Bose–Einstein condensation is a remarkable manifestation of quantum statistics and macroscopic quantum coherence. Superconductivity and superfluidity have their origin in Bose–Einstein condensation. Ultracold quantum gases have provided condensates close to the original ideas of Bose and Einstein, while condensation of polaritons and magnons has introduced novel concepts of non-equilibrium condensation. Here, we demonstrate a Bose–Einstein condensate of surface plasmon polaritons in lattice modes of a metal nanoparticle array. Interaction of the nanoscale-confined surface plasmons with a room-temperature bath of dye molecules enables thermalization and condensation in picoseconds. The ultrafast thermalization and condensation dynamics are revealed by an experiment that exploits thermalization under propagation and the open-cavity character of the system. A crossover from a Bose–Einstein condensate to usual lasing is realized by tailoring the band structure. This new condensate of surface plasmon lattice excitations has promise for future technologies due to its ultrafast, room-temperature and on-chip nature.

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We thank M. Heikkinen, D.-H. Kim, R. Moerland and M. Nečada for useful discussions. This work is dedicated in memory of D. Jin and her inspiring example. This work was supported by the Academy of Finland through its Centres of Excellence Programme (2012–2017) and under project numbers 284621, 303351 and 307419, and by the European Research Council (ERC-2013-AdG-340748-CODE). This article is based on work from COST Action MP1403 Nanoscale Quantum Optics, supported by COST (European Cooperation in Science and Technology). K.S.D. acknowledges financial support by a Marie Skłodowska-Curie Action (H2020-MSCA-IF-2016, project id 745115). Part of the research was performed at the Micronova Nanofabrication Centre, supported by Aalto University. The Triton cluster at Aalto University was used for the computations.

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  1. These authors contributed equally: Tommi K. Hakala and Antti J. Moilanen.


  1. COMP Centre of Excellence, Department of Applied Physics, Aalto University School of Science, Aalto, Finland

    • Tommi K. Hakala
    • , Antti J. Moilanen
    • , Aaro I. Väkeväinen
    • , Rui Guo
    • , Jani-Petri Martikainen
    • , Konstantinos S. Daskalakis
    • , Heikki T. Rekola
    • , Aleksi Julku
    •  & Päivi Törmä


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P.T. initiated and supervised the project. T.K.H., A.J.M., R.G. and A.I.V. performed the experiments. A.J.M., T.K.H. and A.I.V. analysed the data. T.K.H., K.S.D. and H.T.R. built the experimental set-up. A.J.M., J.-P.M. and A.J. performed the theoretical modelling. R.G. fabricated the samples. All authors discussed the results. P.T., A.J.M. and T.K.H. wrote the manuscript together with all authors.

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The authors declare no competing interests.

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Correspondence to Päivi Törmä.

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