Time crystals are one of the most exciting metamaterials that have been discovered in the last decade. Just as a regular crystal has properties that repeat in space, time crystals have properties that vary in time. These peculiar objects are being studied with multiple applications in mind, and one of them has to do with better mastery of light.
These are the so-called photonic time crystals. It is their electromagnetic properties that change with time. There are many challenges when trying to create a three-dimensional photonic crystal. There are stringent requirements to not just make these objects, but also to study them. But an international team has worked out a way to get around this. They used a metasurface. They simply made the crystal in two dimensions.
“We have found that reducing the dimensionality from a 3D to a 2D structure greatly simplifies implementation. This made it possible to realize photonic time crystals," lead author Dr. Xuchen Wang, from the Karlsruhe Institute of Technology, said in a statement.
So the time crystal is a peculiar electromagnetic structure that changes in time. It contains components that are tunable and this ability also changes with time. It is possible to imagine it by thinking of the way the crystal refracts light changing with time. But that is not all. It can also massively amplify light.
Similar to the recent creation of the double-slit experiment in time, interacting with a photonic time crystal also changes the frequency of the light source involved. And frequency, for light, is proportional to energy. In these crystals, energy is not conserved, so light can get exponentially amplified, at least in theory.
And using the metasurface created by this team, that theory is being put to the test. They indeed confirmed that exponential wave amplification takes place inside a photonic time crystal. The light used for this experiment was microwaves, but the team think it possible to work with millimeter wavelengths. That’s the range of wavelengths used by 5G and future 6G communications.
It is too early to tell if these crystals will revolutionize telecommunications or other light-based technologies, but they do show potential.
The study is published in the journal Science Advances.