Vacancy-Dynamics in Niobium and its Native Oxides and their implications for Quantum Computing and Superconducting Accelerators

In recent years, superconducting radio-frequency (SRF) cavities have been considered as candidates for qubits in quantum computing, showing a significantly longer decoherence time compared to many other realizations. Originally, SRF cavities are the workhorse of modern particle accelerators and ongoing R&D pursuits to improve their properties, to increase the accelerating field and reduce the surface resistance in order to increase the energy reach and duty cycle of accelerators. Although few experimental milestones have been realized, the underlying mechanisms of the still observed losses have not been fully understood. In this contribution we are going to show that a recently reported temperature treatment of Nb SRF cavities in the temperature range of 573-673 K, which reduces the residual surface resistance to unprecedented values, is linked to a reorganization of the niobium oxide and near-surface vacancy structure and that this reorganization can explain the observed improved performance in both applications, quantum computing and SRF cavities.