Multi-Layer Technology for Superconducting Quantum Processors

Superconducting technology is one of the main challengers in the race to develop quantum computers. Currently, state-of-the-art circuits are made up of a few tens of qubits, with Google demonstrating quantum supremacy using a 53-qubit processor last year. These circuits are made using two-dimensional circuitry on one side of a substrate. However, to move towards a quantum computer that can utilise 1000 qubits or beyond, we must develop methods of fabricating circuits that extend into 3 dimensions and that have, at least, layers on both sides of the substrate, thus enabling further scaling opportunities. Moving to circuits with a larger number of qubits is essential for the practical implementation of quantum algorithms by allowing, for example, much improvederror correction methods. One way to achieve this is to use so-called though-silicon-vias (TSVs.) TSVs are already in use in the semiconductor industry but the standard process is not compatible with high-quality qubits as it introduces decoherence mechanisms. The main objective of this project would be to work with our partners, National Physical Laboratory (NPL) and Oxford Instruments Plasma Technology (OIPT) to develop superconducting, low-loss TSVs compatible with superconducting qubits. This would entail establishing a new fabrication process in the James Watt Nanotechnology Centre (JWNC) and characterising the performance of the resulting TSVs at NPL and The University of Glasgow. The challenge will be to make TSVs that both have low loss at mK temperatures and that do not introduce any additional decoherence mechanisms due to, for example, material defects that would degrade the performance of the qubits.The project will:-For the first time, establish a capability for making multi-layer quantum processor circuits in the UK.-Establish a key technology for the scaling of quantum processors of interest to the whole community, so would result in high-impact publications and potentially new IP. -Lay the ground work for making more complex multi-layersuperconducting circuits at the JWNC which would benefit the UK as a whole.-Realize high coherence superconducting quantum bits with high fidelities in quantum state control and readout.My own interest in quantum computing originated from reading aboutquantum cryptography and the potential for revolutionary methods of provably secure communication and, indeed, the obsolescence of modern encryption methods. This interest was fostered while studying a quantum information course during my Master's degree at The University of Glasgow, where I learned about the fascinating abstract mathematical background to the subject. However, through the proposed project, I am keen to work towards a physical implementation of these concepts and contribute to the advancement of the field in a high-impact area.
The project will provide me with state-of-the-art facilities and support by world-leading experts. I will gain expertise in the modelling and fabrication of quantum circuits, measurement using advanced microwave setups, data processing, cryogenics and quantum technologies. The project is multi-disciplinary in nature and I will have the opportunity to work with industry and academia. Throughout, I will receive training in highly specialised nanofabrication and analysis techniques while also developing many highly transferable skills, for example the modelling of complex systems or the writing of formal scientific research. Further to this, opportunities such as the ability to publish my research in leading journals, or to attend international conferences in the field ideally prepare me for an academic career or for employment outside the academic sector in the burgeoning quantum technologies industry.