The evolution of free-space quantum key distribution

Abstract

In this paper we are looking at the milestones that were achieved in free−space quantum key distribution as well as the current state of this technology. First a brief overview introduces the technical prerequisites that will help to better understand the rest of the paper. After looking into the first successful demonstrations of short range free space QKD both indoor and outdoor, we are examining the longer range terrestrial QKD experiments. In the next step we look at some experiments that were aiming to take free space QKD to the next level by placing the sender or the receiver on moving vehicles. After the terrestrial demonstrations we focus on satellite based experiments. Finally, we explore hyper-dimensional QKD, util-ising energy−time, polarization and orbital angular momentum (OAM) degrees of freedom.