Increasing entanglement between Gaussian states by coherent photon   subtraction
  We experimentally demonstrate that the entanglement between Gaussian entangled states can be increased by non-Gaussian operations. Coherent subtraction of single photons from Gaussian quadrature-entangled light pulses, created by a non-degenerate parametric amplifier, produces delocalized states with negative Wigner functions and complex structures, more entangled than the initial states in terms of negativity. The experimental results are in very good agreement with the theoretical predictions. 
Alexei Ourjoumtsev (LCFIO), Aurelien Dantan (LCFIO), Rosa   Tualle-Brouri (LCFIO), Philippe Grangier (LCFIO)