{
  "abstract": "Hybrid superconducting architectures combining different types of qubits offer a promising platform for exploiting their complementary advantages, yet high-fidelity entangling gates remain challenging because of strong nonlinearities and residual qubit-qubit interactions. Here, we propose a high-fidelity controlled-Z (CZ) gate for a hybrid circuit comprising a fluxonium qubit, a fixed-frequency transmon qubit, and a flux-tunable transmon coupler. By modulating only the external magnetic flux applied to the coupler, the qubit-qubit interaction is dynamically engineered for conditional-phase accumulation while the residual interaction is suppressed at idle, mitigating spectator-induced errors. We employ a low-dimensional Fourier-cosine pulse parameterization and a physically motivated cost function to independently suppress conditional-phase errors and leakage from the computational subspace. Numerical simulations demonstrate that a microwave-free CZ gate can be realized within $25 \\mathrm{ns}$, with an average gate fidelity exceeding $99.99\\%$ and leakage below $10^{-5}$. Using experimentally relevant superconducting-qubit parameters and accounting for decoherence, the proposed scheme maintains a CZ-gate fidelity of approximately $99.9\\%$. We further extend the analysis to larger coupled architectures and find that the CZ-gate infidelity remains below $10^{-4}$ in the presence of spectator qubits. These results establish single-parameter flux control as a simple and robust approach for realizing high-fidelity entangling gates in heterogeneous superconducting quantum architectures.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.14197",
  "author_total": 7,
  "authors": [
    {
      "name": "Peng Xu"
    },
    {
      "name": "Yunlong Wang"
    },
    {
      "name": "Yuechen Mu"
    },
    {
      "name": "Ling Jiang"
    },
    {
      "name": "Peng Zhao"
    },
    {
      "name": "Shengjun Wu"
    },
    {
      "name": "Xiaohong Yan"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/ddk5fvwbr210h.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.14197",
  "fulltext_url": null,
  "id": "ddk5fvwbr210h",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.14197",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "quant-ph"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2609.14197",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-13",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/ddk5fvwbr210h.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:21:25Z",
      "native_id": "2609.14197",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.14197"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:quant-ph",
      "subfield": "quantum"
    }
  ],
  "title": "Fast CZ gate in hybrid fluxonium-transmon systems with tunable couplers",
  "title_text": "Fast CZ gate in hybrid fluxonium-transmon systems with tunable couplers",
  "type": "preprint",
  "updated_at": "2026-10-30T12:21:25Z",
  "url": "https://research.draconitic.com/paper/ddk5fvwbr210h",
  "venue": "arXiv",
  "versions": []
}