Xiaojuan Liao

We propose a discrete-modulated coherent-state basis-encoding quantum key distribution (DMCS-BE-QKD) protocol, where the secret keys are encoded in the random choice of two measurement bases and it only needs simple binary sequence error correction. We analyze the secret key rate of DMCS-BE-QKD protocol under collective attacks in the linear Gaussian channel. The results show that DMCS-BE-QKD can greatly enhance the ability to tolerate the channel loss and excess noise compared to the original DMCS-CVQKD protocol. Finally, a proof-of-principle experiment is conducted under a 50.5 km optical fiber to verify the feasibility of DMCS-BE-QKD.

The advent of quantum computers has significantly challenged the security of traditional cryptographic systems, prompting a surge in research on quantum key distribution (QKD). Continuous-variable QKD (CVQKD) resists noise well, but the local local oscillator (LLO) CVQKD has limits in high-attenuation channels. Bottleneck challenges include ensuring stable low-noise transmission and accurately estimating parameters under fluctuating channel conditions. We propose a LLO-CVQKD scheme that combines the main quantum system with an auxiliary quantum system, featuring time-varying parameter compensation and time-varying channel transmittance estimation capabilities. Through experimental validation, we first demonstrate high-rate secure quantum key distribution over high-loss free-space channels. Specifically, we achieve asymptotic key rates of 403.896 kbps in 21.5 dB average attenuation free-space channels with turbulence at a 1 GHz repetition rate.

Quantum networks revolutionize the way of information transmission and are an essential step in building a quantum internet. Generally, the information capacity per user-channel in a quantum network drastically decreases with the increase of network capacity, making it difficultly scale to large-user scenarios. To break this limit, we propose a network capacity-independent quantum network (NCI-QN) that maintains constant information capacity per user-channel regardless of network scale, overcoming the scalability bottleneck in conventional quantum networks. The architecture employs a multi-mode time-frequency framework, with theoretical analysis extending PLOB and Holevo bounds to network scenarios to establish capacity independence. Experimentally, we demonstrate a 19-user NCI-QN using optical frequency combs in quantum key distribution, achieving a record 8.75 Gbps composable finite-size secure key rate.