Momentum Distributions: An Overview

J. W. Clark, MANFRED L. RISTIG

Abolhassani, Rojan

This thesis includes two main projects that explore the use of structured light, especially photonic orbital angular momentum (OAM), in quantum key distribution protocols. Particular attention has been paid to how different modes behave in turbulent channels and how adaptive optics systems can mitigate the distortions induced in the beam. Based on the results of these experiments, we propose a new protocol designed to combine the qualities that make a light mode ideal for turbulent channels and adaptive optics systems. The security analyses and performance evaluations of this new protocol are discussed. In the first chapter, a brief overview of the field is provided. Following that, the second chapter aims to explore the necessary background for understanding the two projects in more detail. We discuss the different degrees of freedom of light and how they can be utilised to help achieve our goals. In the third chapter, the mathematical background relevant to the first project is covered. This includes the modes investigated in the turbulent channel and AO system. In the fourth chapter, an overview of the theory of security in quantum key distribution is presented, followed by an article on a new protocol for QKD. Finally, the conclusions and outlooks are outlined in the last chapter.

MANFRED L. RISTIG, J. W. Clark

Tamas Bisztray, László Bacsárdi

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, utilising energy−time, polarization and orbital angular momentum (OAM) degrees of freedom.

Huan Zhang, Zhenyu Cao, Yu Sun +1 more

High-dimensional quantum key distribution (HD-QKD) enhances information efficiency and noise tolerance by encoding data in large Hilbert spaces. The orbital angular momentum (OAM) of light provides a scalable basis for such encoding and supports high-dimensional photonic communication. Practical OAM-based implementations remain constrained by challenges in state generation, transmission, and detection. This survey offers a consolidated overview of OAM-encoded HD-QKD, outlining fundamental principles, representative experiments, and system-level limitations. Recent progress in hybrid encodings, mode sorting, adaptive optics, and TF, CV, MDI, and DI frameworks is summarized with emphasis on practical feasibility.