Atomic-ensemble-based quantum repeater against general polarization and phase noise

We present a quantum repeater architecture based on atomic ensembles, which is free of polarization and phase noise. With only simple optical elements, we can obtain the uncorrupted entanglement in the noisy channel. Even if the channel suffers from the general polarization and phase noise, the fidelity of transmitted qubits in our protocol can be stable and have no dependence on the noise parameter, which is a significant advantage compared with previous protocols. Moveover, we can even improve the fidelity by using time delayers. The proposed quantum repeater is feasible and useful in the long-distance quantum entanglement distribution and may be promising in other quantum-information applications.