A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, May 3, 2016. / Spatial modes of light hold the possibility to power the next leap in classical and quantum communications. They provide the ability to pack more information into light, even into single photons themselves, while increasing the level of information security. In this quest, spatial modes carrying orbital angular momentum (OAM) have come under the spotlight due to their discrete in nite dimensional Hilbert space allowing, in theory, for an in nite amount of information to be carried by a photon. Here we study, theoretically and experimentally, spatial modes of two avours: scalar and vector modes. the dichotomy between the two avours is in their polarisation characteristics: scalar modes have spatially homogeneous polarisation elds, while vector modes do not. One facet of our work focusses on scalar mode carrying OAM; using digital holographic methods, we demonstrate the techniques used to tailor and analyse scalar optical elds. We discuss principles of generation and detection for scalar modes based on manipulations of the dynamic phase of light with spatial light modulators. We apply these techniques to characterise free-space and optical bre links, and demonstrate an increase in bandwidth with the additional modal channels. In the other facet of our work, we study vector vortex modes. A particular property exhibited by these modes is the non-separability of their degrees of freedom, a property traditionally associated with entangled quantum states. This raises the question: could quantum entangled systems be modelled with bright sources of vector vortex modes? We answer this question by applying vector vortex modes to the study of quantum transport of entangled states. We borrow techniques from quantum mechanics to evaluate the degree of non-separability of vector vortex modes, using the concurrence as our measure. By determining the evolution of the concurrence, and therefore the entanglement, of vector vortex modes in bres and free-space turbulent channels, we show that indeed, bright classical sources can be used to model the evolution of entangled quantum states in these channels. / TG2017

Ho Chiu Man. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 100-103). / Text in English; abstracts in English and Chinese. / Ho Chiu Man. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Historical Background --- p.1 / Chapter 1.2 --- Motivations of the Project --- p.3 / Chapter 1.3 --- Outline of Thesis --- p.4 / Chapter 2 --- Review on a One-dimensional Vibrating Cavity --- p.5 / Chapter 2.1 --- The R Function --- p.5 / Chapter 2.2 --- Photon Generation --- p.7 / Chapter 2.3 --- Instantaneous Mode Expansion --- p.10 / Chapter 2.4 --- Vacuum Energy Density --- p.15 / Chapter 3 --- Graphical Method --- p.17 / Chapter 3.1 --- Construction of R-function --- p.17 / Chapter 3.2 --- Fixed-point Analysis --- p.19 / Chapter 3.3 --- A Special Class of Mirror Trajectories --- p.23 / Chapter 3.4 --- Further Analysis --- p.27 / Chapter 4 --- Wave Evolution in a One-dimensional Vibrating Cavity --- p.32 / Chapter 4.1 --- Instantaneous Mode Expansion Method --- p.32 / Chapter 4.2 --- Transformation Method --- p.34 / Chapter 4.3 --- R-Method --- p.34 / Chapter 4.4 --- Consistency between Different Methods --- p.35 / Chapter 5 --- Floquet's Theory --- p.40 / Chapter 5.1 --- System of Linear Differential Equations with Time-dependent Coefficients --- p.40 / Chapter 5.2 --- Fundamental Set of Solutions and Matrizant --- p.41 / Chapter 5.3 --- System of Linear Differential Equations with Periodic Coefficients --- p.42 / Chapter 5.4 --- Possible Properties of the Solution --- p.43 / Chapter 5.5 --- Eigenvalues for the One-dimensional Vibrating Cavity --- p.44 / Chapter 6 --- Photon Creation in an Oscillating Spherical Cavity --- p.46 / Chapter 6.1 --- Mode Decomposition --- p.46 / Chapter 6.2 --- Bogoliubov Transformation --- p.48 / Chapter 6.3 --- Photon Creation --- p.51 / Chapter 6.4 --- Mean Electric Field Operator --- p.53 / Chapter 6.5 --- Illustrations and Observations --- p.54 / Chapter 7 --- Multiple Scale Analysis --- p.61 / Chapter 7.1 --- Photon Creation by First-order Multiple Scale Analysis --- p.61 / Chapter 7.2 --- Parametric Resonance --- p.64 / Chapter 7.3 --- Nonstationary Medium --- p.71 / Chapter 7.4 --- Photon Statistics --- p.74 / Chapter 7.5 --- Finite Temperature Correction --- p.75 / Chapter 8 --- Squeezing Effect of the Classical Waves --- p.76 / Chapter 8.1 --- Squeezing Effect in the One-dimensional Vibrating Cavity --- p.76 / Chapter 8.2 --- Squeezing Effect in the Oscillating Spherical Cavity --- p.81 / Chapter 9 --- Supersymmetric Approach to Photon Generation --- p.88 / Chapter 9.1 --- Field Quantization --- p.88 / Chapter 9.2 --- Adiabatic Approximation --- p.90 / Chapter 9.3 --- Scattering Interpretation --- p.91 / Chapter 9.4 --- Supersymmetric Approach --- p.93 / Chapter 9.5 --- Examples --- p.94 / Chapter 10 --- Conclusion --- p.98 / Bibliography --- p.100

Quantum photonic technologies have many exciting applications including secure commu- nication, quantum enhanced measurement and quantum computing. Linear optical quantum computing (LOQC) is a technology of particular interest - especially given that recent progress in on-chip waveguide technology removes the requirement for complex and costly bulk optics setups and state-of-the-art detectors have detection efficiencies of over 90%. Arguably the largest remaining technological hurdle for LOQC is the development of a suitable photon source. A suitable source would produce single, indistinguishable photons deterministically. Additionally, it would be beneficial if the generated photons were entangled, as this can significantly reduce the degree of multiplexing needed to implement LOQC. Quantum dots are a suitable candidate system for these photon sources as they exhibit bright single photon emission and can act as the interface between light and a trapped spin qubit. These properties have resulted in proposals to generate multi-photon entangled states suitable for use in LOQC. This thesis presents some of the progress we have made towards the creation of a suitable photon source. After introducing the background material, we demonstrate pulsed resonant excitation using a single-electron-charged quantum dot. Deterministic excitation is demonstrated by performing Rabi oscillations and Ramsey interference in the excitonic population. We also investigate Ramsey interference in a Faraday geometry magnetic field and observe a variety of beats and oscillations in the interferograms. We develop a model to explain our results and conclude that controlling the phase between the two Ramsey interference pulses allows a degree of control over the state of the trapped spin. We then also demonstrate the coherent optical manipulation of a trapped spin in a Voigt geometry magnetic field. Once we have presented the manipulation of the excitonic state and the state of the trapped spin, we proceed to investigate the properties of the light produced by the resonant excitation of a quantum dot. Hong Ou Mandel interference experiments allow us to probe the indistinguishability of the photons resulting from the resonant excitation of the negative trion transition. Repeating the measurement using light generated from a similar system (this time with a trapped hole rather than a trapped electron) that is embedded in a micropillar cavity, we find that the cavity enhancement of the transition results is higher indistinguishabilities. We make use of this bright source of indistinguishable photons to perform an on-chip quantum enhanced measurement and observe the phase superresolution associated with N00N states. In the final experimental chapter, we propose and implement a scheme to generate multi- qubit single photon states. We show that by repeatedly driving a micropillar-cavity-enhanced Raman transition of a single-hole-charged quantum dot in a Voigt geometry magnetic field it is possible to coherently superpose a photon across multiple time bins. The scheme is conceptually similar to proposed schemes for producing multi-photon entangled states. Lastly, we propose a scheme that makes use of the capabilities shown in the three experimental chapters to overcome several of the experimental difficulties associated with generating multi-photon entangled states.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 79-81). Also available in electronic version.

This dissertation presents the results of a search in the exclusive photon plus missing transverse energy (gamma + E/_T) final state in proton antiproton collisions at center of mass energy of 1.96 TeV using the Collider Detector at Fermilab experiment. The strategy used here is to search for delayed photons coming from gauge mediated supersymmetric events with the exclusive production of ~X(0 1) -> gamma~G. In these models the ~X(0 1) is the lightest neutralino and has nanosecond lifetime before decaying to a photon (gamma) and gravitino (~G) which exits the detector unrecorded. In order to search for this process we select collisions that have a single photon plus missing transverse energy and little other activity in the detector and examine the arrival time of the photon. This arrival time is then compared against expectations from a data driven background of the standard model sources. In the data collected from the Fermilab Tevatron collider from December 2004 to June 2010, representing 6.3 fb^-1 of data, we observe 322 events in the photon arrival timing region from 2 nanoseconds to 7 nanoseconds with a data driven background prediction of 257 +/- 35. An excess of 65 events is observed, equivalent to a standard deviation (N_sigma) of 1.65 from the null hypothesis.

Diss.--Hamburg Universität, 2000. / Bibliogr. p.169-178.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

For applications in Quantum Information and Quantum Key Distribution an on-demand source of single photons is desirable because absolute security is of utmost importance. Photons are quantum systems; hence encoding information onto them offers a secure alternative to classical cryptography as a measurement cannot be performed on photons without altering their properties. The Nitrogen Vacancy (NV) centre in diamond is a good source of such photons. It is photo-stable and its location in diamond offers robustness. It has zero phonon line at 637 nm and its relative short luminescence life-time of about 12 ns makes it suitable for generating single photons. This thesis covers two aspects: Firstly the characterization of defects in diamonds and subsequent selection of diamonds suitable for use in the single photon setup and secondly, the development of the experimental setup for single photon generation. This thesis sets out to describe the development of a laboratory based single photon source using the NV centre in diamond. For this purpose a suite of diamond samples were selected and subjected to various spectroscopic tests in order to characterize and classify the samples, especially the presence of the NV centres and their concentrations. The characterization of the defects was done through the use of the following spectroscopic techniques: Ultraviolet-Visible-Near infrared spectroscopy, Infrared spectroscopy, Electron Spin Resonance and Photoluminescence. These techniques enabled us to understand the types and origins of crystal defects that were present in the diamond samples used in this study and to use this to select diamonds that are most suitable for use in generation of single photons. The experimental setup for single photon generation using the NV centre is based on a confocal microscope arrangement. Single NV centres were identified by measuring the second order autocorrelation function of the fluorescence light emitted by the sample when illuminated with a laser. This measurement was done using a Hanbury-Brown Twiss (HBT) interferometer. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2009.

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