Screening of electric field and nuclear EDM in non-stationary states of atoms and molecules

Abstract

According to the Schiff theorem, an external electric field vanishes at atomic nucleus in a neutral atom in a stationary state, i.e. it is completely shielded by electrons. This makes a nuclear electric dipole moment (EDM) unobservable. We show that if atom or molecule is not in a stationary state (e.g. in a superposition of two stationary states), electric field on the nucleus is not zero and interaction with nuclear EDM does not vanish. In molecules this effect is enhanced by the ratio of nuclear mass to to electron mass, $M_n/m_e$ , since nuclei in a molecule are slow (compare to electrons) and do not provide efficient screening in a non-stationary environment. Electric field on the nucleus may also affect nuclear reactions.