Do we live in a Quantum World? Coherent multidimensional studies of quantum coherence effects in biological systems
The relative importance of quantum coherence effects in biological systems has long been debated. At the molecular level, the discussion reduces to the spatial and temporal coherence of the corresponding wavefunction describing the biological response function. This talk will briefly explore the biological functions of energy transport in photosynthetic systems and photoisomerization processes to provide two different examples ofevolutionarlyoptimization. The focus will be on the photoisomerization process of rhodopsin (Rh) and bacteriorhodopsin (bR). In 2D spectra for Rh andbR, we observe very strong modulation of spectra related to the reactant/product surfaces by the very modes involved in the structural transition. In the case of Rh, the steric repulsive forces of the excited cis conformation state impulsively direct the system to the conical intersection (CI) within a half period of the localized C11-C12 bond, the key torsional motion directing the isomerization. InbR, the trans conformation allows exploration of larger nuclear configuration phase space; yet strong vibrational coherences are still observed. By comparison to multi-configuration quantum chemistry calculations, we assign this unusual nuclear-electronic coupling to principally the bond elongation coordinate periodically mixing the S1 and S2 electronic surfaces. It is this coupling that dynamically directs the photoisomerization inbR.Nature has found 2 solutions to beat rapid intramolecular vibrational redistribution processes for such high vibrational density of states that normally occur within 100 fs time scales. The vibrational coupling to electronic surfaces and imposed direction is dissipation driven. Nature does not try to engineer the protein/bath to conserve coherences but rather exploits dissipation to direct biological processes. This simple concept, mastered by nature over all relevant time and spatial dimensions is truly the marvel of biology.