Potential Nanoscale Sources of Decoherence in Niobium based Transmon Qubit Architectures

Authors:
  • AMAkshay A. Murthy
    Akshay A. Murthy
  • PDPaul Masih Das
    Paul Masih Das
  • SRStephanie M. Ribet
    Stephanie M. Ribet
  • CKCameron Kopas
    Cameron Kopas
  • JLJaeyel Lee
    Jaeyel Lee
  • MRMatthew J. Reagor
    Matthew J. Reagor
  • LZLin Zhou
    Lin Zhou
  • MKMatthew J. Kramer
    Matthew J. Kramer
  • MHMark C. Hersam
    Mark C. Hersam
  • MCMattia Checchin
    Mattia Checchin
  • AGAnna Grassellino
    Anna Grassellino
  • RRRoberto dos Reis
    Roberto dos Reis
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Abstract
Superconducting thin films of niobium have been extensively employed in transmon qubit architectures. Although these architectures have demonstrated remarkable improvements in recent years, further improvements in performance through materials engineering will aid in large-scale deployment. Here, we use information retrieved from electron microscopy and analysis to conduct a detailed assessment of potential decoherence sources in transmon qubit test devices. In the niobium thin film, we observe the presence of localized strain at interfaces, which may amplify interactions between two-level systems and impose limits on T$_1$ and T$_2$ relaxation times. Additionally, we observe the presence of a surface oxide with varying stoichiometry and bond distances, which can generate a broad two-level system noise spectrum. Finally, a similarly disordered and rough interface is observed between Nb and the Si substrate. We propose that this interface can also degrade the overall superconducting properties.