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

  1. Tokunoshin Uchida,
  2. Shingo Nozaki,
  3. Daiki Kurihara,
  4. Hiroki Kutsuma,
  5. Shotaro Shirai,
  6. Atsushi Noguchi,
  7. Hirotaka Terai,
  8. and Taro Yamashita
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 μs, 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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