We have observed a dispersionlike absorption (or gain) spectrum at the D1 transition in a Rb vapor cell filled with a buffer gas, due to Zeeman coherence of the ground states in a double A configuration. Meanwhile, we have also observed superluminal pulse propagation. It is experimentally demonstrated that the front speed of a light pulse still equals the light speed c in vacuum, although the group velocity of the light pulse is (-2.2±0.6)×104 m/s.
Scopus Subject Areas
- Atomic and Molecular Physics, and Optics