Simulation and measurement of a fluxonium qubit inductively coupled to a readout resonator

Prototypical circuit QED experiments can be performed using a fluxonium qubit that shares a portion of its superinductance with an on-chip LC oscillator, dubbed an ``antenna,'' that is used as a readout resonator. However, the complete fluxonium-antenna artificial atom had not been previously understood in all coupling regimes. We have measured Hamiltonian parameters and decay rates by channeling microwave pulses into a rectangular waveguide containing the antenna-qubit system. Accurate modeling of energy spectra, dispersive shifts, and Purcell loss is achieved by diagonalizing the effective circuit Hamiltonian. We will present spectroscopy data, coherence times, and simulation results.