  We introduce an infinite sequence of quantum channels for which the Holevo
capacity is additive. The channel series is closely related to the quantum
channels arising from universal quantum cloning machines. The additivity proof
is motivated by a special property the studied channels enjoy: the property of
conjugate degradability. As a consequence of the announced proof, we also
provide an easy way of proving the additivity of the Holevo capacity for the
original Unruh channel for which the quantum capacity is already known.
Consequently, we present not only an infinite series of finite-dimensional
channels but also a nontrivial example of an infinite-dimensional channel for
which the classical and quantum channel capacities are easily calculable.
