  We model single photon nonlinearities resulting from the dipole-dipole
interactions of cold polar molecules. We propose utilizing ``dark state
polaritons'' to effectively couple photon and molecular states; through this
framework, coherent control of the nonlinearity can be expressed and
potentially used in an optical quantum computation architecture. Due to the
dipole-dipole interaction the photons pick up a measurable nonlinear phase even
in the single photon regime. A manifold of protected symmetric eigenstates is
used as basis. Depending on the implementation, major sources of decoherence
result from non-symmetric interactions and phonon dispersion. We discuss the
strength of the nonlinearity per photon and the feasibility of this system.
