Design and Operation of Fluxonium Superconducting Qubits at Integer Flux Quanta

Yu-Chi Chang^1*, Chin-Yeh Chen¹, Wei-Chen Lin¹, Yen-Hsiang Lin¹

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Yu-Chi Chang, email:std111022529@gapp.nthu.edu.tw

The fluxonium superconducting qubit is a Cooper-pair box (CPB) shunted by a superinductance. Due to its large anharmonicity and high coherence time, fluxonium has attracted significant attention for applications in quantum information science. Conventionally, fluxonium qubits are optimally biased at half-integer flux quanta. However, recent studies have shown that fluxonium devices with larger inductance can operate at integer flux quanta with qubit frequency around 3 GHz, while maintaining strong anharmonicity and high coherence.

In this work, we identify a parameters regime where the ground state (|0⟩) and first excited state (|1⟩) exhibit high coherence even at integer flux bias. Moreover, the second excited states (|2⟩) also shows long coherence time. We realize this new fluxonium design at the integer flux bias point, a lambda-type system formed by |0⟩, |2⟩, and |3⟩ states emerge within a single circuit without introducing additional degrees of freedom.

Using this system, we perform stimulated Raman adiabatic passage (STIRAP) to coherently transfer population between dipole-forbidden states and investigate their coherence properties. The realization of a Λ-system in fluxonium further opens the possibility of implementing qutrit-based protocols for quantum information processing also establishes a platform bridging superconducting circuits and quantum optics.

Keywords: Fluxonium Superconducting Qubits, Qutrits, Quantum coherent control