Transmon qubit modeling and characterization for Dark Matter search

  1. R. Moretti,
  2. D. Labranca,
  3. P. Campana,
  4. R. Carobene,
  5. M. Gobbo,
  6. M. A. Castellanos-Beltran,
  7. D. Olaya,
  8. P. F. Hopkins,
  9. L. Banchi,
  10. M. Borghesi,
  11. A. Candido,
  12. H. A. Corti,
  13. A. D'Elia,
  14. M. Faverzani,
  15. E. Ferri,
  16. A. Nucciotti,
  17. L. Origo,
  18. A. Pasquale,
  19. A. S. Piedjou Komnang,
  20. A. Rettaroli,
  21. S. Tocci,
  22. S. Carrazza,
  23. C. Gatti,
  24. and A. Giachero
This study presents the design, simulation, and experimental characterization of a superconducting transmon qubit circuit prototype for potential applications in dark matter detection experiments. We describe a planar circuit design featuring two non-interacting transmon qubits, one with fixed frequency and the other flux tunable. Finite-element simulations were employed to extract key Hamiltonian parameters and optimize component geometries. The qubit was fabricated and then characterized at 20 mK, allowing for a comparison between simulated and measured qubit parameters. Good agreement was found for transition frequencies and anharmonicities (within 1\% and 10\% respectively) while coupling strengths exhibited larger discrepancies (30\%). We discuss potential causes for measured coherence times falling below expectations (T1∼1-2 \textmu s) and propose strategies for future design improvements. Notably, we demonstrate the application of a hybrid 3D-2D simulation approach for energy participation ratio evaluation, yielding a more accurate estimation of dielectric losses. This work represents an important first step in developing planar Quantum Non-Demolition (QND) single-photon counters for dark matter searches, particularly for axion and dark photon detection schemes.
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