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 fiber. 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 (1560 nm) 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.