Collective modes in the fluxonium qubit

TL;DR

This paper investigates whether the complex structure of the fluxonium qubit limits its coherence, concluding that under certain conditions, collective modes do not significantly affect decoherence, supporting its viability for quantum computing.

Contribution

The study demonstrates that fluxonium's additional degrees of freedom do not inherently cause significant decoherence if coupling to the environment remains weak.

Findings

Collective modes do not significantly contribute to decoherence under weak coupling.

Fluxonium's complexity does not pose a major obstacle for quantum computing.

Conditions for minimal decoherence are identified.

Abstract

Superconducting qubit designs vary in complexity from single- and few-junction systems, such as the transmon and flux qubits, to the many-junction fluxonium. Here we consider the question of wether the many degrees of freedom in the fluxonium circuit can limit the qubit coherence time. Such a limitation is in principle possible, due to the interactions between the low-energy, highly anharmonic qubit mode and the higher-energy, weakly anharmonic collective modes. We show that so long as the coupling of the collective modes with the external electromagnetic environment is sufficiently weaker than the qubit-environment coupling, the qubit dephasing induced by the collective modes does not significantly contribute to decoherence. Therefore, the increased complexity of the fluxonium qubit does not constitute by itself a major obstacle for its use in quantum computation architectures.