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E. Acknowledgments:-we-acknowledge, F. Rousseau, N. L. Cadiz, A. Jacubowiez, P. L. Browaeys et al., Grangier for fruitful discussions Funding: The research was supported by a DGA-MRIS (Direction Générale de l' Armement? Mission Recherche et Innovation Scientifique) scholarship, by RTRA (Réseau Thématique de Recherche Avancée) Triangle de la Physique, and by a public grant overseen by the French National Research Agency (ANR) as part of the Investissements d' Avenir " program (reference: ANR-10-LABX-0035, Labex NanoSaclay). J.-J.G. is a senior member of Institut Universitaire de France Author contributions: P initiated the project. The plasmonic chip design and multiphoton characterization were supervised by built the setup and performed all quantum experiments under the supervision of, H. designed the chipG. wrote the paper. All authors discussed the results. Competing interests: The authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from F.M. (francois.marquier@ institutoptique.fr)