20 research outputs found
Optical signatures of quantum delocalization over extended domains in photosynthetic membranes
The prospect of coherent dynamics and excitonic delocalization across several
light-harvesting structures in photosynthetic membranes is of considerable
interest, but challenging to explore experimentally. Here we demonstrate
theoretically that the excitonic delocalization across extended domains
involving several light-harvesting complexes can lead to unambiguous signatures
in the optical response, specifically, linear absorption spectra. We
characterize, under experimentally established conditions of molecular assembly
and protein-induced inhomogeneities, the optical absorption in these arrays
from polarized and unpolarized excitation, and demonstrate that it can be used
as a diagnostic tool to determine the coherent coupling among iso-energetic
light-harvesting structures. The knowledge of these couplings would then
provide further insight into the dynamical properties of transfer, such as
facilitating the accurate determination of F\"orster rates.Comment: 4 figures and Supplementary information with 7 figures. To appear in
Journal of physical chemistry A, 201
Energy conversion in Purple Bacteria Photosynthesis
The study of how photosynthetic organisms convert light offers insight not
only into nature's evolutionary process, but may also give clues as to how best
to design and manipulate artificial photosynthetic systems -- and also how far
we can drive natural photosynthetic systems beyond normal operating conditions,
so that they can harvest energy for us under otherwise extreme conditions. In
addition to its interest from a basic scientific perspective, therefore, the
goal to develop a deep quantitative understanding of photosynthesis offers the
potential payoff of enhancing our current arsenal of alternative energy sources
for the future.
In the following Chapter, we consider the trade-off between dynamics,
structure and function of light harvesting membranes in Rps. Photometricum
purple bacteria, as a model to highlight the priorities that arise when
photosynthetic organisms adapt to deal with the ever-changing natural
environment conditions.Comment: Chapter, to appear in Photosynthesis 2011, INTEC
Light-harvesting in bacteria exploits a critical interplay between transport and trapping dynamics
Light-harvesting bacteria Rhodospirillum Photometricum were recently found to
adopt strikingly different architectures depending on illumination conditions.
We present analytic and numerical calculations which explain this observation
by quantifying a dynamical interplay between excitation transfer kinetics and
reaction center cycling. High light-intensity membranes (HLIM) exploit
dissipation as a photo-protective mechanism, thereby safeguarding a steady
supply of chemical energy, while low light-intensity membranes (LLIM)
efficiently process unused illumination intensity by channelling it to open
reaction centers. More generally, our analysis elucidates and quantifies the
trade-offs in natural network design for solar energy conversion.Comment: 4 pages and 4 figures. Accepted for publication in Physical Review
Letters
Memory in the Photon Statistics of Multilevel Quantum Systems
The statistics of photons emitted by single multilevel systems is
investigated with emphasis on the nonrenewal characteristics of the
photon-arrival times. We consider the correlation between consecutive
interphoton times and present closed form expressions for the corresponding
multiple moment analysis. Based on the moments a memory measure is proposed
which provides an easy way of gaging the non-renewal statistics. Monte-Carlo
simulations demonstrate that the experimental verification of non-renewal
statistics is feasible.Comment: 5 pages, 3 figure
The nature of the low energy band of the Fenna-Matthews-Olson complex: vibronic signatures
Based entirely upon actual experimental observations on electron-phonon
coupling, we develop a theoretical framework to show that the lowest energy
band of the Fenna- Matthews-Olson (FMO) complex exhibits observable features
due to the quantum nature of the vibrational manifolds present in its
chromophores. The study of linear spectra provides us with the basis to
understand the dynamical features arising from the vibronic structure in
non-linear spectra in a progressive fashion, starting from a microscopic model
to finally performing an inhomogenous average. We show that the discreteness of
the vibronic structure can be witnessed by probing the diagonal peaks of the
non-linear spectra by means of a relative phase shift in the waiting time
resolved signal. Moreover, we demonstrate the photon-echo and non-rephasing
paths are sensitive to different harmonics in the vibrational manifold when
static disorder is taken into account. Supported by analytical and numerical
calculations, we show that nondiagonal resonances in the 2D spectra in the
waiting time, further capture the discreteness of vibrations through a
modulation of the amplitude without any effect in the signal intrinsic
frequency. This fact generates a signal that is highly sensitive to
correlations in the static disorder of the excitonic energy albeit protected
against dephasing due to inhomogeneities of the vibrational ensemble.Comment: 14 pages, 6 figure
Design principles for long-range energy transfer at room temperature
Typical room temperature conditions hinder ballistic long-range transfer of
excitations, rendering quantum phenomena unimportant as potential tools for the
design of efficient and controllable energy transfer over significant time and
length scales. However, it is well-known that many properties of macroscopic
systems depend on the quantum properties of minimal repeating units and, as we
show here, excitonic energy transfer is no exception. With the support of an
exactly solvable model, we are able to show how exciton delocalization and the
ensuing formation of dark states within unit cells can be harnessed to support
classical propagation over macroscopic distances. We specifically discuss the
role of such factors in nano-fabricated arrays of bacterial photosynthetic
complexes via extensive simulations. This allows us to resolve the to-date
unexplained experimental observation of exciton diffusion lengths in such
arrays in terms of an interplay between intra-unit cell thermalization and
delocalization, which conspire to create and use robust dark states at room
temperature.Comment: Revised presentation and new title, main results unchanged, 11+10
pages, 3+5 figure