Theoretical Study of Coherent Excitation Energy Transfer in Cryptophyte Phycocyanin 645 at Physiological Temperature

Recent two-dimensional photon-echo experiments suggest that excitation energy transfer in light harvesting systems occurs coherently rather than by incoherent hopping. The signature quantum beating of coherent energy transfer has been observed even at ambient temperatures. In this letter, we use an iterative linearized density matrix (ILDM) propagation approach to study this dynamics in a realistic multistate system-bath model. Our calculations reproduce the observed 400 fs decoherence time, and studies that vary the system Hamiltonian and structured spectral density describing the chromophore network-protein environment interactions give results that enable us to explore the role of initial coherence in energy transfer efficiency of the model network. Our findings suggest that the initial coherence has only a slight effect on energy transfer in this model system. We explore energy transfer optimization of different chromophores in the network by controlling environmental properties. This study points to the importance of stochastic resonance behavior in determining optimal network throughput.