1. Institut für Theoretische Physik, Universität Innsbruck, A-6020 Innsbruck, Austria
2. Laboratory of Quantum Communication and Computation, USTC, Hefei 230026, China
3. Physics Department and ITAMP, Harvard University, Cambridge, Massachusetts 02138, USA

Correspondence to: J. I. Cirac¹ Correspondence and requests for materials should be addressed to J.I.C. (e-mail: Email: ignacio.cirac@uibk.ac.at).

Abstract

Quantum communication holds promise for absolutely secure transmission of secret messages and the faithful transfer of unknown quantum states. Photonic channels appear to be very attractive for the physical implementation of quantum communication. However, owing to losses and decoherence in the channel, the communication fidelity decreases exponentially with the channel length. Here we describe a scheme that allows the implementation of robust quantum communication over long lossy channels. The scheme involves laser manipulation of atomic ensembles, beam splitters, and single-photon detectors with moderate efficiencies, and is therefore compatible with current experimental technology. We show that the communication efficiency scales polynomially with the channel length, and hence the scheme should be operable over very long distances.