Influence of a structured environment on the energy transfer in molecular assemblies: An approach based on Stochastic Schrödinger equations
Final Report Abstract
In the project we investigated transfer of excitation energy in photosynthetic light harvesting complexes. We focused mainly on the Fenna-Matthews-Olson (FMO) complex of green sulfur bacteria. It consists of Bacteriochlorophyll (BChl) molecules surrounded by a protein scaffold. The FMO complex transfers electronic excitation from large antenna complexes (chlorosomes) to a reaction center where the excitation energy is converted into a transmembrane chemical potential. This excitation transfer is mediated by quasi-resonant transition dipole-dipole coupling between the BChls. The main goal of the project was to understand how the coupling of electronic transitions to vibrations of the BChls and the protein influences the excitation transfer. To treat this challenging many-body problem at finite temperature, we developed quantum stochastic methods, which can efficiently be solved numerically. In particular, we demonstrated that an approach based on the general non-Markovian quantum state diffusion equation can accurately reproduce results of numerically much more expensive methods. As an application we showed that the transfer efficiency in the FMO can change drastically when certain modes are neglected. Thus it is important to take vibrations into account in a detailed manner. Our results give hints how to tailor the energy transfer by a suitable design of the vibrational environment. This might be helpful in constructing artificial light harvesting systems or, in a more general sense, exciton processing devices. Our stochastic approaches, as well as many other open system approaches, require a so called spectral density as input. The spectral density describes the density of vibrational modes and their couplings to the electronic transitions. At present there are only experimental spectral densities available that are averaged over all BChls of the FMO. We demonstrated that from mixed molecular dynamics quantum chemistry simulations it is possible to extract spectral densities for the individual BChls, whose average is in good agreement with the experimental spectral densities. During the project we also investigated alternative ways to calculate the transfer dynamics coupled to a complicated environment. We demonstrated that superconducting circuits can be used to simulate transport in the FMO complex. There has been much discussion about quantum coherence and entanglement in the transfer dynamics in the FMO. We have shown that for the parameters of the FMO the electronic quantum transfer dynamics can accurately be described by a set of coupled classical oscillators which undergo stochastic frequency modulations.
Publications
- Quantum simulator of an open quantum system using superconducting qubits: exciton transport in photosynthetic complexes. New J. Phys.
S. Mostame, P. Rebentrost, A. Eisfeld, A.J. Kerman, D.I. Tsomokos, A. Aspuru-Guzik
- Reason is but choosing: On the alternatives for bath correlators and spectral densities from mixed quantum-classical simulations. J Chem. Phys.
S. Valleau, A. Eisfeld and A. Aspuru-Guzik
- Absence of Quantum Oscillations and Dependence on Site Energies in Electronic Excitation Transfer in the Fenna-Matthews-Olson Trimer. J. Phys. Chem. Lett. 2, 2912 (2011)
G. Ritschel, J. Roden, W.T. Strunz, A. Aspuru-Guzik and A. Eisfeld
- An efficient method to calculate excitation energy transfer in light-harvesting systems: application to the Fenna-Matthews-Olson complex. New Journal of Physics 13, 113034 (2011)
G. Ritschel, J. Roden, W.T. Strunz and A. Eisfeld
- Classical master equation for excitonic transport under the influence of an environment. Phys. Rev. E 85, 046118 (2012)
A. Eisfeld and J.S. Briggs
(See online at https://doi.org/10.1103/PhysRevE.85.046118) - Dynamics of a nanoscale rotor driven by single-electron tunneling. Europhys Lett 98, 68004 (2012)
A. Croy and A. Eisfeld
(See online at https://doi.org/10.1209/0295-5075/98/68004) - Intermolecular torsional motion of a pi-aggregated dimer probed by two-dimensional electronic spectroscopy. J. Chem. Phys. 136, 024109 (2012)
J. Seibt and A. Eisfeld
(See online at https://doi.org/10.1063/1.3674993)
