  In a semiconductor quantum dot, the Px and Py transitions to the polarization
eigenstates, |x> and |y>, naturally form a three-level V-type system. Using
low-temperature polarized photoluminescence spectroscopy, we have investigated
the exciton dynamics arising under strong laser excitation. We also explicitly
solved the density matrix equations for comparison with the experimental data.
The polarization of the exciting field controls the coupling between the
otherwise orthogonal states. In particular, when the system is initialized into
|y>, a polarization-tailored pulse can swap the population into |x>, and
vice-versa, effectively operating on the exciton spin.
