Entangled Photon Spectroscopy.

The enhanced interest in quantum-related phenomena has provided new opportunities for chemists to push the limits of detection and analysis of chemical processes. As some have called this the second quantum revolution, a time has come to apply the rules learned from previous research in quantum phenomena toward new methods and technologies important to chemists. While there has been great interest recently in quantum information science (QIS), the quest to understand how nonclassical states of light interact with matter has been ongoing for more than two decades.

Efficient Modeling of Organic Chromophores for Entangled Two-Photon Absorption.

The use of a nonclassical light source for studying molecular electronic structure has been of great interest in many applications. Here we report a theoretical study of entangled two-photon absorption (ETPA) in organic chromophores, and we provide new insight into the quantitative relation between ETPA and the corresponding unentangled TPA based on the significantly different line widths associated with entangled and unentangled processes. A sum-over-states approach is used to obtain classical TPA and ETPA cross sections and to explore the contribution of each electronic state to the ETPA process.

Modern Anesthetic Ethers Demonstrate Quantum Interactions with Entangled Photons.

Despite decades of research, the mechanism of anesthetic-induced unconsciousness remains incompletely understood, with some advocating for a quantum mechanical basis. Despite associations between general anesthesia and changes in physical properties such as electron spin, there has been no empirical demonstration that general anesthetics are capable of functional quantum interactions. In this work, we studied the linear and non-linear optical properties of the halogenated ethers sevoflurane (SEVO) and isoflurane (ISO), using UV-Vis spectroscopy, time dependent-density functional theory (TD-DFT) calculations, classical two-photon spectroscopy, and entangled two-photon spectroscopy.

Two-Photon Excitation of Flavins and Flavoproteins with Classical and Quantum Light.

In this contribution, the entangled two-photon absorption (ETPA) process on naturally occurring flavoproteins was studied. Low temperature responsive protein (LOT6P) and b-type dihydroorotate dehydrogenase (DHOD B), which possess flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) chromophores embedded in the protein environment, were investigated. The ETPA cross-section was measured, and we found that it increases when going from an aqueous solution of the free flavin chromophore to the chromophore embedded in the protein.

Entangled Two Photon Absorption Cross Section on the 808 nm Region for the Common Dyes Zinc Tetraphenylporphyrin and Rhodamine B.

We report the measurement of the entangled two-photon absorption (ETPA) cross section, σ, at 808 nm on organic chromophores in solution in a low photon flux regime. We performed measurements on zinc tetraphenylporphyrin (ZnTPP) in toluene and rhodamine B (RhB) in methanol. This is, to the best of our knowledge, the first time that σ is measured for RhB.

Measuring different types of transverse momentum correlations in the biphoton's Fourier plane.

In this Letter, we present a theoretical and experimental study about the spatial correlations of paired photons generated by Type II spontaneous parametric down-conversion. In particular, we show how these correlations can be positive or negative, depending on the direction in which the far-field plane is scanned and the polarization postselected. Our results provide a straightforward way to observe different kind of correlations that complement other well-known methods to tune the spatial correlations of paired photons.

Dynamics of the higher lying excited states of cyanine dyes. An ultrafast fluorescence study.

The electronic relaxation dynamics of the second singlet excited states of several cyanine dyes was studied through the femtosecond fluorescence up-conversion technique. Our interest in these molecules comes from the potential applications of systems with upper excited singlet states with a long lifetime, which can include electron and energy transfer from the higher lying singlets after one- or two-photon absorption. We studied three series of cyanines with 4-quinolyl, 2-quinolyl, or benzothiazolyl type end groups, each with varying sp(2) carbon conjugation lengths in the methinic bridge.

Ultrafast excited state dynamics of allopurinol, a modified DNA base.

The decay of electronically excited allopurinol riboside was studied through the fluorescence up-conversion technique and high level ab initio calculations. For the allopurinol system with a pyrazolic five-membered ring, we observed an ultrafast decay of the fluorescence signal in water (τ < 0.2 ps), similar to what has been observed for hypoxanthine and inosine (with an imidazolic five-membered ring).

On the accessibility to conical intersections in purines: hypoxanthine and its singly protonated and deprotonated forms.

The dynamics following electronic excitation of hypoxanthine and its nucleoside inosine were studied by femtosecond fluorescence up-conversion. Our objective was to explore variants of the purinic DNA bases in order to determine the molecular parameters that increase or reduce the accessibility to ground state conical intersections. From experiments in water and methanol solution we conclude that both dominant neutral tautomers of hypoxanthine exhibit ultrashort excited state lifetimes (τ < 0.