Lang Li

The quantum internet has the potential to enable applications that are fundamentally unattainable with classical internet technologies. One of its most notable applications is the quantum key distribution (QKD) network, which enables two distant nodes to establish a secure cryptographic key based on the principles of quantum mechanics. However, the heavy reliance on interference in existing QKD protocols undermines the robustness of both the system and the corresponding network infrastructure. We propose an interference-free quantum network architecture based on a Kramers-Kronig receiver. Specifically, we introduce a continuous-variable QKD protocol employing direct detection without the need for interference, wherein the quadrature components are recovered via the Kramers-Kronig relation. Building upon this foundation, we extend the protocol to continuous-variable quantum access networks, thereby demonstrating the enhanced robustness and cost-effectiveness afforded by interference-free detection. Experimental results indicate that each user within the access network can achieve a secret key rate of 200 kbit/s using only a single photodetector and without the inclusion of interference structures. This approach offers a promising direction for constructing interference-free quantum networks and represents a significant step toward the realization of a large-scale quantum internet.

A chip-based continous-variable quantum-key-distribution (CVQKD) system with a high practical confidentiality performance is crucial for constructing quantum metropolitan communication networks, but imperfections in the chip-based modulation will threaten the practical security of the chip-based CVQKD system. In this paper, we combine the plasma dispersion effect of free carriers to model the carrier fluctuations and reveal the essential mechanism of carrier fluctuations’ influence on the system. The simulations show that the chip-based CVQKD system may face potential loophole threats or its performance will dramatically decrease under different carrier fluctuations. Moreover, two preliminary defense strategies are proposed to completely solve the practical security problems commonly induced by modulators in general chip-based CVQKD systems. This work proposes a set of modeling and analysis methods for general chip-based CVQKD systems’ modulators, which provides constructive methods to build the chip-based CVQKD system with more rigorous practical security.