Chinese scientists on Thursday reported a successful transmission of "entangled" photon pairs from space to ground stations separated by 1,200 km, a major technical breakthrough towards quantum communication over great distances. The study, published as a cover story by the US journal Science, distributed such "entangled" photons, or light particles, from a satellite 500 km above the Earth's surface, known as Micius, which was launched last year and equipped with specialised quantum tools.
It's another effort to prove that a physical phenomenon once described by Albert Einstein as "spooky" exists at a large distance and eventually on a global scale, Xinhua news agency reported. "This work lays a reliable technical foundation for large-scale quantum networking and quantum communication experimental research, as well as experimental testing of basic principles of physics, such as general theory of relativity and quantum gravity, in outer space in the future," Pan Jianwei, chief scientist for the quantum satellite project, told Xinhua.
Quantum entanglement, which Einstein referred to as "a spooky action at a distance," is a curious phenomenon in which particles are "linked" together in such a way that they affect one another regardless of distance. It is of great significance for secure communications, quantum computation and simulation, and enhanced metrology. Yet, efforts to entangle quantum particles, such as photons, have been limited to about 100 km, mostly because the entanglement is lost as they are transmitted along optical fibers, or through open space on land, Pan said.
In the new study, Pan, a professor at the University of Science and Technology of China, and his colleagues used the Chinese satellite Micius to demonstrate the latter feat. By combining so-called narrow-beam divergence with a high-bandwidth and high-precision acquiring, pointing and tracking technique to optimize link efficiency, the team established entanglement between two single photons, separated at a distance of over 1,200 km apart, for the first time, Pan said.