Derivation of classical capacity of quantum channel for discrete   information source
  In this letter, we prove that the classical capacity of quantum channel for $M$ symmetric states is achieved by an uniform distribution on a priori probabilities. We also investigate non-symmetric cases such as a ternary amplitude shift keyed signal set and a 16-ary quadrature amplitude modulated signal set in coherent states. 
Kentaro Kato, Masao Osaki, and Osamu Hirota