- By Joshua E. Brown
It’s hard to suck a milkshake through a straw,” says Adrian Del Maestro, assistant professor of physics. Not so with helium. When cooled to just above absolute zero, it forms a bizarre state of matter, called a superfluid, “that has no friction,” Del Maestro says. “It’s a perfect liquid.” Once it has been stirred, a closed ring filled with superfluid helium will continue circulating for months.
Now, “think about a wide river heading into a narrow canyon,” says Del Maestro. “What’s it going to do?” Common sense tells us that liquids speed up as the channel containing them tightens. But what if a faucet were so amazingly tiny that only a few atoms of helium could squeeze through its opening at once? There, slippery perfection—and common sense—reach their quantum limits, it seems.
According to a longstanding model of quantum mechanics, once the pipe shrinks to the nanoscale, the bizarre behavior of superfluid helium should become even more odd: far from speeding up, it should actually slow down. For more than seventy years, scientists have been studying the flow of helium through ever-smaller pipes. Now, Del Maestro and a team of researchers from Canada and Germany have successfully created the world’s smallest faucet: a pore through silicon nitride that is less than thirty atoms wide. In results published in May, in the journal Science Advances, Del Maestro and the other researchers report that the flow of helium through this microscopic pipe does, indeed, appear to slow down.
Del Maestro used computer simulations on the Vermont Advanced Computing Core at UVM to understand just how small the faucet will have to be before this new physics fully emerges. “This ‘Luttinger liquid,’ as it’s sometimes called, is a very strange state of matter,” he says. “Because it exists in strictly one dimension, it’s not really a liquid, it’s not really a superfluid, it’s not really a solid—it’s everything, all at once.”
“We’re almost there,” he adds. “This knowledge could lead to novel technologies including ultra-high-precision rotation sensors with application to the GPS system.”