NYU Researchers Discover Novel Classical Time Crystal

Researchers at New York University (NYU) have reported the discovery of a novel type of time crystal, which they describe as a classical system. This new form utilizes levitated styrofoam beads interacting via sound waves, exhibiting nonreciprocal dynamics and expanding the understanding of these states of matter.

Understanding Time Crystals

Time crystals represent a state of matter where particles exhibit repeating cycles of movement. Unlike spatial crystals, their arrangement forms a pattern that repeats in time. This involves continuous oscillation that breaks time symmetry, meaning the oscillations occur independently of an external clock, with their frequency emerging from the particles' intrinsic interactions.

First theorized and discovered approximately a decade ago, time crystals are an area of research with various observed types, each with distinct properties.

Time crystals are an area of research with potential applications in fields such as quantum computing and data storage.

A Classical Breakthrough at NYU

The NYU team, led by Professor David Grier, Director of NYU's Center for Soft Matter Research, and including graduate student Mia Morrell and undergraduate Leela Elliott, discovered this classical time crystal during research into different physical interactions.

The observed time crystal is composed of polystyrene beads, 1-2 millimeters in size, which are visible to the unaided eye and were suspended on a handheld device during experiments. The system is noted for its simplicity in design and operation.

The Experiment: Nonreciprocal Interactions via Sound

The experimental setup involved an acoustic levitator or speaker array that generated a standing sound wave to hold the styrofoam beads in mid-air. The interaction between these levitated particles occurred through the exchange of scattered sound waves. When the beads were introduced into the sound field, they created disturbances that scattered the sound waves, thereby facilitating interactions between them.

A key finding was the nonreciprocal nature of these interactions. Larger particles scatter more sound than smaller ones, resulting in an unbalanced interaction where a larger particle influences a smaller one more significantly.

This means the particles operate independently rather than adhering to Newton's Third Law of Motion, which dictates that forces occur in balanced pairs.

Under specific conditions, this wave-mediated interaction caused two beads to oscillate spontaneously in a distinct temporal pattern. This oscillation maintained a stable, repeating state for hours without any external stimulus, representing what is described as the smallest possible system to exhibit time crystal behavior.

Broader Implications and Future Directions

While immediate practical applications are not yet specified for this particular classical time crystal, the findings expand the general understanding and potential prospects for time crystals.

The research also offers insights into biological clocks, such as circadian rhythms. This connection arises from similarities between the nonreciprocal interactions observed in the new time crystals and certain biochemical networks, including those involved in the body's food breakdown processes.

The findings suggest new avenues for experimental research, including the study of non-reciprocal interactions in biochemical systems, and indicate that complex physical behaviors can be investigated with accessible equipment.

The findings were published in the journal Physical Review Letters. The research received support from the National Science Foundation.