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arXiv · 2603.06830

Anharmonicity and Charge-Noise Sensitivity of Fraunhofer Qubit

Longyu Ma·Tony Liu·Javad Shabani·Kasra Sardashti·Vladimir E. Manucharyan·Maxim G. Vavilov
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Abstract

We present a theory of a flux-tunable superconducting qubit, the "Fraunhofer qubit," based on the Fraunhofer interference in a wide ballistic Josephson junction. As magnetic flux threads the junction, the Josephson potential is effectively averaged over a phase window proportional to flux. For perfectly transmitting junctions, as flux approaches one flux quantum h/2e, the flux averaging transforms the potential near its minimum from a quadratic to a triangular shape, resulting in significantly enhanced anharmonicity. This enhancement persists for junctions with lower transparency conducting channels. Microscopic tight-binding simulations that include inhomogeneous electrostatic potential and disorder confirm the enhancement of anharmonicity. These results establish a framework for flux control in hybrid superconducting circuits, providing an operating point where anharmonicity and charge-noise protection can be optimally balanced.

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Longyu Ma, Tony Liu, Javad Shabani, Kasra Sardashti, Vladimir E. Manucharyan, Maxim G. Vavilov. 2026-03-06. Anharmonicity and Charge-Noise Sensitivity of Fraunhofer Qubit. https://arxiv.org/abs/2603.06830

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