Experimental realization of free-space continuous-variable quantum key distribution based on fiber Sagnac interferometer.

The Gaussian-modulated coherent state (GMCS) is a well-known continuous-variable quantum key distribution (CV-QKD) protocol that is robust to incoherent background noise and can effectively suppress ambient light in free space. However, it is difficult to implement this protocol in free space using existing polarization coding schemes. In this Letter, we propose a polarization coding structure based on a self-compensating fiber Sagnac interferometer, which can reduce the required modulation voltage by two orders of magnitude and achieve fast and arbitrary polarization modulation, and experimentally demonstrate polarization coding-based GMCS CV-QKD for, it is believed, the first time.

Atmospheric effect study of continuous-variable quantum key distribution.

We proposed a data acquisition method to monitor local oscillator (LO) intensity in real time in unidimensional continuous-variable quantum key distribution protocol. Based on this proposed method, the influence of weather conditions on the average transmittance and excess noise is studied, such as relative wetness, visibility, and beam jitter.