The newest Pentium chip powering PCs and laptops contains 40 million electronic switches packed onto a piece of silicon about the size of a thumbnail. Several years from now, if this incredible shrinking continues, a single chip will hold a billion switches, then a trillion. The logical culmination is a computer in which the switches are so tiny that each consists of an individual atom. At that point something miraculous happens: Quantum mechanics kick in. Anyone who follows the science news or watches "Star Trek" has at least a notion of what that means: particles can be in two or more places at once. Atoms obey a peculiar logic of their own - and if it can be harnessed society will be transformed. Problems that would now take forever would be solved almost instantly. Quantum computing promises nothing less than a shortcut through time.