Understanding the mechanisms that limit high-fidelity readout in circuit quantum electrodynamics is essential for its optimization. Multiphoton resonances are understood to be a limiting factor, causing population transfer from the computational states to higher-energy states under drive. This effect, known as measurement-induced state transitions, has been extensively studied for the transmon qubit. While this exploration has begun for the fluxonium qubit, a systematic study of this effect is lacking. Here, we bridge this gap by theoretically studying measurement-induced state transitions in the fluxonium qubit over a wide range of parameters, comprising essentially all experimentally explored ranges. We find that lighter fluxoniums are less susceptible to these state transitions when compared with their heavier counterparts. We attribute this effect to the combination of lower density of multiphoton resonances, a smaller requisite coupling for a given dispersive shift, and a more harmoniclike structure of the charge operator. We confirm the validity of our analysis by performing time-dependent readout simulations. Finally, we consider the impact of the superinductor’s array modes on measurement-induced state transitions over a large range of parameters.

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• Circuit quantum electrodynamics
• Quantum circuits
• Superconducting qubits
• Superconducting devices