Vacancy dynamics in niobium and its native oxides and their potential implications for quantum computing and superconducting accelerators
Marc Wenskat, Jakub Čı́žek, Maciej Oskar Liedke, Maik Butterling, Martin Stiehl, Guilherme Dalla Lana Semione, Constanze Backes, Christopher Bate, Oksana Melikhova, Eric Hirschmann, A. Wagner, H. Weise, Andreas Stierle, Martin Aeschlimann, W. Hillert
Abstract
In recent years, superconducting radio-frequency (SRF) cavities have been considered as candidates for qubits in quantum computing, showing longer photon lifetimes and, therefore, longer decoherence times of a cavity stored qubit compared to many other realizations. In modern particle accelerators, SRF cavities are the workhorse. Continuous research and development efforts are being undertaken to improve their properties, i.e., to increase the accelerating field and lower the surface resistance, which in turn increase the energy reach and duty cycle of accelerators. While some experimental milestones have been achieved, the mechanisms behind the still observed losses remain not 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.