Optically Excited Entangled States in Organic Molecules Illuminate the Dark

Abstract

We utilize quantum entangled photons to carry out nonlinear optical spectroscopy in organic molecules with an extremely small number of photons. For the first time, fluorescence is reported as a result of entangled photon absorption in organic nonlinear optical molecules. Selectivity of the entangled photon absorption process is also observed and a theoretical model of this process is provided. Through these experiments and theoretical modeling it is found that while some molecules may not have strong classical nonlinear optical properties due to their excitation pathways; these same excitation pathways may enhance the entangled photon processes. It is found that the opposite is also true. Some materials with weak classical nonlinear optical effects may exhibit strong non-classical nonlinear optical effects. Our entangled photon fluorescence results provide the first steps in realizing and demonstrating the viability of entangled two-photon microscopy, remote sensing, and optical communications.

Nonlinear optical signals and spectroscopy with quantum light

“…In section III.C.1, we will further show that for off-resonant intermediate state(s) e -as is the case in most experimental studies to date (Dayan et al, 2004Guzman et al, 2010;Harpham et al, 2009;Lee and Goodson, 2006;Upton et al, 2013) -the two signals carry the same information.…”

Photon statistics of intense entangled photon pulses

“…Hence, even though the linear scaling breaks down at |α| 2 = 0.003, the nonclassical time-bandwidth properties of entangled photon pairs still dominate the signal until the intensity is almost twice as high. We further investigate how this crossover depends on the intermediate state e [42]. To do this, we plot the crossover intensity |α 0 | 2 versus the energy of the intermediate state e in figure 8.…”

Two-photon spectroscopy of excitons with entangled photons

“…The four-point correlation function scales quadratically in the pump intensity for classical laser pulses, but linearly for entangled photons. This favorable intensity scaling [15][16][17][18] has been demonstrated experimentally in various systems, and allows to perform measurements at low intensities, avoiding damage to the sample. Moreover, the non-classical time-bandwidth properties of entangled photon pairs [19][20][21] provide unconventional observation windows, and can be used to selectively excite specific two-exciton states 21 or specific vibrational states, 22,23 and control population transport.…”

“…Similar setups have been used in Ref. 18, where count rates on the order of 10 7 photons/s have been reported. The frequency-dispersed detection proposed here is expected to yield comparable but somewhat lower count rates.…”