Time team: NMR finds crystal

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  • Published: May 15, 2018
  • Channels: NMR Knowledge Base
thumbnail image: Time team: NMR finds crystal

Ticking away

Yale physicists looked for a signature of a discrete time crystal in a crystal of monoammonium phosphate.

Nuclear magnetic resonance (NMR) spectroscopy has been involved in uncovering hints of a time crystal, a form of matter that "ticks" when exposed to an electromagnetic pulse. The time crystal was found in the most unlikely of places: a crystal-garden kit.

Common crystals such as salt or quartz are three-dimensional, ordered spatial crystals with periodicity and regularity of a type known for a century. Time crystals, first identified in 2016, however, are somewhat different. The spin of their atoms flips periodically with an electromagnetic pulse. Researchers have termed this oscillation "ticking" with reference to clocks. Perhaps the most intriguing thing about the ticking though is that even if the pulse is not perfect, the ticking in a time crystal is locked to a particular frequency regardless.

Crystal gardeners' question time

Researchers hope that a better understanding of these time crystals could lead to improved atomic clocks, gyroscopes, and magnetometers, as well as helping us plot a route to future quantum technologies.

Researchers at Yale University and their colleagues discuss new findings in two studies published in the journals Physical Review Letters and Physical Review B. Together the studies represent only the second known experiment observing the telltale signature for a discrete time crystal (DTC) in a solid.

"We decided to try searching for the DTC signature ourselves," after the announcement of the 2016 discovery, explains Sean Barrett. He adds that his student Jared Rovny had grown monoammonium phosphate (MAP) crystals for an entirely different experiment, so we happened to have one in our laboratory. MAP is a common substance used in crystal-growing kits often given to children with a penchant for scientific discovery.

Signature dish

Barrett thought that it would be unusual to find a time crystal signature within a MAP crystal because MAP crystals are considered to be very disordered and activity in a time crystal seemed originally to be linked to internal disorder. However, the researchers have now used NMR spectroscopy to detect the DTC signature and it emerged very quickly from the data.

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

Intriguingly, the team also realized while carrying out the experiments that simply finding the DTC signature would not necessarily prove that the system had a quantum memory of how it came to be. The team was thus spurred on to try a time crystal "echo" which would reveal hidden coherence, or quantum order, within the system. Barrett suggests that the new results when viewed in the context of earlier experiments represent something of a puzzle for theorists to solve in terms of working out how 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 adds.

Related Links

Phys Rev Lett, 2018, online: "Observation of Discrete-Time-Crystal Signatures in an Ordered Dipolar Many-Body System"

Phys Rev B 2018, online: "31P NMR study of discrete time-crystalline signatures in an ordered crystal of ammonium dihydrogen phosphate"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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