Nonequilitrium effects in nanostructures: applications to solid state quantum computation and spintronics

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The longstanding progress of conventional semiconductor technology is expected to come to a halt in the next ten to twenty years. As the size of transistors approach the nanometer scale severe problems related to miniaturization and energy dissipation will hinder further improvement of conventional devices. This anticipation is motivating the development of alternative devices that take advantage of the quantum nature at the atomic scale. A notable example is the quantum computer concept, where each bit is formed by a single atom or a group of a few atoms, and the rules of quantum mechanics dictate the way information is processed. Another interesting alternative is spintronics, where the spin of the electrons instead of their charge forms the basis for classical memory and logic, promising much lower rates of energy dissipation per device. This research project addresses several theoretical questions related to the design and optimization of quantum computer and spintronic devices based on semiconductor, superconductor, and magnetic nanostructures. We will investigate the physical origin of noise and decoherence affecting quantum computers based on superconducting nanostructures. Our goal is to control the imperfections inherent to these devices in order to allow the development of large-scale fault-tolerant quantum hardware. We will also study spin-dependent transport effects in silicon nanostructures implanted with a single or a few paramagnetic impurities. This research is oriented towards optimizing the transduction of the spin state of the impurities into a source-drain voltage in a silicon device, with possible applications to silicon-based quantum computation and spintronics. Another problem that will be addressed is the question of electrical control of magnetism in multiferroic materials. These materials possess coexisting ferroelectric and magnetic order, allowing effective gate control of magnetism with possible applications to novel spintronic devices.