Quantum repeaters create long-distance entanglement between quantum systemswhile overcoming difficulties such as the attenuation of single photons in afiber. Recently, an implementation of a repeater protocol based on singlequbits in atomic ensembles and linear optics has been proposed [Nature 414, 413(2001)]. Motivated by rapid experimental progress towards implementing thatprotocol, here we develop a more efficient scheme compatible with activepurification of arbitrary errors. Using similar resources as the earlierprotocol, our approach intrinsically purifies leakage out of the logicalsubspace and all errors within the logical subspace, leading to greatlyimproved performance in the presence of experimental inefficiencies. Ouranalysis indicates that our scheme could generate approximately one pair per 3minutes over 1280 km distance with fidelity (F>78%) sufficient to violateBell's inequality.
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