Observation of vanishing charge dispersion of a nearly-open superconducting island

TL;DR

This study demonstrates the suppression of charge dispersion in a nanowire transmon with a quantum dot, revealing potential for more stable, charge-insensitive superconducting qubits by increasing junction transparency.

Contribution

We experimentally observe the vanishing charge dispersion in a nearly-open superconducting island, confirming theoretical predictions and highlighting improved qubit coherence at high transparency.

Findings

Charge dispersion rapidly decreases with increased junction transparency.

Suppression of charge dispersion follows a predicted scaling law.

Enhanced qubit coherence times are observed at high transparency.

Abstract

Isolation from the environment determines the extent to which charge is confined on an island, which manifests as Coulomb oscillations such as charge dispersion. We investigate the charge dispersion of a nanowire transmon hosting a quantum dot in the junction. We observe rapid suppression of the charge dispersion with increasing junction transparency, consistent with the predicted scaling law which incorporates two branches of the Josephson potential. We find improved qubit coherence times at the point of highest suppression, suggesting novel approaches for building charge-insensitive qubits.