QUANTUM computing (see article) is not the only game in town when it comes to creating a new computing paradigm. Speaking at the American Physical Society's annual March conference, William Ditto of the University of Florida told of his efforts to create a “chaotic computer”. This is saner than it sounds. Chaos, in the mathematical sense, is not unpredictability: chaotic systems can behave in a predictable and reproducible way. The catch is that the evolution of a chaotic system depends very sensitively on its starting conditions, which leads in the long term to behaviour that is ultimately unpredictable. But by choosing those starting conditions carefully, and only letting the system evolve for a short time, Dr Ditto thinks he can harness chaos to be computationally powerful.
Dr Ditto proposes using “chaotic elements”—which could be specific types of electric circuits, lasers or even neurons—to replace the logic gates that are the basic building blocks of conventional computers. The inputs to each chaotic element, as with a conventional logic element, are binary: that is, either 0 or 1. If the element outputs a value that exceeds a threshold that Dr Ditto chooses, then the result is a 1, while if it is less than that threshold, the result is a 0. This is exactly what happens in a conventional logic gate as well.In 1998, however, Dr Ditto and his collaborator Sudeshna Sinha of the Institute of Mathematical Sciences in Chennai, India, had a key insight. They showed that given a carefully chosen chaotic logic element, different logical operations (such as AND, OR and so on) can be performed simply by varying the threshold value. This would allow a matrix of chaotic logic elements to be simply and dynamically reprogrammed by changing their threshold values. That, in turn, would be useful in reconfigurable circuits. Unlike reconfigurable circuits which already exist today, and are used, for example, in prototyping, a chaotic computer, Dr Ditto says, could be reconfigured so rapidly that it could perform entirely different functions with each tick of the clock. This would be not only a quantitative, but a qualitative change from conventional computers.
But it is also just a starting point, because there are chaotic systems that have many different parameters that depend on one another. By cleverly designing the inputs, outputs and thresholds, such a system can perform many different logical operations simultaneously—offering, in the long run, the possibility of performing calculations far more quickly than conventional logic elements can. Dr Ditto described just how this might be done.
The theory is intriguing, but these circuits are not just theoretical. The team has built an electronic logic element using a collection of simple components, such as resistors and capacitors, which behaves chaotically. They have also made a logic element out of a pair of leech neurons (nerve cells from blood-sucking worms) placed on a microchip. Dr Ditto readily admits that, like quantum computing, this technology is still in its infancy. But it certainly has potential—even though many people feel that existing computers are quite chaotic enough already.
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