  We present an analytic method, based on the Bohmian equations for quantum
mechanics, for approaching the phase-retrieval problem in the following
formulation: By knowing the probability density $\left\vert
\psi\left(\overrightarrow{r},t\right)\right\vert ^{2}$ and the energy potential
$V\left(\overrightarrow{r},t\right)$ of a system, how can one determine the
complex state $\psi\left(\overrightarrow{r},t\right)$? We illustrate our method
with three classic examples involving Gaussian states, suggesting applications
to quantum state and Hamiltonian engineering.
