The refractive index of two- and three-level atoms experienced by a few photon quantum fields

The refractive index of a system is often viewed as the collective response of a medium to an electromagnetic field. Nevertheless, even if targeted at a single atom, the incoming light undergoes the dispersion. Recently, by studying the propagation of a single photon interacting with a two-level atom, we examine the dispersion behavior, calculate the phase and group velocity of the photon wave packet, and further analyze the dispersion experienced by the photon.

In the current work, we have studied the phase shifts that can be produced by a three-level atoms driven by classical fields. We have demonstrated a new opportunity to manipulate a single atom dispersion through driving field parameters. This opens avenues for controlling quantum field dynamics, enabling phase modulation, coherence control. Furthermore, we have discovered a new potential to obtain the emission of the second photon in three-level atoms in controllable way that the photon correlation can be controlled via the driving field. These findings are important for long-distance quantum communications.