Optimizing quantum communication through hybrid technology.

Quantum Key Distribution (QKD) is a symmetric key sharing protocol. The theoretical process exploits the principles of quantum physics to underpin a physical security against any form of eavesdropping. QKD not only ensures an information theoretically secure key exchange but also provides an active real-time means of intrusion detection at a physical level. QKD is therefore considered the encryption technology for the next generation of nano-technology powered ICT solutions. The fundamental science at the basis of QKD has been researched and developed into workable solutions with the current focus on the engineering of quantum technology enabled products. The feasibility of integrating QKD systems into conventional communication solutions remains an active field of research. The implementation of QKD across a conventional communication network requires high levels of resources in terms of the network’s reliability, transparency, delay and bandwidth. This limits the maintainable Quality of Service of the network. Investigations towards overcoming these constraints will promote the uptake of QKD as a mainstream technology. There are two classes of technology that focus on the integration of QKD into conventional architecture. The first, and most immediate, development is the adaptation of conventional systems to handle the additional requirements of quantum technology enabled products. In the case of communication networks, all-optical solutions provide the ideal platform for this expansion. This ensures that the quantum data carriers remain in the quantum regime and are manipulated by only the authenticated end users or trusted nodes. The second, quantum technology enabled products, render techniques to manipulate quantum information in an untrusted environment within the network. This involves the development of quantum memories, repeaters and data collision control. The combination of both these classes as a hybrid solution will ensure an optimal Quality of Service for quantum communication networks. Optimizing Quantum Communication Through Hybrid Technology viii The long-term reasearch into quantum networking solutions is presented as the QuantumCity project. The project investigated the long-term stability of a quantum communication network within a live environment. The network is implemented through the adaptation of conventional switched networks. It has provided positive results with various future opportunities available to expand this initiative. The successful operation of the overall solution is of course dependent of the efficiency of the QKD systems themselves. While the European Telecommunication Standards Institute (ETSI) currently drives the standardisation (ETSI ISG-QKD) of QKD, there is a need for the development of supporting technologies. This thesis aims to understand the current gaps in QKD systems and touch on various technologies that will be essential towards the development of a hybrid QKD solution. This will allow the integration of various established QKD technologies in order to optimally utilise conventional communications networks. The technologies focused on include true random number generators, polarisation-encoded QKD in fibre systems and polarisation tracking in free space units. A study and implementation of each technology is presented in this thesis.