Line narrowing of electromagnetically induced transparency in Rb with a longitudinal magnetic field

Electromagnetically induced transparency (EIT) experiments in Λ-type systems benefit from the use of hot vapor where the thermal averaging results in reducing the width of the EIT resonance well below the natural linewidth. Here, we demonstrate a technique for further reducing the EIT width in room-temperature vapor by the application of a small longitudinal magnetic field. The Zeeman shift of the energy levels results in the formation of several shifted subsystems; the net effect is to create multiple EIT dips each of which is significantly narrower than the original resonance. We observe a reduction by a factor of 3 in the D₂ line of ⁸⁷Rb with a field of 3.2 G.