Inversion of Qubit Energy Levels in Qubit-Oscillator Circuits in the Deep-Strong-Coupling Regime

F. Yoshihara, T. Fuse, Z. Ao, Sahel Ashhab, K. Kakuyanagi, S. Saito, T. Aoki, K. Koshino, K. Semba

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Abstract

We report on experimentally measured light shifts of superconducting flux qubits deep-strongly coupled to LC oscillators, where the coupling constants are comparable to the qubit and oscillator resonance frequencies. By using two-tone spectroscopy, the energies of the six lowest levels of each circuit are determined. We find huge Lamb shifts that exceed 90% of the bare qubit frequencies and inversions of the qubits' ground and excited states when there are a finite number of photons in the oscillator. Our experimental results agree with theoretical predictions based on the quantum Rabi model.

Original languageEnglish
Article number183601
JournalPhysical Review Letters
Volume120
Issue number18
DOIs
Publication statusPublished - 3 May 2018

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ASJC Scopus subject areas

  • Physics and Astronomy(all)

Cite this

Yoshihara, F., Fuse, T., Ao, Z., Ashhab, S., Kakuyanagi, K., Saito, S., Aoki, T., Koshino, K., & Semba, K. (2018). Inversion of Qubit Energy Levels in Qubit-Oscillator Circuits in the Deep-Strong-Coupling Regime. Physical Review Letters, 120(18), [183601]. https://doi.org/10.1103/PhysRevLett.120.183601