Probing Nanostructural Imperfections in Superconducting Quantum Circuits at the Atomic Level

Decoherence in superconducting quantum circuits, caused by loss mechanisms like material imperfections and two-level system (TLS) defects, remains a major obstacle to scaling superconducting quantum devices. Surface and interface defects in thin films have been shown to contribute to qubit relaxation and reduced coherence times. In this work, we show atomic-level characterization of superconducting circuit elements, including cross-sections of a Josephson junction, and discuss the quality of interfaces. Employing high-resolution imaging techniques such as Scanning Transmission Electron Microscopy (STEM) combined with spectroscopic methods like Energy-Dispersive X-ray Spectroscopy (EDS) and Electron-Energy Loss Spectroscopy (EELS), we show structural imperfections originating from various sources and correlate specific imperfections to the fabrication process and surface treatments affecting microstructures and nanostructures. These findings help to understand that certain imperfections, particularly at critical interfaces, may play a key role in limiting device performance, emphasizing the need for highlighting pathways to mitigate their effects through an improved fabrication process.