Towards the real-world implementation of high dimensional quantum key distribution in free-space

Abstract

This thesis consists of multiple projects that work towards the realistic implementation of real-world high-dimensional quantum key distribution protocols within the confines of Earth's atmosphere. First, we investigate the behaviour of the atmosphere of a 5.4 km free-space channel over the city of Ottawa, Ontario, Canada. This data was collected over a period of 9 months, and is ongoing as of the writing of this thesis. Using the data collected, we have created an AI-based approach to predict atmospheric conditions up to 12 hours in advance. We then performed a simulated quantum communication protocol under different atmospheric conditions to predict the performance of such a protocol. This AI tool will be capable of providing performance forecasts of future quantum networks. Next, we investigate the implementation of an adaptive optics system into a laboratory-scale quantum communications channel with turbulence. We investigated the effects of the turbulence on the transmission of the optical modes through the channel as well as the restorative effects of the adaptive optics system. These results are placed in the context of the theoretical performance of a quantum key distribution system, showing that the implementation of adaptive optics allows for quantum communications where it was otherwise impossible. These two works pave the way for future quantum networks operating under atmospheric conditions. We have shown that it is possible to confidently provide predictions of the quality of a quantum channel. However, in the future, this could be applied to a quantum network with many nodes and channels, potentially allowing for optimization of the network according to future weather conditions. The same network would additionally benefit from the implementation of adaptive optics, allowing for quantum communications when it would otherwise render the network ineffective.