= Spin measurement in the yz plane
{title2=$P_\pm=[1\pm\cos\theta\cos(\alpha Bt)]/2$}
For a state initially $z$-up and precessing about $y$, measurement along $\mathbf n=(0,\sin\theta,\cos\theta)$ has the displayed <probabilities>. <eigenvectors> can be chosen as $(\cos(\theta/2),i\sin(\theta/2))^T$ and $(i\sin(\theta/2),\cos(\theta/2))^T$. Their <phases> must be retained when taking <inner products>. Full $2\pi$ rotation changes their signs but leaves isolated-state <probabilities> unchanged.
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