The information capacity of the lambda-system--photon field channel
  The potentially attainable information capacity of a radiatively stable lambda-system, viewed as the input of a quantum information channel, is studied. The output of the channel is formed by the states of the photon field with optical excitation frequencies, which are created as a result of Raman pumping. The analysis is based on the notion of coherent information. 
Boris Grishanin and Victor Zadkov