Controlling the interactions of a few cold Rb Rydberg atoms by   radiofrequency-assisted F\"orster resonances
  Long-range interactions between cold Rydberg atoms, which are used in many important applications, can be enhanced using F\"orster resonances between collective many-body states controlled by an external electric field. Here we report on the first experimental observation of highly-resolved radio-frequency-assisted F\"orster resonances in a few cold Rb Rydberg atoms. We also observed radio-frequency-induced F\"orster resonances which cannot be tuned by a dc electric field. They imply an efficient transition from van der Waals to resonant dipole-dipole interaction due to Floquet sidebands of Rydberg levels appearing in the rf-field. This method can be applied to enhance the interactions of almost arbitrary Rydberg atoms with large principal quantum numbers. 
D.B. Tretyakov, V.M. Entin, E.A. Yakshina, I.I. Beterov, C. Andreeva,   and I.I. Ryabtsev
quant-ph cond-mat.quant-gas physics.atom-ph