Real-world two-photon interference and proof-of-principle quantum key distribution immune to detector attacks

TL;DR

This paper demonstrates a secure quantum key distribution protocol immune to detector attacks, validated over long-distance fiber links and in real-world conditions, advancing practical quantum communication technologies.

Contribution

First proof-of-principle implementation of a detector-attack immune QKD protocol using two-photon interference in real-world environments.

Findings

Successfully implemented QKD over 80 km fiber

Proved robustness of protocol against detector vulnerabilities

Demonstrated controlled two-photon interference in practical settings

Abstract

Several vulnerabilities of single photon detectors have recently been exploited to compromise the security of quantum key distribution (QKD) systems. In this letter we report the first proof-of-principle implementation of a new quantum key distribution protocol that is immune to any such attack. More precisely, we demonstrated this new approach to QKD in the laboratory over more than 80 km of spooled fiber, as well as across different locations within the city of Calgary. The robustness of our fibre-based implementation, together with the enhanced level of security offered by the protocol, confirms QKD as a realistic technology for safeguarding secrets in transmission. Furthermore, our demonstration establishes the feasibility of controlled two-photon interference in a real-world environment, and thereby removes a remaining obstacle to realizing future applications of quantum communication, such as quantum repeaters and, more generally, quantum networks.