Recent experimental developments in the field of semiconductor quantum dot
spectroscopy will be discussed. First we report about single quantum dot
exciton two-level systems and their coherent properties in terms of single
qubit manipulations. In the second part we report on coherent quantum coupling
in a prototype "two-qubit" system consisting of a vertically stacked pair of
quantum dots. The interaction can be tuned in such quantum dot molecule devices
using an applied voltage as external parameter.Comment: 37 pages, 15 figures, submitted to New Journal of Physics, focus
issue on Solid State Quantum Information, added reference