Quantum Key Distribution through atmospheric turbulence: secure satellite-to-ground links

The ever-growing demands of modern telecommunication systems make secure data transmission both an essential requirement and a major challenge, and therefore a very active field of study. Quantum key distribution (QKD) enables the exchange of cryptographic keys whose level of security is intrinsically based on the exploitation of the properties of quantum mechanics. However, the deployment of QKD systems via terrestrial fiber networks is severely limited in distance due to attenuation, and since conventional amplification methods are not compatible with a quantum signal, satellite relays present themselves as an interesting alternative for establishing secure intercontinental quantum links.

We present a complete model of the atmospheric channel in the context of downlink QKD between a low-orbit satellite and the ground. This takes into account turbulence, its partial correction by adaptive optics (AO), geometric losses and the pointing jitter of the satellite. We use this model to evaluate the performance of three QKD protocols, for different system parameters and taking finite size effects into account. The results show the benefits of using an AO system, the performance in terms of key rate of all the protocols analyzed improves when considering an AO correction. To validate our simulation results, we have also begun to implement an experimental test bench based on a simplified emulation of the atmospheric channel and a CV-QKD system.