Measurement-induced state transitions across the fluxonium qubit landscape

TL;DR

This paper systematically studies measurement-induced state transitions in fluxonium qubits, revealing how lighter fluxoniums are less susceptible due to fewer multi-photon resonances and more harmonic charge structure.

Contribution

It provides a comprehensive theoretical analysis of measurement-induced state transitions across all experimentally relevant fluxonium parameters, including the effects of superinductor modes.

Findings

Lighter fluxoniums are less prone to state transitions.

Fewer multi-photon resonances in lighter fluxoniums reduce susceptibility.

Superinductor array modes influence state transition dynamics.

Abstract

Understanding the mechanisms that limit high-fidelity readout in circuit quantum electrodynamics is essential for its optimization. Multi-photon 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 to their heavier counterparts. We attribute this effect to the combination of lower density of multi-photon resonances, a smaller requisite coupling for a given dispersive shift, and a more harmonic-like 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.