Nanowire Superinductance Fluxonium Qubit

TL;DR

This paper introduces a fluxonium qubit with a NbTiN nanowire superinductance, providing detailed spectral analysis, multilevel control, and insights into loss mechanisms, advancing superconducting qubit technology.

Contribution

It presents a comprehensive characterization of a nanowire superinductance fluxonium qubit with a multimode theoretical model and experimental insights into its coherence properties.

Findings

Measured excited state lifetime of 20 microseconds.

Observed multilevel Autler-Townes splitting.

Identified crossover in loss mechanisms from capacitive to inductive.

Abstract

We characterize a fluxonium qubit consisting of a Josephson junction inductively shunted with a NbTiN nanowire superinductance. We explain the measured energy spectrum by means of a multimode theory accounting for the distributed nature of the superinductance and the effect of the circuit nonlinearity to all orders in the Josephson potential. Using multiphoton Raman spectroscopy, we address multiple fluxonium transitions, observe multilevel Autler-Townes splitting and measure an excited state lifetime of $T_\mathrm{1}=20$ $\mu$s. By measuring $T_1$ at different magnetic flux values, we find a crossover in the lifetime limiting mechanism from capacitive to inductive losses.