Physikalisches Kolloquium

4.5.2020 17:15, Raum: T-1004
Kai Müller (TU München)
Semiconductor quantum dots as non-classical light sources and optically-active spin qubits
18.5.2020 17:15, Raum: T-1004
Prof. Philip J. W. Moll (EPFL Lausanne)
Microstructured Topological Materials: A novel route towards topological electronics (tentative)
22.6.2020 17:15, Raum: T-1004
Prof. Dr. Michael Thorwart (Universität Hamburg)
Quantum biology revisited

The first steps of light harvesting in photoactive biomolecular complexes occur on the femtosecond time scale and in principle follow the rules of quantum mechanics. Since about one decade, experiments have challenged the orthodox picture of a mostly incoherent exciton dynamics between different molecular sites. A supportive role of long-lived electronic quantum coherence for the excitation energy transfer has been suggested, despite the ubiquitous “hot and wet” protein host and the solvent environment in which these molecular complexes exist. In this talk, I will report our recent theoretical and experimental results on this question. Early numerically exact path-integral results for the exciton dynamics in the Fenna-Mathews-Olson complex have illustrated [1] that electronic quantum coherence is rapidly destroyed on a time scale of at most 100 fs [1-4] and that the exciton dynamics is largely Markovian [2], in contrast to at that time prevailing interpretation of experimental data. To resolve this controversy, we have carried out additional experiments using optical 2D nonlinear spectroscopy at ambient temperature in aqueous solution, and together with own independent theoretical modelling, have confirmed the ultrafast decay of dynamical quantum coherence on a time scale of 60 fs [3]. Very recent low-temperature measurements are consistent with theoretical calculations and yield coherence times of 150 fs at 77K, about one order of magnitude shorter than previously claimed. Furthermore, a strong vibronic coupling could in principle affect the exciton transfer [4,5]. Recent works have shown theoretically that under ideal conditions of weak dissipation the anticorrelated vibrational motion of two sites could be enhanced by strong coherent vibronic mixing. Our calculations illustrate [4] that neither the electronic coherence between two monomers can be enhanced by vibrations of individual pigments, nor can a coherent vibronic coupling enhance the amplitude of the anticorrelated vibrational mode under realistic conditions. These results confirm the conventional “orthodox” picture of excitation energy transfer [6].

[1] P. Nalbach, D. Braun, and M. Thorwart, Exciton transfer dynamics and quantumness of energy transfer in the Fenna-Matthews-Olson complex, Phys. Rev. E 84, 041926 (2011).

[2] C. Mujica-Martinez, P. Nalbach, and M. Thorwart, Quantification of non-Markovian effects in the Fenna-Matthews-Olson complex, Phys. Rev. E 88, 062719 (2013).

[3] H.-G. Duan, V.I. Prokhorenko, R. Cogdell, K. Ashraf, A.L. Stevens, M. Thorwart, and R.J.D. Miller, Nature does not rely on long-lived electronic quantum coherence for photosynthetic energy transfer, Proc. Natl. Acad. Sci. 114, 8493 (2017).

[4] Hong-Guang Duan, Michael Thorwart, and R. J. Dwayne Miller, Does electronic coherence enhance anticorrelated pigment vibrations under realistic conditions?, J. Chem. Phys. 151, 114115 (2019)

[5] H.-G. Duan, P. Nalbach, V.I. Prokhorenko, S. Mukamel, and M. Thorwart, On the nature of oscillations in twodimensional spectra of excitonically-coupled molecular systems, New J. Phys. 17, 072002 (2015)

[6] J. Cao, R.J. Cogdell, D.F. Coker, H.-G. Duan, J. Hauer, U. Kleinekathöfer, T.L.C. Jansen, T. Mančal, R.J.D. Miller, J.P. Ogilvie, V.I. Prokhorenko, T. Renger, H.-S. Tan, R. Tempelaar, M. Thorwart, E. Thyrhaug, S. Westenhoff, D. Zigmantas, Quantum Biology Revisited, Science Adv., to appear April 3 (2020)

In collaboration with Hong-Guang Duan and R.J. Dwayne Miller (Max Planck Institute for the Structure and Dynamics of Matter, Hamburg)

6.7.2020 17:15, Raum: T-1004
Prof. Dr. Ing. habil. Oliver Gutfleisch (Institut für Materialwissenschaft, Technische Universität Darmstadt)
Hysteresis Design of Magnetic Materials for Efficient Energy Conversion

Die Vorträge finden im Hörsaalzentrum Physik (Gebäude T) statt.

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