  We define a new family of codes for symmetric classical-quantum channels and
establish their optimality. To this end, we extend the classical notion of
generalized perfect and quasi-perfect codes to channels defined over some
finite dimensional complex Hilbert output space. The resulting optimality
conditions depend on the channel considered and on an auxiliary state defined
on the output space of the channel. For certain $N$-qubit classical-quantum
channels, we show that codes based on a generalization of Bell states are
quasi-perfect and, therefore, they feature the smallest error probability among
all codes of the same blocklength and cardinality.
