Noise enhanced transport in light-harvesting complexes and networks

Energy transport in light-harvesting photosynthetic complexes has been a topic of continued interest [1]. It is recognized that the initial steps of natural photosynthesis harness the available light energy at typically about 95–99% efficiency. This has attracted considerable attention recently due to the observation of quantum coherence in the dynamics of photosynthetic complexes using 2D femtosecond spectroscopy [2,3]. On the other hand the dynamics takes place in a very noisy environment and hence it will have to be taken into account when seeking an accurate theoretical description of the dynamics. This has rejuvenated interest in the relative roles of coherent and incoherent dynamics in the enhanced energy transfer in light-harvesting complexes [4–6]. In fact, we find that noise in conjunction with quantum coherence is an essential ingredient for high efficiency excitation transfer in quantum networks. We demonstrate the existence of noise assisted transport at the example of the Fenna-Matthew-Olson (FMO) complex, found in photosynthetic green sulphur bacteria. Similar effects are apparent in other natural systems like LH1 as well as artificial light-harvesting structures like dendrimers. Most importantly, this effect allows us to exploit noise rather than make strenuous attempts to avoid it. In light of this, we can exploit these effects in the transport of energy and information, and other effects [7].