Niobium quarter-wave resonator with the optimized shape for quantum information systems S. V. Kutsaev, K. Taletski, R. Agustsson, P. Carriere, A. N. Cleland, Z. A. Conway, É. Dumur, A. Moro and A. Yu. Smirnov EPJ Quantum Technol., 7 1 (2020) 7 Published online: 17 April 2020 DOI: 10.1140/epjqt/s40507-020-00082-8