May/June 2000

Quantum Computing

Computers that tap the bizarre properties of subatomic particles might calculate with awesome speed-cracking codes that stymie conventional machines.

By M. Mitchell Waldrop

"Every so often," says Isaac Chuang, sitting in his office at IBM's Almaden Research Center in San Jose, "something new comes along in physics, and everybody says Wow!' Then they get caught up in a whirlwind." In the 1970s, the whirlwind was chaos theory. In the late 1980s, it was high-temperature superconductivity. And now?

"Quantum computing," says Chuang, a slender, soft-spoken physicist who has already emerged as one of the leaders in this esoteric-sounding field with potentially enormous impact.

A quantum computer operates by the rules of quantum weirdness, down in the subatomic realm where our everyday intuitions are violated wholesale. This is a world in which an electron can be in two places at once, in which an atomic nucleus can be spinning clockwise and counterclockwise at the same time. It is a bizarre world in which matter itself dissolves into a ghostly blur of possibilities as soon as you try to look at it.

And yet this surreal world is one in which you can do computing, insists Chuang, whose group at Almaden is one of several that have demonstrated the basic principles in the lab. If he and his fellow researchers can ever scale up their demonstrations into practical machines, the payoff will be enormous. Quantum computers could tackle problems that would stymie their conventional counterparts-easily cracking, for instance, the most sophisticated encryption schemes now in use.

Hence the new whirlwind. "It's easy for quantum computing to sound like a fanciful theorist's dream," says physicist Neil Gershenfeld of the MIT Media Lab. "But just extrapolating Moore's Law, the scaling relation that says microchips shrink by a factor of two every two years or so, somewhere around the year 2020 or 2030 is when we hit one bit per atom-and when a new semiconductor fabrication plant will cost the gross national product of the planet. So if we really want to keep getting faster, there aren't many other places to turn. Quantum weirdness is essentially the only resource we have that's still untapped for computing. It's the only big thing that's left in the universe."