Dynamic parity recovery in a strongly driven Cooper-pair box

  1. S. E. de Graaf,
  2. J. Leppäkangas,
  3. A. Adamyan,
  4. A. V. Danilov,
  5. T. Lindström,
  6. M. Fogelström,
  7. T. Bauch,
  8. G. Johansson,
  9. and S. E. Kubatkin
We study a superconducting charge qubit coupled to an intensive electromagnetic field and probe changes in the resonance frequency of the formed dressed states. At large driving strengths, exceeding the qubit energy-level splitting, this reveals the well known Landau-Zener-St\“uckelberg (LZS) interference structure of a longitudinally driven two-level system. For even stronger drives we observe a significant change in the LZS pattern and contrast. We attribute this to photon-assisted quasiparticle tunneling in the qubit. This results in the recovery of the qubit parity, eliminating effects of quasiparticle poisoning and leads to an enhanced interferometric response. The interference pattern becomes robust to quasiparticle poisoning and has a good potential for accurate charge sensing.
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