Three-Dimensional Niobium Coaxial Cavity with $\sim 0.1$second Lifetime

Abstract

We report on the internal quality factor of a three-dimensional niobium quarter-wave coaxial cavity, with mid-temperature annealing, exhibiting $Q_{\mathrm{int}}\gtrsim 3\times 10^9$ at the single-photon level below 20\,mK, which corresponds to an internal photon lifetime of ${\tau }_{\mathrm{int}}\sim 90\mathrm{ms}$. Moreover, $Q_{\mathrm{int}}$ of the mid-temperature annealed cavities remains almost unchanged even after several cooldown cycles and air exposure. These results suggest that stable low-loss niobium oxides might be formed by mid-temperature annealing on the surface of three-dimensional niobium cavity. This surface treatment could be applicable to the fabrication of 2D superconducting circuits and help improve the lifetime of Nb-based superconducting qubits.