  Establishing quantum entanglement between individual nodes is crucial for
building large-scale quantum networks, enabling secure quantum communication,
distributed quantum computing, enhanced quantum metrology and fundamental tests
of quantum mechanics. However, the shared entanglements have been merely
observed in either extremely low-temperature or well-isolated systems, which
limits the quantum networks for the real-life applications. Here, we report the
realization of heralding quantum entanglement between two atomic ensembles at
room temperature, where each of them contains billions of motional atoms. By
measuring the mapped-out entangled state with quantum interference, concurrence
and correlation, we strongly verify the existence of a single excitation
delocalized in two atomic ensembles. Remarkably, the heralded quantum
entanglement of atomic ensembles can be operated with the feature of
delay-choice, which illustrates the essentiality of the built-in quantum
memory. The demonstrated building block paves the way for constructing quantum
networks and distributing entanglement across multiple remote nodes at ambient
conditions.
