Enviroment assisted quantum photo-protection in interacting multi excitons transfer complexes

Transport of excitons through molecular wires is a unique example where the interplay between quantum, environmental and geometrical effects, leads to surprising phenomena such as “environment-assisted quantum transport”, (ENQAT), where, counterintuitively, the environment interrupts quantum transport in a way that enhances the transfer efficiency¹. Suggested as an active mechanism in photosynthesis, ENAQT has been a focus of intense theoretical study. Most previous studies consider a system occupied by a single exciton, working under the assumption that weak coupling cannot excite more than one exciton. In this work, we show that this is not the case, and even weak excitations can lead to multiple-exciton generation. We then consider the transport of two excitons, which can interact between them. We show that in addition to ENAQT, the system can exhibit environment assisted quantum photo-protection, namely the situation in which increasing the external excitation leads to a reduction in exciton transport. The effect, which we show is due to the interplay between environmental effects, exciton interactions and network geometry, may be related to actual photo-protection observed in living photosynthetic systems.

1. Zerah-Harush, E. & Dubi, Y. Universal Origin for Environment-Assisted Quantum Transport in Exciton Transfer Networks. J. Phys. Chem. Lett.1689–1695 (2018)