2 research outputs found
Exciton Dynamics in Photosynthetic Complexes: Excitation by Coherent and Incoherent Light
In this paper we consider dynamics of a molecular system subjected to
external pumping by a light source. Within a completely quantum mechanical
treatment, we derive a general formula, which enables to asses effects of
different light properties on the photo-induced dynamics of a molecular system.
We show that once the properties of light are known in terms of certain
two-point correlation function, the only information needed to reconstruct the
system dynamics is the reduced evolution superoperator. The later quantity is
in principle accessible through ultrafast non-linear spectroscopy. Considering
a direct excitation of a small molecular antenna by incoherent light we find
that excitation of coherences is possible due to overlap of homogeneous line
shapes associated with different excitonic states. In Markov and secular
approximations, the amount of coherence is significant only under fast
relaxation, and both the populations and coherences between exciton states
become static at long time. We also study the case when the excitation of a
photosynthetic complex is mediated by a mesoscopic system. We find that such
case can be treated by the same formalism with a special correlation function
characterizing ultrafast fluctuations of the mesoscopic system. We discuss
bacterial chlorosom as an example of such a mesoscopic mediator and propose
that the properties of energy transferring chromophore-protein complexes might
be specially tuned for the fluctuation properties of their associated antennae.Comment: 12 page
Quantum entanglement in photosynthetic light harvesting complexes
Light harvesting components of photosynthetic organisms are complex, coupled,
many-body quantum systems, in which electronic coherence has recently been
shown to survive for relatively long time scales despite the decohering effects
of their environments. Within this context, we analyze entanglement in
multi-chromophoric light harvesting complexes, and establish methods for
quantification of entanglement by presenting necessary and sufficient
conditions for entanglement and by deriving a measure of global entanglement.
These methods are then applied to the Fenna-Matthews-Olson (FMO) protein to
extract the initial state and temperature dependencies of entanglement. We show
that while FMO in natural conditions largely contains bipartite entanglement
between dimerized chromophores, a small amount of long-range and multipartite
entanglement exists even at physiological temperatures. This constitutes the
first rigorous quantification of entanglement in a biological system. Finally,
we discuss the practical utilization of entanglement in densely packed
molecular aggregates such as light harvesting complexes.Comment: 14 pages, 7 figures. Improved presentation, published versio