Schematic diagram of ⁸⁵Rb–⁸⁷Rb dual-species atom interferometer. (a) Related sub-levels of rubidium atoms. Raman lasers with frequencies ω₁, ω₂, and ω₃ are used for ⁸⁵Rb atoms, while those with frequencies ω₁, ω₂, and ω₄ are for ⁸⁷Rb atoms; ω₁ and ω₂ are detuned to the blue side of transitions ⁸⁵Rb|F = 3〉 to |F′ = 4〉 and ⁸⁷Rb|F = 2〉 to |F〉 = 3〉. (b) Schematic diagram of 4WDR interference path for ⁸⁵Rb atoms, k₁, k₂, and k₃ are wave vectors of Raman beams ω₁, ω₂, and ω₃, respectively. For ⁸⁷Rb atoms, states ⁸⁷Rb|F = 1〉 and ⁸⁷Rb|F = 2〉 are involved, and k₃ is replaced by k₄.