Temperature and Magnetic-Field Dependence of Relaxation in a Fluxonium Qubit

Flux and charge noise from defects on material surfaces and interfaces are known to limit the coherence of superconducting circuits, yet a complete understanding of their underlying physics is still lacking. The fluxonium qubit, which consists of a single Josephson junction shunted by a capacitor and a linear inductor, can be made with transition frequencies as low as tens of MHz, and its relaxation time T1 may have contributions from both dielectric loss and low-frequency magnetic flux noise. To probe the characteristics of the surrounding defect baths, we can measure their response to thermodynamic quantities such as temperature and magnetic field. Here we present temperature and in-plane-magnetic-field characterizations of a fluxonium qubit with a minimum frequency of ~50 MHz, utilizing T1 relaxometry as a noise probe. We observe new trends in the noise with these quantities, which may provide further constraints for microscopic theories of flux and charge noise and offer a clearer path toward mitigating their effects.