Spectral properties of two superconducting artificial atoms coupled to a resonator in the ultrastrong coupling regime

We experimentally investigate a superconducting circuit composed of two flux qubits ultrastrongly coupled to a common LC resonator. Owing to the large anharmonicity of the flux qubits, the system can be described well by a generalized Dicke Hamiltonian containing spin-spin interaction terms. In the experimentally measured spectrum, we observed two key phenomena. First, an avoided level crossing provides evidence of the exotic interaction that allows the simultaneous excitation of two artificial atoms by absorbing one photon from the resonator. Second, we identified a pronounced spectral asymmetry that is a clear signature of light-matter decoupling. This multi-atom ultrastrongly coupled system opens the door to studying novel processes for quantum optics and quantum-information tasks on a chip.

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Publication Details

Journal
Nature Communications
Published
2025-06-17
DOI
https://doi.org/10.1038/s41467-025-60589-5
Citations
4
Primary Topic
Cold Atom Physics and Bose-Einstein Condensates
Type
article
Field-Weighted Citation Impact
4.99

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article

Spectral properties of two superconducting artificial atoms coupled to a resonator in the ultrastrong coupling regime

Akiyoshi Tomonaga, Franco Nori, Fumiki Yoshihara, Hiroto Mukai et al.
4 citations
Nature Communications
Cold Atom Physics and Bose-Einstein Condensates
4.99
article

Spectral properties of two superconducting artificial atoms coupled to a resonator in the ultrastrong coupling regime

Akiyoshi Tomonaga, Franco Nori, Fumiki Yoshihara, Hiroto Mukai, Roberto Stassi, J. S. Tsai
article en
4 citations

Abstract

We experimentally investigate a superconducting circuit composed of two flux qubits ultrastrongly coupled to a common LC resonator. Owing to the large anharmonicity of the flux qubits, the system can be described well by a generalized Dicke Hamiltonian containing spin-spin interaction terms. In the experimentally measured spectrum, we observed two key phenomena. First, an avoided level crossing provides evidence of the exotic interaction that allows the simultaneous excitation of two artificial atoms by absorbing one photon from the resonator. Second, we identified a pronounced spectral asymmetry that is a clear signature of light-matter decoupling. This multi-atom ultrastrongly coupled system opens the door to studying novel processes for quantum optics and quantum-information tasks on a chip.

Nature CommunicationsVol. 16(1)
University of Messina (IT), Tokyo University of Science (JP), University of Michigan (US), RIKEN Nishina Center (JP), RIKEN Center for Advanced Photonics (JP), National Institute of Advanced Industrial Science and Technology (JP), National Institute of Information and Communications Technology (JP)
New Energy and Industrial Technology Development Organization, Japan Society for the Promotion of Science, Japan Science and Technology Agency, Core Research for Evolutional Science and Technology
Openalex Percentile: Top 5%
Cold Atom Physics and Bose-Einstein Condensates
4.99
DOIOpen Access PDFOpenAlex
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Spectral properties of two superconducting artificial atoms coupled to a resonator in the ultrastrong coupling regime — Akiyoshi Tomonaga, Franco Nori, et al. · Nature Communications (2025) | TGRS Research Map | TGRS