Codes that can't be hacked without revealing the hackers may be on the horizon, thanks to a team of Austrian physicists who sent pairs of entangled photons across a distance of 89 miles (144 kilometers).
Entangled photons are pairs of ordinary light particles that are mysteriously connected at the quantum level.
For each pair, one photon seems to "know" what has happened to the other no matter how far apart they are, an effect Albert Einstein once referred to as "spooky action at a distance."
(Related: "Einstein and Beyond" in National Geographic magazine.)
Cryptographers believe that this property makes entangled photons ideal for sending secret messages.
While the method won't prevent people from intercepting a communiqué, if someone does, the entangled pair will instantly reveal the spy.
"You immediately know that there was somebody on the line," said team member Anton Zeilinger of the University of Vienna.
Finding the Photons
Transmitting photons over long distances is difficult, because the beam quickly loses intensity, like the fading reach of a flashlight. This makes the entangled photons harder to detect the farther they travel.
"We lose many photons by scattering in the atmosphere and absorption," Zeilinger said. "Only about one in ten million arrive on the other side."
Making detectors that can "find" the key photons among the background light is therefore a crucial part of the experiment.
The team had previously managed to detect lone members of entangled pairs sent over a 90-mile (144-kilometer) distance.
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