Quantum Cryptography Goes a Long Way

Encryption is critical in many aspects of modern life, such as the millions of credit card transactions that occur every day. However, perfectly secure communication can only be achieved using the strong correlations, or entanglement, between quantum objects. Now, Jian-Wei Pan at the University of Science and Technology of China and his colleagues have experimentally shown that a secure quantum protocol known as measurement-device-independent quantum key distribution (MDIQKD) can be implemented over a distance of 404 km. The result breaks the previous MDIQKD record by over a factor of 2 and paves the way for secure quantum communications between distant cities.