Suppressing Dissipative Paths in Superconducting Coplanar Waveguide Resonators

The electromagnetic environment can have a significant effect on the resonant line-shape and loaded Q-factor of superconducting coplanar waveguides in the low temperature (<; 100 mK) and low microwave power regime. Here, electromagnetic simulations are used to visualize the electric field strength throughout the resonator environment, highlighting situations in which parasitic modes lead to increased dissipation. Methods used to suppress parasitic coupling include increasing the density of wire bonds and vias, reducing the width of the transmission line (whilst maintaining the characteristic impedance at 50 Ω) and establishing strong grounding to the sample enclosure. The effect of reducing the parasitic coupling on the microwave transmission spectrum is reported.