Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session L38: Focus Session: Quantum Coherence in Biology II |
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Sponsoring Units: DCP DBP Chair: Andreas Buchleitner, University of Freiburg Room: A130/131 |
Tuesday, March 22, 2011 2:30PM - 3:06PM |
L38.00001: The role of quantum coherence in excitonic energy transfer: quantum process tomography, molecular dynamics and efficiency measures Invited Speaker: Long-lived electronic coherences in various photosynthetic complexes at cryogenic and room temperature have generated vigorous efforts both in theory and experiment to understand their origins and explore their potential role to biological function. The ultrafast signals resulting from the experiments that show evidence for these coherences result from many contributions to the molecular polarization. Quantum process tomography (QPT) is a technique whose goal is that of obtaining the time-evolution of all the density matrix elements based on a designed set of experiments with different preparation and measurements. The QPT procedure was conceived in the context of quantum information processing to characterize and understand general quantum evolution of controllable quantum systems, for example while carrying out quantum computational tasks. We introduce our QPT method for ultrafast experiments, and as an illustrative example, apply it to a simulation of a two-chromophore subsystem of the FMO photosynthetic complex, which was recently shown to have long-lived quantum coherences. Our FMO model is constructed using an atomistic approach to extract relevant parameters for the simulation of photosynthetic complexes that consists of a quantum mechanics/molecular mechanics approach combined with molecular dynamics and the use of state-of-the-art quantum master equation approaches. We provide a set of methods that allow for quantifying the role of quantum coherence, dephasing, relaxation and other elementary processes in energy transfer efficiency in photosynthetic complexes, based on the information obtained from the atomistic simulations, or, using QPT, directly from the experiment. The possible presence or absence of effects due to correlated protein motion is discussed. The role of non-Markovianity will be discussed. The ultimate goal of the combination of this diverse set of methodologies is to provide a reliable way of quantifying the role of long-lived quantum coherences and obtain atomistic insight of their causes. [Preview Abstract] |
Tuesday, March 22, 2011 3:06PM - 3:42PM |
L38.00002: Multidimensional electronic spectroscopy of phycobiliproteins from cryptophyte algae Invited Speaker: We describe new spectroscopic measurements which reveal additional information regarding the observed quantum coherences in proteins extracted from photosynthetic algae. The proteins we investigate are the phycobiliproteins phycoerythrin 545 and phycocyanin 645. Two new avenues have been explored. We describe how changes to the chemical and biological environment impact the quantum coherence present in the 2D electronic correlation spectrum. We also use new multidimensional spectroscopic techniques to reveal insights into the nature of the quantum coherence and the nature of the participating states. [Preview Abstract] |
Tuesday, March 22, 2011 3:42PM - 3:54PM |
L38.00003: Simulation study of 2D spectrum of molecular aggregates coupled to correlated vibrations Darius Abramavicius, Vytautas Butkus, Leonas Valkunas, Shaul Mukamel Oscillatory dynamics of two-dimensional (2D) spectra of photosynthetic pigment-protein complexes raise the questions of how to disentangle various origins of these oscillations, which may include quantum beats, quantum transport, or molecular vibrations. We study the effects of correlated overdamped fluctuations and under-damped vibrations on the 2D spectra of Fenna-Matthews-Olson (FMO) aggregate, which has well-resolved exciton resonances, and a circular porphyrin aggregate (P6), whose absorption shows vibrational progression. We use a generic exciton Hamiltonian coupled to a bath, characterized by a spectral density. Fluctuations have smooth, while vibtations have $\delta$-type spectral densities. We show how various scenarios of correlated molecular fluctuations lead to some highly oscillatory crosspeaks. Molecular vibrations cause progression of diagonal peaks in the 2D spectrum and make their corresponding cross-peaks highly oscillatory. We, thus, demonstrate that bath fluctuations and molecular vibrations of realistic molecular aggregates are highly entangled in 2D spectroscopy. [Preview Abstract] |
Tuesday, March 22, 2011 3:54PM - 4:06PM |
L38.00004: Coherent Control of Single Molecules at Room Temp Niek van Hulst, Daan Brinks, Richard Hildner Electronic coherence plays a key role in natural processes like ultrafast energy transfer and charge separation. Coherent control has proven powerful, however in complex biosystems with different conformations and environments, the intrinsic inhomogeneity of the synchronized subset severely limits the achievable degree of control. The ultimate solution to overcome intrinsic inhomogeneities is the investigation of the behavior of one molecule at a time. Here we report the observation and manipulation of vibrational wave-packet interference and electronic coherence in \textit{individual molecules} at ambient conditions. Adapting time and phase distribution of the optical excitation field to the dynamics of each molecule we achieve a superior degree of control. The time-phase maps show distinct diversity between different, yet chemically identical, molecules. We induce Rabi-oscillations and control the coherent superposition state in a single molecule. Broadly distributed coherence decay times are found for different individual molecules giving direct insight into the structural heterogeneity of the local surroundings. Our approach allows single-molecule coherent control in a variety of complex inhomogeneous systems and thus to study the role of coherence in energy transfer of single biocomplexes under natural conditions. D.Brinks\textit{ et al. Nature} \textbf{465}, 905 (2010); R.Hildner\textit{ et al. Nat.Physics} doi:10.1038/nphys1858 (2010). [Preview Abstract] |
Tuesday, March 22, 2011 4:06PM - 4:18PM |
L38.00005: Shaped ultrafast pulses for coherent control of energy flow in light harvesting complexes Mohan Sarovar, K. Birgitta Whaley We report on preliminary investigations of the use of evolutionary algorithms for the design of shaped femtosecond laser pulses to control energy flow in the Fenna-Matthews-Olson (FMO) light harvesting complex. We shape the experimentally accessible phase degrees of freedom of pulses of various duration and assess the ability to control (i) the exciton population on distinct chromophores, and (ii) the purity of the FMO complex state at short times. We assess the experimental feasibility of the designed pulses and sketch directions for future improvement of the pulse design technique. [Preview Abstract] |
Tuesday, March 22, 2011 4:18PM - 4:30PM |
L38.00006: Towards experimental verifications of the transport mechanisms in light-harvesting dynamics F. Caruso, S. Montangero, T. Calarco, S.F. Huelga, M.B. Plenio Recently, we identified the key mechanisms explaining the very- high efficiency and robustness of excitation energy transfer in bacterial photosynthesis, finding that dephasing noise may remarkably enhance the capability of transmitting energy (classical/quantum information) in light-harvesting systems (in communication complex networks [Caruso et al., PRL 2010]), by opening up additional transport pathways and suppressing the ineffective ones. To verify the relevance of such mechanisms in the actual bio-molecular systems, we propose how to gain control over the light-harvesting dynamics by using quantum optimal control tools. In this way, by means of optimally shaped and `robust' laser pulses, we can: i) faithfully prepare the photosystem in some specific initial state (local site or coherent superposition, e.g. quasi-dark and -bright states), and ii) probe efficiently the dynamics, under realistic experimental conditions, i.e. sample of randomly oriented light-harvesting complexes and extra laser constraints related to an experiment in progress. These results could allow us to more easily discriminate the different transport pathways, to characterize the environmental properties, and so enhance our comprehension of coherent processes in biological complexes. [Preview Abstract] |
Tuesday, March 22, 2011 4:30PM - 4:42PM |
L38.00007: Photobiomodulation (PBM) Applications in Ophthalmology Robert Dotson In a very real sense, we are all creatures of light. This fact is just now beginning to impact medicine, as quantum theory begins to spread outside the confines of physics and into the life sciences. No longer can living organisms simply be viewed as retorts for biochemical reactions. They also demonstrate an energy component that will prove to be the unifying force of life in all its varied forms. With the advent of this shift in the life sciences, light is becoming an increasingly important diagnostic and therapeutic tool within medicine. Ophthalmologists have long been concerned with light and its application and, consequently, have an interest in the coming scientific revolution, photomedicine. A brief history of the use of low energy light for healing, a review of known mechanisms by which photons interact with living cells, and a review of some of the established cellular effects will be presented. Finally, brief clinical studies will be presented illustrating the benefits of PBM - specifically regarding: corneal healing, glaucoma, and dry age-related macular degeneration. The purpose of this talk is to introduce the emerging field of PBM to the physics community at large. [Preview Abstract] |
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