The familiar “random number generators” used in computers and calculators are actually based on the outputs of deterministic algorithms. So although the sequences they generate may pass established statistical tests of randomness, they’re not entirely unpredictable, because an attacker could guess the algorithm itself. That’s not a problem for some applications, such as Monte Carlo simulations or randomized music playlists. But others, such as online gaming or secure communications, benefit from sequences that are truly unguessable, such as can be generated from measurements of a stochastic physical process. A simple example of such a process is the roll of a die. More sophisticated possibilities, and ones that can generate sequences more quickly and be automated more easily, involve quantum or thermal noise.

As computing and communications speeds increase, there is a growing need for faster methods of generating random sequences. Last year Atsushi Uchida, now of Saitama University in Japan,...

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