Satellite-to-ground quantum key distribution model under time-evolving turbulence

Atmospheric turbulence is the major challenge to satellite-to-ground quantum key distribution (QKD), yet most performance models treat turbulence only through average statistics, masking temporal loss fluctuations that dominate real links. Here we present an end-to-end, time-evolving satellite-to-ground QKD model that embeds a phase-screen description of turbulence into beam propagation, focusing, tracking, adaptive-optics compensation, and single-mode fiber (SMF) coupling. The simulation delivers the instantaneous channel loss L channel ( t ) and thermal photon dark counts D C bgn , from which we estimate the finite-size secret key rate (SKR) and evaluate the performance of turbulence mitigation techniques. For a GEO-to-Lijiang Station link, the optimized configuration enables day-and-night QKD operation under favorable weather conditions, although the daytime link margin remains limited. This study complements conventional time-averaged models by offering a more realistic and detailed framework for analyzing satellite-to-ground QKD performance and the effectiveness of mitigation techniques under time-evolving turbulence.