Project Area A - Hard Matter: Nonlinear transport and quantum optics in semiconductors

Nanostructured semiconductors (NS) such as nanocrystals or quantum dots constitute ideal theoretical model systems for investigating interactions between mesoscopic systems and their reservoirs. In contrast to single, isolated atoms, three dimensional NS consist of thousands of atoms. Since NS are usually embedded in a host material or used in colloidal suspension, their electronic excitations are coupled to external reservoirs, representing environmental fluctuations. The correspondingly modified nonlinear transport and optical properties of NS embedded in reservoirs provide a basis for applications such as reservoir-pumped light sources and new concepts in few-electron transport. Additionally, Coulomb-mediated or reservoir-induced coupling also provides a prerequisite to study collective effects between individual NS.
The research in project area A focuses on fundamental interactions in coupled quantum systems and on typical examples of three-dimensional quantum-confined semiconductors such as self-organized or colloidal quantum dots (QD). They exhibit different aspects of QD-reservoir coupling: whereas self-organized QDs are permanently embedded within a semiconductor host material (often represented by a two-dimensional electron reservoir), colloidal QDs are subject to Brownian motion in their suspension. Our projects focus on disordered ensembles of externally pumped quantum systems (typically QDs) that couple to each other via electric/ magnetic dipole-dipole interaction or via a joint electronic reservoir. Some of these systems can be explored as specific quantum networks and show new collective properties on a mesoscopic scale.

To have a common basis for our research and the training of our Ph.D. students, we have selected specific projects dealing with new aspects of the mesoscopic system-reservoir interaction in individual and coupled quantum systems (QDs):

• A.1: Dynamics of complex laser structures under optical injection and feedback [1]
• A.2: Collective non-equilibrium dynamics in quantum systems near criticality [2]
• A.3: Quantum transport in random networks [3]
• A.4: The interplay of coherence and Brownian motion for excitation transfer in colloidal quantum dots [4]
• A.5: Collective carrier dynamics in spatially and spectrally inhomogeneous environment [5]