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A new laser-based random number generator is the fastest of its kind

By normal standards, designing a new laser is a total mistake. Instead of producing a sharp, steady beam, the laser casts a blurry patch of light full of randomly blinking bright spots. But for a team of physicists, messy laser production is their biggest asset. Chaotic fluctuations in laser light can translate into 254 trillion random digits per second, more than 100 times faster than other laser-powered random number generators, researchers reported on Feb. 26.

“This is a wonderful step” toward a more efficient generation of random numbers, says Rajarshi Roy, a physicist at the University of Maryland in College Park who did not participate in the work.

Random number generators are valuable tools in computing (SN: 27/05/16). They are used to create encryption keys that scramble private data, such as passwords and credit card numbers, so that information can travel securely over the Internet. Computer simulations of complex systems, such as the Earth’s climate or the stock market, also require many random numbers to adequately capture fortuitous events that occur in real life.

Lasers can generate sequences of random numbers thanks to small fluctuations in the frequency of light over time. But using a laser beam to produce random numbers is like repeatedly rolling a single die. To generate many random digit strings from a single laser at a time, physicist Hui Cao of Yale University and his colleagues came up with a new design.

In the equipment laser, light bounces between mirrors at the ends of an hourglass-shaped cavity before exiting the device. This irregular shape allows light waves of various frequencies to bounce through the laser and overlap with each other. As a result, when the laser shines on a surface, its light contains a constantly changing pattern of small tweezers that illuminate and dim randomly. The brightness at each point of the pattern over time can be translated by a computer into a random series of ones and zeros.

Cao and his colleagues aimed the laser at a high-speed camera, which measured light intensity at 254 points across the beam at approximately every trillionth of a second. But that camera tracked the laser light for just a couple of nanoseconds before the memory filled up, after which the data was uploaded to a computer to encode it as 0s and 1s, says Daniel Gauthier, an Ohio State University physicist who wrote a comment on the study in the same issue of Science. To work in the real world, this random number generator would have to be equipped with light detectors that could send rapid fire brightness measurements to computers in real time.

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