Entanglement in optical information processing

Summary form only given. We analyze a general quantum channel, and describe how entanglement changes due to interaction with the environment. We obtain information, entanglement and coherent information. Based on these we relate the two separate uses of the quantum channel and obtain a relationship between the Holevo bound and the amount of entanglement transmitted through a quantum channel. The channel might also represent actions of an eavesdropper so that these results can be used to put bounds on the eavesdropping efficiency. We apply these results to a pair of entangled optical modes when one of them is transmitted through a decoherent channel