Absorption-Dispersion Properties in a Four-Level Atomic System with Vacuum-Induced Coherence

摘要

＜正＞ We discuss and analyze absorption-dispersion response for the probe field in a typical four-level atomicsystem with vacuum-induced coherence（VIC） arising from the cross coupling pathways associaed with a pair of upperexcited hyperfine levels.We find that VIC effect can preserve electromagetically induced transparency（EIF）by usingthe detailed numercal simulations based on the density-matrix equations and analytical calculationa in the dressed-statepicture.We also show the atomic hyperfine strure cannot be a hindrance to obtaining EIT.