NCTS (South)


DATE2009-11-09

TIME12:00

PLACER203, 2F, NCTS, NCKU

FIELDQuantum Information Science

SPEAKER Prof. Yuan-Chung Cheng(鄭原忠) - 台灣大學化學系

TITLEElectronic Quantum Coherence in Photosynthetic Light Harvesting

ABSTRACTPhotosynthesis converts solar energy into stable chemical energy that sustains all life forms on the surface of earth. Highly efficient energy harvesting and trapping performed by photosynthetic complexes are critical to the success of photosynthesis; however, the physical mechanisms that are responsible for the remarkable efficiency remain largely unclear. Here, we report recent experimental and theoretical investigations into the mechanisms of excitation energy transfer in photosynthetic complexes (1,2). The results provide evidence that quantum coherences between excitonic states play an important role in the dynamics of energy transfer in photosynthetic complexes, i.e. the energy transfer is described by wave-like coherent motion instead of incoherent hopping. Moreover, using a novel two-color photon echo technique, we directly observe the coherence dynamics in a photosynthetic bacterial reaction center and reveal a long-lasting electronic coherence between two electronic states that are formed by mixing of the bacteriopheophythin and accessory bateriochlorophyll excited states. The long-lasting coherence can only be explained by strong correlations between protein motions that modulate electronic transition energies of neighboring chromophores. To understand the effects of excitonic coherence in photosynthetic energy transduction, we perform theoretical simulations of coherent energy transfer dynamics and demonstrate that excitonic coherences allow the excitation to move coherently in space, thereby enabling highly efficient energy harvesting and trapping in photosynthesis. Finally, we discuss insights from quantum information and open questions that remain to be answered before we can eventually exploit quantum coherence in photosynthesis complexes to quantum information applications. References 1.G. S. Engel et al., Nature 446, 782 (2007). 2.H. Lee, Y.-C. Cheng, G. R. Fleming, Science 316, 1462 (2007).