Long-term stability of Ta superconducting resonators enabled by in situ deposited Al₂O₃

Achieving long-term stability in superconducting quantum circuits is essential for the advancement of quantum computing technologies. Superconducting resonators, which typically consist of native oxides (formed under ambient conditions or O₂-rich environment), often exhibit significant degradation in internal quality factors over time due to oxide regrowth or environmental contamination. In this study, we demonstrated that superconducting resonators fabricated with in situ Al₂O₃ films grown on pristine Ta films under UHV exhibit exceptional resistance to aging. X-ray photoelectron spectroscopy revealed that a 2-nm-thick Al₂O₃ layer effectively shields the underlying Ta film from reacting with atmospheric oxygen-containing species. The Ta films, exhibiting excellent crystallographic quality, were epitaxially grown on chemically cleaned and annealed sapphire substrates within a dedicated UHV chamber. These samples were then transferred under UHV to a separate chamber for oxide deposition, ensuring preservation of the pristine surface quality. The internal quality factors of the freshly fabricated Ta resonators exceeded one million and maintained exceptional stability, with minimal to no degradation after several weeks and even up to ten months of air exposure. This technique can be employed in the fabrication of superconducting quantum circuits with enhanced stability and coherence.