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Spectral signature of high-order photon processes enhanced by Cooper-pair pairing

Author

Listed:
  • W. C. Smith

    (Université PSL, Inria
    Santa Barbara)

  • A. Borgognoni

    (Université PSL, Inria)

  • M. Villiers

    (Université PSL, Inria)

  • E. Roverc’h

    (Université PSL, Inria)

  • J. Palomo

    (Université PSL, Inria)

  • M. R. Delbecq

    (Université PSL, Inria)

  • T. Kontos

    (Université PSL, Inria)

  • P. Campagne-Ibarcq

    (Université PSL, Inria)

  • B. Douçot

    (Sorbonne Université and CNRS UMR 7589)

  • Z. Leghtas

    (Université PSL, Inria)

Abstract

Inducing interactions between individual photons is key for photonic quantum information and studying many-body photon states. Superconducting circuits are well suited to combine strong interactions with low losses. Typically, microwave photons are stored in an LC oscillator shunted by a Josephson junction, where the zero-point phase fluctuations across the junction determine the strength and order of photon interactions. Most superconducting nonlinear oscillators operate with small phase fluctuations, where two-photon Kerr interactions dominate. In our experiment, we shunt a high-impedance LC oscillator with a dipole element favoring the tunneling of paired Cooper pairs. This leads to large phase fluctuations of 3.4, accessing a regime where transition frequencies shift non-monotonically with excitation number. From spectroscopy, we extract two-, three-, and four-photon interaction energies, all of similar strength and exceeding the photon loss rate. Our results open a new regime of high-order photon interactions in microwave quantum optics.

Suggested Citation

  • W. C. Smith & A. Borgognoni & M. Villiers & E. Roverc’h & J. Palomo & M. R. Delbecq & T. Kontos & P. Campagne-Ibarcq & B. Douçot & Z. Leghtas, 2025. "Spectral signature of high-order photon processes enhanced by Cooper-pair pairing," Nature Communications, Nature, vol. 16(1), pages 1-8, December.
    • Handle: RePEc:nat:natcom:v:16:y:2025:i:1:d:10.1038_s41467-025-62047-8
    DOI: 10.1038/s41467-025-62047-8
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