Theory of strong system-bath and electron-light interaction in coupled nanosystems Photosynthetic pigment-protein complexes and coupled quantum dots

Photosynthetic units in plants contain large antenna systems, which transfer the absorbed energy of sun light to the main reaction center. These antenna systems consist of pigment-protein complexes, whose pigments are mainly chlorophyll molecules. The electrons of the chlorophyll molecules are coupled to the bath of the molecular vibrations of the protein and additionally to each other via interchlorophyll Forster-Coulomb coupling. For semiconductor quantum dots the situation is similar. The quantum dots are coupled to phonons of the semiconductor material and also the Forster-Coulomb coupling between the quantum dots needs to be considered. The aim of this work is to develop uni ed theories to describe the optical response of these two types of systems. Therefore the commons and the di erences of these systems are discussed. In the pigment-protein complex the electron-bath coupling is strong and of similar strength as the intermolecular Coulomb coupling. This is not the case for coupled GaAs quantum dots, but for other materials like GaN or CdSe. Thus, methods to simultaneously treat system-bath memory e ects and Coulomb coupling are developed for the χ3−limit. Therefore the standard method of cumulant expansion in a delocalized basis is extended to arbitrary pulse shapes in nonlinear optics. Also the time convolutionless (TCL)-theory is generalized to include system-bath correlation including relaxation processes. In contrast to several standard techniques a lot of memory and also non Markovian e ects can be kept within this method. New many particle memory e ects of system bath correlations on ultrafast timescales appear in the generalized TCL-theory for parameter sets in a range typical for pigment protein complexes and coupled semiconductor quantum dots. The improved theory will show a pump delay dependent lineshape in pump probe experiments. This was previously not included in TCL theories, since it is caused by the system-bath correlations, which can be rst described in TCL theory with the generalized method. The generalized TCL-theory may be the rst TCL approach that can handle this e ect in a non Markovian way. The extended theory may make it possible to think about experiments to explore the establishment of system-bath correlations after optical excitation. On the other hand, the response of these coupled nano systems to high light intensities is of interest. In this context the method of Bloch equations derived from correlation expansion in a local basis is adapted from general semiconductors to coupled quantum dots and coupled chlorophylls. After an application of the equations, that show an interplay of local eld e ects and long time dephasing in photon echo experiments of quantum dot ensembles, the terms for a joint interaction of the Forster-Coulomb coupling and electron-bath interaction are derived. It is shown that these terms are responsible for the excitation energy transfer and lifetime broadening in the framework of Bloch equations. Additional terms are derived, that describe the e ects of exciton-exciton annihilation. The new developed framework permits to simulate experiments at high light intensities. This is applied to a prominent example of protein-pigment complexes: the Light Harvesting Complex II (LHC II). The uorescence saturation and pump probe experiments are simulated within this theory and compared to experimental data and yield a good agreement.