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Café com Física | |
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26 de maio de 2026
16h00 Sala F-210 (IFSC-USP) Tom Bienaimé Centre Européen de Sciences Quantique Institut de Science et d'Ingénierie Supramoléculaires Cooperative Photon-Photon Interactions in Cold Rydberg Ensembles Light propagating in atomic media under the paraxial approximation acquires an effective mass and tunable interactions, enabling fluid-like behavior. While experiments in warm atomic vapors have demonstrated moderate photon-photon interactions (Kerr indices n2 ~ 10-11 m2/W), Rydberg electromagnetically induced transparency (EIT) offers a unique opportunity to enhance these interactions by several orders of magnitude, leveraging both slow-light effects and cooperative atomic responses. We report interferometric measurements of photon-photon interactions using a Mach-Zehnder interferometer, achieving Kerr indices n2 ~ 10-3 m2/W. We experimentally demonstrate the cooperative nature of these interactions, revealing how collective atomic responses enhance photon-photon interaction, and show that their strength and sign can be tuned by adjusting experimental parameters. Our results indicate that dispersive optical nonlinearities at the single-photon level, corresponding to n2 ~ 1 m2/W, are attainable by increasing atomic density, in agreement with recent experimental advances. This paves the way for exploring strongly correlated states of light. Furthermore, the nonlocal and long-range character of these interactions, even at moderate Kerr indices, may lead to novel nonlinear optical phenomena, such as photonic analogs of modulation instability, crystallization, and quantum droplets. 
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