Characterizing GHZ Correlations in Nondegenerate Parametric Oscillation   via Phase Measurements
  We present a potential realization of the Greenberger, Horne and Zeilinger ALL or NOTHING contradiction of quantum mechanics with local realism using phase measurement techniques in a simple photon number triplet. Such a triplet could be generated using nondegenerate parametric oscillation. 
W.J.Munro and G.J.Milburn