Optimal generalized quantum measurements for arbitrary spin systems
A. Acín, José Ignacio Latorre, Pedro J. Pascual · Physical Review A · 2000
Positive-operator-valued measurements on a finite number of N identically prepared systems of arbitrary spin J are discussed. Pure states are characterized in terms of Bloch-like vectors restricted by a $\mathrm{SU}(2J+1)$ covariant constraint. This representation allows for a simple description of the equations to be fulfilled by optimal measurements. We explicitly find the minimal positive-operator-valued measurement for the $N=2$ case, a rigorous bound for $N=3,$ and set up the analysis for arbitrary N.