Integrated Chip for Continuous-variable Quantum Key Distribution using Silicon Photonic Fabrication
Gong Zhang, Lushuai Cao, Jing Yan Haw, Xiaojun Jia, Xingliang Su, L. C. Kwek, Joseph F. Fitzsimons, Ping Koy Lam, Xiaoqi Zhou, Weibo Gao, Jiangbin Gong, Y. D. Chong, Alexander Szameit, W. Ser, A. Q. Liu
A continuous-variable quantum key distribution system based on silicon photonic chip is designed and tested. A proof-of-principle test shows the secure key-rate can reach 1.92 Mbit/s at 0 km and 37 kbit/s at 45 km distance.
Quantum key distribution, which ensures information-theoretically secret key generation, is currently advancing through photonic integration to achieve high performance, cost reduction, and compact size, thereby facilitating the large-scale deployment. Continuous-variable quantum key distribution is an attractive approach for photonic integrations due to its compatibility with off-the-shelf optical communication devices. However, its chip-based systems have encountered significant limitations primarily related to the shot-noise-limited receiver design, which demands low noise, wide bandwidth, high clearance, and well stability. Here, we report the implementation of a real local oscillator continuous-variable quantum key distribution system with an integrated silicon photonic receiver chip. Thanks to the well-designed chip-based homodyne detectors with a bandwidth up to 1.5 GHz and a clearance up to 7.42 dB, the transmission distance of the system has been extended to 28.6 km, achieving a secret key generation rate of Mbps level. This technological advancement enables the quantum key distribution systems with photonic integrated receivers to achieve the coverage in both access network scenarios and short-distance metropolitan interconnections, paving the way for the development of the next-generation quantum key distribution networks on a large scale.
Silicon photonic technologies exploit silicon as an optical material to build a wide array of devices and systems. The flexibility, modularity, and stability of silicon photonic systems provide unprecedented opportunities for next-generation quantum key distribution (QKD) and quantum networking. This doctoral thesis focuses on the design, simulation, fabrication, and experiment of QKD chips based on silicon photonics. Crucial components for QKD chips are designed and fabricated, including the grating coupler, polarization beam splitter, polarization rotator, modulator, photodetector, ring resonator, and interferometer. Using these components, chip-based continuous variable quantum key distribution (CV-QKD) is demonstrated for the first time. The chip-based CV-QKD system is capable of producing a secret key rate of 9.3 kbits/s (under collective attack) at a distance of 100 km in fiber. The successful demonstration of a single chip-based QKD offers new possibilities for low-cost, scalable and portable quantum networks.
Fully integrated photonic continuous-variable quantum key distribution is a promising route toward compact and scalable secure optical links, yet the achievable transmission distance has been limited by the performance of integrated receiver chips and excess noise suppression methods. Here, we demonstrate a Gaussian-modulated continuous-variable quantum key distribution system with an integrated silicon photonic receiver, operating over 60 km. Enabled by a high-clearance, broadband silicon photonic receiver, in conjunction with a robust digital signal processing framework that utilizes a time-domain superposition algorithm and secure dynamic single-tap equalization, the system effectively achieves an asymptotic secret key rate of 1.68 Mbps, and a finite-size secret key rate of 0.80 Mbps at a data block length of 1.55×10 9 . This work extends chip-based continuous-variable quantum key distribution to metropolitan-scale distances, confirming the viability of integrated receivers for large-scale quantum networks.
Photonic chip integration would greatly benefit quantum key distribution (QKD) systems for secure communication, in terms of compactness, scalability, and well-established fabrication techniques. This study demonstrates proof of concept for an all-chip measurement-device-independent QKD system using integrated silicon photonic technology. The prototype generates a key rate per pulse of $2.923\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ over a distance corresponding to 50 km of standard fiber with 25% detection efficiency; the system is projected to be able to work at 120 km with 85% detection efficiency. This technology shows great promise for highly integrated quantum communication networks.
Quantum key distribution (QKD) stands as the most successful application of quantum information science, providing information-theoretic security for key exchange. While it has evolved from proof-of-concept experiments to commercial products, widespread adoption requires chip-based integration to reduce costs, enable mass production, facilitate miniaturization, and enhance system performance. Here, we demonstrate a fully photonic-integrated continuous-variable QKD (CV-QKD) system operating at a classical telecom symbol rate of 16 GBaud. Our system integrates a silicon photonic transmitter circuit (excluding the laser source) and a 20 GHz shot-noise-limited photonic–electronic receiver, which features a phase-diverse silicon photonic integrated circuit and custom-designed GaAs pHEMT transimpedance amplifiers. Advanced digital signal processing allows our system to achieve a secure key rate for discrete-modulated coherent state CV-QKD that reaches 0.289 Gb/s and 0.246 Gb/s over a 20 km fiber link in the asymptotic regime and with finite-size parameter estimation, respectively. These results represent a critical step toward scalable, cost-effective, and mass-deployable quantum-secure communication using photonic-integrated CV-QKD systems.