Ultrastrong Coupling and Coherent Dynamics in a Gate-Tunable Transmon Qubit

  1. I. Casal Iglesias,
  2. F. J. Matute-Cañadas,
  3. G. O. Steffensen,
  4. A. Ibabe,
  5. L. Splitthoff,
  6. T. Kanne,
  7. J. Nygard,
  8. V. Rollano,
  9. D. Granados,
  10. A. Gomez,
  11. R. Aguado,
  12. A. Levy Yeyati,
  13. and E. J. H. Lee
Ultrastrong light-matter coupling (USC) gives access to exotic quantum phenomena and promises faster quantum gates, yet coherent time-domain control in this regime remains largely unexplored.
Here, we realize USC in a hybrid system consisting of an InAs nanowire-based gatemon qubit coupled to a superconducting resonator. Spectroscopy reveals an avoided crossing that cannot be captured by the Jaynes-Cummings (JC) model, as well as photon-number-dependent transitions whose energies deviate markedly from the JC ladder expected in the strong coupling regime. Beyond demonstrating USC, we achieve time-resolved coherent control of the qubit and measure coherence times comparable to gatemons operating outside the USC regime. These results establish that hybrid semiconductor-superconductor qubits can retain coherent control in USC and provide a platform for exploring quantum dynamics and device concepts in this regime.