High-rate quantum digital signatures over 250 km of optical fiber

TL;DR

This paper demonstrates a high-rate, loss-tolerant quantum digital signature system over 250 km of optical fiber, significantly advancing practical quantum cryptography for long-distance networks.

Contribution

The authors develop a robust QDS system combining phase-stable polarization modulation, gigahertz-rate encoding, and superconducting detectors, achieving unprecedented loss tolerance and signature rates.

Findings

Signature rate exceeds 100 times previous systems.

Maintains operation at 49.05 dB channel loss.

Establishes scalable pathway for real-world quantum networks.

Abstract

Quantum digital signatures (QDS) offer information-theoretic security for message integrity, authenticity, and non-repudiation, and constitute a fundamental cryptographic primitive for future quantum networks. Despite significant progress, the practical deployment of QDS has been severely constrained by limited signature rates and poor tolerance to channel loss, particularly in long-distance and metropolitan-scale networks. Here, we report a high-rate, loss-resilient QDS system that overcomes these two key bottlenecks simultaneously. Our implementation combines intrinsically phase-stable polarization modulation based on a Sagnac interferometer with gigahertz-rate quantum state encoding and low-timing-jitter superconducting nanowire single-photon detectors, enabling robust and continuous operation at high repetition frequencies. By integrating this hardware platform with a one-time universal hashing-based QDS protocol, we achieve a signature rate improvement of more than two orders of magnitude compared with existing QDS implementations under comparable channel-loss conditions. Notably, the system maintains a non-zero effective signature rate of approximately 1.25 times per second at a total channel loss of up to 49.05 dB, representing the highest loss tolerance reported for QDS to date. These results establish a practical and scalable technological pathway for deploying QDS in real-world quantum communication networks.