Ultra-cold atoms chilled and trapped with light enable unimaginable discoveries
The simplest way to describe David Weiss’s research may be just to say that he does experiments with ultra-cold atoms, using lasers to cool them to extremely low temperatures and trap them so they can be manipulated with microwaves, magnetic fields, and more lasers.
“We cool these atoms to temperatures that are, really, pretty clearly the lowest temperatures that could exist anywhere in the universe,” Weiss explained. “Deep space is 2.7 degrees Kelvin but we can cool, in my lab, to about one nanokelvin, or about a billionth of a degree above absolute zero.”
At these temperatures, matter behaves very differently from what we experience in normal, everyday conditions, and Weiss uses this—as well as the ultra-precision of his tools—to study a range of fundamental physics.
Each of his experiments, of which there are several, requires dozens of laser beams, all carefully computer-controlled and precisely aligned by as many as 1,000 individual optics. And while to many of us, much of Weiss’s research may be beyond comprehension—having to do with quantum mechanics, bosons and fermions, and things that go by names such as Maxwell’s Daemon, a quantum Newton’s Cradle, and Bose-Einstein condensates— one of his experiments does involve something we have all heard of, and that’s quantum computing.
In essence, a quantum computer exploits certain properties of atoms in a way that’s conceptually similar to how the computers that sit in our laps, on our desktops, and in our hands as smartphones work; but while these “classical” computers rely on physical switches set to either 1 or 0, a quantum computer encodes its ones and zeros in the spin of individual atoms, in what is called a qubit.
“Don’t try it at home,” Weiss quipped. “It’s really more complicated than you might think.”
While Weiss and other scientists have made incredible strides toward achieving functioning qubits and assembling them into useful arrays for storing information, the biggest challenge in building a quantum computer is one of scale.
“It will be a while before there will be useful quantum computers on people’s desktops,” Weiss said.
He and his team have so far assembled a 5x5x5 array—more qubits than anyone else has put together in any other system—and they still do not have a fully functioning quantum computer.
But, Weiss said, with the ability to scale up their technology with a few additional modifications, “you could imagine getting to something which is a lot more. For instance, at the spacing that we have, we could t a million atoms into a half-millimeter cube. That’s a lot of qubits—way more than really anyone’s considering—but even if you had them, making them work together as a quantum computer would be difficult.”
And there are still other issues, such as error correction, of which Weiss said “It’s a little harder to predict how well that’s going to work. There are a lot of smart people working on it, so there’s a point at which they might be able to succeed.”
There’s a great deal of uncertainty in this type of research, as in much truly groundbreaking science, because it represents the very farthest edge of human knowledge—a frontier to be explored and illuminated by pioneering scientific minds.
“A lot of times, what happens in science is that the things that become technologically important, you don’t really exactly know in advance,” Weiss said. “You’re pursuing scientific questions and then you get answers which you couldn’t have guessed. My research, in the big picture view, is trying to take advantage in different ways of this relatively new technology—which is the ability to cool and trap atoms—and then that technical handle opens the range to this wide gamut of physics, from the ability to model condensed-matter systems, to maybe build devices like quantum computers, or to make measurements of fundamental physical properties. So it’s all built upon these ideas like, ‘Can you cool particles and trap them?’ You think, ‘Well, you could, but why would you want to?’ The point is that once you to do something like that, you can then do things that are hard to even imagine.”
David Weiss is a professor of physics at Penn State.
