163 research outputs found
Limits of quantum speedup in photosynthetic light harvesting
It has been suggested that excitation transport in photosynthetic light
harvesting complexes features speedups analogous to those found in quantum
algorithms. Here we compare the dynamics in these light harvesting systems to
the dynamics of quantum walks, in order to elucidate the limits of such quantum
speedups. For the Fenna-Matthews-Olson (FMO) complex of green sulfur bacteria,
we show that while there is indeed speedup at short times, this is short lived
(70 fs) despite longer lived (ps) quantum coherence. Remarkably, this time
scale is independent of the details of the decoherence model. More generally,
we show that the distinguishing features of light-harvesting complexes not only
limit the extent of quantum speedup but also reduce rates of diffusive
transport. These results suggest that quantum coherent effects in biological
systems are optimized for efficiency or robustness rather than the more elusive
goal of quantum speedup.Comment: 9 pages, 6 figures. To appear in New Journal Physics, special issue
on "Quantum Effects and Noise in Biomolecules." Updated to accepted versio
Realistic and verifiable coherent control of excitonic states in a light harvesting complex
We explore the feasibility of coherent control of excitonic dynamics in light
harvesting complexes, analyzing the limits imposed by the open nature of these
quantum systems. We establish feasible targets for phase and phase/amplitude
control of the electronically excited state populations in the
Fenna-Mathews-Olson (FMO) complex and analyze the robustness of this control
with respect to orientational and energetic disorder, as well as decoherence
arising from coupling to the protein environment. We further present two
possible routes to verification of the control target, with simulations for the
FMO complex showing that steering of the excited state is experimentally
verifiable either by extending excitonic coherence or by producing novel states
in a pump-probe setup. Our results provide a first step toward coherent control
of these complex biological quantum systems in an ultrafast spectroscopy setup.Comment: 12 pages, 8 figure
Spatial propagation of excitonic coherence enables ratcheted energy transfer
Experimental evidence shows that a variety of photosynthetic systems can
preserve quantum beats in the process of electronic energy transfer, even at
room temperature. However, whether this quantum coherence arises in vivo and
whether it has any biological function have remained unclear. Here we present a
theoretical model that suggests that the creation and recreation of coherence
under natural conditions is ubiquitous. Our model allows us to theoretically
demonstrate a mechanism for a ratchet effect enabled by quantum coherence, in a
design inspired by an energy transfer pathway in the Fenna-Matthews-Olson
complex of the green sulfur bacteria. This suggests a possible biological role
for coherent oscillations in spatially directing energy transfer. Our results
emphasize the importance of analyzing long-range energy transfer in terms of
transfer between inter-complex coupling (ICC) states rather than between site
or exciton states.Comment: Accepted version for Phys. Rev. E. 14 pages, 7 figure
electrochemical properties, electronic structures and catalysis
A mesoionic carbene with a ferrocene backbone is used as a metalloligand to
generate the first example of their Fe–Au heterobimetallic complexes. The
details of geometric and electronic structures in different redox states and
preliminary catalytic results are presented
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