Multipartite device-independent quantum key distribution using W states

TL;DR

This paper demonstrates the feasibility of multipartite device-independent quantum key distribution using W states, introduces Bell inequalities tailored for W states, and proposes long-distance protocols surpassing GHZ-based methods.

Contribution

It constructs Bell inequalities for W states enabling DI-QKD and develops long-distance protocols with detailed physical implementation analysis.

Findings

W states can be used for multipartite DI-QKD.

Proposed protocols achieve longer distances than GHZ-based methods.

Bell inequalities for W states are largely violated, enabling secure key distribution.

Abstract

Multipartite device-independent quantum key distribution (DI-QKD), also known as device-independent conference key agreement, enables more than two remote parties to share a common key with information-theoretic security even without trusting the devices. So far, several multipartite DI-QKD protocols have been proposed where Greenberger-Horne-Zeilinger (GHZ) states are used as multipartite entanglement. A natural question is then whether one can construct multipartite DI-QKD with the other type of multipartite entanglement. W state is of particular interest since it is intrinsically different from GHZ state and in some cases, easier to optically implement. In this paper, we show that multipartite DI-QKD is possible with W states. To this end, we construct Bell inequalities largely violated by W states, which can be used for the multipartite DI-QKD. Furthermore, we consider several different implementation scenarios. First, we analyze the minimum required detection efficiencies to extract finite amount of keys. Then we propose a long-distance multipartite DI-QKD protocol with single-photon interference and make detailed analyses with several physical implementation scenarios. We show that the protocol enables secret key distribution over longer distances than the existing multipartite DI-QKD protocols based on GHZ states. This study provides new insight about the relationship between multipartite entanglement and device-independent quantum information processing as well as opens an alternative path toward long-distance multipartite DI-QKD.