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The Best PhD Thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing Prize,1995-1997 / published_or_final_version / Physics / Doctoral / Doctor of Philosophy

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The study is focused on the thermal entanglement of spin chains. Chains consisting of two and three qubits are considered. These chains are considered open because they are coupled to bosonic baths at different temperatures. The baths represent the environment. The dynamics of these open systems are examined as are the effects of different parameters - such as bath temperature - on the entanglement of the spins. The measure of entanglement used in these cases is the concurrence. Comparisons are made between a model that assumes a strong spinspin interaction and one that assumes a weak one. In all these cases, analytical solutions for the system dynamics are presented. It is found that at large times, all systems converge to a state that depends only on bath temperature. It is also found that increases in bath temperatures diminish the entanglement between spins and that at high enough temperatures the entanglement vanishes altogether. The time and temperature dependence of the entanglement is different for the two models that are studied. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2010.

In this thesis I address two different topics in quantum theory. The first one is the long discussed Schrodinger's cat problem, and the issues related to having a macroscopic superposition state. I show that the quantum theory provides full explanation to the problem. In the second part, I discuss the time measurement related issues in quantum mechanics. Since there does not exist any time operator in quantum mechanics generally, time is not directly measurable. Therefore we should devise other methods to register time. We study different time-energy relations and will find that accurate clocks have high energy uncertainties. If we use accurate clocks in quantum systems to observe their time evolutions, their high energy uncertainties interfere with system's normal evolution and slows it down. I also provide a formal proof to a previously suggested limiting accuracy relation on the measurements of the time-of-arrival experiments.

This thesis studies deformation quantization and its application to contact interactions and systems with dissipation. We consider the subtleties related to quantization when contact interactions and boundaries are present. We exploit the idea that discontinuous potentials are idealizations that should be realized as limits of smooth potentials. The Wigner functions are found for the Morse potential and in the proper limit they reduce to the Wigner functions for the infinite wall, for the most general (Robin) boundary conditions. This is possible for a very limited subset of the values of the parameters -- so-called fine tuning is necessary. It explains why Dirichlet boundary conditions are used predominantly. Secondly, we consider deformation quantization in relation to dissipative phenomena. For the damped harmonic oscillator we study a method using a modified noncommutative star product. Within this framework we resolve the non-reality problem with the Wigner function and correct the classical limit. / iii, 188 leaves ; 29 cm

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This thesis compares the concepts presented in the Seventeenth Discussion of al-Ghazali's Tahafut al-Falasifa with concepts currently being discussed in the field of quantum physics. Written as an attack on the neo-Platonic and Aristotelian thinking which challenged the orthodox theology of Medieval Islam, Tahafut al-Falasifa (Incoherence of the Philosophers) questions the understanding of physical reality forwarded by the philosophers of al-Ghazali's times. The Seventeenth Discussion ('On causality and miracles') in particular, with its aim of proving the possibility of miracles, questions the acceptance of notions such as necessary causality and the validity of scientific observation in the natural world. / Although several scholars have examined al-Ghazali's argument in the Seventeenth Discussion in terms of causality, observation and the nature of human conceptions of physical reality, and many others have noted the implicit potential connections between quantum theory and concepts of religiosity, only one, Karen Harding, has attempted a synthesis of the ideas put forth within these two seemingly diverse subjects. This thesis, then, carries forward from the ideas of Harding and attempts an original comparative analysis of the two. (Abstract shortened by UMI.)

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Unable to copy abstract. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.