A team of Chinese scientists has managed to transmit "entangled" photons, tiny particles acting in sync, over long distances from space to Earth, in what it is claimed to be a landmark experiment in quantum communication. The scientists successfully beamed about six billion photon pairs per second to separate ground telescopes that were about 1,200 kilometres apart.

So far, only line-of-sight links across cities or between mountaintops have been exploited in free-space demonstrated since link separations have been limited to around 100 kilometres due to issues like scattering and coherence decay. This is the first time that scientists have effectively demonstrated the satellite-based entanglement distribution to receiver stations over such a long distance.

A successful quantum communication network depends a lot on the distribution of entangled photons over large distances between receiver stations. Therefore, the latest results essentially suggest that a future global quantum communication network, linking quantum computers and quantum sensors, could indeed be a reality.

According to scientists, the entangled photons were distributed from the world's first quantum-enabled satellite called Micius. Launched in August 2016, Micius is equipped with specialised quantum tools and is situated nearly 500 kilometres above the Earth's surface.

"Long-distance entanglement distribution is essential for both foundational tests of quantum physics and scalable quantum networks. Owing to channel loss, however, the previously achieved distance was limited to ~100 kilometres. Here we demonstrate the satellite-based distribution of entangled photon pairs to two locations separated by 1203 kilometres on Earth," scientists said in a study, published in the journal Science on Friday.

This entanglement of photons, which Albert Einstein once described as "a spooky action at a distance," is a curious physical phenomenon in which particles are linked together to affect one another regardless of distance. Scientists believe that this quantum entanglement is vital for secure communications, quantum computation and simulation, China's state-run Xinhua news agency reported.

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Conventional computers store information in binary bits whose value can be either 1 or 0. Quantum computing, on the other hand, exploits the ability of photons to exist in multiple states at any time, allowing them to store much more information than just 1 or 0. It's the way these tiny particles behave that allows quantum computing perform operations more quickly while using less energy than traditional computers.

Seth Lloyd, director of the Center for Extreme Quantum Information Theory at the Massachusetts Institute of Technology, called the latest research "a true breakthrough" in the technology of entanglement distribution.

"The experiment shows that long-range quantum communication is indeed technologically feasible and holds out the promise of the construction of long-range quantum communication networks in the near future," Xinhua quoted Lloyd as saying.