Universal approach to sending-or-not-sending twin field quantum key distribution

TL;DR

This paper introduces a universal, improved sending-or-not-sending twin-field quantum key distribution protocol that enhances key rates and robustness by utilizing all heralded events and automatic parameter optimization.

Contribution

The authors develop a universal approach to SNS protocol that uses all heralded events and automatic optimization, significantly improving key rates and experimental robustness.

Findings

Key rate increases up to 80% compared to previous methods.

All heralded events can be used for key distillation, not just specific time-window events.

Larger decoy pulse intensities improve protocol robustness.

Abstract

We present the method of decoy-state analysis after bit-flip error correction and using confidential observed numbers. Taking this tool we then construct a universal approach to sending-or-not-sending (SNS) protocol of twin-field quantum key distribution. In this improved protocol, the code bits are not limited to heralded events in time windows participated by pulses of intensity $\mu_z$ and vacuum. All kinds of heralded events can be used for code bits to distill the final keys. The number of intensities (3 or 4) and the kinds of heralded events for code bits are automatically chosen by the key rate optimization itself. Numerical simulation shows that the key rate rises drastically in typical settings, up to 80\% improvement compared with the prior results. Also, larger intensity value can be used for decoy pulses. This makes the protocol more robust in practical experiments.