We propose and demonstrate a fully passive discrete-state continuous-variable quantum key distribution (CV-QKD), which can eliminate all modulator side channels on the source side, using a local local oscillator (LLO). The CV-QKD system achieves a maximum transmission length of 100 km with a repetition rate of 1 GHz using specially designed phase rotation and discretization methods, and the corresponding secret key bit rate is 127 kbps, as estimated based on the amplitude of prepared states at the transmitter, as well as the first- and second-order moments of quadratures at the receiver by employing the convex optimization without imposing any assumptions on the quantum channel. The performance of the protocol is similar to that of modulated CV LLO protocols and better than those of passive discrete-variable and CV protocols. Our protocol is expected to play an important role in the quantum metropolitan area networks and quantum access networks with high realistic security.
@article{arxiv.2507.23327,
title = {High-Performance Fully Passive Discrete-State Continuous-Variable Quantum Key Distribution With Local Local Oscillator},
author = {Yu Zhang and Xuyang Wang and Chenyang Li and Jie Yun and Qiang Zeng and Zhiliang Yuan and Zhenguo Lu and Yongmin Li},
journal= {arXiv preprint arXiv:2507.23327},
year = {2026}
}