A new type of time crystal has been created that does some interesting things to light up

Scientists are still figuring out the ins and outs of strange materials known as time crystals; structures that hum with movement for eternity. Now, a new strain could help deepen our understanding of the puzzling state of matter.

Just as regular crystals are atoms and molecules that repeat over a volume of space, time crystals are collections of particles that tick in patterns over a span of time in ways that initially appear to defy science.

Theorized in 2012 before first being observed in the lab four years later, researchers have been busy tinkering with the structures to probe the deeper underpinnings of particle physics and uncover potential applications.

In this latest study, a new type of “photonic” time crystal has been created. Operating at microwave frequencies, it is able to reduce and amplify electromagnetic waves, promising future applications in wireless communication systems, laser development and electronic circuits.

“In a photonic time crystal, photons are arranged in a pattern that repeats over time,” says lead author Xuchen Wang, a nanoengineer at Germany’s Karlsruhe Institute of Technology.

“This means the photons in the crystal are synchronized and coherent, which can lead to constructive interference and light amplification.”

Additionally, the research team discovered that electromagnetic waves traveling along surfaces could be amplified as well as waves from the surrounding environment.

Central to the research is a 2D approach based on ultra-thin sheets of man-made materials called metasurfaces. Previously, photonic time crystal research has relied on bulk 3D materials: making and studying these materials is extremely difficult for scientists, but the move to 2D means a faster and easier path to experimentation – and to find out how these crystals could be applied in real-world settings.

Although simpler than full 3D structures, they share some important characteristics with photonic time crystals and can mimic their behavior, including how they interact with light. This is the first time that photonic time crystals have amplified light in this particular way and to such a significant extent.

A conceptual image of the light-amplifying metasurface. (Wang et al., Scientists progress2023)

“We found that reducing the dimensionality from a 3D structure to a 2D structure greatly facilitated the implementation, which made it possible to realize photonic time crystals in reality,” says Wang.

Although real-world applications are still a long way off, the approach of using 2D metasurfaces as a means to produce and examine photonic time crystals will make this type of research much easier in the future.

The discovery of the amplification of electromagnetic waves along surfaces, for example, could eventually help to improve the integrated circuits found everywhere, from telephones to cars: communication within these circuits would potentially be faster and more transparent.

Then there’s wireless communications, which can suffer from signal decay at a distance (which is why you might not be able to get Wi-Fi to the top of your house). Coating surfaces with 2D photonic time crystals promises to improve this situation.

“As a surface wave propagates, it suffers material losses and the signal strength is reduced,” says physicist Viktar Asadchy from Aalto University in Finland.

“With 2D photonic time crystals integrated into the system, the surface wave can be amplified and communication efficiency improved.”

The research has been published in Scientists progress.

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