WHY THIS MATTERS IN BRIEF

Time crystals are unique, and new, and it’s believed they could open the door to creating incredibly weird and useful new materials.

Physicists at Yale University have discovered something extraordinary, a new material that more and more people are calling “Time Crystals,” a form of matter that exists in four dimensions not just three like most materials, where the forth dimension is time. Unlike conventional materials time crystals tick, like a clock, when exposed to an electromagnetic pulse, and the first one was discovered in a most unlikely place – in a crystal in a child’s toy.

The discovery means there are now new puzzles to solve, in terms of how time crystals form in the first place. Ordinary crystals such as salt or quartz are examples of three dimensional, ordered spatial crystals. Their atoms are arranged in a repeating system, something scientists have known for a century.

Time crystals, which were first identified in 2016, are different. Their atoms spin periodically, first in one direction and then in another, as a pulsating force is used to flip them. That’s the “ticking.” In addition, the ticking in a time crystal is locked at a particular frequency, even when the pulse flips are imperfect.

Scientists say that understanding time crystals may lead to improvements in atomic clocks, gyroscopes, and magnetometers, as well as aid in the development of new quantum technologies, such as quantum computers. Even the US Department of Defense is getting in on the act after they recently announced a program to fund more research into “time crystal systems.”

Yale’s new findings are described in a pair of studies, one in Physical Review Letters and the other in Physical Review B. The studies represent the second known experiment observing a telltale signature for a so called Discrete Time Crystal (DTC) in a solid.

“We decided to try searching for the DTC signature ourselves,” said Yale physics professor Sean Barrett, principal investigator for the two new studies. “My student Jared Rovny had grown Monoammonium Phosphate (MAP) crystals for a completely different experiment, so we happened to have one in our lab.”

MAP crystals are considered so easy to grow that they are sometimes included in crystal growing kits aimed at youngsters. It would be unusual to find a time crystal signature inside a MAP crystal, Barrett explained, because time crystals were thought to form in crystals with more internal “disorder.”

The researchers used Nuclear Magnetic Resonance (NMR) to look for a DTC signature, and quickly found it.

“Our crystal measurements looked quite striking right off the bat,” Barrett said. “Our work suggests that the signature of a DTC could be found, in principle, by looking in a children’s crystal growing kit.”

Another unexpected thing happened, as well.

“We realized that just finding the DTC signature didn’t necessarily prove that the system had a quantum memory of how it came to be,” said Yale graduate student Robert Blum, a co-author on the studies. “This spurred us to try a time crystal ‘echo,’ which revealed the hidden coherence, or quantum order, within the system,” added Rovny, also a Yale graduate student and lead author of the studies.

Barrett noted that his team’s results, combined with previous experiments, “present a puzzle” for theorists trying to understand how these weird time crystals form.

“It’s too early to tell what the resolution will be for the current theory of discrete time crystals, but people will be working on this question for at least the next few years,” Barrett said.