Study of loss in superconducting coplanar waveguide resonators

TL;DR

This paper investigates how materials, geometry, temperature, and power affect the performance of superconducting coplanar waveguide resonators, revealing insights into loss mechanisms and potential control methods for optimizing their quality factors.

Contribution

It provides a detailed analysis of the dependence of resonator quality factors on materials, geometry, temperature, and power, and demonstrates a method to control dielectric loss.

Findings

Quality factors exceed 2 million at high power

Dielectric loss causes degradation at lower power and temperature

Dielectric loss can be controlled with separate excitation

Abstract

Superconducting coplanar waveguide (SCPW) resonators have a wide range of applications due to the combination of their planar geometry and high quality factors relative to normal metals. However, their performance is sensitive to both the details of their geometry and the materials and processes that are used in their fabrication. In this paper, we study the dependence of SCPW resonator performance on materials and geometry as a function of temperature and excitation power. We measure quality factors greater than $2\times10^6$ at high excitation power and $6\times10^5$ at a power comparable to that generated by a single microwave photon circulating in the resonator. We examine the limits to the high excitation power performance of the resonators and find it to be consistent with a model of radiation loss. We further observe that while in all cases the quality factors are degraded as the temperature and power are reduced due to dielectric loss, the size of this effect is dependent on resonator materials and geometry. Finally, we demonstrate that the dielectric loss can be controlled in principle using a separate excitation near the resonance frequencies of the resonator.