Influence of Nearly Resonant Light on the Scattering Length in Low-Temperature Atomic Gases

We develop the idea of manipulating optically the scattering length $a$ in low-temperature atomic gases. If the incident light is close to resonance with one of the bound $p$ levels of electronically excited molecules, virtual radiative transitions of a pair of interacting atoms to this level can significantly change the value and even reverse the sign of $a$. The decay of the gas due to photon recoil and due to photoassociation can be minimized by selecting the frequency detuning and the Rabi frequency. Our calculations show the feasibility of optical manipulations of trapped Bose condensates through a light-induced change in the mean field interaction between atoms, which is illustrated for ${}^7\mathrm{Li}$.