Abstract: A scheme was proposed to realize subluminal and superluminal propagation for the probe field by controlling the strength of a microwave field in a four-level system at zero-absorption. The effect of the energy-level difference between the two upper superfine levels on the group velocity of the probe field was analyzed. The results between Λ-type three-level and the four-level system were compared. 

Key words: uantum coherence, subluminal, superluminal, zero-absorption