# Experimental Twin-Field Quantum Key Distribution Through Sending-or-Not-Sending

## TL;DR

This paper demonstrates a practical implementation of twin-field quantum key distribution over 300 km using advanced laser locking and phase compensation techniques, achieving secure key rates surpassing repeaterless limits.

## Contribution

It introduces a sending-or-not-sending protocol with phase stabilization methods for long-distance quantum communication, improving real-world key rates.

## Key findings

- Secure key rate at 300 km is higher than repeaterless secret key capacity.
- Utilizes frequency and time transfer technology for laser phase locking.
- Achieves stable quantum key distribution over 300 km with finite size effects considered.

## Abstract

Channel loss seems to be the most severe limitation on the practical application of long distance quantum key distribution. The idea of twin-field quantum key distribution can improve the key rate from the linear scale of channel loss in the traditional decoy-state method to the square root scale of the channel transmittance. However, the technical demanding is rather tough because it requests single photon level interference of two remote independent lasers. Here, we adopt the technology developed in the frequency and time transfer to lock two independent lasers' wavelengths and utilize additional phase reference light to estimate and compensate the fiber fluctuation. Further with a single photon detector with high detection rate, we demonstrate twin field quantum key distribution through the sending-or-not-sending protocol with realistic phase drift over 300 km optical fiber spools. We calculate the secure key rates with finite size effect. The secure key rate at 300 km ($1.96\times10^{-6}$) is higher than that of the repeaterless secret key capacity ($8.64\times10^{-7}$).