Characteristic spectra of circuit quantum electrodynamics systems from the ultrastrong- to the deep-strong-coupling regime

F. Yoshihara, T. Fuse, Sahel Ashhab, K. Kakuyanagi, S. Saito, K. Semba

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24 Citations (Scopus)


We report on spectra of circuit-quantum-electrodynamics (QED) systems in an intermediate regime that lies between the ultrastrong- and the deep-strong-coupling regimes, which have been reported previously in the literature. Our experimental results, along with numerical simulations, demonstrate that as the coupling strength increases, the spectrum of a circuit-QED system undergoes multiple qualitative transformations, such that several coupling regimes are identified, each with its own unique spectral features. The different spectral transformations can be related to crossings between energy level differences and to changes in the symmetries of the energy eigenstates. These results allow us to use qualitative spectral features to infer certain properties and parameters of the system.

Original languageEnglish
Article number053824
JournalPhysical Review A
Issue number5
Publication statusPublished - 9 May 2017


ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

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