  We study the feasibility of meaningful proof-of-principle demonstrations of
several quantum repeater protocols with photon (single-photon and photon-pair)
sources and atomic-ensemble based quantum memories. We take into account
non-unit memory efficiencies that decay exponentially with time, which
complicates the calculation of repeater rates. We discuss implementations based
on quantum dots, parametric down-conversion, rare-earth-ion doped crystals, and
Rydberg atoms. Our results provide guidance for the near-term implementation of
long-distance quantum repeater demonstrations, suggesting that such
demonstrations are within reach of current technology.
