Cavity-modified static polarizabilities of atoms and small molecules within QED full configuration interaction

Abstract

Static dipole polarizabilities of H$_2$, LiH, and helium confined in a single-mode optical cavity are computed using quantum-electrodynamical full configuration interaction (QED-FCI). Response properties are obtained as finite-field derivatives of the coupled electron-photon energy. The cavity-induced modification is found to arise from the competition of two contributions of opposite sign, the dipole self-energy and photon exchange, whose relative strength depends on both the cavity frequency and the number of photons involved in the exchange. The residual change suppresses the response of the molecular ground electronic states. For the metastable states of helium atom this balance changes qualitatively, and the differential response of the $2\,^3S_1 \to 2\,^1S_0$ clock transition, which governs its sensitivity to static electric fields and to thermal radiation, is strongly enhanced instead. Cavity confinement can therefore either reduce or increase the dc Stark and blackbody-radiation shifts of a frequency standard, depending on the electronic structure of the states involved. The reported data serve as a reference for cavity-modified response and underscore the need for an exact treatment of light-matter correlation in cavity-QED predictions.