Quantum communications in a moderate-to-strong turbulent space

Abstract Since the invention of laser in 60s, one most fundamental communication channels has been free-space optical channel. For this type channel, a number effects generally need to be considered, including diffraction, refraction, atmospheric extinction, pointing errors and, importantly, turbulence. Because all these adverse features, (FSO) channel is more difficult study than stable fiber-based link. same reasons, only recently it possible establish ultimate performances achievable quantum communications via channels, together with practical rates for continuous variable (CV) key distribution (QKD). Differently from previous literature, mainly focused on regime weak turbulence, work considers FSO challenging moderate-to-strong where beam widening and breaking are important wandering. This may occur long-distance links ground, uplink high-altitude platform systems (HAPS) interestingly, downlink near-horizon satellites. In such we rigorously investigate limits show that composable keys can extracted using CV-QKD.