Ultracoherent superconducting cavity-based multiqudit platform with error-resilient control

  1. Taeyoon Kim,
  2. Tanay Roy,
  3. Xinyuan You,
  4. Andy C. Y. Li,
  5. Henry Lamm,
  6. Oleg Pronitchev,
  7. Mustafa Bal,
  8. Sabrina Garattoni,
  9. Francesco Crisa,
  10. Daniel Bafia,
  11. Doga Kurkcuoglu,
  12. Roman Pilipenko,
  13. Paul Heidler,
  14. Nicholas Bornman,
  15. David van Zanten,
  16. Silvia Zorzetti,
  17. Roni Harnik,
  18. Akshay Murthy,
  19. Shaojiang Zhu,
  20. Changqing Wang,
  21. Andre Vallieres,
  22. Ziwen Huang,
  23. Jens Koch,
  24. Anna Grassellino,
  25. Srivatsan Chakram,
  26. Alexander Romanenko,
  27. and Yao Lu
Superconducting radio-frequency (SRF) cavities offer a promising platform for quantum computing due to their long coherence times and large accessible Hilbert spaces, yet integrating nonlinear elements like transmons for control often introduces additional loss. We report a multimode quantum system based on a 2-cell elliptical shaped SRF cavity, comprising two cavity modes weakly coupled to an ancillary transmon circuit, designed to preserve coherence while enabling efficient control of the cavity modes. We mitigate the detrimental effects of the transmon decoherence through careful design optimization that reduces transmon-cavity couplings and participation in the dielectric substrate and lossy interfaces, to achieve single-photon lifetimes of 20.6 ms and 15.6 ms for the two modes, and a pure dephasing time exceeding 40 ms. This marks an order-of-magnitude improvement over prior 3D multimode memories. Leveraging sideband interactions and novel error-resilient protocols, including measurement-based correction and post-selection, we achieve high-fidelity control over quantum states. This enables the preparation of Fock states up to N=20 with fidelities exceeding 95%, the highest reported to date to the authors‘ knowledge, as well as two-mode entanglement with coherence-limited fidelities reaching up to 99.9% after post-selection. These results establish our platform as a robust foundation for quantum information processing, allowing for future extensions to high-dimensional qudit encodings.
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