Seth Lloyd of MIT turns atoms into computers and thinks about how to program the universe.
Eric Smalley
How does a mechanical engineer become a leading authority on using atoms and subatomic particles as the basis for next-generation computing?
“I’m kind of a faux mechanical engineer,” says Seth Lloyd, a professor of mechanical engineering at MIT. “I never studied mechanical engineering. My background is all in physics.” But the first full-time faculty position he landed 13 years ago was in a mechanical engineering department.
His training in physics and information theory was ideal for a career in quantum computing, but the field didn’t really exist when he was looking for an academic job. In the 1980s, a few scientists, including famed physicist Richard Feynman, had played around with the idea of using the quantum properties of atoms and subatomic particles to process information, but it was only a thought experiment. No one had actually tried it out.
In 1993, shortly before joining the MIT faculty, Lloyd figured out that it would be possible to make a quantum computer using off-the-shelf components, like lasers and microwave generators. A year later, a researcher from AT&T Research, Peter Shor, now at MIT, showed how such a computer could break cryptographic codes. It was the “killer app” of quantum computing. Both accomplishments helped launch this new way of computing as a full-fledged field of research.
“The field exploded from under 10 [people] back in 1993 to many thousands worldwide today,” says Lloyd.
Today, Lloyd’s research has two seemingly divergent focuses: practical applications of today’s simple prototype quantum computers, such as more-accurate clocks, and the cosmological implications of quantum information theory, which get at the very nature of the universe.
Both lines of research are connected by the fundamentals of physics: the smallest units of matter process information. “Every atom—and indeed every elementary particle—registers bits of information, and whenever two atoms collide those bits are flipped,” says Lloyd. “Not only can the universe be thought of as a computer, the universe is a computer—a quantum computer,” he says.
The notion of information as a physical entity dates back to the origins of information theory in the mid-20th century. But few people had thought through the implications of linking information theory with quantum physics until Lloyd worked out the physical limits of computation in a 2000 article in Nature. He expanded on the idea and put it in plain English in his book, Programming the Universe: A Quantum Computer Scientist Takes on the Cosmos, published this year.
“Seth Lloyd is one of a new breed of people who take seriously the idea that information is a physical quantity,” says Robert Joynt, a professor of physics and quantum computing researcher at the University of Wisconsin, Madison. “He combines deep physical intuition with the computer scientist’s feel for information and how to process it.” The combination has made him “one of the deities of quantum computing,” Joynt said.
When Lloyd isn’t thinking about the universe, he works on more mundane applications. One such application is more accurate atomic clocks like those used by the National Institute of Standards and Technology to keep official time.
Another is small quantum computers capable of doing complex simulations. Scientists who study high-energy particle physics or biomolecular processes like protein folding often run simulations that require large supercomputers. Small quantum computers could do the job better.
Lloyd and his MIT colleague, David Cory, have built special-purpose quantum analog computers that can process simulations beyond the reach of any classical computer. “Even if a classical computer were the size of the universe itself, it would never be able to follow the quantum analog computations we’re doing,” Lloyd says.