# Tag Info

The angles $\phi$ and $\theta$ never contain a non-zero imaginary part (they are always purely real numbers). The general solution to Eq. 1 is: $$\tag{1} |\Phi(t)\rangle = e^{-\textrm{i}H t} | \Phi(0)\rangle.$$ This can be written as: $$\tag{2} \begin{bmatrix} a(t) \\ b(t) \end{bmatrix} = U \begin{bmatrix} a(0) \\ b(0) \end{bmatrix} .$$ where the ...