Photon-number entangled states generated in Kerr media with optical   parametric pumping
  Two nonlinear Kerr oscillators mutually coupled by parametric pumping are studied as a source of states entangled in photon numbers. Temporal evolution of entanglement quantified by negativity shows the effects of sudden death and birth of entanglement. Entanglement is preserved even in asymptotic states under certain conditions. The role of reservoirs at finite temperature in entanglement evolution is elucidated. Relation between generation of entangled states and violation of Cauchy-Schwartz inequality for oscillator intensities is found. 
Anna Kowalewska-Kud{\l}aszyk, Wies{\l}aw Leo\'nski, Jan Pe\v{r}ina Jr
quant-ph physics.optics