Generation of entangled photon pairs using small-coherence-time continuous wave pump lasers.

We address the generation of entangled photon pairs by parametric downconversion from solid state cw lasers with small coherence time. We consider a compact and low-cost setup based on a two-crystal scheme with type-I phase matching. We reconstruct the full density matrix by quantum tomography and analyze in detail the entanglement properties of the generated state as a function of the crystal's length and the coherence time of the pump. We verify the possibility to improve the visibility using a purification protocol based on a compensation crystal.