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Practical countermeasure against attacks exploiting detection-efficiency mismatch in quantum key distribution

Ben J. Taylor1,2,*, Peter R. Smith1, James F. Dynes1, Robert I. Woodward1, Marco Lucamarini2, R. Mark Stevenson1, and Andrew J. Shields1

  • 1Toshiba Europe Limited, 208 Cambridge Science Park, Cambridge CB4 0GZ, United Kingdom
  • 2School of Physics, Engineering & Technology and York Centre for Quantum Technologies, University of York, York YO10 5FT, United Kingdom

  • *Contact author: ben.taylor@toshiba.eu
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Phys. Rev. Applied 25, 054029 – Published 12 May, 2026

DOI: https://doi.org/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 gigahertz-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.

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Corrections

29 June, 2026

Correction: A figure was missing from the published version and has been inserted as Fig. 2. All captions now correlate with the intended figures. A block of text was missing from Sec. II and has been inserted.

Article Text

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Outline

Information

Phys. Rev. Applied 25, 054029– Published 12 May, 2026
  • Received 30 December 2025
  • Revised 17 February 2026
  • Accepted 26 March 2026
  • Corrected 29 June 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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