# Anharmonicity of a Gatemon Qubit with a Few-Mode Josephson Junction

## TL;DR

This paper investigates the anharmonicity of gatemon qubits with semiconductor Josephson junctions, revealing a significant reduction compared to metallic junctions and its dependence on gate voltage, supported by experimental and theoretical analysis.

## Contribution

It provides the first experimental measurement of anharmonicity in semiconductor-based gatemon qubits and links it to mode transmission properties.

## Key findings

- Anharmonicity is reduced by about half compared to metallic junctions.
- Anharmonicity varies with gate voltage.
- Results align with a model of few highly transmitting modes.

## Abstract

Coherent operation of gate-voltage-controlled hybrid transmon qubits (gatemons) based on semiconductor nanowires was recently demonstrated. Here we experimentally investigate the anharmonicity in epitaxial InAs-Al Josephson junctions, a key parameter for their use as a qubit. Anharmonicity is found to be reduced by roughly a factor of two compared to conventional metallic junctions, and dependent on gate voltage. Experimental results are consistent with a theoretical model, indicating that Josephson coupling is mediated by a small number of highly transmitting modes in the semiconductor junction.