Coherent-information analysis of quantum channels in simple quantum systems - art. no. 032303

The coherent-information concept is used to analyze a variety of simple qua ntum systems. Coherent information was calculated for the information decay in a two-level atom in the presence of an external resonant field, for the information exchange between two coupled two-level atoms, and for the info rmation transfer from a two-level atom to another atom and to a photon fiel d. The coherent information is shown to be equal to zero for all full-measu rement procedures, but it completely retains its original value for quantum duplication. Transmission of information from one open subsystem to anothe r one in the entire closed system is analyzed to learn quantum information about the forbidden atomic transition via a dipole active transition of the same atom. It is argued that coherent information can be used effectively to quantify the information channels in physical systems where quantum cohe rence plays an important role.