Thesis (Ph. D.)--University of California, Berkeley, 1985. / Includes bibliographical references.

Thesis (M.S. in computer science)--Washington State University, August 2006. / Includes bibliographical references (p. 111-115).

Thesis (M.S.C.I.T.)--Regis University, Denver, Colo., 2009. / Title from PDF title page (viewed on Jun. 26, 2010). Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (p. 137-154).

Thesis (M.S.)--Rochester Institute of Technology, 1993. / Typescript. Includes bibliographical references.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 62-63). Also available via the Internet.

The development of a quantum computer presents one of the greatest challenges in science and engineering to date. The promise of more efficient computing based on entangled quantum states and the superposition principle has led to a worldwide explosion of interest in the fields of quantum information and computation. Among the number of hurdles which must first be cleared before we witness a physical realization are problems associated with environment-induced decoherence and noise more generally. However, the discovery of quantum error correction and the establishment of the accuracy threshold theorem provide us with the hope of someday harnessing the potential power a functioning fault-tolerant quantum information processor has to offer. This dissertation contributes to this effort by investigating a particular class of quantum error correcting codes, namely noiseless subsystem encodings. The passive approach to error correction taken by these encodings provides an efficient means of protection from symmetrically coupled system-environment interactions. Here I will present methods for determining the subsystem-preserving evolutions for noiseless subsystem encodings supported by arbitrary-dimensional physical quantum systems. Implications for universal, collective decoherence-free quantum computation using the derived operations are discussed. Moreover, I will present a proposal for an optical device which is capable of preparing a variety of these noiseless subsystem encodings through a postselection strategy.

Trapped atomic ions are one of the most promising systems for building a quantum computer -- all of the fundamental operations needed to build a quantum computer have been demonstrated in such systems. The challenge now is to understand and reduce the operation errors to below the 'fault-tolerant threshold' (the level below which quantum error correction works), and to scale up the current few-qubit experiments to many qubits. This thesis describes experimental work concentrated primarily on the first of these challenges. We demonstrate high-fidelity single-qubit and two-qubit (entangling) gates with errors at or below the fault-tolerant threshold. We also implement an entangling gate between two different species of ions, a tool which may be useful for certain scalable architectures. We study the speed/fidelity trade-off for a two-qubit phase gate implemented in ⁴³Ca^+ hyperfine trapped-ion qubits. We develop an error model which describes the fundamental and technical imperfections / limitations that contribute to the measured gate error. We characterize and minimise various error sources contributing to the measured fidelity, allowing us to account for errors due to the single-qubit operations and state readout (each at the 0.1% level), and to identify the leading sources of error in the two-qubit entangling operation. We achieve gate fidelities ranging between 97.1(2)% (for a gate time t_g = 3.8 μs) and 99.9(1)% (for t_g = 100 μs), representing respectively the fastest and lowest-error two-qubit gates reported between trapped-ion qubits by nearly an order of magnitude in each case. We also characterise single-qubit gates with average errors below 10^-4 per operation, over an order of magnitude better than previously achieved with laser-driven operations. Additionally, we present work on a mixed-species entangling gate. We entangle of a single ⁴⁰Ca^+ ion and a single ⁴³Ca^+ ion with a fidelity of 99.8(5)%, and perform full tomography of the resulting entangled state. We describe how this mixed-species gate mechanism could be used to entangle ⁴³Ca^+ and ⁸⁸Sr^+, a promising combination of ions for future experiments.

L’objectif de cette thèse est d’étudier des machines électriques à aimants permanents polyphasées et leur commande pouvant fonctionner en modes dégradés sur une large plage de vitesse dans le cadre d’une application de génération d’énergie hydrolienne. Ceci se justifie par le fait que, pour les applications liées à l’extraction d’énergie marine, les installations ne sont pas facilement accessibles pour des opérations de maintenance. Ainsi, des stratégies de commande ont été élaborées, pour des MSAP pentaphasées et à 2X3 phases, en mode sain et en modes dégradés, sur une large plage de vitesse avec un mode de défluxage. Une étude comparative a été faite sur le comportement en vitesse variable, en mode sain et en modes dégradés d’un certain nombre de MSAP à bobinage concentré autour des dents. Cette étude s’appuie sur un modèle analytique, qui estime à partir d’un cahier des charges et de la combinaison encoche/pôle, les inductances et les Forces électromotrices. Cet outil a permis également d’effectuer une première évaluation qualitative les phénomènes perturbateurs internes à la machine (Pertes dans les aimants et répartition des forces radiales) vis-à-vis de ces stratégies de commande. Enfin l’énergie extraite sur une durée significative en mode sain et en modes dégradés pour une turbine à pas fixe associée à plusieurs types de génératrices polyphasées a été quantifiée sur un site hydrolien typique (Raz de Sein). / The aim of this thesis is to study multiphase permanent magnet electrical synchronous machines (PMSM) and associated control strategies for tidal energy harnessing. These systems must be able to operate in fault mode in a wide range of speed. Indeed, for marine energy extraction applications, it is difficult to access to the site for maintenance operations. Specific control strategies in healthy and faults modes have been proposed, for 5 phases and 2X3 phases PMSM in a wide range of speed including flux weakening operations. A comparative study has also been done by evaluating the torque speed characteristics of several PMSM with fractional slot concentrated winding. This study is based on an analytical model which allows evaluating inductance values and EMF waveforms, from the knowledge of slot/pole combination of the machine windings. This analytical model allows evaluating qualitatively the impact of the control strategies on magnet losses and radial forces. Finally a practical case of tidal current energy extraction has been studied by quantifying extracted energy, in healthy and in faults modes for several multiphase electrical generators associated with a fixed pitch turbine in a typical tidal site.

Over the past several decades, we have experienced tremendous growth of real-time systems in both scale and complexity. This progress is made possible largely due to advancements in semiconductor technology that have enabled the continuous scaling and massive integration of transistors on a single chip. In the meantime, however, the relentless transistor scaling and integration have dramatically increased the power consumption and degraded the system reliability substantially. Traditional real-time scheduling techniques with the sole emphasis on guaranteeing timing constraints have become insufficient. In this research, we studied the problem of how to develop advanced scheduling methods on hard real-time systems that are subject to multiple design constraints, in particular, timing, energy consumption, and reliability constraints. To this end, we first investigated the energy minimization problem with fault-tolerance requirements for dynamic-priority based hard real-time tasks on a single-core processor. Three scheduling algorithms have been developed to judiciously make tradeoffs between fault tolerance and energy reduction since both design objectives usually conflict with each other. We then shifted our research focus from single-core platforms to multi-core platforms as the latter are becoming mainstream. Specifically, we launched our research in fault-tolerant multi-core scheduling for fixed-priority tasks as fixed-priority scheduling is one of the most commonly used schemes in the industry today. For such systems, we developed several checkpointing-based partitioning strategies with the joint consideration of fault tolerance and energy minimization. At last, we exploited the implicit relations between real-time tasks in order to judiciously make partitioning decisions with the aim of improving system schedulability. According to the simulation results, our design strategies have been shown to be very promising for emerging systems and applications where timeliness, fault-tolerance, and energy reduction need to be simultaneously addressed.