  Resonant energy transfer mechanisms have been observed in the sensitized
luminescence of solids, in quantum dots and in molecular nanostructures, and
they also play a central role in light harvesting processes in photosynthetic
organisms. We demonstrate that such mechanisms, together with the
exciton-exciton binding energy shift typical of these nanostructures, can be
used to perform universal quantum logic. In particular, we show how to generate
controlled exciton entanglement and identify two different regimes of quantum
behaviour.
