Large Scale Simulations of Photosynthetic Antenna Systems: Interplay of Cooperativity and Disorder

Large-scale simulations of light-matter interaction in natural photosynthetic antenna complexes containing more than one hundred thousands of\r\nchlorophyll molecules, comparable with natural size, have been performed. Photosynthetic antenna complexes present in Green sulfur bacteria and Purple bacteria have\r\nbeen analyzed using a radiative non-Hermitian Hamiltonian, well-known in the field of\r\nquantum optics, instead of the widely used dipole−dipole Frenkel Hamiltonian. This\r\napproach allows us to study ensembles of emitters beyond the small volume limit\r\n(system size much smaller than the absorbed wavelength), where the Frenkel\r\nHamiltonian fails. When analyzed on a large scale, such structures display superradiant\r\nstates much brighter than their single components. An analysis of the robustness to\r\nstatic disorder and dynamical (thermal) noise shows that exciton coherence in the\r\nwhole photosynthetic complex is larger than the coherence found in its parts. This\r\nprovides evidence that the photosynthetic complex as a whole plays a predominant role\r\nin sustaining coherences in the system even at room temperature. Our results allow a better understanding of natural photosynthetic\r\nantennae and could drive experiments to verify how the response to electromagnetic radiation depends on the size of the\r\nphotosynthetic antenna.