We demonstrate the first CV-QKD system featuring a custom-designed monolithic silicon photonic dual-polarisation transceiver. Leveraging PS-64-QAM, we achieved 1.9 Mbit/s secret key rate across 25 km of standard single-mode fibre, highlighting the potential of electronic-photonic integration for practical QKD.
Continuous-variable quantum key distribution (CVQKD) is a promising technology for enabling quantum-secure networks, valued for its compatibility with conventional telecommunication hardware and maturing security proofs. Although the need for quantum-safe infrastructure is driven by the threat of advancing quantum computing, the widespread deployment of QKD remains elusive because current discrete-component solutions suffer from high cost, high energy consumption, and lack of conformity with the existing telecom network infrastructure. In this work, we demonstrate a compact CV-QKD system based on a custom-designed, monolithically integrated silicon photonic dualpolarization transceiver, operated with an off-chip seed laser. Taking into account the block length of 2 × 107 and employing 64-quadrature amplitude modulation (QAM) shaped probabilistically, our system achieves a secret key rate of 1.9 Mbit/s in 25km of standard single-mode fiber. This work highlights the significant potential of electronic-photonic integration to advance the practical deployment of QKD networks.
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.
Metropolitan quantum key distribution (QKD) networks face scalability bottlenecks from limited fiber resources and high deployment costs. Although photonic integration enables miniaturization, current implementations are largely restricted to unidirectional configurations, limiting topological flexibility. Here, we report a monolithic silicon photonic continuous-variable (CV) QKD transceiver tailored for simultaneous bidirectional operation. Integrating high-linearity modulators and high-sensitivity coherent detectors on a silicon-on-insulator (SOI) platform, we employ a frequency division duplexing (FDD) strategy combined with pilot-aided digital signal processing to effectively suppress crosstalk and backscattering. The system achieves a total asymptotic secret key rate (SKR) of 4.65 Mbps in a single-fiber, same-band bidirectional configuration over 50.4 km. Demonstrating practical viability, we further establish a finite-size SKR of 1.41 Mbps over a 65.5 km link. By resolving the crosstalk challenges inherent to bidirectional integration, this work provides a hardware-ready foundation for the uni-transceiver quantum key distribution ring network (UT-QKDRN). These results mark a pivotal step in transitioning quantum secure networks from laboratory demonstrations to scalable metropolitan infrastructure.
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.
Multiplexing and photonic-electronic integration offer a route to scalable and high-throughput quantum key distribution (QKD) networks through parallel transmission and compact hardware suited to volume manufacturing. Realizing this route requires multichannel transmitters and receivers, and a security analysis accounting for mode coupling. Here we present a CMOS-compatible photonic-electronic multimode continuous-variable QKD architecture, using polarization multiplexing as a two-mode example. Silicon-photonic transmitter and receiver chips prepare and detect two polarization modes in parallel. The receiver is co-integrated with a dual-channel 28-nm CMOS transimpedance amplifier, providing shot-noise clearances exceeding 20 dB in both channels. Pilot-assisted unitary digital recovery removes the need for active optical polarization control, while a multimode security analysis accounts for the mode crosstalk. At 2 percent residual crosstalk, the multimode analysis extends the simulated secure distance from 39 to 84 km, near the crosstalk-free limit of 89 km. Over 10 km of deployed fibre, the mean total finite-size secret-key rate estimate is 6.69 Mbit/s, 12 percent above the single-mode analysis from the same digitally recovered data. These results establish a route to scalable multimode quantum-secured networks built on technology suited to mass production.
Quantum key distribution (QKD) is a quantum communication technology that offers absolute security. Among its various implementations, continuous-variable (CV) QKD has garnered significant attention due to its high secret key generation rates and compatibility with conventional optical telecommunication infrastructure, which operates under ambient conditions. However, chip-based integration is crucial for realizing practical and scalable CV-QKD networks, and photonic integrated circuit technology is a potential solution, leveraging the on-chip integration of essential optical components onto silicon photonic circuits. Therefore, this work presents a compact, stable, and cost-effective quantum photonic CV-QKD system on a chip. Our architecture combines time- and polarization-multiplexing with high-extinction-ratio pulse generation to mitigate excess noise. At the same time, a real-time feedback control mechanism compensates for polarization drift, ensuring robust system performance. Fiber-based evaluations reveal secret key generation rates of 2.55 Mbps over 25 km and 0.737 Mbps over 50 km with 12 h stable operation, establishing, to our knowledge, a new benchmark for integrated photonic CV-QKD systems with both the transmitter and receiver on-chip. These results mark a significant milestone in on-chip quantum communication, paving the way for widespread adoption of photonic integrated circuits in future metropolitan quantum-secure networks.