Science

Unbreakable: China doubles down on quantum internet

breaking barriers

China has set a new distance record for photon entanglement, the foundation for a communications network secured by the code to end all codes.

A Chinese researcher works on an ultracold atom device at the CAS-Alibaba Quantum Computing Laboratory in Shanghai, China, July 30, 2015. Such experiments promise future computers capable of breaking modern encryption in minutes, a danger cryptographic experts urge preparing for today.
Zhejiang Daily/AP
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In the race for safer ciphers, China just quantum-leap frogged the rest of the world.

Ever since Mesopotamian potters used codes to protect early trade secrets, a battle has raged between information guardians and those who would break that custody. Modern mathematical schemes rely on huge prime numbers to encrypt messages, but experts say this bulwark too will someday join its fallen forerunners.

Now, China aims to escape that contest entirely with the creation of a communication network not secured by math, but guaranteed by the fundamental rules of nature. A team has demonstrated mastery over the secret sauce behind such a “quantum internet” with their satellite Micius, which recently smashed the distance record for creating a bizarre link between light particles known as entanglement.

“They are years ahead of everyone else in this technology,” says Vadim Makarov, head of a quantum hacking lab at the University of Waterloo in Canada, who was not involved. “It’s absolutely awesome.”

Launched August 2016, the Micius satellite successfully entangled photons between two Chinese towns almost 750 miles apart. The experiment bested former fiber-optics setups by a factor of 10, a feat chief architect Jian-Wei Pan says others dismissed as “a crazy idea” when he first proposed it back in 2003. The accomplishment proves possible the ultimate aim of cryptography: an invincible code system theoretically capable of instantly connecting any two (or more) points on Earth. 

Protecting secrets with light

Quantum networks are in part built on the coupling of photons, or particles of light.

Entangled photons share a connection allowing an observer of one to indirectly infer the condition of its mate, just as seeing a heads-up penny lets you assume the other side shows tails. Photons too have randomly determined, opposing states. But unlike penny faces, photon pairs are free agents. Micius produces two streams of these partners, beaming each to a different lab, which could use that special connection to turn the random string of “heads and tails” into a shared secret key useful for encryption.

Any attempt to steal the code mid-stream would destroy that fragile connection, creating an obviously unsafe, error-riddled key, just as a third person eavesdropping on a two-way Skype call could slow down the video, alerting the speakers. But unlike the Skype disruption, which the eavesdropper could avoid with sneakier tools, ironclad physical laws forbid the quantum key from being intercepted and re-transmitted intact, and guaranteed keys mean unbreakable codes.  

Dr. Pan says the final design far exceeds his team’s early expectations, approaching functionality, but others suggest the fledgling network isn’t quite ready for secret swapping yet.

“This is a science experiment,” says Dr. Makarov. Few ground stations under the satellite’s path have the large telescopes needed to pick up the particles. And the signal is quite weak, with only one entangled photon pair in six million making the journey intact. Pan says upcoming papers will showcase additional techniques, which Makarov suspects will include faster key distribution.

And Micius isn't China's only foray into quantum cryptography. A 1,200-mile fiber optic network stretching from Beijing to Shanghai already shuttles useful quantum keys between hundreds of nodes. But light scatters as it moves through the cables, requiring new links every hundred kilometers that add weak spots to the chain. Micius represents a doubling down on quantum technology that could allow the nation to scale up the network in a big way. 

Tomorrow's encryption, needed today

While China is the undisputed leader in quantum cryptography, Canada is also pursuing a quantum satellite, expected to launch in four to five years. If other nations have similar programs, they are taking shape under wraps.

This pursuit reflects a near certainty in the cryptographic community that advanced computing will someday lay bare today’s sensitive information. Quantum computers would slice through the mathematics underpinning modern cryptography – and experts say it's more of a question of “when” than “if.”

Even if that “when” remains decades away, many believe intelligence agencies are thinking ahead. “All of today’s secrets are getting recorded, and in the future the NSA will read them. It’s a time bomb,” explains Makarov.

Researchers who can't afford satellites aim to shore up this weakness with a different technique called “post quantum” encryption, new math-based codes that are strong against both classical and quantum adversaries, but advocates say this approach takes time, too.

“It takes 10 to 20 years to properly deploy new crypto.... We still have many years of scrutiny to really build up confidence in their quantum resilience,” explains Michele Mosca, professor at Waterloo’s Institute for Quantum Computing.

A mission 'beneficial to all human beings'

But building those higher mathematical walls merely starts the next heat of the millennia-old cryptographic race, spurring a new generation of record-breaking ladders.

Which is why China aims to end the race entirely. Shepherding finicky photons from a satellite moving at 18,000 miles per hour through jostling air molecules to ground stations hundreds of miles below isn't the easiest way to pass a note, but the loophole-free physical guarantee proves irresistible.

“This is the sole reason why people do quantum cryptography,” says Makarov. “It is secure today. It is secure for all the future.”

But that safety isn’t quite the type election organizers and ransomware victims imagine, points out Dr. Mosca, who cautions against describing any network as “unhackable.” Current computers can’t crack modern encryption, but that doesn’t stop hackers from tricking users or exploiting software.

Rather, quantum cryptography safeguards against a catastrophic collapse of the core technology. “Imagine if the underlying mathematical algorithm gets broken. Then everything becomes unsecure. That will be an order of magnitude bigger problem,” explains Makarov.

And security is just the beginning. Future quantum networks will make possible applications we haven’t begun to imagine, deepening our understanding of and command over the smallest bits of our universe along the way, experts say.

To that end, Pan describes Micius as a pathfinder satellite with a twofold mission: to experiment with quantum communication and further quantum science in a way “beneficial to all human beings.”