Overcoming quantum noise in optical fibers

Noise in optical telecommunication fibers is an important limitation on optical quantum data transmission. Unfortunately, the classically successful amplifiers cannot be used in quantum communication because of the no-cloning theorem. We propose a simple method to reduce quantum noise: the insertion of phase shifters and/or beam splitters at regular distance intervals into a fiber. We analyze in detail the case of qubits encoded into polarization states of low-intensity light, which is of central importance to various quantum information tasks, such as quantum cryptography and communication. We discuss the experimental feasibility of our scheme and propose a simple experiment to test our method.