Structural and Chemical Analysis of Amorphous Compounds in Surface Encapsulated Superconducting Qubits

Although superconducting qubits have emerged as a leading technology platform for quantum computing, the presence of defects, impurities, interfaces, and surfaces in the constituent materials continue to limit performance and present a critical barrier in achieving scalable systems with sufficiently long coherence times. As part of the Superconducting Quantum Materials and Systems (SQMS) center, we have applied state-of-the-art materials characterization techniques, including scanning/transmission electron microscopy, secondary ion mass spectrometry, and x-ray photoelectron spectroscopy, to examine high coherence, surface-encapsulated Nb transmon qubit devices. As deviations from crystalline order can lead to quantum decoherence, we apply these techniques to examine the surface morphology and chemical homogeneity of amorphous oxides at the surface of thin films of niobium, tantalum, aluminum, and titanium nitride. Through this comprehensive comparative study, we gain insight into the types of defective structures prevalent in these lossy oxides. Equipped with these findings, we examine alternative materials as surface capping layers in order to systematically and intelligently improve the coherence times of superconducting qubits.