Ultrafast dynamics of coherent exciton-polaritons in van der Waals semiconductor metasurfaces
Luca Sortino, Armando Genco, Cristina Cruciano, Michele Guizzardi, Daniel Timmer, Thomas Weber, Jonathan O. Tollerud, Francesco Gucci, Matteo Corti, Gianluca Valentini, Cristian Manzoni, Stefano Dal Conte, Christoph Lienau, Jeffrey A. Davis, Stefan A. Maier, Andreas Tittl, Giulio Cerullo
Published: 2025/10/3
Abstract
Enabling coherent light-matter interactions is a critical step toward next-generation quantum technologies. However, achieving this under ambient temperature conditions remains challenging due to rapid dephasing in optically excited systems. Optical metasurfaces based on quasi-bound states in the continuum have recently emerged as a powerful platform for reaching the strong light-matter coupling regime in flat, subwavelength thickness devices. Here, we investigate ultrafast exciton-polariton dynamics in self-hybridized WS$_2$ thin-film metasurfaces. Using hyperspectral momentum-resolved imaging, we reconstruct the highly anisotropic exciton-polariton dispersion, with a transition from positive to negative effective mass along orthogonal symmetry axes. Femtosecond pump-probe and multidimensional spectroscopy reveal detuning-dependent polariton dynamics with a coherence time up to ~110 fs, and allow direct observation of the coherent dynamics through ultrafast Rabi oscillations with ~45 fs period. We describe this behaviour with a three-eigenstate model that couples the photonic resonance with both bright and dark excitons, extending the conventional two-state picture of strong coupling. Our results establish van der Waals metasurfaces as a promising platform for next-generation polaritonic devices, enabling coherent quantum transfer of matter excitations at room temperature.