Quantum information analysis of simple quantum systems

Quantum information potentially available in a variety of simple quantum systems is analyzed with the help of the coherent information concept. The coherent information was calculated for the case of information decay in a two-level atom under action of external resonant field, information exchange between two coupled two-level atoms, and information transfer from a two-level atom on to another one and to the vacuum photon field. It was shown that the calculated coherent information is equal to zero for all types of the full measurement procedures, whereas it completely preserves its value for the quantum duplication procedure. Transmission of information from an open subsystem to another one of the entire close system is analyzed in connection with the problem of learning quantum information on the forbidden atomic transition via a dipole active transition of the same atom. It is shown that the coherent information can be effectively used for quantifying the information channels in physical systems, where quantum coherence plays an important role.