Quantitative study of the destructive quantum-interference effect on coherent population trapping

We investigate experimentally and theoretically the coherent population trapping (CPT) effect occurring in ⁸⁷Rb D₁ line due to the interaction with linearly polarized laser light (lin∥lin CPT). In this configuration, the coherence is strongly influenced by the structure of the excited state; consequently, the quantum interference between dark states is an essential feature of this interaction scheme. We study the lin∥lin CPT resonance as a function of the laser optical detuning. The comparison between experimental and theoretical results allows us to quantify the contribution from different dark states to the total signal. Based on these results, we investigate the signal depending on both the pressure broadening of the optical transition and the laser linewidth, and we find in which conditions the laser linewidth does not degrade the lin∥lin CPT resonance.