  We describe how quantum dot semiconductor cavity systems can be engineered to
realize anisotropy-induced dipole-dipole coupling between orthogonal dipole
states in a single quantum dot. Quantum dots in single-mode cavity structures
as well as photonic crystal waveguides coupled to spin states or linearly
polarized excitons are considered. We demonstrate pronounced dipole-dipole
coupling to control the radiative decay rate of excitons and form pure
entangled states in the long time limit. We investigate both field-free
entanglement evolution and coherently pumped exciton regimes, and show how a
double pumping scenario can completely eliminate the decay of coherent Rabi
oscillations and lead to population trapping. In the Mollow regime, we explore
the emitted spectra from the driven dipoles and show how a non-pumped dipole
can take on the form of a spectral triplet, quintuplet, or a singlet, which has
applications for producing subnatural linewidth single photons and more easily
accessing regimes of high-field quantum optics and cavity-QED.
