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Resolving buried coordination heterogeneity in Al/AlOx/Al Josephson junctions

Paul Corbae1,*,†, Alex Abelson2,†, Shivani Srivastava2, Heemin Lee1, Bevin Huang2, Lyrik R-J Lee2, Davis B. Rash2, Cheng-Tai Kuo1, Donghui Lu1 et al.

Mihir Pendharkar3,4, Loren D. Alegria2, Tian T. Li2, Keith G. Ray2, Shannon P. Harvey3, Apurva Mehta5, David I. Schuster3,4,6, Vincenzo Lordi2, Paul B. Welander3, and Jun-Sik Lee1,‡

  • *Contact author: pjcorbae@slac.stanford.edu
  • †These authors contributed equally to this work.
  • ‡Contact author: jslee@slac.stanford.edu
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Phys. Rev. Applied 26, 044071 – Published 23 October, 2026

DOI: https://doi.org/10.1103/lvjh-dxr8

Abstract

Decoherence remains a critical obstacle to achieving high-fidelity, scalable superconducting qubits, with the tunnel barrier of Josephson junctions a key source of loss, yet the microscopic structure of this buried layer has remained difficult to probe experimentally. Here, we use resonant x-ray reflectivity to resolve the coordination environments within the AlOx barrier of Al/AlOx/Al Josephson junctions as a function of oxidation conditions. We find that the barrier coordination evolves from more tetrahedral toward octahedral character with increasing oxidation pressure, while the lower metal-oxide interface is comparatively undercoordinated and disordered relative to the upper interface. Comparison with simulated x-ray absorption spectra identifies the dominant coordination motifs within the oxide and at its interfaces, providing depth-resolved structural insight that informs microscopic models of two-level system formation. These results link growth conditions, local coordination environments, and junction electronic properties, providing a materials-level foundation for interpreting how the tunnel barrier influences coherence in superconducting qubits.

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Phys. Rev. Applied 26, 044071– Published 23 October, 2026
  • Received 5 March 2026
  • Revised 10 June 2026
  • Accepted 18 September 2026
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