Entangled Photon Excited Fluorescence in Organic Materials: An Ultrafast Coincidence Detector

We report the fluorescence emission from organic systems selectively excited by entangled pairs of photons. We have demonstrated a linear dependence of this two-photon excited fluorescence on the excitation intensity which is a unique nonclassical feature of two-photon interactions induced by entangled photons. The entangled photon (ETPA) excited fluorescence has been detected in several organic molecules possessing a high entangled photon absorption cross section. The ETPA fluorescence showed a nonmonotonic dependence on the delay between signal and idler beams. The fluorescence signal was detectable within the signal idler relative delay time interval of, similar to 100 fs. This time is comparable with the estimated entanglement time, T-E, making the ETPA-excited fluorescence in organic materials an ideal ultrafast coincidence detector. These results have widespread impact in applications ranging from spectroscopy to chemical and biological sensing, imaging, and microscopy.