QUANTUM COMMUNICATION AND THE CREATION OF MAXIMALLY ENTANGLED PAIRS OF ATOMS OVER A NOISY CHANNEL

We show how to create maximally entangled Einstein-Podolsky-Rosen pair s between spatially distant atoms, each of them inside a high-Q optica l cavity, by sending photons through a general noisy channel, such as a standard optical fibre. An error-correction scheme that uses few aux iliary 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 f or quantum communication with single qubits over distances much larger than the coherence length of the channel.