Utilising novel microwave filtering techniques for improved performance in superconducting quantum devices

The coming revolution in quantum computing technologies creates some exciting challenges for engineers and equally exciting business opportunities for existing companies and new start-ups. One of these challenges is that existing superconducting quantum computers are already overcrowded with dense wiring and bulky microwave components, there is simply limited physical space in the dilution refrigerators. Moving to the 100-1000-qubit level and beyond requires new solutions for scalable and cost-effective microwave control and measurement circuity. Simply put, the microwave control systems need to be of much lighter weight and smaller physical size than at present with a high level of integration while being cost-effective and energy efficient.

Some of the critically required cryogenic microwave control components are dense wiring, attenuators, and circulators, which are used to bring control signals from the electronics into the cryostat, to allow the transmission of desired frequency bands while rejecting unwanted bands and to protect quantum processors against reflected signals and decoherence. Typically, dense wiring connections, filters and circulators occupy quite a large size in the cryostat and the number of them needed is growing rapidly as we scale up the number of qubits. For example, in order to scale to 1-million-qubit-computer, the control system would also need 1-10 million filters, circulators, and coaxial cables, occupying more than three football fields of floor space and consume roughly 40 MW of dc power (assuming no power loss associated with signal distribution). It is vital to develop miniature, low-cost, reliable, insertion loss and highly integrated microwave technologies for superconducting quantum computing for the UK to be successful in this rapidly growing sector, with a projected global market of £4B by 2024.

In order to move to the 100s-qubit level and beyond, where quantum computing becomes truly useful, innovation for scalable microwave control systems is needed. A short time-window is available for the UK to invest in real-world demonstration of superconducting quantum computing. Without this, the potential for a UK researcher to lead the world in this emerging area and build strong academic and industrially facing leadership will be lost. My fellowship aims to bring modern microwave approaches to supercondcting quantum computing and demonstrate improved quantum pefromance with reduced hardware overheads and thermal loaads, paving the way to move towards 100s-qubit level, where quantum computing becomes truly useful