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

By normal standards, the design for a new laser is a total dud. Rather than producing a crisp, steady beam, the laser casts a fuzzy patch of light full of randomly flickering speckles of brightness. But to a team of physicists, the laser’s messy output is its greatest asset. The chaotic fluctuations in the laser’s light can be translated into 254 trillion random digits per second — more than 100 times faster than other laser-powered random number generators, researchers report in the Feb. 26 Science.

“This is a marvelous step” toward more efficient random number generation, says Rajarshi Roy, a physicist at the University of Maryland in College Park who was not involved in the work.

Random number generators are valuable tools in computing (SN: 5/27/16). 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 Earth’s climate or the stock market, also require many random numbers to properly capture chance occurrences that happen in real life.

Lasers can generate random number sequences thanks to tiny, naturally occurring fluctuations in the light’s frequency over time. But using a laser beam to produce random numbers like that is sort of like repeatedly rolling a single die. To generate many strings of random digits from a single laser at once, physicist Hui Cao of Yale University and colleagues came up with a new design.

In the team’s laser, light bounces between mirrors positioned at either end of an hourglass-shaped cavity before exiting the device. This irregular shape allows light waves of various frequencies to ricochet through the laser and overlap with each other. As a result, when the laser is shined on a surface, its light contains a constantly changing pattern of tiny pinpricks that brighten and dim randomly. The brightness at each spot in the pattern over time can be translated by a computer into a random series of ones and zeros.

Cao and her colleagues pointed the laser at a high-speed camera, which measured light intensity at 254 spots across the beam about every trillionth of a second. But that camera tracked the laser light for only a couple of nanoseconds before its memory filled up, after which the data were uploaded to a computer to be encoded as 0s and 1s, says Daniel Gauthier, a physicist at Ohio State University who cowrote a commentary on the study in the same issue of Science. To work in the real world, this random number generator would need to be outfitted with light detectors that could send rapid-fire brightness measurements to computers in real time.