Title:
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Point-to-point and passive optical network quantum key distribution systems
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The emergence of a digital communications infrastructure over recent decades has fuelled
the parallel development of advanced cryptographic techniques, to secure the ever increasing
quantities of digital infonnation. From its foundation, quantum key distribution
has generated significant theoretical and experimental research interest since it offers what
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is currently the only method of verifiably secure cryptographic key distribution. By using
the Heisenberg Uncertainty Principle, quantum key distribution offers a technique by which
authorised parties can detect the potential presence of an eavesdropping unauthorised party
and take appropriate action.
Previous demonstrations of quantum key distribution have typically concentrated on
extending the maximum transmission distance over which communication may be
performed at the expense of bit-rates. This thesis investigates a quantum key distribution
system operating at a wavelength of 850 nm in standard telecommunications
fibre using commercially available silicon single-photon avalanche diodes to achieve
clock rates in excess of 1 GHz, with a corresponding increase in received bit-rates. The
principles of currently implemented passive optical networks are then applied to the system
to demonstrate multi-user quantum key distribution systems. In addition, the
point-to-point (single-user) system is demonstrated at a clock-rate of 3.3 GHz using low
timing jitter niobium nitride nanowire superconducting detectors to demonstrate the highest
clock-rate transmission in standard telecommunications optical fibre and the highest channel
loss to date. Finally, single-photon sources based on quantum dot microcavity resonators
are also examined for use in quantum key distribution.
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