Improving the performance of superconducting coplanar waveguide resonators using interface engineering*

Superconducting resonators are a key component in quantum circuits. While extensive research has explored techniques to improve the quality factor of such devices, the precise structure of amorphous dielectric layers on surfaces and interfaces and their associated loss mechanism remains a topic of active discussion. In this study, we explore the characterization and the fabrication of niobium coplanar waveguide resonators with more than 10⁶ internal quality factor at single-photon-excitation power (measured at 100 mK) for a variety of different surface treatments. Following electrical measurements, resonator samples have been probed using a suite of structural characterization tools (XPS, TEM and AFM) in order to correlate the efficacy of surface treatment with resonator quality factor. We also compare our measurement results with numerical simulations.