Energy Transfer In Photosynthesis

The most attractive features of photosynthesis are that the light energy can be captured and transported to the reaction center within about 100ps and with more than 95%efficiency.This sparks enormous research interest in the understanding of the physics behind the energy transfer.This thesis mainly focuses on the excitation energy and charge transfer in photo-synthesis.Applying the theory of open quantum system,we inspect the effects of quantum coherence and environment noise on energy transfer.This thesis consists of five chapters and the main contents are given in Chapter 3-5.In Chapters 1 and 2,a briefly introduction of the background and importance of this work is made and the research history of quantum mechanics,quantum biology is reviewed.The concepts and methods,such as quantum state,density operator,quantum master equation,as well as several important phenomena in quantum biology including excitation energy transfer in photosynthesis,magnetoreception in avian compass are presented in detail.In Chapter 3,how the coherent evolution and the noise-induced decoherence work to-gether to reach efficient excitation energy transfer(EET)and the role of the phase factor attached to the coupling constant in the EET are illustrated.By comparing the differences between the Markovian and non-Markovian dynamics,we discuss the effect of environment on the dynamics and the efficiency of EET.Employing the simple model,we show the robust-ness of EET efficiency under the influence of the environment and elucidate the important role of quantum coherence in EET.We go further to study the quantum feature of the EET dynamics by quantumness and show the importance of quantum coherence from a different perspective.We calculate the energy current in the EET and its quantumness,and results for different system parameters are presented and discussed.In Chapter 4,we propose a biological quantum heat engine(BQHE)motivated by Plio-tosystem ? reaction center(PSII RC)to describe the charge separation.By calculating the steady-state current-voltage(j-V)and power-voltage(P-V)characteri,stics,we explore how various cross-couplings influence the current and power in charge separation and discuss the effects of multiple reaction pathway.The robustness of the BQHE against the charge recombination in natural PSII RC and dephasing induced by environments is also explored,and extension from two pathways to multiple pathways is made.In Chapter 5,we apply the polaron master equation to study how system-bath couplings affect the exciton transfer processes in Photosystem ? reaction center(PSII RC)described by quantum heat engine(QHE)model in a wide parameter range.The effects of bath corre-lation and temperature,together with the combined effects of these factors are also discussed in details.We interpret these results in terms of noise-assisted transport effect and dy-namical localization which correspond to two mechanisms underpinning the transfer process in photosynthetic complexes:One is resonance energy transfer and the other is dynamical localization effect captured by the polaron master equation.The effects of system-bath cou-pling and bath correlation are incorporated in the effective system-bath coupling strength determining whether noise-assisted transport effect or dynamical localization dominates the dynamics and temperature modulates the balance of the two mechanisms.Furthermore,these two mechanisms can be attributed to one physical origin:bath-induced fluctuations.The two mechanisms is manifestations of dual role played by bath-induced fluctuations depending on the range of parameters.The origin and role of coherence are also discussed.It is the constructive interplay between noise and coherent dynamics,rather than the mere presence or absence of coherence or noise,that is responsible for the optimal heat engine performance.Finally,the conclusions and discussion are given.