Experimental study on the effects of photon-pair temporal correlations in entangled two-photon absorption

TL;DR

This study experimentally investigates how photon-pair temporal correlations affect entangled two-photon absorption in organic molecules, revealing no systematic change with time delay and suggesting lower cross-sections than previously reported.

Contribution

It provides a thorough experimental analysis of ETPA in Rhodamine B and ZnTPP, challenging prior assumptions about the influence of photon correlations and flux on ETPA measurements.

Findings

Time delay did not affect ETPA cross-sections in experiments.

Photon flux may be insufficient to induce measurable ETPA.

Actual absorption cross-sections are likely lower than previously reported.

Abstract

Entangled two-photon absorption (ETPA) has recently become a topic of lively debate, mainly due to the apparent inconsistencies in the experimentally-reported ETPA cross sections of organic molecules. In this work, we provide a thorough experimental study of ETPA in the organic molecules Rhodamine B (RhB) and Zinc Tetraphenylporphirin (ZnTPP). The goal of this contribution is twofold: on one hand, it seeks to reproduce the results of previous experimental reports and, on the other, it aims to determine the effects of different temporal correlations -- introduced as a controllable time-delay between the photons to be absorbed -- on the strength of the ETPA signal. In our experiment, the samples are excited by entangled pairs produced by type-I SPDC, with a spectral distribution centered at 810 nm. Surprisingly, and contrary to what was expected, the time delay did not produce in our experiments any systematic change in the cross-sections when monitoring the ETPA signal using a transmission measurement scheme. As a plausible cause of this unexpected result, we argue that the photon-pair flux, typically-used in these experiments, is not sufficient to promote the two-photon absorption process in these molecules. This suggests that the actual absorption cross-section values are lower than those previously reported, and therefore do not lead to a measurable ETPA effect for the transmission method.