  Recent theoretical and experimental papers have shown how one can achieve
Heisenberg limited measurements by using entangled photons. Here we show how
the photons in non-collinear down conversion process can be used for improving
the sensitivity of magneto-optical rotation by a factor of four which takes us
towards the Heisenberg limit. Our results apply to sources with arbitrary
pumping. We also present several generalizations of earlier results for the
collinear geometry. The sensitivity depends on whether the two-photon or
four-photon coincidence detection is used.
