Optimal thermal bath for robust excitation energy transfer in disordered light-harvesting complex 2 of purple bacteria

The existence of an optimal thermal bath to facilitate robust energy transfer between the spectrally separated B800 and B850 rings in light-harvesting complex 2 (LH2) of purple bacteria is investigated via the multichromophoric Forster theory. Due to the inherent energy bias between the two rings, the energy transfer rate from B800 to B850 is maximized as a function of the bath coupling strength, establishing an optimization criterion. Critically, upon inclusion of energetic disorder, this maximum is averaged out. However, noting the distribution of transfer rates, we find that the bath coupling strength can yield a minimal dispersion for the rate distribution, i.e. a maximum ratio of mean to standard deviation, thus achieving maximum energy transfer robust to the effects of static disorder.