Behold the world's most feeble computer network: sitting in a classroom building at Caltech, it connects a grand total of two processors, crosses all of a basement corridor, and transmits a whopping single bit of information. Or would if it were working, which it isn't. "We think it would be nice if it were up and running by the new millennium," says Caltech researcher Jeff Kimble. Given the pathetic specs, it might seem just a little surprising to hear that Kimble's network is widely considered to be one of the most challenging projects in all of computer science. That's because the one bit of data his network is designed to transmit won't be an ordinary "1" or "0" of the sort that everyday networks traffic in. It will be a mixture of the two--a so-called quantum bit, or "qubit."
Kimble is trying to build the world's first quantum computer network. In a sense, he's getting a little ahead of himself, since neither he nor anyone else has yet come close to building a practical quantum computer--a computer, that is, that makes calculations on data in the weird multiple-reality state that is the hallmark of quantum mechanics. Still, the benefits of this stunningly radical approach to processing promise to be so great that the young field of quantum computing has been steadily attracting researchers not only from computer science but also from physics, math, and chemistry. Just a few years ago most computer scientists doubted that a quantum computer could ever be built. Now the tide of opinion seems to be turning, and the past year or two have seen some important advances. Neil Gershenfeld, for example, a physicist at MIT, has actually built a simple quantum computer. It can't do much--what it does is pick out one name from a list of four--but it does it faster than a conventional computer.
What's the big deal about quantum computing? Imagine you were in a large office building and you had to retrieve a briefcase left on a desk picked at random in one of hundreds of offices. In the same way that you'd have to walk through the building, opening doors one at a time to find the briefcase, an ordinary computer has to make its way more or less serially through long strings of 1's and 0's until it arrives at an answer. Of course, you could speed up the briefcase hunt by organizing a team, coordinating a floor-by-floor search, and then getting them all back together again to compare results. Ordinary computers can do this sort of thing, too, by breaking up a task and running the components in parallel on several processors. That sort of extra coordinating and communicating, however, exacts a huge toll in overhead.
