Our research is focussed on the study of quantum effects in optically active nanostructured solid-state systems. We exploit the fact that the information about the quantum state of a nanosystem is encoded in its optical response. The excitation spectum of a nano-emitter is conceptually similar to that of atoms or ions: charged particles (electrons and holes) are spatially localized and reside in discrete states with quantized energy, angular momentum and spin degrees of freedom. Photons promote charge carriers from one quantum state to another while dipolar selection rules dictate the respective coupling strength. The solid-state character of semiconductor nanosystems implies effects that reach beyond the physics explored with atom spectroscopy. Nuclear spins or phonons are among inherently present reservoirs that drastically modify the nature of discrete quantum states in nanostructures and therefore their elementary optical signatures.
Quantum dots
Self-assembled InGaAs quantum dots embedded in a field-effect device represent an advanced solid-state system for the study of quantum optical phenomena in nanostructured semiconductors. With a static electric field we control the doping of a quantum dot down to the elementary charge level and use the electric component of an oscillating laser field to resonantly induce discrete excitations within the quantum dot. By combining both static and oscillating electromagnetic fields we establish means for coherent preparation, manipulation and readout of charge and spin states in quantum dot systems.
Carbon nanotubes
Optical emission from semiconducting single-wall carbon nanotubes covers a broad spectral window from visible to infrared. When cooled down to cryogenic temperatures, single carbon nanotubes show photon emission statistics that are characteristic of quantum emitters: they emit merely one photon at a time. The underlying mechanism that ensures single photon emission is strong carrier localization along the nanutube axis - the manifestation of a carbon-based quantum dot. We develop carbon nanotube devices that allow for controlled carrier doping for the study of spin phenomena in carbon-based quantum dots.