Download or read book In Pursuit of Quantum Hardware written by Samuel Neyens and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The potential power of quantum algorithms to solve problems that are currently computationally intractable has launched investigations into a wide range of quantum systems with the goal of developing quantum hardware. Among these candidate systems for encoding quantum bits (qubits), electron spins localized in gate-defined quantum dots are promsing. In particular, quantum dots defined in Si/SiGe heterostructures have a number of advantages, including a low defect density and a low intrinsic density of interfering nuclear spins. This work presents a series of investigations into gate-defined quantum dots formed in Si/SiGe heterostructures. A key parameter for the performance of quantum dot qubits hosted in Si is the valley splitting energy. In Si/SiGe heterostructures, controlling the valley splitting remains an outstanding challenge. Here we present measurements of valley splitting in Si/SiGe heterostructures with varied Ge concentration profiles. The measured scaling of the valley splitting with vertical electric field is compared with tight-binding simulations of heterostructures with interfacial steps, and the agreement in scaling provides evidence for the important role played by interfacial disorder in setting the valley splitting in these samples. Additionally, for gate-defined quantum dots, a key device element is the dielectric layer which mediates the electric fields between the gate electrodes and the gate-defined dots. We discuss experiments to test a novel method for generating a gate dielectric for Si/SiGe quantum dots using thermal oxidation at 700 degrees C. Another critical component towards developing quantum processors based on quantum dots is the engineering of strong and controllable inter-qubit coupling. For double quantum dot qubits with an effective charge dipole moment, a capacitive dipole-dipole interaction can generate coherent coupling between neighboring qubits. Here we also discuss investigations into the capacitive interaction between double quantum dots in a quadruple quantum dot device. This includes a demonstration of the tuning of the capacitive coupling energy over a wide range using barrier gate voltages and analysis of the dependence of that coupling energy on device geometry. Finally, we present procedures for fabricating quadruple quantum dot devices in Si/SiGe using an architecture based on overlapping self-oxidized Al gates.