  A basic property of distinguishability is that it is non-increasing under
further quantum operations. Following this, we generalize two measures of
distinguishability of pure states--fidelity and von Neumann entropy, to mixed
states as self-consistent measures. Then we extend these two measures to
quantum operations. The information-theoretic point of the generalized Holevo
quantity of an ensemble of quantum operations is constructed. Preferably it is
an additive measure. The exact formula for SU(2) ensemble is presented. With
the aid of the formula, we show Jozsa-Schlienz paradox that states as a whole
are less distinguishable while all pairwise are more distinguishable in an
ensemble of quantum states, also occurs in an ensemble of quantum operations,
even in the minimal dimensional case SU(2) ensemble.
