Coupling of quantum states in a single CdSe/ZnSe quantum dot molecule

We study the emission from exciton states in a single CdSe/ZnSe quantum dot molecule (QDM) with different separation distances between the upper and the lower dot by applying micro-photoluminescence spectroscopy at low temperature. The observed splitting of the emission peaks demonstrates the coupling of quantum states that results in the bonding and antibonding configurations of exciton states in the QDM. As the separation distance decreases, the coupling strength increases gradually and brings forth the red-shift of the emission peaks. Furthermore, the coupling strength exhibits a lower dependence on the separation distance compared with a III-V QDM. By pumping the sample with circularly polarized photons, we investigate the fine splitting that arises from the asymmetric disk-like shape of the dots.