We calculate the binary decision costs of different strategies for measurement of a given ensemble of $N$ independent and identically prepared polarized spin 1/2 particles. The results obtained prove that, for arbitrarily given values of the prior probabilities and an arbitrary number of constituent particles, the cost of a combined measurement is the same as that for sequential measurements of the individual particles.

• Received 18 July 1995

DOI:https://doi.org/10.1103/PhysRevLett.76.1