Technologies for Scaling Silicon-MOS Quantum Processors

Gate-defined quantum dots have been identified as a promising platform for quantum information processing thanks to low error rates, and the possibility for large-scale integration with industrial semiconductor manufacturing processes. With multiple recent demonstrations in semiconductor-based material stacks showing high-performance single- and two-qubit gates, the focus turns to how to scale-up these technologies. In this thesis, three advancements are presented in-depth for the scale-up of Silicon-MOS based quantum dot devices for quantum computation. Firstly, a passive filter/combiner is developed that behaves as a DC-coupled bias tee. This allows for linear combination of DC-bias voltages with broadband pulses (DC - 500 MHz) from an Arbitrary Waveform Generator (AWG), without AC-coupling the AWG line. These combiners are then optimised for low-power and integrated into the cryostat at the 4 K stage to reduce electrical noise. Secondly, we investigate devices based on Fully-Depleted Silicon-On-Insulator (FDSOI) technology manufactured in a full-scale 300mm wafer process as a platform for quantum dot based quantum processors. A double-nanowire device is configured such that a 2x2 array of quantum dots is formed in one nanowire, with a Single Electron Transistor (SET) formed in the other nanowire which is used as a charge sensor. The SET sensitivity is improved by the addition of floating gates between the nanowires, which increases capacitive coupling. The tunnel coupling between adjacent quantum dots is modelled, motivating modifications to the device design, and delineating a pathway towards adoption of CMOS industry processes for scalable manufacture. Finally, we demonstrate a technique that enables fully electrical control of electron spins by enhancing the intrinsic spin-orbit coupling (SOC), which is naturally weak for electrons in silicon. The SOC is enhanced by manipulating the energy quantisation spectrum of the quantum dot to create a level degeneracy. This can be achieved with pulses on gate electrodes, so that the SOC can be enhanced on-demand, allowing for a switchability between ON and OFF control modes. Microwave electrical control of quantum dots in the ON mode shows Rabi oscillation frequencies up to 81 MHz, and single qubit gate fidelities above 99.9%. The effect is reproducible across multiple devices and charge configurations. This technique could alleviate the need to integrate antennas or micromagnets on-chip.

Grantor dc:publisher

UNSW, Sydney

Year dc:date

2023

Author dc:creator

• Gilbert, William

• silicon
• quantum computing
• quantum dots
• electronics
• radio frequency
• CMOS
• anzsrc-for: 400912 Quantum engineering systems (incl. computing and communications)

Statement dc:rights

• open access
• CC BY 4.0
• free_to_read

Licence

• https://purl.org/coar/access_right/c_abf2
• https://creativecommons.org/licenses/by/4.0/

Language dc:language

en

Identifier

https://doi.org/10.26190/unsworks/24622

OAI identifier oai:identifier

oai:unsworks.library.unsw.edu.au:1959.4/100915