We report on the internal quality factor of a three-dimensional niobium quarter-wave coaxial cavity, with mid-temperature annealing, exhibiting Qint≳3×109 at the single-photon level below 20\,mK, which corresponds to an internal photon lifetime of τint∼90ms. Moreover, Qint 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.
Cite
@article{arxiv.2510.01819,
title = {Three-Dimensional Niobium Coaxial Cavity with $\sim0.1\,$second Lifetime},
author = {Takaaki Takenaka and Takayuki Kubo and Imran Mahboob and Kosuke Mizuno and Hitoshi Inoue and Takayuki Saeki and Shiro Saito},
journal= {arXiv preprint arXiv:2510.01819},
year = {2025}
}