Tianxiang Zhan

Continuous-variable quantum key distribution (CVQKD) can allow remote users to share high-rate and unconditionally secure secret keys with capabilities of well compatibility with classical optical communication networks and effective resistance against background noise. We overcome the excess noise due to atmospheric effects especially in daylight without extra wavelength conversion and spectral filtering, and demonstrate for the first time all-day free-space quantum key distribution over 7 km in an urban atmosphere and 9.6 km in a marine atmosphere with Gaussian-modulated continuous variables. This achieved distribution distance of secure quantum secret keys is well beyond the effective thickness of the aerosphere, hence presenting a possible alternative way for realizing satellite-based quantum cryptography communication in daylight. Moreover, given that the CVQKD system is naturally compatible with existing ground fibre telecommunication networks, it marks an essential step for realizing integrated air-ground quantum access networks with cross-domain applications.