Quantum properties of nanostructured semiconductorsSpin-orbit, entanglement and valley physics

Resumen

Silicon is the most important semiconductor material, being present in all the electronic devices around us. This material has also drawn attention due to its useful properties for the construction of a scalable quantum computer which, at the same time, would be compatible with classical devices. Among these features, its extraordinary quantum coherence, due to the negligible spin-orbit interaction for electrons and the ability to get rid of nuclear spins by isotopic purification, stands out. However, quantum state manipulation requires the application of oscillating and, often, localized magnetic fields which require too much power while being experimentally challenging. Besides, the original proposals for entanglement protocols impose complex restrictions to the devices, which are technologically complicated. In this thesis, alternatives for quantum computation in semiconductors are proposed. The first of these options is the use of hole bound states instead of electron states. Holes bound to acceptors in Silicon are inherently susceptible to the spin-orbit interaction, which allows the possibility to define quantum bit (qubit) electrically manipulable, potentially much more efficient to manipulate than with magnetic fields. At the same time, it paves the way for new possibilities to generate entanglement between qubits. The effects of spin-orbit interactions on the qubit coherence will also be addressed. When electrons are considered, the degenerate minima (valleys) in the conduction band add a new degree of freedom which has to be taken into account. In this thesis, the valley physics of quantum dot bound states is analyzed in two different geometries. These states also allow the interaction with electric fields, simplifying the scalability. In exchange, the coherence properties can be affected. The valley degree of freedom is affected by the nanostructure confinement and electric fields, which gives a particular flexibility that can be used to improve the coherence properties. Finally, the use of two-dimensional materials is proposed as another alternative. Two-dimensional materials are being studied for their many unusual properties and potential applications. We explore the feasibility of using dopants in these materials to define qubits.