  Quantum repeater networks that allow long-distance entanglement distribution
will be the backbone of distributed quantum information processing. In this
paper we explore entanglement distribution using quantum repeaters with
optimized buffer time, equipped with noisy quantum memories and performing
imperfect entanglement purification and swapping. We observe that increasing
the number of memories on end nodes leads to a higher entanglement distribution
rate per memory and higher probability of high-fidelity entanglement
distribution, at least for the case with perfect operations. When imperfect
operations are considered, however, we make the surprising observation that the
per-memory entanglement rate decreases with increasing number of memories. Our
results suggest that building quantum repeaters that perform well under
realistic conditions requires careful modeling and design that takes into
consideration the operations and resources that are finite and imperfect.
