Xinyue Zhang, Hongming Zhang, Yaofeng Zhu, Hang Zhou, Song Luo, Long Xu, Xin Li, Yuquan Zhou, Yan Liu, Zheng Lv, Yuxin Duan, Zhao Xu, Haodong Cheng, Long Zhang, Zhanghai Chen
The interaction of light with correlated quantum matter in two-dimensional (2D) materials offers a powerful platform for exploring emergent quantum phenomena. Here, we report the realization of Landau polaritons in a monolayer tungsten diselenide (WSe_{2}) integrated into an optical microcavity. By embedding a two-dimensional electron gas (2DEG) in the monolayer and applying a perpendicular magnetic field, we achieve strong coupling between cavity photons and interband Landau level (LL) transitions, giving rise to hybrid light-matter quasiparticles. These Landau polaritons exhibit valley-dependent oscillations in the coupling strengths and resonance energies, driven by the electrical and magnetic filling of valley-contrasting Landau levels. Moreover, intervalley correlations between LL transitions and opposite-valley electrons lead to nonlinear renormalization of both LL transition energies and Landau-polariton coupling strengths. Our results establish a new paradigm for cavity quantum electrodynamics in correlated 2D systems and demonstrate control of Landau polaritons via the valley degree of freedom, opening new avenues for light-mediated manipulation of quantum phases.