Data Sheet 1_Round-the-clock QKD over a free-space-fiber channel with passive polarization-basis compensation.pdf

By combining spectral, temporal, and spatial filtering with optimized coincidence-window selection, threshold-compatible average QKD performance is maintained across these acquisition campaigns. The optimized daylight key rate and QBER are (6.39±0.81 kHz, 8.05±1.48%), while nighttime operation yields (6.98±0.81 kHz, 8.25±0.85%). Under representative operating conditions with 8.3% QBER, we obtain a final secure key rate of 351 Hz after reconciliation and privacy amplification.

To assess loss tolerance, we further emulate attenuation equivalent to a 1 km free-space link using controlled attenuation, demonstrating approximately 6 kHz raw key rate under 30% additional link loss. This attenuation study reproduces the additional loss budget only and does not constitute a physical kilometer-scale free-space demonstration. These results demonstrate that tomography-assisted measurement-basis correction can enable stable free-space entanglement-based QKD without high-bandwidth polarization tracking during key acquisition, providing a basis for future studies of more dynamic terrestrial and satellite-relevant quantum communication links.</p>