Einstein’s Theories Revisited: Scientists Produce Pseudogravity Using Photonic Crystals

Scientists have manipulated light to behave as if influenced by gravity using distorted photonic crystals, paving the way for advances in optics and 6G communication.

Manipulating the behavior of lights with pseudogravity

A group of researchers manipulated the behavior of light as if it were under the influence of gravity. The results, published in the journal Physical examination A on September 28, 2023, will have considerable implications for the world of optics and materials science, and will be of particular importance for the development of 6G communications.

A conceptual image of the distorted photonic crystal and photonic crystal. Credit: K. Kitamura et.al.

Einstein theory and pseudogravity

Albert Einstein’s theory of relativity long established that the path of electromagnetic waves, including light and terahertz electromagnetic waves, can be deflected by gravitational fields. Scientists have recently theoretically predicted that replicating the effects of gravity, i.e. pseudogravity, is possible by deforming crystals in the lower normalized energy (or frequency) region.

We sought to determine whether lattice distortion in photonic crystals could produce pseudogravity effects, said Professor Kyoko Kitamura of Tohoku University’s Graduate School of Engineering.

The experimental setup and simulation results of the beam trajectory in a DPC. Credit: K. Kitamura et.al.

The role of photonic crystals

Photonic crystals have unique properties that allow scientists to manipulate and control the behavior of light, thereby serving as controllers of the flow of light within crystals. They are constructed by periodically arranging two or more different materials with varying abilities to interact with and slow down light in a regular, repeating pattern. Additionally, pseudogravity effects due to adiabatic changes have been observed in photonic crystals.

Kitamura and his colleagues modified the photonic crystals by introducing lattice distortion: a gradual distortion of the regular spacing of the elements, which disrupted the grid-like pattern of the proton crystals. This manipulated the photonic band structure of the crystals, resulting in a curved beam path in the medium, much like a light ray passing through a massive celestial body such as a black hole.

The experimental results, with the transmission difference between ports B and C, clearly show the beam curvature in a DPC. Credit: K. Kitamura et.al.

Experiment details and implications

Specifically, for their experiment, the scientists used a distorted silicon photonic crystal with a primal lattice constant of 200 micrometers and terahertz waves. Experiments have successfully demonstrated the deflection of these waves.

Just as gravity bends the path of objects, we found a way to bend light in certain materials, Kitamura adds. Such in-plane beam steering in the terahertz range could be exploited in 6G communication. Academically, the results show that photonic crystals could exploit gravitational effects, opening new avenues in the field of graviton physics, said Associate Professor Masayuki Fujita of Osaka University.

Reference: Deflection of electromagnetic waves by pseudogravity in distorted photonic crystals by Kanji Nanjyo, Yuki Kawamoto, Hitoshi Kitagawa, Daniel Headland, Masayuki Fujita and Kyoko Kitamura, September 28, 2023, Physical examination A.
DOI: 10.1103/PhysRevA.108.033522