Physicists have just made a new breakthrough in the enigmatic realm of time crystals.
For the first time, a time crystal has been built that can be directly seen by human eyes, rippling in an array of neon-hued stripes. The material's construction could open up a whole new world of technological possibilities, including new anti-counterfeiting measures, random number generators, two-dimensional barcodes, and optical devices.
"They can be observed directly under a microscope and even, under special conditions, by the naked eye," says physicist Hanqing Zhao of the University of Colorado Boulder.
Related: Two Time Crystals Have Been Successfully Linked Together For The First Time
Time crystals are a very recent phenomenon. Predicted in 2012 by US theoretical physicist Frank Wilczek, they were initially dismissed by some physicists as a law-breaking concept that risked breaking a key rule of thermodynamics.
Then, in 2016, a team of US physicists reported actually observing them in an experiment.
So here's the short version. Crystalline materials like diamond, quartz, and salt are three-dimensional atomic lattices composed of particles that repeat in space, a bit like a geometric jungle gym with the atoms sitting at the junctions. You can take any section of the lattice and superimpose it over another perfectly.
A time crystal is a pattern of particles in a temporal dimension: in other words, time crystals repeat not just in space, but in time as well. Their particles oscillate with a timing that repeats in such a way that it, too, can be superimposed. Critically, the oscillation breaks time symmetry, operating in seeming defiance of any rhythms in their environment.
The potential of time crystals, both for exploration of quantum behavior and for technological applications, is pretty exciting. This is why scientists like to probe their properties and figure out what makes them (ahem) tick.
Zhao and his colleague, physicist Ivan Smalyukh of the University of Colorado Boulder, created their time crystal out of liquid crystals – the same material that can be found in the LCDs that are commonly used as screens on clocks and TVs. These consist of rod-shaped molecules that behave a little like a liquid, and a little like a crystal.
The researchers sandwiched their liquid crystal between glass plates coated with a photoresponsive dye. When they shone particular types of light on the sample, the dye molecules polarized, or changed their orientation, exerting pressure on the liquid crystal.
This pressure created kinks in the liquid crystal that interacted with each other in a complex series of steps, generating a pattern of motion that repeated for hours, even under changing light and temperature conditions.
These patterns were observed in the sample as an undulating series of colored stripes.
"Everything is born out of nothing," Smalyukh says. "All you do is shine a light, and this whole world of time crystals emerges."
While the results of the study meet the stringent requirements to be classified as a time crystal, the researchers say there's ample room for further exploration of time crystal properties in different systems. In exploring how time crystals manifest in different regimes, the researchers believe that different sets of criteria may emerge.
Meanwhile, the practical application potential that can be seen now is deeply intriguing.
"Potential technological applications in optical devices, photonic space-time crystal generators, telecommunications, and anti-counterfeiting designs may signal the beginning of an exciting frontier for time and space-time crystals, where fundamental research advances could drive technological utility," Zhao and Smalyukh write.
The research has been published in Nature Materials.