---
author:
- |
    Hang Li,$^{1,2,\dagger}$ Jian-Peng Dou,$^{1,2,\dagger}$ Xiao-Ling Pang,$^{1,2}$ Chao-Ni Zhang,$^{1,2}$\
    Zeng-Quan Yan,$^{1,2}$ Tian-Huai Yang,$^{1,2}$ Jun Gao,$^{1,2}$ Jia-Ming Li,$^{3,\ast}$ Xian-Min Jin$^{1,2,\ast}$\
    \
    \
    \
    \
    \
    \
    \
    \
    \
    \
title: Multipartite Entanglement of Billions of Motional Atoms Heralded by Single Photon
---

Quantum entanglement is of central importance to quantum computing, quantum metrology, quantum information as well as the nature of quantum physics. Quantum theory does not prevent entanglement from being created and observed in macroscopic physical systems, in reality however, the accessible scale of entanglement is still very limited due to decoherence effects. Recently, entanglement has been observed among atoms from thousands to millions level in extremely low-temperature and well-isolated systems. Here, we create multipartite entanglement of billions of motional atoms in a quantum memory at room temperature, and certify the genuine entanglement via $M$-separability witness associated with photon statistics. The information contained in a single photon is found strongly correlated with the excitation shared by the motional atoms, which intrinsically address the large system and therefore stimulate the multipartite entanglement. Remarkably, our heralded and quantum memory built-in entanglement generation allows us to directly observe the dynamic evolution of entanglement depth and further to reveal the 