Xinlun Cai

Photonic integration in quantum communication holds significant potential for miniaturization and enabling commercial applications. Among various platforms, thin-film lithium niobate (TFLN) stands out due to its exceptional combination of high electro-optical efficiency, low propagation loss, and compact footprint. Here, we demonstrate a 2.5 GHz chip-to-chip fully integrated quantum key distribution (QKD) system based on a TFLN platform, which incorporates high-speed dual-polarization time-bin phase encoding and decoding functionalities. We achieve an extremely low quantum bit error rate of 0.53% and a secret key rate exceeding 10 Mbps over 25 km fiber spools. The design of cascaded Mach–Zehnder modulators effectively suppresses the patterning effect in high speed QKD. Notably, the TFLN chips used in both the transmitter and receiver share a similar architecture, highlighting the potential for creating a homogeneous transceiver. This work paves the way for high-speed, miniaturized QKD systems based on the lithium niobate integrated platform.