Finite-key analysis for a practical decoy-state twin-field quantum key distribution

TL;DR

This paper provides a finite-key security analysis for practical decoy-state twin-field QKD, demonstrating that secure key rates can surpass the linear bound even with source fluctuations and limited signals.

Contribution

It introduces a finite-key analysis considering intensity fluctuations and employs Azuma's inequality for security proof, advancing practical TF-QKD security understanding.

Findings

Secret key rate exceeds linear bound with limited signals.

Intensity fluctuations significantly impact small sample sizes.

Finite-key analysis ensures security under realistic source instability.

Abstract

Twin-field quantum key distribution (TF-QKD), which is immune to all possible detector side channel attacks, enables two remote legitimate users to perform secure communications without quantum repeaters. With the help of a central node, TF-QKD is expected to overcome the linear key-rate constraint using current technologies. However, the security of the former TF-QKD protocols relies on the hypothesis of infinite-key and stable sources. In this paper, we present the finite-key analysis of a practical decoy-state twin-field quantum key distribution with variant statistical fluctuation models. We examine the composable security of the protocol with intensity fluctuations of unstable sources employing Azuma's inequality. Our simulation results indicate that the secret key rate is able to surpass the linear key-rate bound with limited signal pulses and intensity fluctuations. In addition, the effect of intensity fluctuations is extremely significant for small size of total signals.