Characterization of qutrit channels in terms of their covariance and   symmetry properties
  We characterize the completely positive trace-preserving maps on qutrits (qutrit channels) according to their covariance and symmetry properties. Both discrete and continuous groups are considered. It is shown how each symmetry group restricts arbitrariness in the parameters of the channel to a very small set. Although the explicit examples are related to qutrit channels, the formalism is sufficiently general to be applied to qudit channels. 
Vahid Karimipour, Azam Mani, Laleh Memarzadeh
quant-ph math-ph math.MP