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.
Due to its vital role in many quantum information and communication protocols, much theoretical and experi- mental work has been conducted in order to investigate the fundamental properties of entanglement. In this work we describe an experimental investigation into the behavior of continuous-variable entanglement and quantum mutual information upon propagation through slow- and fast-light media. A four-wave mixing process in warm atomic vapor is used to generate an entangled two-mode squeezed vacuum state of light. One of the two modes of the resulting state is then sent through a second four-wave mixing process that is tuned to exhibit either slow- or fast-light properties. The cross-correlation and quantum mutual information shared between the resulting modes is quanti ed, and di erences in their behavior after propagation through slow- and fast-light media are discussed.