3D cavity characterization of niobium thin films in the quantum regime

Niobium thin films are the critical component to the majority of 2D superconducting qubit architectures. To isolate the loss channel associated with the intrinsic properties of niobium thin film, we studied niobium film deposited onto the inner surface of a high-Q (>1010) 3D bulk niobium cavity and investigated the microwave dissipation over a wide temperature range down to ~ 10 mK. Microwave measurements reveal that the intrinsic loss associated with the thin film is comparable to the bulk niobium loss. Structural microanalysis, chemical composition, and superconducting properties of the niobium thin films deposited with the same technique used for the cavity are conducted. Film annealing reduces surface oxides and shows a reduction in microwave loss, similar to the results observed with the bulk niobium cavities.