A scanning quantum probe microscopy suite to boost the development of quantum circuits

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Noise and decoherence poses a critical challenge for the development of quantum computing in the solid-state. Usually, this decoherence and associated qubit parameter drift can be attributed to atomic-scale material defects, of which little is known, present in the materials used to build quantum circuits. The semiconductor industry (classical computing) faced very similar material challenges in its early days, yet today it shows remarkable quality and yield. Apart from a tremendous engineering effort, much of this can be attributed to the emergence of new nanoscale material characterisation tools. For instance, the development of atomic force microscopy and scanning tunnelling microscopy, together with a broad range of derived scanning probe microscopy (SPM) techniques has allowed to gain in-depth knowledge of materials and perfect device fabrication. Quantum computing has now matured to a level where similar challenges related to materials remains before it can fully be exploited. It is thus clear that quantum SPM ('scanning quantum probe microscopy', SQPM) tools for defect mitigation will be essential to drive quantum computing (and quantum technologies in general) forward in the decades to come. However, the challenge (in particular with quantum devices operating in the microwave regime, such as superconducting circuits) is that they are sensitive to defects in a completely unprecedented way: the defects have very low energy scales and low densities, making the relevant defects impossible to detect by conventional techniques. Yet these otherwise minute defects still have detrimental effects on the coherence of quantum circuits. To date none of the existing nanoscale characterisation tools are capable of 'seeing the material defects' the way quantum circuits sees and suffers from them. This project aims to take the first fundamental steps in developing the SQPM tools that will one day drive the progress of refined materials for quantum processors posed to revolutionise computing. This will be achieved by building on existing capabilities developed by the PI in detection and control of individual material defects and cryogenic SPM instrumentation in the quantum regime, to construct a SQPM platform capable of hosting high coherence quantum circuits where individual defects can be located - correlating spatial, structural, and spectral defect properties directly with device performance.