PhD Thesis

PhD Thesis of
Matthew A. Broome
M.Phys. (Hons I) The University of Warwick

A thesis submitted for the degree of Doctor of Philosophy at
The University of Queensland in 2012
School of Mathematics and Physics
Supervisor: Professor Andrew White
Examiners: Professor Ian Walmsley (University of Oxford) & Professor Philip Walther (Universit├Ąt Wien)

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Title
Photonic Quantum Information and Quantum Walks

Abstract
Controlling quantum states of light is of central importance to many fields of modern physics. The technology to do so underpins the only feasible means for long-distance quantum communication using quantum-key-distribution, and plays a pivotal role in the application of quantum computing, quantum metrology and investigations of fundamental physics. Motivated by these applications, in this thesis we present a number of experimental results that demonstrate an enhanced level of control over photonic states. First, we tackle one of the most important technological issues currently facing the field, namely the creation of pure multi-photon Fock states from pulsed parametric downconversion. Our technique shows a marked improvement over previous photon sources when employed for quantum information tasks. At a more foundational level, we experimentally examine the properties of quantum correlations in the temporal domain, where our results highlight surprising differences between its spatial-domain counterpart of multipartite entanglement. Finally, we experimentally implement single- and multi-photon quantum walks in the discrete- and continuous-time regimes respectively. Quantum walks have received much attention in recent years due to their vast applicability in quantum information science, especially for quantum simulation and emulation. On this front we use the quantum walk formalism to perform a full experimental simulation of topological phases in a 1-dimensional configuration. Aside from being the first demonstration of topological phases in this regime, our system exhibits unprecedented control over the topological properties in a quantum system. As such we are able to observe the exotic behaviour of trapped bound states, and discover the new phenomenon of paired bound states—a feature unique to periodically driven systems.