Does coherence enhance transport in photosynthesis?

TL;DR

This paper investigates whether quantum coherence influences photosynthetic efficiency under natural sunlight, distinguishing types of coherence and identifying mechanisms that enhance transport in vivo.

Contribution

It clarifies the role of different coherence types in photosynthesis and highlights mechanisms like ENAQT and supertransfer that can improve transport efficiency under natural conditions.

Findings

Stationary states dominate natural photosynthesis.

Wavelike motion and microscopic coherence do not enhance efficiency alone.

ENAQT and supertransfer can enhance transport in sunlight.

Abstract

Recent observations of coherence in photosynthetic complexes have led to the question of whether quantum effects can occur in vivo, not under femtosecond laser pulses but in incoherent sunlight and at steady state, and, if so, whether the coherence explains the high exciton transfer efficiency. We distinguish several types of coherence and show that although some photosynthetic pathways are partially coherent processes, photosynthesis in nature proceeds through stationary states. This distinction allows us to rule out several mechanisms of transport enhancement in sunlight. In particular, although they are crucial for understanding exciton transport, neither wavelike motion nor microscopic coherence, on their own, enhance the efficiency. By contrast, two partially coherent mechanisms---ENAQT and supertransfer---can enhance transport even in sunlight and thus constitute motifs for the optimisation of artificial sunlight harvesting. Finally, we clarify the importance of ultrafast spectroscopy in understanding incoherent processes.