Continuous Variable Entanglement Distribution for Long-Distance Quantum Communication

We develop a frequency-tunable two-color continuous variable entangled state and demonstrate the entanglement distribution over a telecom single mode Bber.One beam of the entangled state(795 nm) can be continuously tuned over a range of 2.4 GHz and the hyperfine transitions of a rubidium D1 line are measured based on saturated absorption spectroscopy The other beam(1560nm) is injected into a 5-km single mode fiber to distribute the entanglement,and the entanglement evolution between the transmitted beam and its entangled counterpart is investigated.The system presented here will find potential applications in long-distance quantum information processing.