Direct Measurement of Light Speed Reduction in a Rubidium Vapor Medium Coherently Prepared by Electromagnetically InducedTransparency

We have experimentally observed the reduction of light speed in a rubidium vapor medium coherently prepared by electromagnetically induced transparency. The light speed reduction was deduced by directly measuring the time delay of a probe light when it passed through the medium. The time delay varies with the intensity of the coupling laser, and the typical time delay we recorded was 1.8μs, corresponding to a light speed of 56000m/s.