  The construction of large-scale quantum networks relies on the development of
practical quantum repeaters. Many approaches have been proposed with the goal
of outperforming the direct transmission of photons, but most of them are
inefficient or difficult to implement with current technology. Here, we present
a protocol that uses a semi-hierarchical structure to improve the entanglement
distribution rate while reducing the requirement of memory time to a range of
tens of milliseconds. This protocol can be implemented with a fixed distance of
elementary links and fixed requirements on quantum memories, which are
independent of the total distance. This configuration is especially suitable
for scalable applications in large-scale quantum networks.
