Shuaishuai Liu

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 high signal-to-noise ratio 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 high secret key rates of 14.7 and 2.46 Mbps over 25.8 and 50.4 km standard single-mode fiber, respectively, using an 8-phase-shift keying discrete modulation. Our fully integrated CV-QKD system with high symbol rate and long transmission distance pays the way for the quantum secure communication network at metropolitan area.

Communication and sensing technologies play crucial roles in various aspects of modern society. The seamless combination of communication and sensing systems has attracted significant interest in recent years. Without adding core devices, vibration-sensing functions can be integrated to build a quantum network with high efficiency and versatility. In this study, we propose and demonstrate a network architecture that integrates a downstream quantum access network (DQAN) and vibration sensing in optical fibers. By encoding the key information of eight users simultaneously on the sidemode quantum states of a single laser source and successively separating them using a specially designed narrow-bandwidth filter network, we achieved a secure and efficient DQAN with an average key rate of 19.4 kbps over an 80 km single-mode fiber. Meanwhile, vibration locations with spatial resolutions of 131, 25, and 4 m at vibration frequencies of 100 Hz, 1 kHz, and 10 kHz, respectively, were implemented using the existing DQAN system infrastructure. The results indicate that the backward probe beam has a negligible effect on the DQAN system. Our integrated architecture provides a viable and cost-effective solution for building a quantum communication sensor network and paves the way for the functionality expansion of quantum communication networks.

In this study, a high integrated and broadband entropy source of quantum random number generator (QRNG) based on the vacuum fluctuation is designed and verified experimentally. The size of hybrid chip, which is the heart core of entropy source, composed of laser chip and silicon photonics chip is reduced to 6.3×2.6×1.5 mm3. The 3 dB bandwidth of the balanced homodyne detector in entropy source based on cascaded radio frequency amplifier is 2.4 GHz, and the common mode rejection ratio was greater than 25 dB. A quantum to classical noise ratio of 9.48 dB was achieved when the photoelectron current is 1 mA. The noise equivalent power is 8.85 pW/√Hz, and the equivalent transimpedance is 22.8 K. The equalizer technology is utilized to optimize the quantum random number generation rate by eliminate the dependence of the adjacent samples. The quantum random number generation speed can achieve 67.9 Gbps under average conditional minimum entropy and 61.9 Gbps under worst-case conditional minimum entropy. The hybrid chip in our paper promote the QRNG entropy source based on vacuum fluctuation to a higher integration and faster stage.