication by demonstrating entanglement distribution using merely a separable ancilla mode.