Photonic crystals are optical nanostructures that influence the propagation of photons within them, similar to how semiconductor crystals affect the movement of electrons.
Photonic crystals are a regular optical structure formed from a periodically arranged medium with different refractive indices. Due to the photonic bandgap nature of these materials, they can block photons of specific frequencies, thereby affecting the movement of photons. This effect is analogous to the impact of semiconductor crystals on electron behavior. Given the applications of semiconductors in electronics, it is speculated that the movement of photons could be controlled through devices made from photonic crystals, such as in the development of quantum computers.
However, photonic crystals can do more than just control the transmission of light; they can also simulate the behavior of light in strong gravitational fields. This is because changes in the shape or size of the photonic crystal alter its periodicity, thus changing its band structure and effective potential. By selecting the right parameters, we can make this effective potential resemble a gravitational field, allowing light to follow a curved trajectory – this is known as the pseudo-gravitational effect.
Photonic crystals are formed from a periodically arranged medium with different refractive indices. (Illustrative image).
The pseudo-gravitational effect is a phenomenon where a new type of crystal bends light similarly to a black hole, causing light to deviate from its normal straight path. Authors of a recent study, published in the journal Physical Review A, stated that this phenomenon could be utilized in 6G communication technology. As photonic crystals mimic what happens when light passes through black holes and other extremely dense objects in space, this new technique could also be applied to study quantum gravity, a theory that combines quantum mechanics and Einstein’s theory of relativity.
According to the theory of relativity, light and other electromagnetic waves are influenced by gravity. This is known as gravitational lensing, and astronomers have long used it to study massive cosmic objects like quasars. Reproducing this effect in a laboratory setting is challenging due to the need for enormous masses, but scientists have suspected for a long time that they could simulate this phenomenon using crystalline materials.
The Esherby twist has been used to create spiral nanowires similar to Christmas trees. (Illustrative image).
To achieve this goal, Kyoko Kitamura, a professor at the Graduate School of Engineering at Tohoku University in Japan, and her colleagues began with photonic crystals. They exploited a defect in the crystal known as helical distortion, a “flaw” in the ordered crystal structure that generates a twisting force – the “Esherby twist”, named after scientist John D. Esherby, has been used to create spiral nanowires resembling Christmas trees. However, this study marks the first time that the Esherby twisting technique has been used to create crystals made from layers of two-dimensional semiconductors stacked at atomic thickness.
The research team gradually twisted these crystals, disrupting the crystal lattice, then transmitted a beam through the crystals and observed their deflection. They found that the path of light within the crystal closely resembled its trajectory in a strong gravitational field. They also discovered that the angle at which light was deflected was related to the degree of distortion of the crystal.
The path of light within the crystal closely resembles its trajectory in a strong gravitational field. (Illustrative image).
Kitamura stated: “Just as gravity bends the trajectory of an object, we have found a way to bend light within a specific material.”
Controlling light in this manner presents a potential pathway for next-generation communication technology. The next generation of communication technology will need to transmit information at terahertz frequencies or above 100 gigahertz. Researchers believe that creatively controlling light is a way to achieve these frequencies. The new materials may also have applications in research.
Masayuki Fujita, an associate professor at Osaka University in Japan and a co-author of the study, stated in a statement: “Academically, these findings indicate that photonic crystals can harness gravitational effects, paving a new path in the field of graviton physics.”
There is a remarkable similarity between this formula and the formula describing the gravitational field. (Illustrative image).
The presence of helical distortion causes changes in the periodicity of the crystal, thus altering its optical properties. This change can be described by mathematical formulas. Researchers found a striking similarity between this formula and the one describing the gravitational field. This suggests that helical distortion could simulate the effects of a gravitational field.
An example of this effect is the deflection of light. When light passes through a crystal with helical distortion, it follows a curved path. This path closely resembles that of light in a strong gravitational field. This is the pseudo-gravitational effect.
One application of the pseudo-gravitational effect is in 6G communication technology. 6G communication technology refers to wireless communication technology that uses terahertz frequencies. It offers higher speeds and lower latency compared to current 5G communication technology. However, the propagation of terahertz waves is strongly attenuated and scattered by the atmosphere. Therefore, there is a need for technology that can effectively control the direction and shape of terahertz waves.
Another application of the pseudo-gravitational effect is the study of quantum gravity. (Illustrative image).
The pseudo-gravitational effect could provide such a technique. By changing the shape or size of the helical-distorted crystal, we can adjust the angle of light deflection. This way, we could achieve precise control of terahertz waves. This is highly beneficial for the development of 6G communication technology.
Another application of the pseudo-gravitational effect is in the study of quantum gravity. Quantum gravity is a theory that attempts to unify quantum mechanics and relativity. It can explain some challenging issues in physics, such as the singularity of black holes and the origin of the Big Bang. However, experimentally verifying quantum gravity is extremely difficult as it requires extreme conditions, such as extremely high energy and small scales.
The pseudo-gravitational effect may provide a new basis for experimentally verifying quantum gravity. It allows scientists to simulate the effects of a gravitational field in the lab and observe the behavior of photons. This could help us explore some phenomena and evidence of quantum gravity.
