Overcoming fundamental bounds on quantum conference key agreement

TL;DR

This paper extends Twin-Field Quantum Key Distribution to a multipartite setting, enabling multiple parties to securely establish a conference key over long distances using practical optical methods, surpassing existing rate bounds.

Contribution

It introduces a practical multipartite conference key agreement protocol based on WCPs and linear optics, with a security proof using a multiparty decoy-state method, overcoming recent rate bounds.

Findings

Protocol enables arbitrary parties to establish a secret conference key.

Uses only weak coherent pulses and linear optics.

Surpasses bounds on conference key rate in quantum networks.

Abstract

Twin-Field Quantum Key Distribution (TF-QKD) enables two distant parties to establish a shared secret key, by interfering weak coherent pulses (WCPs) in an intermediate measuring station. This allows TF-QKD to reach greater distances than traditional QKD schemes and makes it the only scheme capable of beating the repeaterless bound on the bipartite private capacity. Here, we generalize TF-QKD to the multipartite scenario. Specifically, we propose a practical conference key agreement (CKA) protocol that only uses WCPs and linear optics and prove its security with a multiparty decoy-state method. Our protocol allows an arbitrary number of parties to establish a secret conference key by single-photon interference, enabling it to overcome recent bounds on the rate at which conference keys can be established in quantum networks without a repeater.