Thesis defense of Andreas Fischer

We study the spin dynamics in an ensemble of singly charged semiconductor quantum dots. The spin of the confined charge carriers can be polarized by coherent laser pulses. Due to the strong localization of the charge carrier, the hyperfine interaction with the local nuclear spin bath is the main contribution to the electron spin decoherence. Two-color pump-probe experiments indicate a coherent long-ranged interaction between the electron spins in different quantum dots. In this thesis, we develop a semiclassical approach based on spin-coherent states that allows for the efficient simulation of large spin systems and in addition preserves quantum mechanical properties on the level of single spins. We extend the semiclassical approach to open quantum systems using a quantum jump approach. We perform an in-depth analysis of the coherent optical manipulation of an interacting quantum dot ensemble employing pulse sequences with tailored spectra. Moreover, we study the cross-correlation spectra of second and fourth order to obtain complementary information about the spin system. Finally, we examine the intertwined dynamics of the electron spin and the nuclear spins at low temperatures to study the formation of a highly correlated nuclear-spin polaron state.