Entangled Quantum States as Direction Indicators
Asher Peres, Petra F. Scudo · Physical Review Letters · 2001
We consider the use of $N$ spin- $\frac{1}{2}$ particles for indicating a direction in space. If $N>2$, their optimal state is entangled. For large $N$, the mean square error decreases as ${N}^{\ensuremath{-}2}$ (rather than ${N}^{\ensuremath{-}1}$ for parallel spins).