Right-sizing fluxonium against charge noise

TL;DR

This paper investigates how the coherence time of fluxonium qubits depends on the number of array junctions, revealing an optimal junction count that balances dephasing and relaxation for improved performance.

Contribution

It provides a detailed analysis of charge-noise effects on fluxonium coherence, identifying an optimal number of junctions for enhanced qubit performance.

Findings

Pure dephasing decreases with more junctions.

Relaxation rate increases with more junctions.

Optimal junction number yields maximum coherence time.

Abstract

We analyze the charge-noise induced coherence time $T_2$ of the fluxonium qubit as a function of the number of array junctions in the device, $N$. The pure dephasing rate decreases with $N$, but we find that the relaxation rate increases, so $T_2$ achieves an optimum as a function of $N$. This optimum can be much smaller than the number typically chosen in experiments, yielding a route to improved fluxonium coherence and simplified device fabrication at the same time.