Characterization of Nanostructural Imperfections in Superconducting Quantum Circuits

TL;DR

This study uses atomic-level imaging techniques to identify structural imperfections in superconducting quantum circuits, linking fabrication processes to device performance limitations caused by two-level system defects.

Contribution

It provides detailed atomic-scale characterization of imperfections at critical interfaces, highlighting their impact on decoherence in quantum devices.

Findings

Identification of oxide and contamination imperfections

Correlation of imperfections with fabrication steps

Implications for improving fabrication processes

Abstract

Decoherence in superconducting quantum circuits, caused by loss mechanisms like material imperfections and two-level system (TLS) defects, remains a major obstacle to improving the performance of quantum devices. In this work, we present atomic-level characterization of cross-sections of a Josephson junction and a spiral resonator to assess the quality of critical interfaces. Employing scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDS) and electron-energy loss spectroscopy (EELS), we identify structural imperfections associated with oxide layer formation and carbon-based contamination, and correlate these imperfections to the patterning and etching steps in the fabrication process and environmental exposure. These results suggest that TLS imperfections at critical interfaces significantly contribute to limiting device performance, emphasizing the need for an improved fabrication process.