Fluxonium-resonator system in the nonperturbative regime

  1. W. C. Smith,
  2. A. Kou,
  3. U. Vool,
  4. I. M. Pop,
  5. L. Frunzio,
  6. R. J. Schoelkopf,
  7. and M. H. Devoret
We present a method for calculating the low-energy spectra of superconducting circuits with arbitrarily strong anharmonicity and coupling. As an example, we numerically diagonalize the Hamiltonian of a fluxonium qubit inductively coupled to a readout resonator. Our method treats both the anharmonicity of the Hamiltonian and the coupling between qubit and readout modes exactly. Calculated spectra are compared to measured spectroscopy data for this fluxonium-resonator system. We observe excellent quantitative agreement between theory and experiment that is not possible with a purely perturbative approach.
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