Coherent population trapping (CPT) versus electromagnetically induced transparency (EIT)

We discuss the differences between two well-studied and related phenomena—coherent population trapping (CPT) and electromagnetically induced transparency (EIT). Many differences between the two—such as the effect of power in the beams, detuning of the beams from resonance, and the use of vapor cells filled with buffer gas—are demonstrated experimentally. The experiments are done using magnetic sublevels of the $1\to 1$ transition in the D${}_2$ line of ${}^{87}$Rb.