Quantum Memory Link Stretches 420 Kilometers, Setting an Entanglement Distance Record
Physicists in China entangled two quantum memories separated by 420 kilometers of optical fiber, using rubidium atom clouds (Alice and Bob) and a middle node (Charlie). By converting photons to telecom wavelengths, stabilizing phases, and employing a single-photon interference scheme, they achieved matter-to-matter entanglement beyond the direct-transmission limit (PLOB bound), demonstrating a memory-based quantum network can outperform direct fiber links and marking a milestone toward long-range quantum networking, even as practical quantum internet remains a future goal.