Real-World Two-Photon Interference and Proof-of-Principle Quantum Key Distribution Immune to Detector Attacks

TLDR

Vulnerabilities in single‑photon detectors have recently been exploited to compromise the security of quantum‑key‑distribution systems. This Letter reports the first proof‑of‑principle implementation of a quantum‑key‑distribution protocol that is immune to such attacks. The protocol was implemented over more than 80 km of spooled fiber and across multiple locations in Calgary. The demonstration confirmed the protocol’s robustness and enhanced security, established the feasibility of controlled two‑photon interference in a real‑world setting, and underscored QKD’s practicality while removing a key obstacle to future quantum repeaters and networks.

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 fiber-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.