Advanced quantum communications for next-generation secure optical networks

Abstract

New quantum technologies are set to radically change many fields, including computation,
sensing and communication. However, the question of building a large-scale quantum
computer is a matter of when not if. These computers exploit quantum mechanics to
solve hard and complicated mathematical problems which are unsolvable using conventional
classical computers. These mathematical problems are the base of our public-key cryptography
algorithms, which are used in our daily lives and critical infrastructure and will be broken using
a quantum computer.
Quantum key distribution (QKD) enables the exchange of theoretically secure symmetrical
random keys based on the fundamentals of quantum mechanics. QKD relies on the exchange of
single photons between two distant parties in an end-to-end configuration, making it extremely
difficult to integrate with the current classical infrastructure. In this thesis, we will explore the
feasibility of integrating QKD technologies into the existing classical infrastructure.
We first demonstrate commercial QKD systems as a part of a deployed fibre network in the
city of Bristol. The network includes a software-defined networking controller and allows the
coexistence of classical and quantum channels in a single fibre to ensure compatibility with
current and future infrastructure. The network also enables dynamic switching for the QKD
systems overcoming end-to-end configuration and reducing implementation costs. In addition,
we develop several coexistence schemes in advanced mediums, including multicore fibre, hollow
core fibre, and free space, to provide a comprehensive view of different coexistence techniques
and their implementation in different use cases.
Finally, we move towards entanglement-based quantum networks, which are considered
the backbone of future quantum communication applications. We implement an advanced
architecture to provide a flexible and on-demand allocation of entanglement across different
users and allows dynamic networking for multiple quantum protocols in the network. We also
integrate the hollow core fibre into the network to enable the coexistence of quantum and
classical channels in a single fibre.

Date of Award	21 Mar 2023
Original language	English
Awarding Institution	University of Bristol
Supervisor	George Kanellos (Supervisor) & Reza Nejabati (Supervisor)