Role of Initial Coherence in Excitation Energy Transfer in Fenna-Matthews-Olson Complex

TL;DR

This paper demonstrates that initial quantum coherence significantly accelerates excitation energy transfer in the FMO complex, challenging existing models and highlighting the importance of initial states in quantum biological processes.

Contribution

It introduces a simplified eight-level model showing how initial coherence enhances EET speed, considering dipole orientations and excitation energies.

Findings

Initial coherence speeds up EET in FMO complex

A femto-second laser pulse can create initial coherent states

Existing two-pathway models may not fully explain EET dynamics

Abstract

We theoretically show that the initial coherence plays a crucial role in enhancing the speed of excitation energy transfer (EET) in Fenna-Matthews-Olson (FMO) complex. We choose a simplistic eight-level model considering all the bacateriochlorophyll-a sites in a monomer of FMO complex. We make a comparative numerical study of the EET, in terms of non-Markovian evolution of an initial coherent superposition state and a mixed state. A femto-second coherent laser pulse is suitably chosen to create the initial coherent superposition state. Such an initial state relaxes much faster than a mixed state thereby speeding up the EET. In this analysis, we have taken into account the relative orientation of the transition dipole moments of the bacateriochlorophyll-a sites and their relative excitation energies. Our results reveal that for 2D electronic spectroscopy experiments, the existing two-pathway model of energy transfer in FMO complex may not be suitable in our understanding of EET.