Cited by 7Strong Light-Matter InteractionsNonlinear Dynamics and Pattern FormationTopological Materials and Phenomena

Observation of the diffusive Nambu–Goldstone mode of a non-equilibrium phase transition

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Claude, Ferdinand, Jacquet, Maxime J., Glorieux, Quentin, Wouters, Michiel, Giacobino, Elisabeth, Carusotto, Iacopo, Bramati, Alberto·2025·Nature Physics

Abstract

Second-order phase transitions are governed by a spontaneous symmetry-breaking mechanism, which yields collective excitations with a gapless spectrum called Nambu–Goldstone modes. Although these modes propagate as sound waves in conservative systems, non-equilibrium phase transitions have been predicted to feature a diffusive Nambu–Goldstone mode. Here, we present the experimental characterization of such a mode in a non-equilibrium Bose–Einstein condensate of microcavity polaritons. The mode appears in the spectroscopic response of the condensate to an extra probe laser as spectral narrowing, along with the emergence of a tilted frequency plateau. Breaking the symmetry with another phase-fixing beam causes a gap to open in the imaginary part of the spectrum and the disappearance of the Nambu–Goldstone mode. These observations confirm theoretical predictions for the Nambu–Goldstone mode of non-equilibrium phase transitions and reveal the symmetry-breaking mechanism underlying polariton condensation. Gapless modes emerging from non-equilibrium phase transitions are predicted to diffuse rather than propagate as sound waves. Now, the diffusion of these modes and their suppression under symmetry breaking are confirmed in a polariton condensate.

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  • While particle-number conservation makes it difficult to verify this prediction in atomic condensates at equilibrium, the phase of an optical condensate can be pinned by an additional incident coherent laser, and a clear gap in the Goldstone mode dispersion is observed in experiments.

    “While particle-number conservation makes it difficult to verify this prediction in atomic condensates at equilibrium [124], the phase of an optical condensate can be pinned by an additional incident coherent laser [125] and a clear gap in the Goldstone mode dispersion is clearly observed in experiments [106].”

    From How to exploit driving and dissipation to stabilize and manipulate quantum many-body states (2025) · cites this paper as [106]

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  • The theoretical prediction of a diffusive Goldstone mode in a nonequilibrium condensate has been confirmed in a pump-and-probe experimental measurement of the collective-mode dispersion of an exciton-polariton condensate.

    “The theoretical prediction of a diffusive behaviour of the Goldstone mode of a nonequilibrium condensate has been recently confirmed in a pump-and-probe experimental measurement of the dispersion of the collective modes of an exciton-polariton condensate [106].”

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Authors
Claude, F., Jacquet, M. J., Glorieux, Q., Wouters, M., Giacobino, E., Carusotto, I., & Bramati, A.
Affiliations
  • Centre National de la Recherche Scientifique (FR)
  • University of Antwerp (BE)
  • University of Trento (IT)
Venue
Nature Physics
Published
2025-05-02
Volume
21
Issue
6
Pages
924-930
ISSN
  • 1745-2473 (ISSN-L)
  • 1745-2481
OpenAlex
W4410043733
Cited by
7
References
58
Citations by year
2026: 5 · 2025: 2
FWCI
2.56
Type
journal article
Language
en
Open access
Locations
  • Nature Physics (publishedVersion)
  • HAL (submittedVersion)
Funders
  • Institut Universitaire de France
  • Provincia Autonoma di Trento (820392, PE0000023-NQSTI)
  • Horizon 2020 Framework Programme (PE0000023-NQSTI, 820392)
Topics
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Strong Light-Matter Interactions
  • Physical Sciences › Computer Science › Computer Networks and Communications › Nonlinear Dynamics and Pattern Formation
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Topological Materials and Phenomena
Keywords
Goldstone modes, diffusive modes, nonequilibrium phase transitions, exciton-polariton condensates, gapless modes, symmetry breaking, exciton-polaritons

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