Fiber optics cables, like the ones that might send quantum keys.
Photo: Tyler Nienhouse (Flickr)

Toshiba has devised a feasible new way to use the laws of quantum mechanics to send secure messages using present-day technology. Now it just has to build it.

There are plenty of ways that companies and scientists are attempting to integrate the weird effects of quantum mechanics into everyday technology. One potential use is a whole new way of encrypting data, such that the encryption key can’t be broken by any conventional method. Some current methods work, but they fall apart over long distances. Toshiba thinks its new method could set up quantum-secure communications links over fibers up to 550 kilometers long.

The researchers propose that the two users many miles apart, “Alice” and “Bob,” could each bestow an electric field with a certain quantum state and send it over a fiber optic cable to a central, insecure location, where the two fields would join and undergo quantum interference. Each user would then receive back the result of a measurement of the single photon that resulted from the interference. This information would be meaningless to an observer but could serve as Alice and Bob’s unhackable quantum key to decrypt their messages.

This is similar to the method used back in 2016 to send a quantum key between stations 404 kilometers apart. However, that method requires two photons sent over the fiber optic cable, one each from Alice and Bob, rather than what appears to be a single photon sent by either Alice or Bob. Sending fewer photons means the researchers could overcome a previous perceived limit to the distance a quantum key could be sent, Andrew Shields, a researcher at Toshiba Research Europe in the United Kingdom, told Gizmodo.

The method itself, published today in Nature, is just theoretical for now. “We hope to demonstrate it experimentally in the next year then make a prototype in around two years time,” said Shields. Toshiba has been working on distributing quantum keys with existing methods as well.

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“The work is stunning,” Hoi-Kwong Lo, profess at the University of Toronto, told Gizmodo. But he pointed out that it’s unclear whether or not the method could overcome the most general kinds of cyber attacks with the capabilities of quantum mechanics at their disposal.

Quantum key distribution could one day be useful for sharing secure things like genetic data or government data, and then maybe have more general applications in the future. It’s still far off, but lots of scientists and companies are hoping to one day see quantum-secure networks spanning countries and even the world.

[Nature]

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