  It is crucial for physical realization of quantum information networks to
first establish entanglement among multiple space-separated quantum memories
and then at a user-controlled moment to transfer the stored entanglement to
quantum channels for distribution and conveyance of information. Here we
present an experimental demonstration on generation, storage and transfer of
deterministic quantum entanglement among three spatially separated atomic
ensembles. The off-line prepared multipartite entanglement of optical modes is
mapped into three distant atomic ensembles to establish entanglement of atomic
spin waves via electromagnetically-induced-transparency light-matter
interaction. Then the stored atomic entanglement is transferred into a
tripartite quadrature entangled state of light, which is space-separated and
can be dynamically allocated to three quantum channels for conveying quantum
information. The existence of entanglement among released three optical modes
verifies that the system has capacity of preserving multipartite entanglement.
The presented protocol can be directly extended to larger quantum networks with
more nodes.
