  We report on a strong dependence of the phonon-induced damping of Rabi
dynamics in an optically driven exciton-biexciton quantum dot system on the
polarization of the exciting pulse. While for a fixed pulse intensity the
damping is maximal for linearly polarized excitation, it decreases with
increasing ellipticity of the polarization. This finding is most remarkable
considering that the carrier-phonon coupling is spin-independent. In addition
to simulations based on a numerically exact real-time path integral approach,
we present an analysis within a weak coupling theory that allows for analytical
expressions for the pertinent damping rates. We demonstrate that an efficient
coupling to the biexciton state is of central importance for the reported
polarization dependencies. Further, we discuss influences of various system
parameters and show that for finite biexciton binding energies Rabi scenarios
differ qualitatively from the widely studied two-level dynamics.
