  We theoretically investigate the Stark shift of the exciton goundstate in two
vertically coupled quantum dots as a function of the interdot distance. The
coupling is shown to enhance the tuneability of the linear optical properties,
including energy and oscillator strength, as well as the exciton
polarizability. The coupling regime that maximizes these properties results
from the detailed balance between the effects of the single-particle tunneling,
of the electric field and of the carrier-carrier interaction. We discuss the
relevance of these results to the possible implementation of
quantum-information processing based on semiconductor quantum dots: in
particular, we suggest the identification of the qubits with the exciton levels
in coupled- rather than single-dots.
