# Strongly anharmonic flux-tunable transmon based on InAs-Al 2D heterostructure

## TL;DR

This paper introduces a new type of qubit with strong anharmonicity and low charge-noise sensitivity using InAs-Al heterostructures.

## Contribution

A novel flux-tunable transmon with intrinsic strong anharmonicity and simplified control in superconducting-semiconducting heterostructures.

## Key findings

- Anharmonicity exceeding 100% is achieved at the half-integer flux sweet spot.
- Coherent driving with Rabi frequencies over 100 MHz is enabled without pulse shaping.
- High-resolution spectroscopy reveals fine details of the current-phase relation.

## Abstract

The gatemon qubits, made of transparent superconducting-semiconducting Josephson junctions, typically have even weaker anharmonicity than the opaque AlOx-junction transmons. However, flux-frustrated gatemons can acquire a much stronger anharmonicity, originating from the interference of the higher-order harmonics of the supercurrent. Here we investigate this effect of enhanced anharmonicity in split-junction gatemon devices based on InAs-Al 2D heterostructure. We find that anharmonicity in excess of 100% can be routinely achieved at the half-integer flux sweet-spot without any need for electrical gating or excessive sensitivity to the offset charge noise. We verified that such intrinsically large anharmonicity enables our devices to be driven coherently with raw Rabi frequencies exceeding 100 MHz, without any pulse shaping, simplifying implementation and control compared to traditional gatemons and transmons. Furthermore, by analyzing a relatively high-resolution spectroscopy of the device transitions as a function of flux, we were able to extract fine details of the current-phase relation, to which transport measurements would hardly be sensitive. The strong anharmonicity of our anharmonic tunable transmons, along with their bare-bones design, can prove to be a precious resource that transparent superconducting-semiconducting junctions bring to quantum information processing.

Superconducting transmon qubits are limited by a tradeoff between anharmonicity and charge-noise sensitivity. Here, the authors show how highly transparent Josephson junctions in hybrid superconducting-semiconducting heterostructures can remove this tradeoff and achieve both benefits.