Efficient energy transfer in light-harvesting systems, I: optimal temperature, reorganization energy and spatial–temporal correlations

Abstract

Understanding the mechanisms of efficient and robust energy transfer in light-harvesting systems provides new insights for the optimal design of artificial systems. In this paper, we use the Fenna-Matthews-Olson (FMO) protein complex and phycocyanin 645 (PC 645) to explore the general dependence on physical parameters that help maximize the efficiency and maintain its stability. With the Haken-Strobl model, the maximal energy transfer efficiency (ETE) is achieved under an intermediate optimal value of dephasing rate. To avoid the infinite temperature assumption in the Haken-Strobl model and the failure of the Redfield equation in predicting the Forster rate behavior, we use the generalized Bloch-Redfield (GBR) equation approach to correctly describe dissipative exciton dynamics and find that maximal ETE can be achieved under various physical conditions, including temperature, reorganization energy, and spatial-temporal correlations in noise. We also identify regimes of reorganization energy where the ETE changes monotonically with temperature or spatial correlation and therefore cannot be optimized with respect to these two variables.Photosynthetic processes in plants, bacteria and marine algae provide key insights into designing artificial light harvesting systems that operate efficiently and robustly [1, 2]. The initial stages in the conversion of solar energy into chemical and other useful forms of energy for human consumption can be described by exciton dynamics with trapping and dissipation [3,4]. Recent experimental and computational studies suggest that environmental noise can assist exciton transport and can be optimized for maximal energy transfer efficiency (ETE) [5]- [20]. Quantum entanglement in photosynthetic light-harvesting complexes has also been studied with the consideration of environmental noise [21]. In this paper, using two light-harvesting systems, FMO and PC 645, we examine the optimization of the ETE, with respect to reorganization energy, temperature, and spatial-temporal correlations.This paper closely follows the theoretical formulation presented in a recent review [17] and further examines issues relevant for realistic light-harvesting systems. The review article addresses two questions: basic mechanisms of optimal energy transfer and systematic mapping to kinetic networks. Since environmental noise helps maximize energy transfer efficiency, it stands to reason that light-harvesting systems can be optimized to achieve best performance under a given environment, which leads to the proposal of optimal design. Previous work on simple models [10,17] and FMO [13]-[16] use the Haken-Strobl model, an infinite temperature model, and therefore report optimization a function of single parameter, the pure dephasing rate.It remains an open question if the ETE can be optimized as a function of temperature, reorganization energy, bath correlation time, and spatial correlation. In this paper, we will further examine the idea of noise-enhanced optimal energy transfer with explicit considerations of d...

Non-Markovianity during the quantum Zeno effect

“…In a separate study [66], the nonMarkovian processes were seen to be prominent in the reorganization energy regime, also noted by Silbey and coworkers [67] who showed that the reorganization energy and the bath relaxation rate played critical roles during the energy transfer process. Chen et.…”

Microscopic quantum coherence in a photosynthetic-light-harvesting antenna

“…The Hamiltonian for electronic excitations is time dependent because it contains random fluctuations due to the presence of classical noise. This assumption corresponds to stochastic approaches such as the temperature-independent Lindblad equation or the Haken-Strobl model [61], which are extensively employed for examining quantum effects in photosynthetic EET [11,18,20,21,38,39,42,43,62,63]. It should be noticed that the classical noise in this model forces the electronic excitation to remain in a pure quantum state, and therefore an ensemble dephasing effect can be discussed without any influence of decoherence.…”

Energy transfer in structured and unstructured environments: Master equations beyond the Born-Markov approximations

“…These difficulties may be circumvented when noise processes induced by an external environment are also present, providing mechanisms for rapid and efficient EET. [8][9][10][11][12][13][14][15] However, accurately accounting for the effects of the external environment in photosynthetic systems is a daunting theoretical prospect. Strong coupling between the system and its environment leads to the accumulation of significant system-environment correlations that may be present even a) Electronic mail: Jakeilessmith@gmail.com b) Electronic mail: ahsan.nazir@manchester.ac.uk within the steady-state.…”