15.12.2017 QA 14:15-15:00,
(University of Ulm)
Are there (non-trivial) quantum effects in Biology?
A discussion on light harvesting processes
Quantum biology is an emerging field of research that
concerns itself with the experimental and theoretical exploration of non-trivial quantum phenomena in biological systems (See [1, 2, 3, 4] for recent reviews on the subject). We will present an overview aimed to bring out fundamental assumptions and questions in the field, using light harvesting as a prototypical biological process. We will identify basic design principles and develop a key underlying theme – the dynamics of quantum dynamical networks in the presence of an environment and the fruitful interplay that the two may enter.
A fundamental element in the discussion is the formulation of a microscopic model able to explain the observed persisting oscillatory features in the spectral response of different pigment-protein complexes at ambient temperatures. Along delocalized electronic excitations, it is now suspected that quantum coherent interactions with near-resonant vibrations are instrumental for explaining long lived coherence and may contribute to light-harvesting performance [5, 6]. Recent experimental results on artificial systems are in agreement with this vibronic model [7, 8].
A different issue though, is providing a quantitative link between coherence and biological function, that is, proving the actual quantum advantage offered by such coherent vibrational interactions. A thermodynamical approach is particularly useful in this context, in the sense that it allows the introduction of measures of merit to quantify efficiency that depend explicitly on well defined coherence measures. I will discuss initial steps in this direction by showing how a basic quantum design principle, whereby coherent exchange of single energy quanta between electronic and vibrational degrees of freedom, can enhance a light-harvesting system’s power above what is achievable by using thermal mechanisms alone .
Vibronic interactions therefore provide a framework able to encompass long lived oscillations and a consistent multidimensional response as well as allowing for a coherence-enhanced measure of efficiency, thus suggesting its wider relevance as an archetypical framework for quantum biology.
Figure 1: A model system for studying coherent effects in biological light harvesting processes: Structure of the Fenna-Matthew-Olson pigment protein complex, which is found in green sulfur bacteria. Chlorophyll pigments interact via dipole-dipole interaction and are embedded in a protein scaffold that provides a vibrational environment. The multidimensional spectral response of the complex was shown to exhibit oscillatory features on extended times scales, triggering the quest for assessing the actual relevance of quantum coherence in the primary steps of photosynthesis .
 S. F. Huelga and M. B. Plenio, Contemp. Phys. 54, 181 (2013)
 F. Levi et al, Rep. Prog. Phys 78, 082001 (2015)
 G. D. Scholes et al, Nature 543, 647 (2017)
 E. Romero, V. I. Novoderezhkin and R. van Grondelle, Nature 543, 355 (2017)
 M. del Rey, A. W. Chin, S. F. Huelga, and M. B. Plenio, J. Phys. Chem. Lett. 4, 903 (2013)
 A. W. Chin et al, Nature Physics 9, 113 (2013)
 J. Lim et al, Nature Communications 6, 7755 (2015)
 L. Wang et al, Nature Chemistry 9, 219 (2017)
 N. Killoran, S. F. Huelga and M. B. Plenio, J. Chem. Phys. 143, 155102 (2015)