(color online) Schematic diagram of the BBM: energy structure of the ⁸⁷Rb transition (D₁ line, 795 nm). DP: direct pump light resonant with ground state F = 2 to excited state . IP: indirect pump light resonant with the ground state F = 1 to excited state . The probe light detects the polarization on F = 2 hyperfine state with frequency red detuned 5 GHz away from the F = 2 to transition. Both pumps are circularly polarized and the probe is linearly polarized.