Chinese scientists have built the first quantum satellite network
China’s quantum satellite has produced its first successful result. In a paper published today in Science,
researchers from the Chinese Academy of Sciences announced the
satellite had successfully distributed entangled photons between three
different terrestrial base stations, separated by as much as 1,200
kilometers on the ground. The result is the longest entanglement ever
demonstrated, and the first that spanned between the Earth and space.
Researchers say the system “opens up a new avenue to both practical
quantum communications and fundamental quantum optics experiments at
distances previously inaccessible on the ground.”
Launched in August,
the satellite uses a crystal to produce pairs of entangled photons in
orbit. The photons are then transmitted down to base stations in China,
traveling as much as 2,400 km through space.
In theory, entangled photons can remain linked across any
distance, but in practical terms, it’s often difficult to distribute
photon pairs without disrupting entanglement. If entanglement can be
maintained, the result is a communication channel that’s effectively
impossible to intercept. The simplest application is what cryptographers
call a quantum key distribution network, using the network to securely
distribute long and complex encryption keys. Anyone trying to intercept
those keys would be easy to detect, since it’s impossible to observe the
photons in transit without altering them.
Quantum networking has already shown promise in
terrestrial fiber networks, where specialized routing equipment can
perform the same trick over conventional fiber-optic cable. The first
such network was a DARPA-funded connection established in 2003 between
Harvard, Boston University, and a private lab. In the years since, a
number of companies have tried to build more ambitious connections. The
Swiss company ID Quantique has mapped out a quantum network
that would connect many of North America’s largest data centers; in
China, a separate team is working on a 2,000-kilometer quantum link
between Beijing and Shanghai,
which would rely on fiber to span an even
greater distance than the satellite link. Still, the nature of fiber
places strict limits on how far a single photon can travel.
According to ID Quantique, a reliable satellite link
could connect the existing fiber networks into a single globe-spanning
quantum network. “This proves the feasibility of quantum communications
from space,” ID Quantique CEO Gregoire Ribordy tells The Verge.
“The vision is that you have regional quantum key distribution networks
over fiber, which can connect to each other through the satellite
link.”
China isn’t the only country working on bringing quantumA collaboration
between the UK’s University of Strathclyde and the National University
of Singapore is hoping to produce the same entanglement in cheap,
readymade satellites called Cubesats. A Canadian team is also developing a method of producing entangled photons on the ground before sending them into space.
networks to space. theVerge
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