Extracting Contributions to Qubit Loss from Superconducting Microwave Resonators. Part 2

Superconducting coplanar waveguide resonators play a critical role in information storage and qubit state measurement in superconducting quantum information processing. At the same time, these resonators are a versatile testbed for characterizing the various contributions to qubit loss. Ideally, the internal quality factors of these resonators should reach ten million or higher, limited only by the loss tangent of the silicon or sapphire substrate. For practical devices, however, dielectric loss at interfaces is a dominant contributor to relaxation. In this work, we explore the dependence of interface losses on the details of device fabrication process. We investigate the impact on resonator quality factor of various silicon wafer treatments prior to metal deposition and various approaches to deposition and etch of the superconducting metals. In addition, we explore the dependence of metal-substrate and substrate-air losses on ion beam bombardment over a range of ion energies. These results will guide the optimization of fabrication processes for improved qubits.