arXiv subjects

Felipe Caycedo-Soler

Publications and source records attributed to Felipe Caycedo-Soler.

17 recordsLinked to original sources

arXiv2021

Design principles for long-range energy transfer at room temperature

Under physiological conditions, ballistic long-range transfer of electronic excitations in molecular aggregates is generally expected to be suppressed by noise and dissipative processes. Hence, quantum phenomena are not considered to be relevant for the design of efficient and controllable energy transfer over significant length and time scales. Contrary to this conventional wisdom, here we show that the robust quantum properties of small configurations of repeating clusters of molecules can be used to tune energy transfer mechanism that take place on much larger scales. With the support of an exactly solvable model, we demonstrate that coherent exciton delocalization and dark states within unit cells can be used to harness dissipative phenomena of varying nature (thermalization, fluorescence, non-radiative decay and weak inter-site correlations) to support classical propagation over macroscopic distances. In particular, we argue that coherent delocalization of electronic excitations over just a few pigments can drastically alter the relevant dissipation pathways which influence the energy transfer mechanism, and thus serve as a molecular control tool for large-scale properties of molecular materials. Building on these principles, we use extensive numerical simulations to demonstrate that they can explain currently not understood measurements of micron-scale exciton diffusion in nano-fabricated arrays of bacterial photosynthetic complexes. Based on these results we provide quantum design guidelines at the molecular scale to optimize both energy transfer speed and range over macroscopic distances in artificial light-harvesting architectures.

cond-mat.mes-hall↗

arXiv2020

A cyanine dye rotaxane porphyrin nanoring complex as a model light harvesting system

A nanoring-rotaxane supramolecular assembly, with a Cy7 cyanine dye (hexamethylindotricarbocyanine) threaded along the axis of the nanoring, has been synthesized as a model for the energy transfer between the light harvesting complex LH1 and the reaction center in purple bacteria photosynthesis. The complex displays efficient energy transfer from the central cyanine dye to the surrounding zinc porphyrin nanoring. We present a theoretical model that reproduces the absorption spectrum of the nanoring and quantifies the excitonic coupling between the nanoring and the central dye, explaining the efficient energy transfer and elucidating the similarity with structurally related natural light harvesting systems.

physics.chem-ph↗

arXiv2020

Temporal correlations of sunlight may assist photoprotection in bacterial Photosynthesis

Photosynthetic systems utilize adaptability to respond efficiently to fluctuations in their light environment. As a result, large photosynthetic yields can be achieved in conditions of low light intensity, while photoprotection mechanisms are activated in conditions of elevated light intensity. In sharp contrast with these observations, current theoretical models predict bacterial cell death for physiologically high light intensities. To resolve this discrepancy, we consider a unified framework to describe three stages of photosynthesis in natural conditions, namely light absorption, exciton transfer and charge separation dynamics, to investigate the relationship between the statistical features of thermal light and the Quinol production in bacterial photosynthesis. This approach allows us to identify a mechanism of photoprotection that relies on charge recombination facilitated by the photon bunching statistics characteristic of thermal sunlight. Our results suggest that the flexible design underpinning natural photosynthesis may therefore rely on exploiting the temporal correlations of thermal light, manifested in photo-bunching patterns, which are preserved for excitations reaching the reaction center.

physics.bio-ph↗

arXiv2018

Which-way interference within biomimetic unit-cells for efficient energy transfer

We show that `which-way' interference within unit-cells enhances the propagation along linear arrays made upon these basic units. As a working example, we address the exciton transfer through linear aggregates of ring-like unit cells, the latter resembling the circular structure of the Light-Harvesting complexes of purple bacteria. After providing an analytic approximate solution of the eigenvalue problem for such aggregates, we show that the population transferred across the array is not a monotonic function of the coupling between nearest-neighbor rings, contrary to what is found from situations where this intra-unit cell interference is not displayed. The non-monotonicity depends on an interesting trade off between the exciton transfer speed and the amount of energy transferred, which is associated with the rupture of symmetry among paths within the ring-like cells, due to the inter-ring coupling strength.

quant-ph↗

arXiv2018

On the theory of excitonic delocalization for robust vibronic dynamics in LH2

Nonlinear spectroscopy has revealed long-lasting oscillations in the optical response of a variety of photosynthetic complexes. Different theoretical models which involve the coherent coupling of electronic (excitonic) or electronic-vibrational (vibronic) degrees of freedom have been put forward to explain these observations. The ensuing debate concerning the relevance of either one or the other mechanism may have obscured their potential synergy. To illustrate this synergy, we quantify how the excitonic delocalization in the LH2 unit of Rhodopseudomonas Acidophila purple bacterium, leads to correlations of excitonic energy fluctuations, relevant coherent vibronic coupling and, importantly, a decrease in the excitonic dephasing rates. Combining these effects, we identify a feasible origin for the long-lasting oscillations observed in fluorescent traces from time-delayed two-pulse single molecule experiments performed on this photosynthetic complex.

q-bio.BM↗

arXiv2017

Quantum redirection of antenna absorption to photosynthetic reaction centres

The early steps of photosynthesis involve the photo-excitation of reaction centres (RCs) and light-harvesting (LH) units. Here, we show that the --historically overlooked-- excitonic delocalisation across RC and LH pigments results in a redistribution of dipole strengths that benefits the absorption cross section of the optical bands associated with the RC of several species. While we prove that this redistribution is robust to the microscopic details of the dephasing between these units in the purple bacterium Rhodospirillum rubrum, we are able to show that the redistribution witnesses a more fragile, but persistent, coherent population dynamics which directs excitations from the LH towards the RC units under incoherent illumination and physiological conditions. Stochastic optimisation allows us to delineate clear guidelines and develop simple analytic expressions, in order to achieve directed coherent population dynamics in artificial nano-structures.

physics.bio-ph↗

arXiv2017

Regulating the Energy Flow in a Cyanobacterial Light Harvesting Antenna Complex

Photosynthetic organisms harvest light energy, utilizing the absorption and energy transfer properties of protein-bound chromophores. Controlling the harvesting efficiency is critical for the optimal function of the photosynthetic apparatus. Here, we show that cyanobacterial light-harvesting antenna may be able to regulate the flow of energy in order to switch reversibly from efficient energy conversion to photo-protective quenching via a structural change. We isolated cyanobacterial light harvesting proteins, phycocyanin and allophycocyanin, and measured their optical properties in solution and in an aggregated-desiccated state. The results indicate that energy band structures are changed, generating a switch between two modes of operation: exciton transfer and quenching; achieved without dedicated carotenoid quenchers. This flexibility can contribute greatly to the large dynamic range of cyanobacterial light harvesting systems.

physics.bio-ph↗

arXiv2017

Exploring the effects of photon correlations from thermal sources on bacterial photosynthesis

Thermal light sources can produce photons with strong spatial correlations. We study the role that these correlations might potentially play in bacterial photosynthesis. Our findings show a relationship between the transversal distance between consecutive absorption and the efficiency of the photosynthetic process. Furthermore, membranes where the clustering of core complexes (so-called RC-LH1) is high, display a range where the organism profits maximally from the spatial correlation of the incoming light. By contrast, no maximum is found for membranes with low core-core clustering. We employ a detailed membrane model with state-of-the-art empirical inputs. Our results suggest that the organization of the membrane's antenna complexes may be well-suited to the spatial correlations present in an natural light source. Future experiments will be needed to test this prediction.

physics.bio-ph↗

arXiv2016

Exploiting non-trivial spatio-temporal correlations of thermal radiation for sunlight harvesting

The promise of any small improvement in the performance of light-harvesting devices, is sufficient to drive enormous experimental efforts. However these efforts are almost exclusively focused on enhancing the power conversion efficiency with specific material properties and harvesting layers thickness, without exploiting the correlations present in sunlight -- in part because such correlations are assumed to have negligible effect. Here we show, by contrast, that these spatio-temporal correlations are sufficiently relevant that the use of specific detector geometries would significantly improve the performance of harvesting devices. The resulting increase in the absorption efficiency, as the primary step of energy conversion, may also act as a potential driving mechanism for artificial photosynthetic systems. Our analysis presents design guidelines for optimal detector geometries with realistic incident intensities based on current technological capabilities

physics.optics↗

arXiv2015

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 Förster rates.

physics.chem-ph↗

arXiv2015

Vibronic origin of long-lived coherence in an artificial molecular light harvester

Natural and artificial light harvesting processes have recently gained new interest. Signatures of long lasting coherence in spectroscopic signals of biological systems have been repeatedly observed, albeit their origin is a matter of ongoing debate, as it is unclear how the loss of coherence due to interaction with the noisy environments in such systems is averted. Here we report experimental and theoretical verification of coherent exciton-vibrational (vibronic) coupling as the origin of long-lasting coherence in an artificial light harvester, a molecular J-aggregate. In this macroscopically aligned tubular system, polarization controlled 2D spectroscopy delivers an uncongested and specific optical response as an ideal foundation for an in-depth theoretical description. We derive analytical expressions that show under which general conditions vibronic coupling leads to prolonged excited-state coherence.

physics.chem-ph↗

arXiv2012

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.

q-bio.BM↗

arXiv2011

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.

physics.optics↗

arXiv2011

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.

cond-mat.soft↗

arXiv2011

Witnessing entanglement beyond decoherence

We address the witnessing of quantum correlations beyond the limits imposed by an ensemble statistical average. By relying upon the continuous observation of a single quantum open system under the action of classical or quantum noise, we show how the statistical distribution of outcomes of physically measurable quantities provides enough information to detect entanglement in situations where a simple averaging procedure yields to a vanishing value. In this way, we are able to specify the meaning of decoherence when single read-out measurements are available, to demonstrate that these distributions are capable to predict/detect entanglement well beyond the ensemble average provided by a dephasing-sensitive mixed state. Few-spin and fluorescent systems are used to illustrate entanglement survival when a mixed state average predicts none or under the conditions where the sudden-death of entanglement is expected.

quant-ph↗

arXiv2010

Interplay between excitation kinetics and reaction-center dynamics in purple bacteria

Photosynthesis is arguably the fundamental process of Life, since it enables energy from the Sun to enter the food-chain on Earth. It is a remarkable non-equilibrium process in which photons are converted to many-body excitations which traverse a complex biomolecular membrane, getting captured and fueling chemical reactions within a reaction-center in order to produce nutrients. The precise nature of these dynamical processes -- which lie at the interface between quantum and classical behaviour, and involve both noise and coordination -- are still being explored. Here we focus on a striking recent empirical finding concerning an illumination-driven transition in the biomolecular membrane architecture of {\it Rsp. Photometricum} purple bacteria. Using stochastic realisations to describe a hopping rate model for excitation transfer, we show numerically and analytically that this surprising shift in preferred architectures can be traced to the interplay between the excitation kinetics and the reaction center dynamics. The net effect is that the bacteria profit from efficient metabolism at low illumination intensities while using dissipation to avoid an oversupply of energy at high illumination intensities.

cond-mat.soft↗

arXiv2010

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.

cond-mat.soft↗