Secure gated detection scheme for quantum cryptography

TL;DR

This paper introduces bit-mapped gating, a technique to ensure secure detection timing and single-photon sensitivity in quantum cryptography, enhancing security against detector-based attacks.

Contribution

The paper proposes bit-mapped gating to secure detector timing and sensitivity, and provides a method to measure detector parameters relevant for security proofs.

Findings

Bit-mapped gating effectively forces detections in the middle of the gate.

The technique allows direct measurement of detector blinding parameters.

Ensures detection scheme aligns with security proof assumptions.

Abstract

Several attacks have been proposed on quantum key distribution systems with gated single-photon detectors. The attacks involve triggering the detectors outside the center of the detector gate, and/or using bright illumination to exploit classical photodiode mode of the detectors. Hence a secure detection scheme requires two features: The detection events must take place in the middle of the gate, and the detector must be single-photon sensitive. Here we present a technique called bit-mapped gating, which is an elegant way to force the detections in the middle of the detector gate by coupling detection time and quantum bit error rate. We also discuss how to guarantee single-photon sensitivity by directly measuring detector parameters. Bit-mapped gating also provides a simple way to measure the detector blinding parameter in security proofs for quantum key distribution systems with detector efficiency mismatch, which up until now has remained a theoretical, unmeasurable quantity. Thus if single-photon sensitivity can be guaranteed within the gates, a detection scheme with bit-mapped gating satisfies the assumptions of the current security proofs.