  We derived an asymptotic bound the accuracy of the estimation when we use the
quantum correlation in the measuring apparatus. It is also proved that this
bound can be achieved in any model in the quantum two-level system. Moreover,
we show that this bound of such a model cannot be attained by any quantum
measurement with no quantum correlation in the measuring apparatus. That is, in
such a model, the quantum correlation can improve the accuracy of the
estimation in an asymptotic setting.
