Practical Countermeasure Against Attacks Exploiting Detection Efficiency Mismatch in Quantum Key Distribution
arXiv:2605.22580 · doi:10.1103/7zhl-5vv1
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.
Copyright 2026 American Physical Society. This is the accepted manuscript of the following article: Ben J. Taylor, Peter R. Smith, James F. Dynes, Robert I. Woodward, Marco Lucamarini, R. Mark Stevenson, and Andrew J. Shields, 'Practical Countermeasure Against Attacks Exploiting Detection Efficiency Mismatch in Quantum Key Distribution', Phys. Rev. Applied 25, 054029, (2026)
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