Quantum state preparation of time-bin encoding based on TFLN integrated chips

We demonstrate a thin-film lithium niobate (TFLN) integrated photonic chip for time-bin–encoded quantum key distribution (QKD). The chip enables on-chip preparation of both time-basis and phase- basis quantum states required by the BB84 protocol. By exploiting the linear Pockels effect in TFLN, high-fidelity phase modulation is achieved without phase-dependent loss, resulting in stable and low-noise quantum state generation. The measured interference visibility reaches up to 98.74% for phase-basis states, while extinction ratios exceeding 22 dB are obtained for time-basis states. Furthermore, a chip-to-chip QKD experiment is implemented using TFLN integrated circuits at both the transmitter and the receiver to validate integrated time-bin quantum-state preparation and decoding. Based on experimentally measured device parameters, a one-decoy security analysis predicts positive secret key generation over a 10 km standard single-mode fiber link.