  Quantum key distribution (QKD) can provide fundamentally proven security for
secure communication. Toward application, the secret key rate (SKR) is a key
figure of merit for any QKD system. So far, the SKR has been limited to about a
few megabit-per-second. Here we report a QKD system that is able to generate
key at a record high SKR of 115.8 Mb/s over 10-km standard fibre, and to
distribute key over up to 328 km of ultra-low-loss fibre. This attributes to a
multi-pixel superconducting nanowire single-photon detector with ultrahigh
counting rate, an integrated transmitter that can stably encode polarization
states with low error, a fast post-processing algorithm for generating key in
real time and the high system clock-rate operation. The results demonstrate the
feasibility of practical high-rate QKD with photonic techniques, thus opening
its possibility for widespread applications.
