QUIE2T Quantum Information Entanglement-Enabled Technologies

The optical properties of an atomic medium can be changed dramatically by the coherent interaction with a near-resonant control light field: An optically dense medium can be rendered transparent and group velocities can be strongly reduced. So far the demonstration of this electromagnetically induced transparency (EIT) has relied on macroscopic ensembles of atoms probed by relatively intense light fields. Here we demonstrate the most elementary case, where the medium is formed by a single atom inside an optical cavity, probed by single photons. Changing the frequency of the control light field, we can switch the atom from transparent to absorptive or dispersive. Moreover, a strong cooling effect has been observed at two-photon resonance. Our result points towards all-optical switching with single photons.