Tunable anharmonicity in Sn-InAs nanowire transmons beyond the short junction limit

  1. Amrita Purkayastha,
  2. Amritesh Sharma,
  3. Param J. Patel,
  4. An-Hsi Chen,
  5. Connor P. Dempsey,
  6. Shreyas Asodekar,
  7. Subhayan Sinha,
  8. Maxime Tomasian,
  9. Mihir Pendharkar,
  10. Christopher J. Palmstrom,
  11. Moïra Hocevar,
  12. Kun Zuo,
  13. Michael Hatridge,
  14. and Sergey M. Frolov
The anharmonicity of a transmon qubit, defined as the difference in energy level spacing, is a key design parameter. In transmons built from hybrid superconductor-semiconductor Josephson elements, the anharmonicity is tunable with gate voltages that control both the Josephson energy and the weak link transparency. In Sn-InAs nanowire transmons, we use two-tone microwave spectroscopy to extract anharmonicity ranging in absolute value from the transmon charging energy Ec to values smaller than Ec/10. This behavior contrasts with the predictions of the multi-channel short-junction model, which sets a lower limit on anharmonicity at Ec/4. Coherent operation of the qubit is still possible at the point of the lowest anharmonicity. These findings demonstrate the potential of quantum circuits that benefit from widely electrically tunable anharmonicity.
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