An Approach to Optimising the Design of a Repeaterless Global Quantum Network

Abstract

A global quantum network will soon be possible, however investigations on its design are limited. Fibre-based optimisations focus on device placement. Cost analysis including nodes, fibres and usage of optical switching has been insufficiently explored. Satellite quantum key distribution is important for global reach. Research focuses mainly on optimal satellite configuration and satellite access. The integration of satellite-ground station networks into core fibre networks is insufficiently explored. This thesis aims to develop a mathematical foundation and investigate how to best design a repeaterless global quantum network. We propose a new optical switched quantum network paradigm using Twin-Field quantum key distribution. We show that this paradigm improves key rates and coverage area from prior designs. We develop mixed-integer linear programming models to optimise detector placement and consider switching in such networks, proving it to be very beneficial. We develop mixed-integer linear programming models to optimise trusted node and fibre placement in trusted node quantum networks with and without switching. We show that switching is beneficial at low transmission requirements but detrimental at higher transmission requirements. All models show the importance of low insertion loss and infrequent switching in ensuring switch usage remains viable. We adapt these models to investigate a proposed UK quantum network and determine the optimal design. We show the importance of identifying bottlenecks, demonstrating bottleneck bypasses can significantly improve performance. We investigate the problem of minimising detector nodes in trusted node quantum networks using a mixed-integer linear programming optimisation model. We demonstrate that our proposed heuristic generally determines optimal solutions significantly faster. Finally, we design mixed-integer linear programming models optimising the integration of core fibre networks with satellite quantum key distribution, using them to demonstrate that appropriate satellite-ground station allocation and satellite network optimisation in tandem with the core fibre network significantly reduces network costs.