Quantum coherent biomolecular energy transfer with spatially correlated fluctuations

We show that the quantum coherent transfer of excitations between biomolecular chromophores is strongly influenced by spatial correlations of environmental fluctuations. The latter are due either to propagating environmental modes or to local fluctuations with a finite localization length. A simple toy model of a single donor–acceptor pair with spatially separated chromophore sites allows one to investigate the influence of these spatial correlations on quantum coherent excitation transfer. The sound velocity of the solvent determines the wavelength of the environmental modes, which, in turn, has to be compared to the spatial distance of the chromophore sites. When the wavelength exceeds the distance between donor and acceptor sites, we find a strong suppression of decoherence. In addition, we consider two spatially separated donor–acceptor pairs under the influence of propagating environmental modes. Depending on their wavelengths fixed by the sound velocity of the solvent material, the spatial range of correlations may extend over typical interpair distances, which can lead to an increase in the decohering influence of the solvent. Surprisingly, this effect is counteracted by increasing temperature.