Spin rotation
= Spin rotation
{title2=$U(\boldsymbol\theta)=e^{-i\boldsymbol\theta\cdot\mathbf S}$}
A <spin rotation> acts on a <quantum state> through the <unitary representation> generated by its <angular momentum operators>. With $\hbar=1$, <rotation> by angle $\theta$ about axis $\hat{\mathbf n}$ is $e^{-i\theta\hat{\mathbf n}\cdot\mathbf S}$. Simultaneously rotating every site is a global <symmetry> of an isotropic <Heisenberg model>.