Why China's Quantum Satellite Is Incredible—And Will Surely Be Overhyped
A word of caution so we can all be excited for the right reasons.
On Tuesday, the joint Chinese-Austrian Quantum Experiments at Space Scale (QUESS) satellite launched from the Jiuquan Satellite Launch Center in northern China. Over the next two years it will probe quantum entanglement at vast distances and further explore the practicality of space-based quantum communication and long-distance quantum encryption via open-air optical channels (lasers!).
The project and underlying concept are probably even cooler than they sound. Quantum satellites aren't some far-fetched idea—sending quantum information in a practical sense almost demands the medium of space for the simple reason that optical channels are highly sensitive to atmospheric perturbations. A bit of weather can really fuck things up, and it's nigh impossible to not encounter a bit of weather when you're trying to beam messages between two distant points on Earth's surface. In sending information to space, once you've gotten eight or nine miles, it's clear sailing to orbit.
Broadly, the thing that we're trying to protect from interference is a quantum state. When we want to send some secure information across a future quantum internet—which would rely on satellite relays—we need to encode it in certain properties of particles that don't make a whole lot of sense in our classical world of large and deterministic phenomena. Using particles, we can take strange probabilistic combinations of mutually exclusive traits (like spinning left and right at once) and use them to encode information. These combinations have the neat property of being pretty much the most fragile form of organization in the universe. It's fundamentally impossible to eavesdrop on information encoded in this way without disturbing the state and being revealed. That's quantum encryption.
The thing most likely to be encrypted is itself an encryption key. Using quantum means, it should be possible send random keys from place to place with 100 percent security. What the QUESS team hopes to accomplish is a secure quantum channel linking Beijing and Vienna via satellite through which encryption keys can be securely transmitted. By 2030 China plans on having a whole network of quantum satellites supporting its very own quantum internet (a communications network protected via quantum encryption schemes, that is).
The satellite's first task, however, will be setting a new distance record for quantum entanglement. This is a somewhat different, but very related, idea. Entanglement is a pretty wild phenomenon in which groups of particles are able to share single quantum states, becoming indistinguishable to the point that they might as well be just a single particle that happens to live in multiple locations all at once.
Entanglement is closely related to the quantum superposition that allows for quantum encryption schemes and it too is extremely fragile. The current distance record for entanglement is 143 kilometers, where it was maintained between observatories located on two of the Canary islands. The QUESS experiment will attempt entanglement across 1,200 km, which is a hell of a way to break a record.
China is hardly the only player chasing space-based quantum technology. Alexander Ling and colleagues at the National University of Singapore's SpooQy lab launched a CubeSat last year carrying a small photon entanglement system, for example. Meanwhile, Eutelsat Communications in partnership with Airbus and the ESA are planning on having a software-defined—read: adaptable to future needs—quantum satellite in orbit by 2018. A collaboration based at the University of Waterloo in Ontario is working on its own quantum microsatellite mission, dubbed QEYSSat. It's now being assembled.
Finally, a word of caution. This is a science experiment, not a node in China's hack-proof internet or itself a hack-proof communications satellite. It's demonstrating the transmission of a quantum-secured encryption key—which is itself a key without a lock, a proof-of-concept. That's cool as hell, but beware the hype.
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