Abstract
The Holevo quantity and the SU(2)-invariant states have particular importance in quantum information processing. We calculate analytically the Holevo quantity for bipartite systems composed of spin-j and spin-1/2 subsystems with SU(2) symmetry, when the projective measurements are performed on the spin-1/2 subsystem. The relations among the Holevo quantity, the maximal values of the Holevo quantity and the states are analyzed in detail. In particular, we show that the Holevo quantity increases in the parameter region F<F_d and decreases in region F>F_d when j increases, where F is function of temperature in thermal equilibrium and F_d=j/(2j+1), and the maximum value of the Holevo quantity is attained at F=1 for all j. Moreover, when the dimension of system increases, the maximal value of the Holevo quantity decreases.