Finite-key analysis for twin-field quantum key distribution based on generalized operator dominance condition

TL;DR

This paper introduces an improved finite-key analysis method for twin-field quantum key distribution, enabling higher secret key rates and approaching the asymptotic bound by utilizing a more general operator dominance condition.

Contribution

The paper develops a new, more general operator dominance condition for finite-key analysis in TF-QKD, allowing for increased decoy states and higher key rates.

Findings

Enhanced secret key rate with more decoy states

Approaches the asymptotic key rate bound

Applicable directly in experimental setups

Abstract

Quantum key distribution (QKD) can help two distant peers to share secret key bits, whose security is guaranteed by the law of physics. In practice, the secret key rate of a QKD protocol is always lowered with the increasing of channel distance, which severely limits the applications of QKD. Recently, twin-field (TF) QKD has been proposed and intensively studied, since it can beat the rate-distance limit and greatly increase the achievable distance of QKD. Remarkalebly, K. Maeda et. al. proposed a simple finite-key analysis for TF-QKD based on operator dominance condition. Although they showed that their method is sufficient to beat the rate-distance limit, their operator dominance condition is not general, i.e. it can be only applied in three decoy states scenarios, which implies that its key rate cannot be increased by introducing more decoy states, and also cannot reach the asymptotic bound even in case of preparing infinite decoy states and optical pulses. Here, to bridge this gap, we propose an improved finite-key analysis of TF-QKD through devising new operator dominance condition. We show that by adding the number of decoy states, the secret key rate can be furtherly improved and approach the asymptotic bound. Our theory can be directly used in TF-QKD experiment to obtain higher secret key rate. Our results can be directly used in experiments to obtain higher key rates.