Physicists Shatter Quantum Entanglement Distance Record With 420 Kilometers of Optical Fiber

Key Points:

• Researchers at the University of Science and Technology of China achieved the longest fiber-based matter-to-matter quantum entanglement to date, successfully linking quantum memories across a 420-kilometer optical fiber.
• The experiment used laser-cooled rubidium atom clouds as quantum memories named Alice and Bob, with a middle node, Charlie, detecting photon interference to confirm entanglement without direct contact between the memories.
• Key innovations included converting photons to telecom wavelengths to reduce signal loss, a sophisticated stabilization system to counteract environmental interference, and a single-photon entanglement scheme enhancing transmission efficiency.
• The team surpassed the PLOB bound limit for direct transmission beyond 320 kilometers, demonstrating that memory-based quantum networks can outperform direct optical fiber links in entanglement distribution.
• The breakthrough supports the development of future quantum internet infrastructure by enabling high-rate entanglement generation over long distances and advancing quantum repeater technology essential for scalable quantum communication.