Epitaxial NbN-junction-based self-shunted superconducting flux qubit with high anharmonicity

Tokunoshin Uchida; Shingo Nozaki; Daiki Kurihara; Hiroki Kutsuma; Shotaro Shirai; Atsushi Noguchi; Hirotaka Terai; Taro Yamashita

arXiv · 2610.04821

Epitaxial NbN-junction-based self-shunted superconducting flux qubit with high anharmonicity

Tokunoshin Uchida·Shingo Nozaki·Daiki Kurihara·Hiroki Kutsuma·Shotaro Shirai·Atsushi Noguchi·Hirotaka Terai·Taro Yamashita

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Abstract

We report a demonstration of a self-shunted superconducting flux qubit (SSFQ) as an ultracompact, strongly anharmonic, and long-lifetime qubit by using the full epitaxially grown NbN/AlN/NbN Josephson junctions. The NbN-junction-based SSFQ achieved a high anharmonicity of 797 MHz as well as drastically reduced footprint of the qubit compared to capacitively shunted (C-shunt) flux qubits with a large shunt capacitor. The lifetime of the SSFQ reached 13 - 25 $μ$s, which is comparable to or relatively higher than that of NbN-based C-shunt flux qubits and Al-based flux qubits with more than 10 times smaller junctions. This indicates that the large epitaxial NbN-based junction can be adopted for SSFQ as well as merged-element transmon with the relatively large junctions. The results presented in this work will offer a new choice of the scalable qubits as well as the material platform toward the realization of large-scale superconducting quantum computers.

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Tokunoshin Uchida, Shingo Nozaki, Daiki Kurihara, Hiroki Kutsuma, Shotaro Shirai, Atsushi Noguchi, Hirotaka Terai, Taro Yamashita. 2026-10-04. Epitaxial NbN-junction-based self-shunted superconducting flux qubit with high anharmonicity. https://arxiv.org/abs/2610.04821

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