A decade with quantum coherence: How our past became classical and the future turned quantum

Some twelve years ago, Nature published an article reporting an evidence for wavelike energy transfer in the Fenna-Mattews-Olson complex, a small photosynthetic antenna isolated from green bacteria (Engel et al., 2007). In a broader sense, this publication marks a start of a complicated series of events, which constitute a part of what could be called a quantum revolution in biology. In this paper, we revisit the past decade of development in theoretical understanding of excitation energy transfer (EET) in photosynthesis under the influence of the new quantum vision of this field. In order to set the context, we review the status of the quantum theory of EET before the field has become a part of the broader discipline of quantum biology. We rephrase some of its former concepts in terms of decoherence theory and in the language of quasi-particles, to show the place, which theoretical photosynthesis research occupied in the big picture of quantum mechanics, physical chemistry and solid state physics before the supposed quantum revolution. We examine the influence of the new quantum-biological vocabulary, established over past ten years, on the development of the field. While the field has shown steady progress, directly related to the finds of Engel et al., we demonstrate that concepts ill-defined in the context of photosynthesis research, and imported from other branches of physics, actually hinder understanding of important natural photo-physical processes. Without providing suitable equivalent or added value, they threaten to replace concepts, which tie photosynthesis research to the related disciplines of chemistry and solid state physics. We demonstrate these claims by analyzing in some detail several recent paradigmatic papers from high profile journals.