Abstract

Dynamic quantum effects in biological systems is a hotly debated question, which lately has been experiencing a renewed wave of broad attention. The discussion was initiated by the application of multidimensional spectroscopy techniques for investigating dynamics in biological complexes. Is nature really optimized to use non-trivial quantum effects, like dynamically evolving coherent superpositions to optimize biological functions, or we simply observe the beatings of quantum coherences, because we use lasers that are coherent light sources? An important step towards improved understanding in this area is investigation of the origin of coherent beatings observed in the time-resolved spectroscopy measurements. Only the beatings with electronic character can in principle indicate the importance of dynamical quantum mechanical effects. We have investigated oscillating coherences in several biological complexes. Possible vibrational and electronic origins of measured coherent beatings were investigated. Generally, distinguishing between the two phenomena is quite difficult. In addition, it appears that nuclear decrees of freedom (vibrations) and electronic degrees of freedom can be mixed resulting in beatings of mixed character. To get a deeper insight into the problem, we employed various tools, e.g. Fourier analysis of 2D spectra sequences and the polarization scheme specifically targeting electronic coherences. Furthermore, to understand appearance of beating signals of different origin in the 2D spectra we have employed theoretical modelling, which proves to be crucial in understanding these very complicated signals. In summary, application of different experimental and analysis methods to the selected biological systems as well as modelling enabled us to obtain a deeper insight in to the origin of quantum beats in biology.