{
  "abstract": "Unitary and dissipative models of quantum dynamics are linear maps on the space of states or density matrices. This linearity encodes the superposition principle, a key feature of quantum theory. However, this principle can break down in effective non-Hermitian dynamics arising from postselected quantum evolution. We theoretically characterize and experimentally investigate this breakdown in a dissipative superconducting transmon circuit. Within the circuit's three-level manifold, no-jump postselection generates an effective non-Hermitian Hamiltonian governing the excited two-level subspace and an anti-Hermitian nonlinearity. We prepare different initial states and use quantum state tomography to track their evolution under this effective, nonlinear Hamiltonian. By comparing the evolution of a superposition state to a superposition of individually evolved basis states, we test linearity and observe clear violations, which we quantify across the exceptional-point degeneracy of the non-Hermitian Hamiltonian. We extend the analysis to density matrices, revealing a breakdown in linearity for the two-level subspace while demonstrating that linearity is preserved in the full three-level system. These results provide an operational demonstration of postselection-induced nonlinearity in a controlled superconducting platform. The observed nonlinearity, organized by the exceptional-point degeneracy of the non-Hermitian Hamiltonian, is absent in classical non-Hermitian systems, where norm change reflects real exchange with an environment rather than renormalization.",
  "abstract_shown": true,
  "affiliations": [
    "Washington University, St. Louis",
    "Indiana University Indianapolis",
    "Portland State University",
    "Oregon Health and Science University",
    "University of California, Berkeley"
  ],
  "article_type": "article",
  "arxiv": null,
  "author_total": 4,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Orion Lee",
      "orcid": "0000-0002-9860-398X"
    },
    {
      "affs": [
        0
      ],
      "name": "Qian Cao",
      "orcid": "0009-0004-2848-2280"
    },
    {
      "affs": [
        1,
        2,
        3
      ],
      "name": "Yogesh N. Joglekar",
      "orcid": "0000-0002-3222-1436"
    },
    {
      "affs": [
        0,
        4
      ],
      "name": "Kater Murch",
      "orcid": "0000-0002-1536-294X"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/e37rv134ny23e.bib",
  "cited_by": 0,
  "doi": "10.1103/7w9t-c5xf",
  "fulltext_url": "http://doi.org/10.1103/7w9t-c5xf",
  "id": "e37rv134ny23e",
  "issns": [
    "2643-1564"
  ],
  "landing_url": "http://link.aps.org/doi/10.1103/7w9t-c5xf",
  "language": "en",
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
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      "physics/general"
    ],
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      "lcc",
      "QC1-999"
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  ],
  "openalex": null,
  "pdf_url": "http://doi.org/10.1103/7w9t-c5xf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-23",
  "publisher": "American Physical Society (APS)",
  "ris": "https://research.draconitic.com/paper/e37rv134ny23e.ris",
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      "first_seen": "2026-10-30T12:17:18Z",
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    {
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      "url": "https://doi.org/10.1103/7w9t-c5xf"
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  "subjects": [
    {
      "field": "physics",
      "origin": "journal-openalex:3107|Quantum many-body systems",
      "subfield": "amo"
    }
  ],
  "title": "Nonlinear quantum evolution of a dissipative superconducting qubit",
  "title_text": "Nonlinear quantum evolution of a dissipative superconducting qubit",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T13:44:17Z",
  "url": "https://research.draconitic.com/paper/e37rv134ny23e",
  "venue": "Physical Review Research",
  "versions": [
    {
      "doi": "10.48550/arxiv.2510.25836",
      "pid": null,
      "relation": "preprint",
      "title": null,
      "venue": null
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  ]
}