Quantum communication and the creation of maximally entangled pairs of atoms over a noisy channel

We show how to create maximally entangled EPR pairs between spatially distant atoms, each of them inside a high–Q optical cavity, by sending photons through a general, noisy channel, such as a standard optical fiber. An error correction scheme that uses few auxiliary atoms in each cavity effectively eliminates photoabsorption and other transmission errors. This realizes the ‘absorption free channel’. A concatenation protocol using the absorption free channel allows for quantum communication with single qubits over distances much larger than the coherence length of the channel.