Quantum optics in ARTIFICIAL MOLECULES

In semiconductor quantum dots, often referred to as `artificial atoms`, carriers are confined in all three spatial directions, resulting in a discrete, atomic-like carrier density of states. Analogously to `natural` molecules, coupling between quantum dots allows the formation of `artificial molecules`; these semiconductor nanostructures hold promise for novel device applications as well as for basic-research studies. The primary goal of this project will be to theoretically explore the possibility of measuring in these structures carrier dynamics with nanometric resolution: within the proposed scheme, carrier complexes (multi-excitons) are excited through multi-colored lasers or short laser pulses; interactions with the solid-state environment lead to dephasing, and cause localization of carriers and possibly dissociation of the carrier complexes; finally, frequency-selective photon-correlation measurements allow a direct mapping of the carrier dynamics with nanometer resolution. Besides its basic-research-value, the outcome of this project is expected to have impact on the development of future quantum-dot-based optoelectronic and quantum-information-processing devices.

In semiconductor quantum dots (QDs), often referred to as "artificial atoms", carriers are confined in all three spatial directions, resulting in a discrete atomic-like density of states. Analogously to "natural" molecules, coupling between quantum dots allows the formation of "artificial molecules". The primary goal of this project was to theortically investigate the interplay of coherent and incoherent carrier dynamics in QDs and to elucidate the differences between optical excitations in atoms and artificial atoms, which give -besides the technological relevance of QDs for device applications (e.g., QD lasers) - added value to this new class of material. Firstly, the embedment of quantum dots in a solid-state environment causes an intimate contact between QD carriers and environment excitations (e.g., phonons), leading to fast relaxation and dephasing of excited states as well as to the formation of new quasi-particles. Secondly, because of the compound electron-hole nature of optical excitations in semiconductor QDs, light can not only excite single electron-hole pairs (excitons) but also multiple pairs (multi- excitons), where Coulomb interactions lead to renormalizations of these multi-exciton states Thirdly, control of sample growth allows to couple artificial atoms or to combine QDs with other semiconductor-based components. In fact, all these novel features provide a great flexibility in tailoring and controlling optical excitations in QD samples, which can be successfully exploited for novel device applications (e.g., QD-based single-photon sources) or for basic-research studies of quantum coherence in coupled nanostructures.