Inspiration from chaos

Lasers could be used to create high speed random-number generators, useful for many aspects of daily life, such as encrypting emails and internet transactions. A study online this week in Nature Photonics reveals that the perceived negative qualities of lasers, such as noise and chaos, can actually be used to beneficial effect for a wide range of modern applications.

Trusted random numbers should be unpredictable, irreproducible and statistically unbiased, and thus ensure confidentiality. However, previously reported approaches have produced either pseudo-random numbers that can be generated quickly but are vulnerable to prediction, or true randomness that is limited to a slow generation rate of the order of megabits per second.

Atsushi Uchida and co-workers in Japan report that, by sampling the fluctuating optical output of two chaotic semiconductor lasers, they are able to generate true random bit sequences at rates up to 1.7 gigabits per second ? an order of magnitude faster than previously reported schemes that have verified randomness. The team suggests that the key is to use the unpredictability gained from the lasers’ noise, and the nonlinear amplification and mixing process of laser noise offered by the lasers’ chaotic dynamics.

This achievement of fast generation of truly random bit sequences is anticipated to improve security in the concealing of public information and the speed of secure key generation in future quantum cryptography systems. Further applications include computing in complex situations involving nuclear medicine and computational chemistry.

doi: 10.1038/nphoton.2008.227

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