Laboratoire de Physique Théorique
Toulouse - UMR 5152

The harvest of solar photon energy is at the heart of photosynthetic systems realized by nature in large biomolecular complexes or in man made devices. After a solar photon has transferred its energy to form an exciton, the nonequilibrium quantum dynamics of this quasiparticle ultimately brings the stored energy to a reaction center where chemical reactions are triggered. These first steps of photosynthesis have moved again into the focus of research, since recent advances in ultrafast optical spectroscopy have made it possible to detect this ultrafast motion on the femtosecond time scale. By this, the traditional picture of an incoherent, hopping-like Förster transfer of the excitation energy between different molecular sites has been challenged and a supportive role of quantum coherence for the transfer efficiency has been formulated.

I will show how quantum coherence of biomolecular excitons is influenced by environmental noise stemming from polarization fluctuations of the solvent and from the vibrational motion of the molecular backbone [1-6]. Non-Markovian effects can thereby play a constructive role [1,2,3]. Using a numerically exact deterministic path-integral approach, we demonstrate that a rather slow quantum bath helps to sustain quantum entanglement of two molecular dimers, in contrast to a Markovian environment [1]. The impact of quantum coherent localized modes on the excitonic dynamics is investigated as well for the particularly well characterized Fenna-Matthews Olsen complex [5,6]. Likewise, I will show that environmental fluctuations can have a constructive effect on the efficient energy transfer even in dyes with orthogonal dipoles with vanishing direct dipole coupling [7].

References

[1] M. Thorwart, J. Eckel, J.H. Reina, P. Nalbach, and S. Weiss , Chem. Phys. Lett. 478, 234 (2009) [2] P. Nalbach and M. Thorwart , J. Chem. Phys. 132, 194111 (2010) [3] P. Nalbach, A. Ishizaki, G.R Fleming, and M. Thorwart , New J. Phys. 13, 063040 (2011) [4] P. Nalbach, J. Eckel, and M. Thorwart , New J. Phys. Focus Issue on “Quantum Effects and Noise in Biomolecules” 12, 065043 (2010) [5] P. Nalbach and M. Thorwart , J. Phys. B : At. Mol. Opt. Phys. 45, 154009 (2012) [6] P. Nalbach, D. Braun, and M. Thorwart , Phys. Rev. E 84, 041926 (2011) [7] P. Nalbach, I. Pugliesi, H. Langhals, and M. Thorwart , Phys. Rev. Lett. 108, 218302 (2012).