Measuring the Propagation of Information and Entanglement in Dispersive Media

Although it is widely accepted that information cannot travel faster than the speed of light in vacuum, the behavior of quantum correlations and entanglement propagating through actively pumped dispersive media has not been thoroughly studied. Here we investigate the behavior of quantum correlations and information in the presence of a nonlinear dispersive gaseous medium. We show that the quantum correlations can be advanced by a small fraction of the correlation time while the entanglement is preserved even in the presence of noise added by phase insensitive gain. Additionally, although we observe an advance of the peak of the quantum mutual information between the modes, we find that the degradation of the mutual information due to the added noise appears to prevent an advancement of the mutual information s leading tail. In contrast, we show that both the leading and trailing tails of the mutual information in a slow light system can be significantly delayed in the presence of four-wave mixing (4WM) and electromagnetically induced transparency.