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

TL;DR

This paper demonstrates that Sn-InAs nanowire transmons exhibit highly tunable anharmonicity, surpassing traditional limits, which enhances the flexibility of quantum circuit design.

Contribution

It reveals that anharmonicity in Sn-InAs nanowire transmons can be tuned beyond the short-junction model predictions, enabling new quantum circuit functionalities.

Findings

Anharmonicity ranges from E_c to less than E_c/10.

Coherent qubit operation is possible at minimal anharmonicity.

Contradicts the multi-channel short-junction model predictions.

Abstract

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 $E_c$ to values smaller than $E_c/10$. This behavior contrasts with the predictions of the multi-channel short-junction model, which sets a lower limit on anharmonicity at $E_c/4$. 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.