Abstract: A closed four-level system in atomic vapor was proposed, which was made to possess left handedness by means of the technique of quantum coherence. The density matrix method was utilized in view of the rotating-wave approximation and the local-field effect in high dense gas. The conclusion of the numerical simulation shows that the medium can simultaneously exhibits left handedness in two visible frequency bands, and one can manipulate the width of the frequence bands by changing the intensity of the control field. 

Key words: left-handed material, negative refractive index, quantum coherence