Description
Niobium has emerged as one of the most promising materials for superconducting quantum circuits. However, the coherence time of superconducting qubits is mainly limited by internal loss mechanisms such as two-level system, particularly at device interfaces. To further reduce these losses, thermal annealing is expected to improve the Nb/air interface by diminishing the surface native oxide. Despite extensive studies in 3D cavities, its effect on coplanar waveguide (CPW) resonators remains unclear. In this work, we report two competing mechanisms that dominate the internal loss in Nb CPW resonators. We employed synchrotron-based spectroscopy techniques and microwave measurements to identify thermal-induced changes in the crystal structure and chemistry of high-performance Nb resonators. By identifying these competing mechanisms, we explain a contradictory observation in our Nb resonators, where one case exhibits improved internal quality factors Qint exceeding an average of two million at the single-photon regime whereas the other exhibits significant reduction of Qint. Our findings highlight a key factor for further improving superconducting quantum circuits.
| I am the presenting author | Yes |
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