Resonator-induced transitions in fluxonium qubits

The fluxonium qubit has garnered significant interest recently due to its high gate fidelities and strongly anharmonic spectrum. These valuable features have resulted in the fluxonium being proposed as the basis for a quantum processor, for use in transducing between microwave and optical signals, and as a nonlinear element for manipulating long-lifetime linear cavities. A necessary requirement for using the fluxonium in such schemes is a better understanding of fluxonium behavior Reduring its interaction with a driven resonator. In this talk, I will discuss our results probing the effects on readout photons on fluxonium state evolution. We observe readout-induced transitions both within and out of the qubit subspace. We numerically model our system and find that coupling to an external spurious mode, in addition to the Hamiltonian dynamics of the fluxonium-resonator system, are necessary to explain the observed effects. Finally, I will discuss considerations for mitigating these detrimental effects.