# Proof-of-principle experimental demonstration of twin-field type quantum key distribution

## TL;DR

This paper demonstrates a practical twin-field quantum key distribution experiment that surpasses the fundamental rate-loss limit using phase stabilization and decoy states, showing promise for secure long-distance quantum communication.

## Contribution

It provides the first proof-of-principle experimental demonstration of TF-QKD with phase stabilization, achieving secret key rates above the PLOB bound over long distances.

## Key findings

- Secret key rates beat the PLOB bound at over 40 dB loss
- Phase stabilization via Sagnac loop is effective for long-distance TF-QKD
- Decoy states enable secure key generation in the experiment

## Abstract

The twin-field (TF) quantum key distribution (QKD) protocol and its variants are highly attractive because they can beat the well-known rate-loss limit (i.e., the PLOB bound) for QKD protocols without quantum repeaters. In this paper, we perform a proof-of-principle experimental demonstration of TF-QKD based on the protocol proposed by Curty et al. which removes from the original TF-QKD scheme the need for post-selection on the matching of a global phase, and can deliver nearly an order of magnitude higher secret key rate. Furthermore, we overcome the major difficulty in the practical implementation of TF-QKD, namely, the need to stabilize the phase of the quantum state over kilometers of fiber. A Sagnac loop structure is utilized to ensure excellent phase stability between the different parties. Using decoy states, we demonstrate secret-key generation rates that beat the PLOB bound when the channel loss is above 40 dB.