  A strong, far-detuned laser can shift the energy levels of an optically
active quantum system via the AC Stark effect. We demonstrate that the
polarization of the laser results in a spin-selective modification to the
energy structure of a charged quantum dot, shifting one spin manifold but not
the other. An additional shift occurs due to the Overhauser field of the
nuclear spins, which are pumped into a partially polarized state. This
mechanism offers a potentially rapid, reversible, and coherent control of the
energy structure and polarization selection rules of a charged quantum dot.
