Electromagnetically Induced Transparency in "Encyclopedia of Condensed Matter Physics"

Three-level atomic and molecular systems coupled to two laser fields exhibit transparency effects that result from the cancellation of absorption at a resonance transition frequency. These effects are deliberately induced by one of the two laser fields upon modifying the medium optical response to the other field. The large degrees of transparency in a medium where strong absorption and hence opacity would normally be expected, has then been termed as ‘‘electromagnetically induced transparency’’ (EIT). The effect is a rather subtle one. It relies on atomic states coherence and quantum interference, and the necessary background tools to understand the basic physical ideas behind electromagnetically induced transparency will be presented. Here a brief and preliminary discussion of coherent population trap- ping (CPT), a closely related effect whose observa- tion first raised interest in induced transparency phenomena, is also presented.