A group of researchers from the University of Warsaw in Poland, the Military University of Technology in Poland, and the British University ofSouthampton have shown that it is possible to control exceptional points. Physicists have never seen the annihilation of exceptional points from different points. You can read about the discovery that could lead to the creation of modern optical devices.
Most of the particles that make up the universe have anti particles. Matter and antimatter meet each other and are destroyed. Physicists have been able to create quasiparticles and quasiantiparticles in a wide range of materials.
Jacek Szczytko is a professor of physics at the University of Warsaw.
It would be hard to understand transistors, light-emitting diodes, superconductors and some quantum computers without quasiparticles. If mathematical concepts can be implemented in physical systems, they can become quasi particles. There are exceptional points in one of the abstract concepts.
Theorists from France explain.
Malpuech says that there are specific system parameters that lead to the commonality of two different solutions that can only be found in systems with losses.
They allow the creation of efficient sensors. Each exceptional point has a mathematical feature that allows you to determine which exceptional point will be the antiparticle for another exceptional point.
The scientists from the University of Warsaw and the Military University of Technology analyzed the optical resonator filled with liquid crystal. Liquid crystals are special phases of matter that have different directions.
It can be probed by a light beam, which behaves differently depending on the direction of incidence. The basis for the operation of common liquid crystal displays is based on this feature. The direction of optical axes and the direction of the liquid crystal are related to the direction of the light.
The liquid crystal layer was placed between two mirrors. Through the entire structure, only light with a specific wavelength can be seen.
The so-called cavity resonance modes are light with a certain color and direction of propagation. The situation where a photon can bounce between the two mirrors is similar to this one.
The presence of a liquid crystal allows the energy of the cavity modes to be adjusted. The resonance condition can change when the light is incident at an angle, which can lead to different modes intersecting with each other.
When considering an ideal structure without any losses, only the four specific incidence angles of light should be considered. Light can be scattered or escaped through imperfect mirrors.
The average time the photon stays inside the microcavity can be determined with the help of spectroscopic measurement. Due to the orientation of the liquid crystal layer, a difference was seen in the scattering of light. A pair of exceptional points were observed for which both the energy and lifetime of the photon were the same.
The experiment shows that the position of exceptional points can be changed by changing the voltage applied to the cavity. As the electric bias is reduced, the exceptional points created from different degeneracy points get closer to each other, and so on. The approaching points have an opposite charge and disappear at the time of the encounter.
The annihilation of exceptional points from different points has never been observed before. The annihilation of exceptional points was shown in earlier work, but they appeared and vanished at the same locations.
Many different areas of physics have been studying exceptional points. Barbara Pietka from the Faculty of Physics at the University of Warsaw says that their discovery will allow the creation of optical devices.
More information: M. Król et al, Annihilation of exceptional points from different Dirac valleys in a 2D photonic system, Nature Communications (2022). DOI: 10.1038/s41467-022-33001-9 Journal information: Nature Communications
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