Inversions of qubit energy levels in deep-strongly-coupled qubit-oscillator circuits

ORAL

Abstract

The electromagnetic field inside a cavity renormalizes the transition frequency of an atom inside the cavity. The Lamb (n = 0) and n-photon ac-Stark shifts can be written as Δ - Δn, where Δ and Δn are respectively the transition frequencies of a non-interacting and renormalized atom. In the limit of Δ « ω, where ω is the resonance frequency of the cavity, Δn can be written as [1] Δn/Δ = exp[-2(g/ω)2]Ln[(2g/ω)2], where g is the coupling constant between the atom and the electromagnetic field in the cavity and Ln is a Laguerre polynomial. This equation indicates that Δn changes sign when Ln crosses zero; the atom's ground and excited states are “inverted”. We use circuits of a flux qubit deep-strongly coupled to an LC oscillator [2], where g ≈ ω. The experimentally observed qubit frequencies Δn (n = 0, 1, 2) were very close to those given by the equation above. [1] S. Ashhab and F. Nori, PRA 81, 052311 (2010). [2] F. Yoshihara, T. Fuse et al., Nat. Phys. 13, 44 (2017).

*This work was supported by the Scientific Research (S) Grant No. JP25220601 by the Japanese Society for the Promotion of Science (JSPS), and the Japan Science and Technology Agency’s (JST) CREST program entitled "Creation of an innovative quantum technology platform based on the advanced control of quant

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Presenters

  • Fumiki Yoshihara

    • Advanced ICT Institute, National Institute of Information and Communications Technology

Authors

  • Fumiki Yoshihara

    • Advanced ICT Institute, National Institute of Information and Communications Technology

  • Tomoko Fuse

    • Advanced ICT Institute, National Institute of Information and Communications Technology

  • Ziqiao Ao

    • Department of Applied Physics, Waseda University

  • Sahel Ashhab

    • Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University

  • Kosuke Kakuyanagi

    • NTT Basic Research Laboratories, NTT Corporation
    • NTT Basic Research Labs

  • Shiro Saito

    • NTT Basic Research Laboratories, NTT Corporation
    • NTT Basic Research Labs

  • Takao Aoki

    • Department of Applied Physics, Waseda University
    • Waseda University, Department of Applied Physics

  • Kazuki Koshino

    • College of Liberal Arts and Sciences, Tokyo Medical and Dental University
    • Tokyo Medical and Dental University

  • Kouichi Semba

    • Advanced ICT Institute, National Institute of Information and Communications Technology
    • National Institute of Information and Communications Technology