Mapping Electronic Decoherence Pathways in Molecules

With support from the Chemical Structure and Dynamics (CSD) program in the Division of Chemistry, Professors David McCamant and Ignacio Franco of the University of Rochester will develop experimental and theoretical methods to study quantum decoherence in molecules that are excited with visible light. When a molecule absorbs light, it can be placed in two states at the same time, also known as a coherent superposition. These superposition states are short lived, fading away in less than 100 millionths of a billionth of a second, due to interactions of the molecule with its surroundings. Professors McCamant, Franco, and their students will perform sophisticated femtosecond time-scale laser experiments to understand how specific molecular motions contribute to this rapid decoherence process. These experiments will be interpreted in the context of theoretical models to learn how specific motions disrupt the electronic coherence. Their discoveries could improve our understanding of how to manipulate electronic coherence via molecular design, with the potential to guide future molecular-based quantum technologies. The project will provide research opportunities for graduate and undergraduate students, contributing to the creation of a quantum-enabled workforce. The proposed experiments will use Femtosecond Stimulated Raman Spectroscopy to reconstruct the spectral density of various families of organic dyes, and map decoherence pathways in molecules. The spectral density, which reveals the coupling of electronic superposition states in molecules to vibrations and solvent, can be measured by determining the Raman cross-sections of these vibrations and modeling the Raman intensities and absorption spectra with spectroscopic theories. The chosen molecular families -- oligoacenes, fluorescent dyes and molecules used as single-photon emitters for quantum information application -- will exemplify how the decoherence changes with molecular size, rigidity, chemical functionalization and temperature. The analysis will further reveal the dominant vibrational modes responsible for decoherence, an understanding that is needed to develop chemical strategies for modulating this property. Professors McCamant and Franco will also develop a new pathway for undergraduate chemistry majors that emphasizes quantum mechanics and physical chemistry early in their college curriculum. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.