Spin-Based Quantum Computing with Silicon MOS Quantum Dots by Michael Allan Fogarty A thesis in fulfilment of the requirements for the degree of Doctor of Philosophy School of Electrical Engineering and Telecommunications Faculty of Engineering November 2018 PLEASE TYPE THE UNIVERSITY OF NEW SOUTH WALES Thesis/Dissertation Sheet Surname or Family name: Fogarty First name: Michael Other name/s: Allan Abbreviation for degree as given in the University calendar: PhD School: Electrical Engineering and Telecommunications Faculty: Engineering Title: Spin-Based Quantum Computing with Silicon-MOS Quantum Dots Abstract 350 words maximum: (PLEASE TYPE) This thesis describes advancements in the silicon metal-oxide-semiconductor (SiMOS) quantum dot qubit platform. Recent experimental realisations of coherent single qubit and two qubit operations calls for the demonstration of a fully integrated SiMOS platform, showing a scalable implementation of all necessary elements for quantum computation operating together. Integration of qubit initialisation, control and readout via methods considered robust against scaling qubit array dimensions is the first fundamental step towards realising fully error corrected qubit registers useful for quantum computation. This thesis commences by analysing the result of standard experiments for benchmarking performance and integrity of a singular SiMOS qubit. This experiment, known as Randomised Benchmarking, yields uncharacteristic results for the SiMOS platform when compared to experiment theory and other results in literature. This is addressed through extending the experiment to take low-frequency environmental fluctuations into account. Resulting analysis indicates that fidelities for the majority of qubit operation is considered above the threshold for fault-tolerant quantum computation. Having demonstrated high quality qubit control using SiMOS quantum dots, the capability of preparing and measuring qubits via methods robust against scaling are detailed. Recent studies have detailed how the singlet-triplet basis can be utilised for the initialisation and readout of qubits within a scaled quantum register. These techniques are discussed and experimentally demonstrated in a SiMOS quantum dot device alongside single qubit addressability through electron spin resonance. Electrostatic control over the Heisenburg exchange coupling between two adjacent dots produces a two­ qubit SWAP operation realised in this device. These results together demonstrate, for the first time within a single silicon qubit device, the initialisation and readout of qubit pairs by scalable methods integrated with single qubit addressability and two-qubit logical operations. Furthermore, having experimentally realised integration of fundamental building blocks of a scaled quantum register, what follows is a discussion of how this platform can be scaled into demonstrations of a fully error corrected logical qubit. Experimental state-of-the-art in SiMOS technology is discussed in the context of this logical qubit protocol, which employs quantum dots as both data qubits and singlet-triplet ancillas. 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FOR OFFICE USE ONLY Date of completion of requirements for Awa"rd: i Copyright Statement I hereby grant the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstract International (this is applicable to doctoral theses only). I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertation. Date ,1_�/:.?/�r...... ····•· . ii Authenticity Statement I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format. Date ,1_�/:.?/�r...... ····•· . iii Abstract This thesis describes advancements in the silicon metal-oxide-semiconductor (SiMOS) quantum dot qubit platform. Recent experimental realisations of coherent single qubit and two qubit operations calls for the demonstration of a fully integrated SiMOS platform, showing a scalable implementation of all necessary elements for quantum computation operating together. Integration of qubit initialisation, control and readout via methods considered robust against scaling qubit array dimensions is the first fundamental step towards realising fully error corrected qubit registers useful for quantum computation. This thesis commences by analysing the result of standard experiments for benchmarking performance and integrity of a single SiMOS qubit. This experiment, known as randomised benchmarking, yields uncharacteristic re- sults for the SiMOS platform when compared to experiment theory and other results in literature. This is addressed through extending the experiment to take low-frequency environmental fluctuations into account. Resulting anal- ysis indicates that fidelities for the majority of qubit operation is considered above the threshold for fault-tolerant quantum computation. Having demonstrated high quality qubit control using SiMOS quantum dots, the capability of preparing and measuring qubits via methods robust against scaling are detailed. Recent studies have detailed how the singlet- triplet basis can be utilised for the initialisation and readout of qubits within a scaled quantum register. These techniques are discussed and experimen- tally demonstrated in a SiMOS quantum dot device alongside single qubit addressability through electron spin resonance. Electrostatic control over the Heisenburg exchange coupling between two adjacent dots produces a two-qubit SWAP operation realised in this device. These results together demonstrate, for the first time within a single silicon qubit device, the ini- tialisation and readout of qubit pairs by scalable methods integrated with single qubit addressability and two-qubit logical operations. iv ABSTRACT Finally, having experimentally realised integration of fundamental build- ing blocks of a scaled quantum register, what follows is a discussion of how this platform can be scaled into demonstrations of a fully error corrected log- ical qubit. Experimental state-of-the-art in SiMOS technology is discussed in the context of this logical qubit protocol, which employs constituent quantum dots as both data qubits (the carriers and propagators of quantum informa- tion) or singlet-triplet ancilla qubits for error detection. v Acknowledgement The work presented within this dissertation was primarily supervised by Sci- entia Professor Andrew Dzurak, with co-supervisors Dr. Menno Veldhorst and Professor Andrea Morello. Without the support I received from these three great researchers, this manuscript would not exist. First and foremost, I would like to thank my primary supervisor Andrew Dzurak. The continual support and mentorship he has provided throughout my studies has been invaluable. The passion and enthusiasm Andrew shows for his research is truly inspiring, an attitude which continually fuels a pro- ductive and interesting workplace. He has facilitated many opportunities for me to present my research, form new and fruitful collaborations and develop as a young researcher. It has been a privilege and an honour to be a part of his research team. My co-supervisor, Professor Andrea Morello, was first person to introduce me to the concepts of quantum computing. Taking his course on quantum devices was a pivotal moment, and the advice he has pro- vided to me throughout my early career has been invaluable. The first year of my studies was co-supervised by Dr. Menno Veldhorst, who coached me through my first hands-on experience with an actual qubit device. Many of the skills I learned under his guidance during this time facilitated the success of my experiments in later years of my studies. I would like to acknowledge the past and present members of the Dzurak lab for their support, in particular the post-doctoral