effects of decoherence. Our results verify the existence of genuine multipartite entanglement among billions of motional atoms at ambient condition, significantly extending the boundary of the accessible scale of entanglement. Besides probing the quantum-to-classical transition in an entirely new realm, the developed abilities of manipulating such a large-scale entanglement may enhance a wide spectrum of applications for emerging quantum technologies.\

Introduction. {#introduction. .unnumbered}
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Quantum technologies, incorporating quantum entanglement [@EPR_1935] into communication [@np_QCm_Gisin; @QIPC_2005], simulation [@S.; @Lloyd_Science; @J.Zhang_Nature; @K.; @Eckert_NPhysics; @P.; @Hauke_NPhysics; @X.-L.; @Qi_NPhysics], computation [@prl_cluster-QCp; @science_OQC; @nature_QCp] and metrology [@review_quantum; @metrology], exert great advantages beyond classical approaches. For a large-scale multipartite entangled systems, the dimension of Hilbert space will be exponentially expanded as entangled particles increase, which inspires novel approaches of quantum computing or direct simulation for classically intractable problems [@QIPC_2005; @nature_QCp]. The ability to access large-scale and more practical multipartite entanglement has been regarded as a benchmark for quantum information processing, like the road map towards quantum supremacy [@quantum; @supremacy]. However, decoherence resulting from strong internal interactions and coupling with environment makes entanglement fragile, which also limits the expansion of the scale of multipartite entanglement, especially reaching the level of macroscopic physical systems.

So far, significant experimental progresses 