Entanglement improvement of entangled coherent state via multiphoton catalysis

Based on the conditional measurement and beam splitters, multi-photon catalysis is introduced to each mode of even entangled coherent states (EECSs). The resulted states belong to a kind of Laguerre polynomials excited EECSs. Then the entanglement properties of resulted state are examined according to EPR correlation, concurrence and the teleportation fidelity. For the symmetrical beam splitters, these three quantities can be improved by multi-photon catalysis (>= 3) and only EPR correlation can be enhanced by zero-photon catalysis. Our optimal results over transmissivities of beam splitters show that the unit concurrence can be achieved for all non-zero photon catalysis which indicates that the optimized output approaches Bell-type state. In addition, two single-photon catalysis and zero-photon catalysis present better performance for the improvement of both the EPR correlation and the teleportation fidelity in small and large amplitude regions, respectively. Particularly, it is interesting to notice that both of them can be optimized to be constant for zero-photon catalysis when the amplitude exceeds a certain threshold.