Tuning the anharmonicity and frequency of multilevel system using AC Stark effect

The AC Stark shift of two-level system in superconducting quantum circuits is a well-known phenomenon ^[1], however it will become more complicated for multilevel systems. Based on recent theoretical works on this subject ^[2], we investigated the AC Stark effect experimentally for a four-level system ^[3]. Depending on the drives, we can tune the three of transition frequencies and equalize them pairwise by adjusting the strengths and frequencies of the drives. This study provides some additional insight on the complex non-linear behaviors of Josephson-junction based devices under strong drives.



[1] Schuster, D. I. et al. ac Stark Shift and Dephasing of a Superconducting Qubit Strongly Coupled to a Cavity Field. Phys. Rev. Lett. 94, 123602 (2005).

[2] Zhang, Y. et al. Engineering bilinear mode coupling in circuit QED: Theory and experiment. Phys. Rev. A 99, 012314 (2019).

[3] Paik, H. et al. Observation of High Coherence in Josephson Junction Qubits Measured in a Three-Dimensional Circuit QED Architecture. Phys. Rev. Lett. 107, 240501 (2011).