A stop-motion image that shows pairs of millimetre-scale beads forming a time crystal over approximately one-third of a second in time. The colours represent the beads interacting at different stages during this period. Credit: NYU’s Center for Soft Matter Research.
In research that advances the potential of a new form of matter, scientists have discovered ‘levitating’ time crystals you can hold in your hand.
Time crystals, a collection of particles that ‘tick’ – or move back and forth in repeating cycles – were first theorised and then discovered about a decade ago.
While scientists have yet to create commercial or industrial applications for this intriguing form of matter, these crystals hold great promise for advancing quantum computing and data storage, among other uses.
Over the years, different types of time crystals have been observed or created, with their varying properties offering a range of potential uses.
A team of New York University physics researchers has now observed a new type of time crystal, one whose particles levitate on a cushion of sound while interacting with each other by exchanging sound waves.
In the process, these particles defy Newton’s Third Law of Motion, which states that for every action of an object, there is an equal and opposite reaction, which means forces always occur in balanced pairs, ie equal in magnitude and opposite in direction.
By contrast, in the NYU discovery, the particles, or beads, interact more independently and are not necessarily tied to balanced forces; they move nonreciprocally.
The findings expand the prospects that these crystals hold for technology and industry.
Notably, these time crystals, which can be seen with an unaided eye, are suspended on a one-foot-high device that you can hold in your hand.
Senior author, physics Professor David Grier, director of NYU’s Center for Soft Matter Research, said: “Time crystals are fascinating not only because of the possibilities, but also because they seem so exotic and complicated.
“Our system is remarkable because it’s incredibly simple.”
NYU physics researchers have observed a new type of time crystal—one whose particles levitate on a cushion of sound while interacting with each other by exchanging sound waves. Above, a bead (purple) is suspended in mid-air by sound waves emanating from (black) circular speakers arranged in a six-inch-tall 3D-printed frame. Credit: NYU’s Center for Soft Matter Research.
Acoustic levitator
The research, conducted with Mia Morrell, an NYU graduate student, and Leela Elliott, an NYU undergraduate, also offers insights into our biological clocks, or circadian rhythms.
This is because, like the newly discovered time crystals, some biochemical networks also interact nonreciprocally – including the way our body works to break down food.
The discovered time crystal consists of styrofoam beads, such as those used in packaging, suspended in air by sound waves, which served as an ‘acoustic levitator’ to initially hold the beads motionlessly in mid-air.
Morrell said: “Sound waves exert forces on particles, just like waves on the surface of a pond can exert forces on a floating leaf.
“We can levitate objects against gravity by immersing them in a sound field called a standing wave.”
Crucially, when these levitated particles interacted with each other, they did so by exchanging scattered sound waves.
More specifically, larger particles scatter more sound than smaller particles.
Therefore a large particle will influence a small particle more than the small particle influences the large particle.
As a result, the interaction between a small and large particle is unbalanced.
Morrell said: “Think of two ferries of different sizes approaching a dock; each one makes water waves that pushes the other one around, but to different degrees, depending on their size.”
Moreover, these wave-mediated interactions are not constrained by Newton’s Third Law, allowing the beads to spontaneously oscillate while suspended mid-air, counting off a rhythm that precisely balances the unusual forces they experience.
The study is published in Physical Review Letters.
