  Future quantum communication infrastructures will rely on both terrestrial
and space-based links integrating high-performance optical systems engineered
for this purpose. In space-based downlinks in particular, the loss budget and
the variations in the signal propagation due to atmospheric turbulence effects
impose a careful optimization of the coupling of light in single-mode fibers
required for interfacing with the receiving stations and the ground networks.
In this work, we perform a comprehensive study of the role of adaptive optics
(AO) in this optimization, focusing on realistic baseline configurations of
prepare-and-measure quantum key distribution (QKD), with both discrete and
continuous-variable encoding, and including finite-size effects. Our analysis
uses existing experimental turbulence datasets at both day and night time to
model the coupled signal statistics following a wavefront distortion correction
with AO, and allows us to estimate the secret key rate for a range of critical
parameters, such as turbulence strength, satellite altitude and ground
telescope diameter. The results we derive illustrate the interest of adopting
advanced AO techniques in several practical configurations.
