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This study investigates entangled two-photon absorption (ETPA) using Franson interference to improve the accuracy of cross-section measurements in dye molecules, specifically Rhodamine 6G. By employing delay-dependent coincidence measurements, the researchers reveal a small asymmetry in the interference envelope, leading to an effective cross-section estimate of approximately 2.1 E(-21) cm虏. Although the systematic uncertainty prevents a conclusive ETPA assignment, the work establishes a quantitative bound on the ETPA response, serving as a benchmark for future experiments.
Franson interference reveals a surprising bound on entangled two-photon absorption that could redefine our understanding of quantum correlations in molecular excitation.
Entangled photons offer quantum correlations with no classical analogue. In entangled pair two-photon absorption (ETPA), absorption rate is predicted to scale linearly rather than quadratically with photon flux, promising molecular excitation at fluxes far below the classical threshold. Reported ETPA cross sections nevertheless vary widely across experiments, largely since the observable, the differential of the transmitted flux or weak fluorescence, is difficult to separate from scattering and linear losses. We present a method which uses Franson interference to study entangled two-photon absorption through delay-dependent coincidence measurements on dye molecules. Applying the method to Rhodamine 6G, we observe a small asymmetry in the Franson interference envelope and obtain a model-derived effective cross section of approximately 2.1 E(-21) centimeter squared for Rhodamine 6G. However, the estimated systematic uncertainty does not allow a definitive ETPA assignment. Instead, the experiment establishes a quantitative bound on the ETPA response and provides a background-free benchmark for future measurements.
