Improving the Coherence Time of Superconducting Coplanar Resonators

TL;DR

This paper investigates factors affecting the coherence time of superconducting coplanar resonators, identifying key loss mechanisms and demonstrating methods to improve their quality factor and decay time for quantum applications.

Contribution

It provides new insights into loss mechanisms, such as surface TLS and vortex dissipation, and shows how geometry and material choices can enhance resonator coherence.

Findings

Surface TLS are a significant decay mechanism.

Increasing the gap and using Re reduces losses.

Classical measurements align with quantum decay times.

Abstract

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 surface two-level states (TLS) as an important decay mechanism. 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.