Characterization and reduction of microfabrication-induced decoherence in superconducting quantum circuits

TL;DR

This paper investigates the sources of microwave loss in superconducting quantum circuits, focusing on fabrication-induced surface contamination and surface treatment effects, and proposes methods to reduce decoherence for improved qubit performance.

Contribution

It identifies contamination from fabrication processes as a key decoherence source and introduces techniques to characterize and remove resist residues, enhancing qubit coherence.

Findings

Contamination significantly reduces quality factors without proper cleaning.

Aggressive surface treatments damage substrates and lower resonator quality.

Methods to quantify and minimize surface residues improve device coherence.

Abstract

Many superconducting qubits are highly sensitive to dielectric loss, making the fabrication of coherent quantum circuits challenging. To elucidate this issue, we characterize the interfaces and surfaces of superconducting coplanar waveguide resonators and study the associated microwave loss. We show that contamination induced by traditional qubit lift-off processing is particularly detrimental to quality factors without proper substrate cleaning, while roughness plays at most a small role. Aggressive surface treatment is shown to damage the crystalline substrate and degrade resonator quality. We also introduce methods to characterize and remove ultra-thin resist residue, providing a way to quantify and minimize remnant sources of loss on device surfaces.