Gatemonium: A Voltage-Tunable Fluxonium

TL;DR

This paper introduces gatemonium, a new fluxonium qubit variant using superconductor-semiconductor hybrids with voltage-tunable Josephson junctions, enabling electrostatic control and detailed spectroscopic analysis of hybrid plasmon-fluxon modes.

Contribution

It presents a novel fluxonium qubit design with voltage-tunable Josephson energy using an array of superconductor-semiconductor junctions, and provides detailed spectroscopic and time domain characterization.

Findings

Electrostatic control of Josephson energy demonstrated.

Spectroscopic analysis reveals hybrid plasmon-fluxon spectrum.

Time domain measurements show coherence properties of the new qubit.

Abstract

We present a new style of fluxonium qubit, gatemonium, based on an all superconductorsemiconductor hybrid platform. The linear inductance is achieved using six hundred planar Al-InAs Josephson junctions (JJs) in series. By tuning the single junction with a gate voltage, we demonstrate electrostatic control of the effective Josephson energy, tuning the weight of the fictitious phase particle. One and two-tone spectroscopy of the gatemonium transitions further reveal details of the hybrid plasmon-fluxon spectrum. Accounting for the nonsinusoidal current-phase relation of the single junction, we fit the measured spectra to extract charging and inductive energies. We conduct time domain characterization of the plasmon modes in a second gatemonium device with different charging energy and JJ array inductance. We discuss future directions for this platform in gate voltage-tunable, high plasma frequency, enhanced impedance junction arrays, and enhanced coherence times for voltage tunable architectures.