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Abstract:
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Photosynthetic organisms harvest light using large antenna complexes
with many chlorophyll molecules. Because experiments have shown that
energy transport through antenna complexes—and onward to a reaction
centre—is partially coherent, it has become necessary to treat these
processes using computationally expensive techniques from the theory of
open quantum systems. This often requires integrating complicated
non-Markovian dynamics, followed by averaging over a potentially large
ensemble.

However, many of the quantum effects observed in photosynthetic
complexes are artefacts of the ultrafast laser excitation and are not
relevant in incoherent natural illumination. As a consequence, the
complete description of energy transport in incoherent light is
dramatically simplified. In particular, the often-dubious Markov
approximation becomes exact, while the rotating-wave approximation—often
unjustified but nevertheless imposed to avoid certain
pathologies—becomes unnecessary. With these simplifications, computing
any relevant observable is reduced to a problem of linear algebra. This
allows a rapid analysis of hypothetical scenarios to determine whether
natural light-harvesting architectures are already optimal or whether
they could be improved.

Although some quantum effects are not important for natural light
harvesting, others are nevertheless pronounced. I will provide several
examples of light-harvesting complexes where the underlying coherence
enhances the transport efficiency and use the techniques described above
to show that although some are close to being optimal, others are not.

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(PLEASE NOTE NON-STANDARD DATE AND LOCATION)
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