Quantum Biology: Elucidating Design Principles From Photosynthesis With Keldysh Green’s Functions

Kenley Pelzer, University of Chicago

Long-lived coherences after laser excitation have been observed in photosynthetic complexes and have recently been emulated in synthetic multichromophoric systems. The persistence of these coherences has inspired new theories regarding the extreme quantum efficiency of photosynthetic energy transfer. Whether coherent transport occurs in nature and whether it improves photosynthetic efficiency remain topics of debate. Here, we use a nonequilibrium Green’s function analysis to model exciton transport after excitation from an incoherent source (as opposed to coherent laser excitation). We find that even with an incoherent source, the rate of environmental dephasing strongly affects exciton transport efficiency, suggesting that the relationship between dephasing and efficiency is not an artifact of coherent excitation. Analysis of excitonic fluxes among chromophores reveals that transport occurs by qualitatively different mechanisms as dephasing increases. Our approach can be generalized to complex synthetic systems and may provide a new tool for optimizing synthetic light-harvesting materials.

Abstract Author(s): Kenley Pelzer, Tankut Can, Stephen Gray, Dirk Morr, Gregory Engel