Quantum coherent dynamics in photosynthetic protein complexes

Since the birth of quantum mechanics, there has been a long fascination of the role of quantum effects in the evolution of biological systems, which has inspired decoding quantum coherence effects in photosynthetic systems. In photosynthetic complexes, the pigments do not exist in isolation; they interact with their surrounding protein environment. However, the strength of this system-bath coupling can vary, and one must be careful in characterizing it (with many complexes actually in an intermediate coupling regime). This review will summarize the studies toward unraveling excitonic energy transfer in photosynthetic systems, examining the influence of electronic and vibronic coherence and system-bath interactions on transfer efficiency in photosynthetic protein complexes. The review first examines the absorption properties of chlorophylls and the structural organization of protein complexes, highlighting their role in facilitating ultrafast-energy and charge-transfer processes. It also introduces the principles of multidimensional coherent spectroscopy (a nonlinear four-wave-mixing technique) and related ultrafast spectroscopic methods, which provide key insights into these processes. We also discuss theoretical approaches and models (quantum master equations and other quantum dissipative models) used to simulate the evolution of electronic coherence in photosynthetic systems. Additionally, the review considers recent advancements in both natural and artificial photosynthetic systems, focusing on the critical role of system-bath interactions and dissipation in protein environments. These dynamics are shown to direct energy transfer effectively, overcoming the fragility of quantum coherence under physiological conditions.