China Reaches New Milestone in Space-Based Quantum Communications

China Reaches New Milestone in Space-Based Quantum Communications

The nation’s Micius satellite successfully established an ultrasecure link between two ground stations separated by quite 1,000 kilometers

By Karen Kwon on June 25, 2020
China Reaches New Milestone in Space-Based Quantum Communications
Photo taken on Nov. 26, 2016 shows a satellite-to-earth link established between quantum satellite "Micius" and therefore the quantum communication ground station in Xinglong, north China's Hebei . Credit: Jin Liwang Alamy
The launch of the Chinese satellite Micius in 2016 could are viewed as merely one addition to the two ,700-odd instruments already orbiting Earth. But Micius, which is solely dedicated to quantum informatics , arguably represents the nation’s lead in an emerging contest among great powers at the frontiers of physics. The brainchild of physicist Jian-Wei Pan of the University of Science and Technology of China, the satellite has helped him and his colleagues achieve several groundbreaking results that are bringing the once esoteric field of quantum cryptography into the mainstream. Pan’s team presented a secure method of quantum messaging using Micius during a new paper, published on June 15 in Nature. The achievement brings the world—or China, at least—one step closer to realizing truly unhackable global communications.

In 2017 the team, along side a gaggle of researchers in Austria, was ready to employ the satellite to perform the world’s first quantum-encrypted virtual teleconference between Beijing and Vienna. Despite being an enormous milestone, this method wasn't bulletproof against hacking. Micius itself was the weak point: The satellite “knew” the sequences of photons, or keys, for every location, also as a combined key for decryption. If, somehow, a spy had carefully eavesdropped on its activity, the integrity of the teleconference could are compromised.


To overcome this problem, the new demonstration by Pan and his colleagues ensured that Micius wouldn't “know” anything. The trick was to avoid using the satellite as a communications relay. Instead the team relied thereon solely for simultaneously transmitting a pair of secret keys to permit two ground stations in China, located quite 1,120 kilometers apart, to determine an immediate link. “We don’t got to trust the satellite,” Pan says. “So the satellite are often made by anyone—even by your enemy.” Each secret key's one among two strings of entangled photon pairs. The laws of physics dictate that any plan to spy on such a transmission will unavoidably leave an errorlike footprint which will be easily detected by recipients at either station.

This is the primary time the technique—called entanglement-based quantum-key distribution—has been demonstrated employing a satellite. (The 2017 test also distributed quantum keys. It didn't utilize entanglement to an equivalent degree, however.) “When the satellite was launched, that was an enormous milestone,” says Shohini Ghose, a physicist at Wilfrid Laurier University in Ontario, who wasn't involved within the new study. “But [the researchers] didn’t have the extent of error-detection rates that are required to truly use that entanglement to try to to key distribution.”

The error-detection rate is significant because distinguishing between a true error and an errorlike footprint from eavesdropping is crucial for security. additionally , a high rate could mean that the keys that two ground stations receive differ from each other—a scenario that might render secure communications impossible. to enhance the fidelity of their communications system, the scientists focused on boosting the light-gathering efficiency of telescopes at each of the 2 ground stations that monitored Micius’s transmissions—updating filtering systems and optical components to succeed in the required low error rate required for quantum-key distribution.



Even though this is often the primary time that entanglement-based quantum-key distribution has been performed via satellite, there are successful ground-based experiments. In ground-based quantum communications, however, the optical fibers that connect two locations absorb transmitted photons, and therefore the rate of absorption increases over distance. “Trusted nodes” placed along the fibers decrypt and reencrypt keys to increase the key-transfer distance. But like Micius within the 2017 demonstration, each of those intermediaries possesses all the quantum keys and is thus susceptible to hacking. Although prototype devices called quantum repeaters offer better security, the technology isn't yet advanced enough to be practical. as compared , because signals from a satellite travel through empty space most of the time, photon loss is a smaller amount of a concern—allowing secure transmissions across arbitrarily large distances.

That situation doesn't mean that the satellite-based system is inherently better than the ground-based one. “It’s quite apples and oranges,” says Paul Kwiat, a physicist at the University of Illinois at Urbana-Champaign, who was also not involved within the study. “The satellite features a few problems. One is there aren’t many [quantum research] satellites that are flying at the instant . Two, those satellites aren't always parked over your own telescopes that you simply want.” counting on a satellite’s passage overhead means secure communications can only happen at certain times of day. And even then, the technique presently requires other factors, like reasonably clear skies, to make sure a ground station can receive a key.

“I think it’s not an honest strategy to mention you’re trying to make a decision which of those two you would like to shop for ,” Kwiat says. Instead, he adds, a hybrid system utilizing local fiber networks linked by satellites might be the simplest way forward.

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Pan says that his team’s next great task is to launch and operate a quantum satellite during a higher orbit, 10,000 kilometers above Earth’s surface. That project, he estimates, could achieve liftoff in as little as five years. From such great heights, a satellite could facilitate more frequent communication between ground stations much farther aside from each other . (Micius, as compared , orbits only 500 kilometers above Earth, limiting its coverage of any ground station to twice per day.) With the high orbital quantum satellite, “you can perform quantum-key distribution for the entire day. Then you've got far more communication time,” Pan says. He also estimates that the new satellite are going to be ready to perform entanglement-based quantum-key distribution between two ground stations that are 10,000 kilometers apart, surpassing the space within the new Micius study by an order of magnitude.

As China surges ahead within the go after unbreachable quantum communications, other nations are scrambling to catch up. In 2018 NASA initiated the event of a National Space Quantum Laboratory that might use lasers on the International space platform to realize secure communications between ground stations. In Europe, a Quantum Internet Alliance, under the €1-billion Quantum Flagship project, is in its ramp-up phase. Separately, a joint team between the U.K. and Singapore is making rapid progress toward launching its own quantum satellite next year. And Japan and India also are pursuing such work.

So is China winning the race for a secure quantum Internet? Pan says it's too early to understand . “We will need far more significant output before the quantum Internet are often a sensible thing,” he says.