Dr. Riju Banerjee
NPL

Superconducting quantum devices suffer from decoherence and instabilities arising from intrinsic material defects known as two‑level systems (TLS). These defects present a major obstacle to achieving long coherence lifetimes and scaling up quantum processors. Despite being proposed over five decades ago, the microscopic origin and precise nature of TLS remain elusive, as their extremely low energy scales (~µeV) render them largely inaccessible to conventional condensed-matter probes. In this talk, I will present measurements performed using a custom-built scanning gate microscope that enables the direct interrogation of individual TLS defects in live superconducting circuits and quantify their contributions to loss and decoherence. Beyond studying conventional TLS defects, I will also discuss a newly identified dissipation mechanism originating from Coulomb blockade and charge tunnelling in metallic grains, driven by the microwave fields of the superconducting quantum circuit.