Abstract: Superconducting qubits inherently face a longstanding tradeoff between anharmonicity and susceptibility to charge noise - a limitation that affects even state-of-the-art transmons and gatemons. In this work, we overcome this limitation by demonstrating flux-frustrated transmons [1] that utilize the interference of higher-order harmonics in highly transparent epitaxial Al-InAs Josephson junctions (JJs) to achieve strongly enhanced anharmonicity. We experimentally demonstrate anharmonicity exceeding 100%, reaching as high as 800% with respect to the qubit transition frequency, at the half-integer flux sweet-spot without any increased sensitivity to the o set-charge noise. This enhancement allows us to achieve raw Rabi frequencies exceeding 100 MHz without the need for complex pulse shaping, greatly simplifying qubit control.
Building on this approach, I will then present our ongoing e orts to further generalize these unique qubit architectures into devices with single JJs and multiple sweet-spots, alongside our progress in raising the operating temperature of these qubits to around 1 Kelvin to facilitate easier scaling. Ultimately, this combination of strong intrinsic anharmonicity, flux tunability and a minimalistic bare-bones device architecture - requiring no additional Josephson elements or electrical gating highlights the unique advantages that highly transparent superconducting-semiconducting junctions o er to scalable quantum information processing.
[1] S. Liu*, A. Bordoloi* et al., Nature Communications 17, 740 (2026)