Quantum optical approaches to biological measurement could enable unprecedented sensitivity, specificity, and resolution with minimal sample perturbation. Additionally, quantum optics provides new “knobs to turn” in imaging and spectroscopy that are not approachable with classical means. One such example is through entangled photons, in which groups of photons have properties that are intrinsically and inseparably linked. In this presentation, I will provide an introduction to entangled light applications, our experimental work in two-photon absorption with entangled light, and our experimental work establishing that even post-traversal through micrometers and millimeters of biological tissue/media, time-energy entangled light can maintain this unique linkage.
Entangled two-photon absorption (e2PA) employs advantages of classical two-photon absorption techniques while operating in a linear excitation regime at low fluxes and potentially having greatly enhanced absorption probabilities. A major challenge in measuring the e2PA cross section, σe2PA, is to discriminate e2PA from one- photon losses. Carefully designed transmittance measurements are required to distinguish the two mechanisms. For example, the e2PA signal should depend on the time delay between photons within an entangled pair (in contrast to one-photon losses). Here we present an experimental system implementing this characterization. We perform transmittance experiments for Zinc-tetraphenylporphyrin (ZnTPP) in toluene solution. We use entangled photons produced via spontaneous parametric downconversion at 810 nm wavelength as an excitation source. We show that the change in transmittance associated with e2PA in the sample is less than 1% in our experiment. From our measurements we conclude ZnTPP's σe2PA ≤1:7 x 10-19 cm2.
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