Exciton states in self-assembled InAs/GaAs quantum dot molecules

Self-assembled InAs/GaAs quantum dot molecules have been studied spectroscopically in order to obtain a comprehensive picture of the exciton states confined in them. Photoluminescence studies show a characteristic splitting of the quantum dot shells, which clearly hints at a tunnel coupling of the dots. This coupling was confirmed by exciton fine structure studies, where distinct anticrossings are observed in its magnetic field dispersion. These avoided crossings would not occur if the two dots were decoupled. Four-wave mixing studies show a strong shortening of the exciton dephasing in the molecules as compared to quantum dots which appears to be problematic for application of excitons as the genuine bits in quantum information processing. Finally, we demonstrate that the molecule coupling can be controlled by applying an electric field along the molecule axis.