Enhancing optical delay using cross-Kerr nonlinearity in Rydberg atoms

A scheme to enhance the optical delay in Rydberg atoms is proposed. In the linear case, the optical delay in a four-level system can be significantly enhanced compared to that of the three-level system. However, the width of the transparent window will decrease with an increase in the optical delay. In the nonlinear case, the nonlinear dispersion becomes steep around the transparency window. The enhanced cross-Kerr nonlinearity mainly contributes to the effective dispersion, which dramatically increases the optical delay. The simulation result shows that the optical delay of the system could be enhanced tens of times; moreover, the wide transparency window remains. So the delay-bandwidth product could be significantly improved due to nonlinear dispersion. We further examine Gaussian pulse propagation in the Rydberg atoms.