Superconducting materials hold great potential for solid-state quantum computing. The fabrication of superconducting qubits takes advantage of well-developed semiconductor fabrication technology, such as thin film deposition and lithography. However, the complex processing steps introduce defects at the interfaces and surfaces of the qubits that may be a source of two-level system (TLS) detrimental to the device's coherence time. Thus, identifying and understanding structural features down to the atomic scale that act as possible TLS in both the Josephson junction and resonators is key to superconducting qubit performance improvement.
Advanced electron microscopy techniques, such as (scanning) transmission electron microscopy, with its many different operation modes for imaging, diffraction, and spectroscopy, have become indispensable for simultaneous structure, chemistry, and internal magnetic/electric/strain field probing down to the atomic level. This talk will present our recent studies on the microstructure in 2D-transmon and 3D-Nb cavities. A combination of advanced microscopy techniques, including in-situ heating, high resolution (S)TEM imaging, and spectroscopy (EDS and EELS), is used to identify possible TLS sources. Insights for future coherence time improvement in superconducting qubit will be briefly discussed.