  A high-rate continuous-variable quantum key distribution (CV-QKD) system
based on high-order discrete modulation is experimentally investigated. With
the help of the novel system scheme, effective digital signal processing
algorithms and advanced analytical security proof method, the transmission
results of 5 km, 10 km, 25 km, and 50 km are achieved for the 1 GBaud optimized
quantum signals. Correspondingly, the asymptotic secret key rate (SKR) is
288.421 Mbps, 159.395 Mbps, 50.004 Mbps and 7.579 Mbps for discrete Gaussian
(DG) 64QAM, and 326.708 Mbps, 179.348 Mbps, 50.623 Mbps and 9.212 Mbps for DG
256QAM. Under the same parameters, the achieved SKRs of DG 256QAM is almost
same to ideal Gaussian modulation. In this case, the demonstrated high-rate
discrete modulated CV-QKD system has the application potential for high speed
security communication under tens of kilometers.
