Multi-Modal Electron Microscopy Investigation on Decoherence Sources and Their Stability in Nb Based Superconducting Qubit

• DOI: 10.2139/ssrn.4128730
• Publication Date: 2022-06-07T18:52:37Z
• Authors: Jin-Su Oh; Xiaotian Fang; Tae-Hoon Kim; Matt Lynn; Matt Kramer; Mehdi Zarea; James Sauls; Alex Romanenko; Sam Posen; Anna Grassellino; Cameron J. Kopas; Mark Field; Jayss Marshall; Hilal Cansizoglu; Joshua Y. Mutus; Matthew Reagor; Lin Zhou

Niobium is commonly used for superconducting quantum systems as readout resonators, capacitors, and interconnects. But structural defects at the Nb/Si air/Nb interface may be a major source of two-level system (TLS), which are detrimental to device's coherence time. Thus, identifying understanding microscopic origin possible TLS in Nb-based devices their relationship processing key qubit performance improvement. This work studied structure thermal stability Nb films deposited on Si wafers by physical vapor deposition, including (1) film from transmon (2) without any patterning step, using aberration-corrected (scanning) transmission electron microscopy spectroscopy. Both exhibit columnar growth with strong [110] textures. There double layer between substrate, amorphous niobium silicides different concentrations. After in-situ heating heterostructure 360°C inside microscope, composition layers Nb-Si remains almost same despite thickness changes. The initial oxides surface decomposes into face-centered cubic nanograins Nb-O matrix upon heating, reduce microwave dissipation.