Surface processing of niobium cavities for quantum computing*

Niobium (Nb) superconducting cavities hold great promise for implementing quantum memories due to their high-quality factors. However, a major obstacle towards this goal is oxidation of the Nb surface, which drastically decreases the cavity quality factors due to two-level defects within the amorphous niobium oxides. The resulting photon dissipation can be prevented by application of chemical and thermal treatments of the cavity surface. In this work, we perform an in-depth characterization of the oxidation state and crystallinity, of the niobium oxide as a function of depth and temperature. We discuss novel surface treatment methods, and correlate them with the resulting single-photon lifetimes.