A team in China has stretched the distance over which atoms can remain quantum-entangled to 50 kilometers, four times farther than any previous experiment. The new record, achieved by researchers at the University of Science and Technology of China in Hefei, pushes the boundaries of what is possible in quantum communication and could reshape how future networks are built.
A leap from 12.5 to 50 kilometers
The previous record for atom entanglement stood at 12.5 kilometers. The Chinese team more than quadrupled that, using a setup that involved two laboratories connected by a fiber-optic cable. They managed to entangle two clouds of rubidium atoms, each containing about a billion atoms, across the 50-kilometer span. The experiment relied on a technique that converts the quantum state of the atoms into photons, which then travel through the fiber and are measured at the other end.
Why this matters for future quantum networks
Entanglement is a phenomenon where particles become linked in such a way that the state of one instantly influences the other, no matter the distance. For years, scientists have struggled to maintain this fragile connection over long distances because photons tend to be lost or disturbed in fiber-optic cables. The Chinese team overcame this by using a special memory that stores the quantum state of the atoms and then releases it as a photon, which can travel the 50-kilometer distance with minimal loss. This approach, known as a quantum repeater, is seen as a key step toward building a practical quantum internet.
The experiment took place in the city of Hefei, in Anhui province, where the two labs were set up in different buildings on the university campus. The researchers chose this location because it offered a realistic urban environment, with the fiber cable running through the city's infrastructure. Local residents were not directly involved, but the achievement has drawn attention from the global physics community, as it demonstrates that quantum entanglement can survive over distances that are relevant for real-world applications.
The record is not just a number. It shows that the technology needed for quantum networks is moving from the lab to the field. The ability to entangle atoms over 50 kilometers means that future quantum communication systems could be built using existing fiber-optic infrastructure, without the need for satellites or other exotic hardware. This brings the dream of a secure, quantum-encrypted internet one step closer to reality.
While the experiment is a milestone, it is also a reminder of how much work remains. The team's success relied on extremely precise control of the atoms and the photons, and scaling this up to even longer distances will require further innovation. But for now, the record stands as a testament to what is possible when curiosity and engineering come together.
