Improving the coherence time of superconducting coplanar resonators

The quality factor and energy decay time of superconducting resonators have been measured as a function of material, geometry, and magnetic field. Once the dissipation of trapped magnetic vortices is minimized, we identify a power-dependent decay mechanism that is consistent with the surface two-level state model. A wide gap between the center conductor and the ground plane, as well as use of the superconductor Re instead of Al, are shown to decrease loss. We also demonstrate that classical measurements of resonator quality factor at low excitation power are consistent with single-photon decay time measured using qubit-resonator swap experiments. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3273372]