Practical Countermeasure Against Attacks Exploiting Detection Efficiency Mismatch in Quantum Key Distribution

TL;DR

This paper presents a practical implementation of a countermeasure against detection efficiency mismatch attacks in quantum key distribution systems, restoring the secret key rate close to ideal levels.

Contribution

The authors implement and evaluate a four-state countermeasure on a GHz-clocked QKD system, demonstrating its effectiveness in real-world conditions.

Findings

Almost complete recovery of the secret key rate with the countermeasure

Implementation on a GHz-clocked prototype system

Strong justification for adopting the countermeasure in practical QKD

Abstract

We demonstrate a practical countermeasure against a well-known class of attacks on quantum key distribution (QKD) systems that exploit detection efficiency mismatch, where the receiver's detectors do not exhibit identical responses to incoming photons across all degrees of freedom. This class of quantum hacking strategies is broad and significantly includes the time-shift attack, which targets an arrival-time-dependent side channel at the receiver. The four-state countermeasure, previously only proven to be secure in theory, is implemented here on a GHz-clocked prototype QKD system and evaluated for its security and performance. We show that its presence enables almost complete recovery of the system's ideal secret key rate. Our results provide strong justification for adopting this countermeasure as a standard component in future scalable and practical QKD systems.