Spins and superconducting circuits for advanced spectroscopy (SpinSUPER)

Magnetic resonance is one of the most well established and widely used tools for studying molecules and materials in science, medicine and metrology: from magnetic resonance imaging (MRI) in hospitals, to bench-top instruments used for industrial quality assurance monitoring, to advanced spectroscopy used to push the boundaries of understanding in many fields in science. The most common magnetic resonance technique addresses the nuclei that are found in all atoms; a related and very important variant is electron spin resonance (ESR), which addresses unpaired electrons found in large number of molecules and materials. In recent years, ESR spectroscopy has contributed, for instance, to the discovery of a room-temperature diamond MASER and long-wavelength photosynthesis, as well as studies of primitive organic matter in extra-terrestrial rocks or evaluating materials for quantum technologies. Electron spins are naturally found in many biological systems, such as on metal centres that are found within mechanistically key locations in enzymes, but can also be introduced to targeted locations in molecules using spin-labels.

Despite these successful and wide-ranging uses, the sensitivity of ESR is a critical bottleneck for many important applications. For example, the limited sensitivity may require long signal averaging times (several days) to obtain statistically meaningful data - in many applications, this makes certain studies impractical, or else highly limited in scope. Recent developments, in many cases influenced by advances in superconducting quantum technologies, have shown that under very specific conditions, large improvements in ESR sensitivity are possible, harnessing new types of microwave amplifier and ESR resonator. Our goal is to take inspiration from such results and develop them in a more general manner that can be applied to practical open questions. In this manner, we will be able to deliver advances in the specific systems studied in this proposal, as well as show the wider ESR community how such techniques can be broadly applied in practice. As an illustration, we have recently shown in a collaborative work how cryogenic amplifiers can be introduced into the ESR detection circuit to enhance the signal to noise ratio, reducing the measurement time by almost a factor of 100, compared to typical set-ups.

In this project, we will develop new technologies and methods to enhance the sensitivity in ESR and open up entirely new ways of performing ESR measurements. We will apply these to a number of important systems, including (1) Respiratory complex I, an essential enzyme that contributes approximately 40% to ATP synthesis and whose dysfunction is associated with numerous disorders and with ageing but whose energy-coupling mechanism, which involves radicals, is yet unclear; (2) Photosynthetic complex I, an enzyme that can lead to increased ATP production and is hence of interest for agriculture e.g. to increase crop yields, but whose mechanism - which involves numerous paramagnetic intermediates - is poorly understood; (3) Two enzymes essential for biological methane production; (4) Near-surface spins in materials that are being studied for applications in quantum technologies.

SpinSUPER combines the complementary expertise in the groups of Roessler (Imperial) on the manipulation of complex proteins with multiple redox-active centres to investigate their mechanisms through the application of pulse ESR techniques, and that of Morton (UCL) on superconducting micro-resonators, micro-resonator design and modelling, and novel microwave circuits for enhanced ESR. It promises to redefine the state-of-the-art in ESR instrumentation and methodology, with a focus on practical spin systems. SpinSUPER will push new frontiers for ESR, for example with ESR at the single-cell level, or simultaneous multi-frequency ESR, while being firmly targeted at addressing open scientific questions in the field of ESR.