Quantum key distribution (QKD) guarantees information-theoretic security by the laws of physics, but deployment at scale requires compact, manufacturable photonic terminals. Continuous-variable QKD (CV-QKD) is well suited for this transition through telecom-compatible, room-temperature coherent detection. However, unifying full on-chip core terminal integration, room-temperature operation, high loss tolerance, and composable end-to-end security in long-distance QKD remains a key bottleneck. Here we report a fully integrated CV-QKD platform in which two hybrid III--V/Si
3N
4 integrated lasers, a silicon transmitter, and a silicon coherent receiver implement the core terminal functions, operating with a local local oscillator (LLO) over fibre links of 25--150 km. A Bayesian machine-learning algorithm maintains robust phase lock throughout the long records required for composable security, consistently outperforming the conventional unscented Kalman filter, while rate-matched multidimensional reconciliation approaches the Shannon limit. The system certifies a composable finite-size secret-key rate of 29.3 kbps at 100 km from a 140-billion-symbol block, with 12.9 kbps at 125 km under finite-size analysis and 9.17 kbps at 150 km under asymptotic analysis. By establishing the longest finite-size and asymptotic reaches and the highest secret-key rate per symbol reported for integrated CV-QKD, this work advances the development of practical chip-based quantum networks.
In the continuous-variable quantum key distribution (CV-QKD) system with a local local oscillator (LLO), the center frequency of the sender and the receiver’s source are not exactly the same and a certain frequency drift exists over time, resulting in the frequency of the signal received near the intermediate frequency. Therefore, the LLO system needs an intermediate-frequency balanced homodyne detector (BHD), which needs better symmetry of the arms of the BHD, to obtain the less-common mode noise. Moreover, the traditional intermediate-frequency receiver in classical communication is not available in the CV-QKD system because of the low quantum-to-classical noise ratio. In view of this, in this paper, we construct a broadband intermediate-frequency BHD based on ratio frequency and integrated circuit technology, whose bandwidth can exceed 270 MHz and whose quantum-to-classical noise ratio can reach 14.9 dB. Meanwhile, the BHD has an excellent linear performance with a gain of 22.4 k. By adopting our intermediate-frequency BHD, the secret key rate of the pilot-sequential Gaussian modulated coherent state CV-QKD system with an LLO can reach over 430.8 kbps of 60 km at the standard fiber length, which paves the way to achieve a high-performance LLO CV-QKD system with intermediate-frequency BHD.