= Solution
The result $16\epsilon$ projects the state onto the corresponding nondegenerate <energy eigenstate>. Immediately after an ideal measurement,
$$
\boxed{\psi_{\rm after}(x)=e^{i\chi}\psi_4(x)}
$$
for an unobservable overall phase $\chi$. Subsequent isolated evolution adds $e^{-16i\epsilon t/\hbar}$ but does not mix in other <energy eigenstates>. \b[A repeat ideal <energy> measurement gives $16\epsilon$ with <probability> one], provided the <hamiltonian> is unchanged and no intervening disturbance occurs.
Back to article page
