Thesis ( MSc ( Physics) ) -- University of Limpopo, 2013. / Background and Objectives: To establish whether the profiler 2 scanning system can be used as a substitute for the 3D-water phantom, by comparing the percentage depth doses and beam profiles for both the photons and electron beams, and validating the results using CMS XiO treatment planning system. Methods: Beam data (profiles, percentage depth doses and absolute dosimetry) were acquired for the two systems: (3D-water phantom and profiler 2 scanning system) for beam energies 6 MV and 15 MV photon beams, and 4, 6, 8, 10, 12 and 15 MeV electron beams generated by the Elekta Synergy linear accelerator (linac) for the field sizes of 6 × 6 cm2, 10 × 10 cm2, 14 × 14 cm2, 20 × 20 cm2, and 25 × 25 cm2 at depths of 0.5 cm, 1.0 cm, 2.0 cm, and 5.0 cm respectively. These measurements were acquired using ionization chambers in water and diode detectors in Perspex. The acquired data was sent to CMS XiO treatment planning system for validation. Results: In general, the dose distributions for both systems compared very well with uncertainties within recommended limits. The largest maximum difference in symmetry was 1.6 % for a 6 MV photon beam defined at 25 × 25 cm2 field size. The largest maximum difference in flatness was 2.77 % for a 4 MeV electron beam defined at 10 × 10 cm2 applicator size. The penumbra largest maximum difference was 1.708 cm for 8 MeV electron beam defined at 25 × 25 cm2 applicator size, which was outside the recommended limit of 1.2 cm. The largest maximum difference in field size was 2.388 cm for a 6 MeV electron beam defined at 20 × 20 cm2 applicator size, which was outside the recommended limit of 0.4 cm. The largest maximum difference in percentage depth dose at 10 cm depth was 1.69 % for the 6 MV photon beam. The absolute dose output measurements showed a very good agreement between the two systems to a maximum percentage difference and highest standard deviation of -0.99 % and 0.69 % respectively for the 6 MV photon beam. Validation measurements showed an agreement to less than 1 % and 2 mm for percentage depth doses and beam profiles respectively. Conclusion and recommendation: From the results obtained, it is evident that the profiler 2 scanning system can be used as a substitute for the 3D-water phantom beam data acquisitions during linear accelerator commissioning. The future work based on this study could be to study the limitations involved with the profiler 2 scanning system when used during measurements for commissioning of a linear accelerator. Limitations like field size (maximum field size of 20 × 30 cm2 at SSD = 100 cm), number of Perspex slabs to be used on top of the profiler 2 scanning system and diagonal profile measurements.

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No description available.

Thesis (Ph. D.)--University of California, Berkeley, June 1950. / Includes bibliographical references (p. 28).

Thesis (Ph. D.)--Ohio State University, 1972. / Includes bibliographical references. Available online via OhioLINK's ETD Center

Thesis (M.S.)--Montana State University--Bozeman, 2007. / Typescript. Chairperson, Graduate Committee: Charles W. Spangler. Includes bibliographical references (leaves 54-55).

Realization of linear quantum computation and establishing secure quantum communication among interacting parties demand for triggered quantum sources delivering genuine single and entangled photons. However, the intrinsic energy level spectrum of nanostructures made by the nature or developed under a random growth process energetically lacks the expected figures of merit to produce such quantized states of photons. Here, I present the semi-empirical modeling and experimental investigation on the spin fine structure of strongly confining quantum dots embedded in III-V nanowires. To this end, the quantum dot is numerically modeled via the Configuration Interaction method at two different levels: 1) single-particle level, where its pure energy level structure is resolved in the presence of strain and spin-orbit interaction. 2) Few-particle level, at which the few-body interactions appear as perturbative energy corrections and orbital correlations. I demonstrate the influence of quantum confinement on the binding energies and spin fine structure of excitons in the absence of hyperfine interaction. Importantly, the high-symmetry character of excitonic orbitals in nanowire quantum dots restore the degeneracy of optically-active ground-state excitons, offering an ideal spectrum for the entangled photon pair generation. To experimentally verify the idea, we design and fabricate defect-free nanowire quantum dots with ultra-clean excitonic spectrum, and construct the time correlation function of emitted photons through performing a series of low-temperature statistical quantum optics measurements. We observe a decent performance in terms of single photon generation under low excitation powers. Moreover, photon pairs emitted from the biexciton-exciton cascade of nanowire quantum dots exhibit color indistinguishability and polarization entanglement owing to the trivial fine structure splitting of the ground-state excitons. We further extend the idea by proposing the hybridized states of a nanowire-based quantum dot molecule as the potential source of higher-order entangled states. Tracing the field-dependent spectrum suggests the appearance of dominant features under the weak localization of electrons and coherent tunneling of holes. In addition to their Coulomb correlation, excitons also remain spatially correlated, opening new transition channels normally forbidden in the ground state of a single dot. The proposed structure can be exploited to create tripartite hybrid, GHZ and W-entangled states.

Cette thèse sera centrée sur les analyses des événements diphotons dans le détecteur ATLAS. L'activité évoluera au cours du temps et couvrira différents aspects: compréhension de la réponse du détecteur, participation a la prise de données, analyse physique et recherche de signaux de physique au-delà du modèle standard. / These thesis will be concentrated on the analysis of events involving two photons in the final state. The activity will evolve with time and will cover different aspects: understanding of the detector response, participation to the data taking, physics analysis and search for physics behind the Standard Model

No description available.

A dissertation submitted to the Faculty of Science in partial fulfillment of the requirements for the Degree of Master of Science School of Physics University of Witwatersrand November 1, 2017 / The generation and detection of entangled photons is a topic of interest in quantum communication. With current state-of-the-art methods it is possible to manipulate any degree of freedom (DoF) of photons, e.g, polarisation, transverse momentum, orbital angular momentum and energy. Furthermore, it is possible to combine these DoF to realise hybrid entanglement { entanglement between the DoF of photons. In this dissertation we focus on hybrid entanglement between photon states of coupled orbital angular momentum and polarisation. We engineer hybrid-entanglement using geometric phase control between spatially separated photons produced from spontaneous parametric down conversion. We present a new type of quantum eraser that does not rely on physical path interference. We show that in principle any other degree of freedom can be used and demonstrate this e ectively through polarisation control. The use of high dimensional hybrid photon states in quantum communication, particularly in quantum cryptography, is still in its infancy. Here we tailor photon states that are coupled in their polarisation and spatial DoF (orbital angular momentum) to realise high dimensional encoding alphabets. We show how photons entangled in their internal DoF can be generated and deterministically detected. We exploit them in a demonstration of a high dimensional quantum key distribution protocol and show that our scheme generates secure keys at high rates. / MT 2018