Researchers have built the fastest random-number generator ever made, using a simple laser. Algorithms in conventional computers can produce sequences of numbers that seem random at first, but over time these tend to display patterns. A popular way to tap into quantum randomness is to exploit fluctuations in how photons are emitted by the materials used in lasers. But for random-number generation, researchers aim for the opposite. The fastest existing computers have clock speeds measured in gigahertz, which is much too slow to fully exploit the full power of Cao’s device.