Bell-inequality violations with single photons entangled in momentum and polarization

We present a violation of the Clauser-Horne-Shimony-Holt and the Clauser-Horne inequalities using heralded single photons entangled in momentum and polarization modes. A Mach-Zehnder interferometer and polarization optics are used to rotate the spatial and polarization bases, respectively. With this setup we were able to test quantum mechanics with the original formulation of the Clauser-Horne inequality. The results rule out a wide class of realistic non-contextual hidden-variable theories.