Date of Award

8-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical and Computer Engineering

Committee Chair

Gerhard Klimeck

Committee Member 1

Rajib Rahman

Committee Member 2

Supriyo Datta

Committee Member 3

Michael Manfra

Committee Member 4

Lieven M. K. Vandersypen

Abstract

Spin qubits hosted in electrostatic quantum dots (QD) in Silicon (Si) are among the most promising candidates for building a large-scale quantum computer. Quantum information encoded in electron spins can survive longer in Si due to the scarcity of nuclear spin noise. We can also take advantage of the Si based nano-fabrication technology already in place for classical computers. Quantum computation has already been successfully demonstrated at small scale with Si QD spin qubits. Spin-orbit interaction (SOI) has previously been used to enable electrical manipulation of spins in other semiconductor materials. However, SOI is often ignored in Si as being small. Micro-magnets, that generate inhomogeneous magnetic field, have been integrated in Si QDs as an artificial source of SOI. In this work, a significant SOI, which is essential to understand the spin properties Si QDs even in the presence of micro-magnets, is identified at the Si/SiGe or Si/SiO2 interface. Also the SOI is governed by the atomic scale details of the Si interface. This dependence on the interface condition introduces device-to-device variability in the spin properties and can hamper the scalability of these qubits. A key figure of merit of a qubit is the dephasing time. In this work, a microscopic model of the spin dephasing in Si QDs are developed and recent experimental measurements are explained. SOI makes these qubits susceptible to the electrical noise and causes dephasing. Finally, ways to improve the dephasing time and reduce variability are discussed to aid building a large-scale quantum computer based on Si QD spin qubits.

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