Researchers have overcome a major obstacle to generating random numbers on quantum computers by limiting the possibilities in the otherwise unlimited randomness of a set of quantum particles.

Random numbers play a key role in classical computing by providing an element of chance in games and simulations, a reliable method for encrypting messages, and a means of accurately sampling huge amounts of data.

Researchers from the Massachusetts Institute of Technology and the National Atomic Energy Commission in Argentina have shown that short sequences of random operations—randomly shifting laser pulses or magnetic fields—acting on a string of quantum bits can, in effect, generate random configurations of qubits.

Being able to generate random numbers in quantum computing could make quantum computers easier to build by countering the noise that eventually destroys qubits, which represent the 1s and 0s of computer information. Quantum computers promise to be fantastically fast at solving certain types of large problems, including the mathematics that underpins today's security codes.

Quantum random numbers could also be useful for increasing the efficiency of quantum secret-sharing schemes, quantum encryption and various forms of quantum communications.

Complete noise-estimation experiments could be implemented in rudimentary quantum computers within the next few years, according to the researchers. Researchers generally agree that practical quantum computers are a decade or two away.

The work appeared in the December 19, 2003 issue of Science.

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