High-Rate Free-Space Continuous-Variable QKD with Self-Referenced Passive State Preparation

TL;DR

This paper introduces a self-referenced passive state preparation scheme for continuous-variable QKD, achieving record-high secret key rates over high-loss free-space channels with improved stability and noise performance.

Contribution

It proposes and demonstrates the first self-referenced LLO CVQKD system, improving stability and key rate in high-loss free-space environments.

Findings

Achieved a secret key rate of 10.34 Mbps over 23.5 dB loss channel.

Significantly improved system stability and noise performance.

Validated the theoretical equivalence of PSP and GMCS protocols.

Abstract

Continuous-variable quantum key distribution (CVQKD) using passive state preparation (PSP) offers low-cost, high-rate secure communication. However, the existing PSP-CVQKD scheme with a transmitted local oscillator has high photon leakage noise and poor stability, making it unsuitable for high-loss transmission. In this work, for the first time, we propose and implement a local local oscillator (LLO) CVQKD system using a self-referenced (SR) PSP scheme, and give a theoretical proof of the equivalence of the PSP and GMCS protocol using temporal-mode theory. By employing the novel self-referenced pilot scheme to achieve high-precision time-varying frequency and phase compensation algorithms, we significantly improve the system' s signal-to-noise ratio and stability. The system achieves a record-high asymptotic secret key rate of 10.34 Mbps over a free-space channel with up to 23.5 dB loss, while maintaining low excess noise and robust performance under turbulent conditions. This work establishes the feasibility of SR-LLO CVQKD, providing a practical pathway toward secure, high-rate quantum communication in realistic environments.