  We study the absorption and emission polarization of single semiconductor
quantum dots in semiconductor nanowires. We show that the polarization of light
absorbed or emitted by a nanowire quantum dot strongly depends on the
orientation of the nanowire with respect to the directions along which light is
incident or emitted. Light is preferentially linearly polarized when directed
perpendicular to the nanowire elongation. In contrast, the degree of linear
polarization is low for light directed along the nanowire. This result is vital
for photonic applications based on intrinsic properties of quantum dots, such
as generation of entangled photons. As an example, we demonstrate optical
access to the spin states of a single nanowire quantum dot.
