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arXiv:2508.08722 · Photonics Research

Continuous-variable quantum key distribution over 50.4 km fiber using an integrated silicon photonic transmitter and receiver

Shuaishuai Liu, Yan-Xiang Jia, Yuqi Shi, Yizhuo Hou, Pu Wang, Yu Zhang, Shiwei Yang, Zhenguo Lu, Xuyang Wang, Yongmin Li

Published Aug 21, 2025• 9 citations
arXivHTMLPDF

Abstract

Quantum key distribution (QKD) is the fastest-growing and relatively mature technology in the field of quantum information, enabling information-theoretically secure key distribution between two remote users. Although QKD based on off-the-shelf telecom components has been validated in both laboratory and field tests, its high cost and large volume remain major obstacles to large-scale deployment. Photonic integration, featured by its compact size and low cost, offers an effective approach to addressing the above challenges faced by QKD. Here, we implement a high-performance, integrated local local oscillator continuous-variable (CV) QKD system based on an integrated silicon photonic transmitter and receiver. By employing a high-speed silicon photonic integrated in-phase and quadrature modulator, a low-noise and high-bandwidth silicon photonic integrated heterodyne detector, and digital signal processing, our CV-QKD system achieves a symbol rate of up to 1.5625 GBaud. Furthermore, the system achieves asymptotic secret key rates of 31.05 and 5.05 Mbps over 25.8 and 50.4 km standard single-mode fiber, respectively, using 8-phase-shift keying discrete modulation. Our integrated CV-QKD system with a high symbol rate and long transmission distance paves the way for the quantum secure communication network in metropolitan areas.

DOI
10.1364/prj.561085

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Quantum key distribution (QKD) is the fastest-growing and relatively mature technology in the field of quantum information, enabling information-theoretically secure key distribution between two remote users. Although QKD based on off-the-shelf telecom components has been validated in both laboratory and field tests, its high cost and large volume remain major obstacles to large-scale deployment. Photonic integration, featured by its compact size and low cost, offers an effective approach to addressing the above challenges faced by QKD. Here, we implement a high-performance, integrated local local oscillator continuous-variable (CV) QKD system based on an integrated silicon photonic transmitter and receiver. By employing a high-speed silicon photonic integrated in-phase and quadrature modulator, a low-noise and high-bandwidth silicon photonic integrated heterodyne detector, and digital signal processing, our CV-QKD system achieves a symbol rate of up to 1.5625 GBaud. Furthermore, the system achieves asymptotic secret key rates of 31.05 and 5.05 Mbps over 25.8 and 50.4 km standard single-mode fiber, respectively, using 8-phase-shift keying discrete modulation. Our integrated CV-QKD system with a high symbol rate and long transmission distance paves the way for the quantum secure communication network in metropolitan areas.
Quantum key distribution (QKD) is a well-known application of quantum information theory that guarantees information-theoretically secure key exchange. As QKD becomes more and more commercially viable, challenges such as scalability, network integration, and high production costs need to be addressed. Photonic and electronic integrated circuits that can be produced in large volumes at low cost hold the key to large-scale deployment of next-generation QKD systems. Here, we present a continuous-variable (CV) QKD system using an integrated photonic-electronic receiver that combines a silicon photonic integrated circuit implementing a phase-diverse receiver with custom-designed GaAs pHEMT transimpedance amplifiers. The QKD system operates at a classical telecom symbol rate of 10 GBaud, generating high secret key rates exceeding 0.7 Gb/s over a distance of 5 km and 0.3 Gb/s over a distance of 10 km. The secret keys are secure against collective attacks with finite-size effects taken into account. Well-designed digital signal processing enabled the high-speed operation. Our experiment sets a new record for secure quantum communication and paves the way for the next generation of CV-QKD systems.
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.
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.
Quantum key distribution (QKD) is a prominent application in the field of quantum cryptography, providing information-theoretic security for secret key exchange. The implementation of QKD systems on photonic integrated circuits (PICs) can reduce the size and cost of such systems and facilitate their deployment in practical infrastructures. To this end, continuous-variable (CV) QKD systems are particularly well-suited as they do not require single-photon detectors, whose integration is presently challenging. Here we present a CV-QKD receiver based on a silicon PIC capable of performing balanced detection. We characterize its performance in a laboratory QKD setup using a frequency multiplexed pilot scheme with specifically designed data processing allowing high modulation and secret key rates. The obtained excess noise values are compatible with asymptotic secret key rates of 2.4 Mbit/s and 220 kbit/s at an emulated distance of 10 km and 23 km, respectively. These results demonstrate the potential of this technology toward fully integrated devices suitable for high-speed, metropolitan-distance secure communication.
Quantum key distribution (QKD) provides information-theoretic security based on the laws of quantum mechanics, offering resistance to future computational threats, including quantum computers. While QKD technology shows great promise, its widespread adoption depends heavily on achieving both high performance and system-level practicality. In this work, we report an integrated silicon photonics-based QKD system that achieves a secret key rate of 1.213Gbits −1 , with composable security and finite-size analysis, over a metropolitan distance of 10 km with polarization multiplexing. Our contributions are twofold. First, at the quantum optical layer, we develop an on-chip quantum transmitter and receiver that operate at 40 Gbaud at room temperature, featuring high-performance balanced homodyne detection using low-noise amplifiers with off-the-shelf RF components. Second, we implement a discrete-modulated continuous variable (DM CV) QKD protocol that simplifies hardware requirements and leverages standard telecommunication components, and design a polar-code-based information reconciliation algorithm specifically optimized for DM CV QKD and amenable to real-time implementation. Our results demonstrate a cost-effective QKD solution that achieves high key rates through integrated photonics operating at room temperature with off-the-shelf RF components and digital signal processing for robust operation. We anticipate that this research will pave the way for large-scale quantum secure networks.
Quantum key distribution (QKD) is a widely recognized application of quantum information theory, guaranteeing information-theoretically secure key exchange. However, commercial viability of QKD systems is currently impeded by issues such as scalability, network integration, and high manufacturing costs. Low-cost, high-volume production of photonic and electronic integrated circuits could be the breakthrough needed for broad-scale deployment of cutting-edge QKD systems. Here, we present a continuous-variable (CV) QKD system that is based on an integrated photonic-electronic receiver. It combines a silicon photonic integrated circuit, featuring a phase-diverse receiver, with custom-designed GaAs pHEMT transimpedance amplifiers. Operating at a classical telecom symbol rate of 10 GBaud, our QKD system generates high secret key rates - exceeding 0.7 Gb/s over a 5 km distance and 0.3 Gb/s over a 10 km. The secret keys are secure against collective attacks, even when accounting for finite-size effects in the parameter estimation, thanks to well-designed digital signal processing that enables broadband system operation. Our experiment sets a record for secure key exchange and paves the way for the implementation of real-time broadband CV-QKD systems.