Quantum limits to superluminal advancement

Summary form only given. Using intense electromagnetic fields, it is now possible to tailor the absorption, amplification, and dispersion properties of multi-level atoms. Dramatic examples include the reduction of the group velocity of a pulse of light to 17 m/s, and increasing the group velocity to values greater than c or even to negative values. The interpretation of a negative group velocity is that the peak of the pulse leaves the medium before it enters. We will discuss possible quantum limits to the advancement of the peak of a pulse propagating through a high-anomalous-dispersion medium and our experiments on pulses propagating through a dispersion-tailored potassium vapor.