3D phase-matching conditions for the generation of entangled triplets by   chi(2) interlinked interactions
  An analytical calculation of the interaction geometry of two interlinked second-order nonlinear processes fulfilling phase-matching conditions is presented. The method is developed for type-I uniaxial crystals and gives the positions on a screen beyond the crystal of the entangled triplets generated by the interactions. The analytical results are compared to experiments realized in the macroscopic regime. Preliminary tests to identify the triplets are also performed based on intensity correlations. 
Maria Bondani, Alessia Allevi, Eleonora Gevinti, Andrea Agliati,   Alessandra Andreoni