Observation of the Response of Tantalum Coplanar Waveguide Cavities to Cryogenic Cycle

Tantalum (Ta) has demonstrated its capability as a high-quality, low-loss superconductor supporting high-coherence superconducting qubits. Locating key fabrication processes and understanding the dissipation mechanisms of Ta-based devices are critical for a wider range applications of this material in circuit quantum electrodynamics. In this work, we report our observation that the Ta coplanar waveguide (CPW) cavities respond to cryogenic cycles with boosted intrinsic quality factor (Q_i). Typically, in the initial cryogenic measurement after the fabrication, the Ta CPW cavities show Q_i in the 10⁵ order of magnitude with a weak dependence on the measurement power. However, after warming up and in the following cryogenic test, the identical Ta CPW cavities demonstrate low/high-power Q_i at a level of 10⁶/10⁷ with an expected power dependence. Moreover, the improved Q_i becomes fixed thereafter. We confirm that the response of Ta CPW cavities to the cryogenic cycle is robust against the variance in deposition thickness, etching, and patterning, but is dependent on the deposition power. We conjecture that the effect is connected with the residual and the release of the strain in the Ta film.