{
  "abstract": "The Josephson energy $E_J$ is a key parameter governing the properties of transmon superconducting qubits. In Al/AlO$_x$/Al junctions, $E_J$ is set by electron tunneling through an ultrathin oxide barrier and therefore depends exponentially on the atomic structure of the barrier. We compute $E_J$ by first-principles device modeling based on the NEGF-DFT quantum-transport method, comparing a junction with a crystalline Al$_2$O$_3$ barrier against ten junctions with melt--quenched amorphous Al$_2$O$_3$ barriers of the same thickness. From the Fermi-level transmission and the Ambegaokar--Baratoff relation, we obtain a mean $E_J/h$ of $2.78$ GHz for the amorphous ensemble, with a standard deviation of $4.67$ GHz, compared with $0.73$ GHz for the crystalline reference; individual amorphous values span nearly two orders of magnitude. Scattering-state analysis shows that transport is quantum tunneling and that the variability originates from stoichiometric inhomogeneity of the amorphous oxide: Al-rich, low-barrier regions can connect into percolation-like tunneling pathways that strongly enhance the conductance. A realistic $200\\times200$ nm$^2$ junction self-averages over more than $2\\times10^4$ such microscopic regions. These results establish a quantitative atomistic route from oxide microstructure to the superconducting-circuit energy scale $E_J$.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.09426",
  "author_total": 6,
  "authors": [
    {
      "name": "Wanting Zhang"
    },
    {
      "name": "Aldilene Saraiva-Souza"
    },
    {
      "name": "Félix Beaudoin"
    },
    {
      "name": "Xianghua Kong"
    },
    {
      "name": "Hong Guo"
    },
    {
      "name": "Yu Zhu"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/66gs8ccyez33v.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.09426",
  "fulltext_url": null,
  "id": "66gs8ccyez33v",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.09426",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "quant-ph"
    ],
    [
      "openalex",
      "1702|Quantum Information and Cryptography"
    ]
  ],
  "openalex": "W7212162171",
  "pdf_url": "https://arxiv.org/pdf/2609.09426",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-08",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/66gs8ccyez33v.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:20:12Z",
      "native_id": "2609.09426",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.09426"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:quant-ph",
      "subfield": "quantum"
    }
  ],
  "title": "Josephson energy of superconducting junctions: amorphous versus crystalline tunnel barriers",
  "title_text": "Josephson energy of superconducting junctions: amorphous versus crystalline tunnel barriers",
  "type": "preprint",
  "updated_at": "2026-10-30T12:20:12Z",
  "url": "https://research.draconitic.com/paper/66gs8ccyez33v",
  "venue": "arXiv",
  "versions": []
}