Electromagnetically-induced-transparency-based cross-phase-modulation at attojoule levels

Abstract

We report the experimental demonstration of electromagnetically-induced-transparency-based cross-phase-modulation at attojoule or, equivalently, few-hundred-photon levels. A phase shift of 0.005 rad of a probe pulse modulated by a signal pulse with an energy of $~100$ aJ, equivalent to $~400$ photons, was observed in a four-level system of cold $^{87}\mathrm{Rb}$ atoms.