Quantum Key Distribution based on Silicon Integrated Photonic Devices

We present a compact quantum key distribution (QKD) transmitter near a 1550-nm wavelength using microring modulators implemented on a silicon-on-insulator photonics platform. The transmitter generates time-bin based qubits with a temporal FWHM of 940~ps and an extinction ratio beyond 16~dB. We prove the feasibility of the transmitter with a coherent one-way QKD protocol, where the bit string is encoded in the arrival time of the time-bin qubits and possible eavesdropping is monitored via the intereference visibility of neighboring time-bin qubits~\footnote{B. Korzh, C. C. W. Lim, R. Houlmann, N. Gisin, M. J. Li, D. Nolan, B. Sanguinetti, R. Thew, and H. Zbinden, Nature Photonics \textbf{9}, 163--168 (2015)}. The receiver consists of an asymmetric beamsplitter, which provides a random choice of measurement basis, followed by either a superconducting nanowire single-photon detector (SNSPD) or an unbalanced Michelson interferometer with SNSPDs. This experiment demonstrates the feasibility of high-speed QKD based on CMOS-compatible silicon photonics integrated circuits.