The invention provides systems and methods enabling high fidelity quantum
communication over long communication channels even in the presence of
significant loss in the channels. The invention involves laser
manipulation of quantum correlated atomic ensembles using linear optic
components (110, 120), optical sources of low intensity pulses (10),
interferers in the form of beam splitters (150), and single-photon
detectors (180, 190) requiring only moderate efficiencies. The invention
provides fault-tolerant entanglement generation and connection using a
sequence of steps that each provide built-in entanglement purification
and that are each resilient to realistic noise levels. The invention
relies upon collective rather single particle excitations in atomic
ensembles and results in communication efficiency scaling polynomially
with the total length of the communication channel.