A no-go theorem for matter-wave interferometry with application to the neutronʹs electric-dipole moment

A general theorem for matter-wave interferometry that relies only on the unitary property of the Schroedinger equation and not upon any classical or semi-classical approximation restricts the benefits of using long drift spaces. In particular, it negates some, but not all, suggestions that have been made for measuring the neutronʹs electric-dipole moment by interferometry.