Satellite-Earth Quantum Communication: Modeling Daytime Free-Space Atmospheric Channels and Interfaces

Daytime sky radiance easily overwhelms quantum signals transmitted over satellite-to-Earth quantum channels. Recent demonstrations of satellite-Earth quantum communication were performed under nighttime conditions to avoid this problem. Restricting the ground terminal field of view (FOV) is an effective technique for spatially filtering sky noise. Atmospheric turbulence however limits the extent to which spatial filtering can reduce sky noise without introducing signal losses. Interfaces from the channel to quantum systems are also adversely affected by turbulence. In the case of single-mode-fiber-(SMF-) coupled components, turbulence leads to large mode-coupling losses. This applies to SMF-coupled quantum detectors, atomic systems, integrated photonics and fiber networks. This presentation reviews results from numerical simulations of daytime satellite-Earth quantum channels and SMF interfaces enabled by ultra-narrow spectral filtering and adaptive-optics-based techniques. Numerical simulations include low-Earth-orbit propagation losses, sunrise-to-sunset hemispherical distributions of sky radiance, the statistical nature of Kolmogorov turbulence, and the effects of an atomic-line spectral filter and an adaptive optics system under closed loop control. Quantum information metrics quantify the performance of daytime quantum channels over a range of sky angles where satellite passes can occur.