Triple-quantum dual-comb two-dimensional coherent spectroscopy resolves velocity-synchronized Dicke states in hot atomic vapors

Two-dimensional coherent spectroscopy (2DCS) combined with dual-comb technology offers unprecedented resolution for probing many-body interactions in atomic vapors, yet its application to high-order multi-quantum transitions remains challenging due to weaker nonlinear signals and phase instability. Here, we demonstrate a triple-quantum dual-comb 2DCS technique that achieves λ/110 phase stability through digital correction, enabling the observation of velocity-synchronized Dicke states in a thermal rubidium vapor. By resolving collective hyperfine resonances of ⁸⁵Rb and ⁸⁷Rb isotopes with 100 MHz spectral resolution, the titled and elongated ellipticity of the three-quantum peak line shape (0.94) is higher than that of the two-quantum (0.84), reveals that triple-quantum correlations (0.95) surpass double-quantum counterparts (0.90), indicating tighter velocity matching in higher-order Dicke states. This work provides a pathway for manipulating multi-atom correlations in Doppler-broadened systems, and greatly assists to characterize complex hyperfine many-body interaction in semiconductor exciton and two-dimensional materials. Many-body dipole-dipole interactions constitute the basis of numerous physical phenomena in atom vapor. Here, the authors demonstrate a triple-quantum dual-comb two-dimensional coherent spectroscopy to investigate the dipole-dipole interactions, finding that the triple-quantum correlations (0.95) surpass the double-quantum counterparts (0.90).