Of all the eccentricities of the quantum realm, time crystals—arrangements of atoms that repeat certain motions over time—are among the strangest. But they definitely exist, and to provide much more solid proof, physicists have finally created a time crystal that we can actually see.
In a recent Nature Materials article, physicists at the University of Colorado Boulder presented a new design for a time crystal: a glass cell filled with liquid crystals—ord-shaped molecules stuck in a strange limbo between solid and liquid. It’s the same little thing found in smartphone LCD screens. When hit with light, the crystals jiggle and dance in repeating patterns that the researchers say resemble “psychedelic tiger stripes.”
“They can be observed directly under a microscope and even under special conditions with the naked eye,” Hanqing Zhao, the study’s lead author and a graduate student at the University of Colorado, Boulder, told a release in the Journal. Technically, these crystalline dances can last for hours, like “an eternally spinning clock,” the researchers added.
Asymmetric curiosity
Time crystals first appeared in a 2012 paper by Nobel laureate Frank Wilczek, who proposed the idea of an impossible crystal that breaks several of the symmetry rules of physics. Specifically, a time crystal breaks symmetry because its atoms don’t fit into a continuous lattice, and their positions change over time.
Physicists have since demonstrated versions of Wilczek’s proposal, but those crystals lasted abysmally short time and were microscopic. Zhao and Ivan Smalyukh, the study’s senior author and a physicist at the University of Colorado, Boulder, wanted to see if they could overcome these limitations.
Molecular “kink”
For the new time crystal, the duo exploited the molecule’s “kinks”—their tendency to bunch together when squeezed in a certain way. Once together, these kinks behave like whole atoms, the researchers explained.
“You have these twists and turns, and you can’t easily remove them,” Smalyukh said. “They behave like particles and start interacting with each other.”
The team coated two glass cells with dye molecules, sandwiching a liquid crystal solution between the layers. When they flashed the setup with polarized light, the dye molecules squirmed inside the glass, compressing the liquid crystal. This created thousands of new kinks inside the crystal, the researchers explained.
“That’s the beauty of this time crystal,” Smalyukh said. “You just create some conditions that are not so special. You shine a light, and things happen.”
The team believes that this time-based iteration of the crystal could have practical uses. For example, a “time watermark” printed on invoices could be used to identify counterfeits. The stacked layers could also serve as a tiny data center.
It’s rare for quantum systems to be visible to the naked eye. Only time will tell if this crystal means anything this time around—the researchers “don’t want to specify applications at this time”—but even if it doesn’t, it’s still a neat demonstration of how physical theories exist in strange, unexpected corners of reality.
