Nature reports on a new milestone in the quest for true randomness – a quality that’s vitally useful in things like data security and models of chaotic systems like, say, hurricanes – using a laser-lit superconductor shaped like a bow tie:
True randomness is surprisingly difficult to come by. Algorithms in conventional computers can produce sequences of numbers that seem random at first, but over time these tend to display patterns. This makes them at least partially predictable, and therefore vulnerable to being decoded.
To make encryption safer, researchers have turned to quantum mechanics, where the laws of physics guarantee that the results of certain measurements — such as when a radioactive atom decays — are genuinely random.
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Typical laser devices are designed to minimize these fluctuations to produce light of steady intensity: they make the light waves bounce around inside the material to force its atoms to emit more and more photons in sync with each other.
But for random-number generation, researchers aim for the opposite. “We want the intensity to fluctuate randomly, so we can digitize the intensity to generate random numbers,” says Hui Cao, an applied physicist at Yale University in New Haven, Connecticut.
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Photons bounce between the curved walls of the bow tie multiple times, before coming out as a scattered beam. The researchers can then capture the light with an ultrafast camera. They recorded the light output of 254 independent pixels, which together produced random bits at a rate of around 250 terabits per second, or 250 terahertz. That’s several orders of magnitude faster than previous such devices, which recorded only one pixel at a time.
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The set-up could be made smaller by using simpler light detectors instead of a high-speed camera. This could eventually yield practical devices small enough to fit on a single computer chip, says Cao.
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You can read Cao’s resesarch here, in Science.