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The Role of Quantum Coherence and the Environment in Chromophoric Energy Transport


Recently, direct evidence of long-lived coherence has been experimentally demonstrated for the dynamics of the Fenna-Matthews-Olson (FMO) protein complex at 77K [Engel et al., Nature 446, 782 (2007)].  It was suggested that quantum coherence was important for exploring many relaxation pathways simultaneously.  I will talk about our recent work in developing methods for exploring that question and analyzing the different contributions of the different processes to the efficiency of energy transfer in the complex.  We generalized the concept of continuous-time quantum walks to a Liouville space formalism.  This helped us analyze these contributions and report that at room temperature, this complex has contribution of coherent dynamics of about 10%.  Relaxation processes are responsible for 80% of the efficiency.  The quantum transport efficiency can actually be enhanced by the dynamical interplay of the system Hamiltonian with the pure dephasing dynamics induced by a fluctuating environment.  This occurs in an intermediate regime between fully coherent hopping and highly incoherent transport.  I will finalize with a short discussion of this environment-assisted quantum transport regime.