Efficient Operation of Superconducting Qubits Using Nonadiabatic Transitions

I-Yun Hsiao^1*, You-Ren Chen², Yen-Hsiang Lin³, Yoshiaki Teranishi²

¹Physics Devision, National Center for Theoretical Sciences, Taipei, Taiwan
²Institute of Physics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
³Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:I-Yun Hsiao, email:win820804@gmail.com

     Fast and accurate quantum gate controls are essential for the development of practical quantum computers. Conventional gate operations typically rely on external electromagnetic waves to induce resonance transitions, which require multiple oscillation cycles to complete. In contrast, nonadiabatic transitions offer an alternative that can potentially achieve more efficient gate operations without the need for electromagnetic waves.

     In certain quantum systems, controllable parameters exist within the system's Hamiltonian. For instance, in superconducting qubit systems such as fluxonium, the Hamiltonian is given by H=4E_cn²+½E_Jφ^2-E_Jcos(φ+φ_ext) where n represents the charge operator, φ denotes the flux operator, and φ_ext is the external flux, which is a controllable parameter. By varying the parameter φ_ext , the Hamiltonian changes, consequently altering the system's eigenenergies. For some values of the parameter φ_ext , the gap between eigenenergies may become small, indicating that a time-dependent φ_ext(t) around those points can induce nonadiabatic transitions. This means that by designing φ_ext , quantum control can be achieved. However, to control qubits efficiently and precisely, the design of the parameter φ_ext(t) is crucial.

     We demonstrated efficient gate operation and initialization in fluxonium qubits while also considering the impact of environmental factors on these operations. The robustness and stability of the methods were analyzed, leading to the development of more robust control strategies for nonadiabatic-based schemes.

Keywords: superconducting qubits, quantum control, nonadiabatic transition