Experimental free-space continuous-variable quantum key distribution with thermal source

Passive-state-preparation (PSP) continuous-variable quan-tum key distribution (CVQKD) protocol explores the intrin-sic field fluctuations of a thermal source. Compared with traditional Gaussian-modulated coherent-state CVQKD, it does not need active modulations and has promising appli-cations in chip integration and portable free-space quantum key distribution. In this Letter, we propose and experimen-tally realize a PSP CVQKD scheme with transmitted local oscillator (LO) through fluctuating transmittance free-space channel using an off-the-shelf amplified spontaneous emis-sion source for the first time. By proposing thermal-state polarization multiplexing transmitted LO, synchronized channel transmittance monitoring and fine-grained phase compensation techniques, secure keys within -15 dB trans-mittance of simulated free-space channel with turbulence are generated, with a final average secure key rate of 1.015 Mbps asymptotically. Equivalent atmospheric turbulence model analysis shows that the free-space PSP CVQKD scheme provides a promising outlook for high-speed and chip-based CVQKD for kilometer-level atmospheric chan-nel networks.(c) 2023 Optica Publishing Group

Automated summary

The passive-state-preparation (PSP) continuous-variable quantum key distribution (CVQKD) protocol exploits the inherent field fluctuations of a thermal source. It does not require active modulations, making it promising for chip integration and portable free-space quantum key distribution.