Slow light and superluminality in the coherent population trapping maser Aldo Godone, Filippo Levi, and Salvatore Micalizio

The propagation of a band-limited light pulse through an atomic medium under a Λ excitation scheme is theoretically analyzed in this paper. We consider in particular the case where the light pulse is detected through the coherent microwave emission of the atomic ensemble (coherent population trapping maser). Significant differences are predicted with respect to the more usual optical detection (electromagnetically induced transparency signal) and found in agreement with the experimental results. Higher signal delays were observed in the microwave emission than in the optical signal with an equivalent group velocity of 6 m/s as well as highly superluminal propagation under a proper modulation scheme. The experiments were performed with a thermal 87Rb vapor in buffer gas.