PDF《One-parameter pure state》

1 JS : (15) In this case, the lower bound 1=Tr(LS )2 can be attained by the unbiased estimators T = I +

2 JS d d +K;

8K

2 Ksa();

(16) where I is the identity. Since d=d and K do not commute in general, the measurementwhichattains the lowerbound (15) is not determined uniquely. This fact provides signicant features in the pure state estimation theory. On the other hand, when the dimension n 2, the matrix equality in (14) cannot be attained in general, because of the impossibil........