Quantum dots (QD) have been considered promising candidates for applications in quantum information processing for a long time. Further more, they also offer new insight into the fundamental interactions between a single wavefunction and the semiconductor environment. In both areas the relaxation and decoherence time scales play a central role. For quantum information processing long relaxation and coherence times are essential. For a better understanding of the semiconductor-wavefunction interactions, the dependency of relaxation and decoherence times on parameters like magnetic and electric fields are needed. There is still a vast amount of unanswered fundamental questions, both experimentally and theoretically.
In this seminar I will introduce coherent spectroscopy on single QDs. This concept is based on the direct detection of the homodyne field between a QD and a resonant laser. An extended experimental setup will also allow readout of resonantly created states, collection of the so called resonance fluorescence. Resonant spectroscopy will then be applied to study the relaxation and decoherence times of single hole spin states confined to a QD. Both, relaxation and decoherence times show very promising results. Especially a coherence time of around one microsecond reveals a fundamental difference to electron spin states. Resonance fluorescence will be demonstrated on a negatively charged exciton, realising another bullet point on the roadmap to quantum information processing.