Spectroscopy of two-level system defects in fluxonium

Dielectric loss has been identified as a dominant noise source in superconducting qubits, resulting in limited qubit coherence times that continues to pose challenges to building superconducting quantum processors. Here, we aim to develop a microscopic understanding of this loss mechanism by investigating qubit coupling to individual two-level systems (TLS). We employ fast-flux pulsing techniques to characterize the frequency and time dependence of energy-relaxation errors due to TLS in fluxonium qubits. We make use of the large frequency tuning range of fluxonium to probe the TLS spectrum over several GHz. Our results inform ongoing efforts to improve the coherence of superconducting qubits by providing a baseline calibration for further design iterations and fabrication process development.