Entanglement and Non-Classical Correlations in Light-Harvesting Complexes

This work belongs to the emerging field of quantum biology. The main direction of research in the quantum biological program is to identify and quantify the role of ``quantumness'' in basic biological processes, exploiting appropriate tools of quantum information theory. Using the tight-binding Hamiltonian and the Lindblad form of master equations, we calculate the time evolution of the density matrix of an exciton in the Fenna-Matthews-Olson (FMO) protein complex during the energy transfer from an antenna to a reaction center at cryogenic T=77$^{\circ}$K and physiological T=300$^{\circ}$K temperatures. The quantum information toolbox is then applied to analyze the resulting density matrix. We compute \textit{quantum discord functional} to identify the amount of non-classical quantum correlations and compare the result with \textit{relative entropy of entanglement}. We observe an interesting phenomenon that the value of discord is typically one order of magnitude larger than the value of relative entropy of entanglement, indicating that non-classical correlations may be more robust against phase decoherence than the quantum entanglement.