The Cherenkov radiation phenomena was first seen in two dimensions

 

By Technion Israel Institute of Technology 

January 18, 2023

                                          The first experimental observation of Cherenkov radiation limited in two dimensions has been made by researchers at the Technion—Israel Institute of Technology's Andrew and Erna Viterbi Faculty of Electrical and Computer Engineering. The results show the radiation's quantum characteristics and set a new record for electron-radiation coupling strength.

Cherenkov radiation is a rare physical phenomena that has been employed for many years in laser-driven electron accelerators, particle detection applications, and medical imaging. The discovery made by the Technion team ties this phenomena to upcoming uses for free-electron quantum light sources and photonic quantum computers.

Ph.D. candidates Yuval Adiv and Shai Tsesses from the Technion, as well as Hao Hu from Nanyang Technological University in Singapore, led the work, which was published in Physical Review X. (today professor at Nanjing university in China). Professors Guy Bartal and Ido Kaminer of the Technion served as its directors, working along with professors Hongsheng Chen and Xiao Lin of Zhejiang University from China.

Various known radiation events are caused by the interaction of free electrons with light, which has numerous scientific and industrial uses. The Cherenkov radiation, an electromagnetic radiation produced when a charged particle, such as an electron, moves through a medium at a speed faster than the phase velocity of light in that particular medium, is one of the most significant of these interaction effects. It is an optical representation of a supersonic boom, which happens when a jet travels faster than the speed of sound, for example. As a result, a "optical shock wave" is a term occasionally used to describe Cherenkov radiation. In 1934, the phenomena was identified. The researchers who found it received the Nobel Prize in Physics in 1958.

Since then, during the course of more than 80 years of study, Cherenkov radiation has been the subject of several applications, the majority of which are for particle identification detectors and medical imaging. Despite the significant interest in the phenomena, the majority of theoretical study and all practical demonstrations focused on Cherenkov radiation in three-dimensional space and their descriptions were based on classical electromagnetism.

The Technion researchers have now made the first experimental observation of 2D Cherenkov radiation, proving that radiation behaves quite differently in two-dimensional space. This is the first time that the quantum description of light is necessary to explain the experiment's findings.

The scientists created a unique multilayer structure that allows free electrons and light waves propagating along a surface to interact. The structure's clever architecture made it possible to take the first measurement of 2D Cherenkov radiation. A count of the number of photons (quantum particles of light) emitted from a single electron and indirect proof of the entanglement of the electrons with the light waves they emit were both made possible by the low dimensionality of the effect, which provided a glimpse into the quantum nature of the process of radiation emission from free electrons.

Entanglement in this case refers to a correlation between the characteristics of the electron and those of the light produced, such that learning more about one by measurement of the other. It is noteworthy that the execution of a series of experiments proving the effects of quantum entanglement resulted in the awarding of the 2022 Nobel Prize in Physics (in systems different to those demonstrated in the present research).

Says Yuval Adiv: "The experiment's efficiency at emitting radiation from electrons is what surprised us the most about the study's findings. Whereas the most sophisticated experiments that came before this one were able to reach an interaction regime in which only about one electron in 100 emit radiation, we were able to do so here. In other words, we were able to show an increase in interaction efficiency of almost two orders of magnitude (also called the coupling strength). This outcome advances current research towards effective electron-driven radiation sources."

According to Professor Kaminer, "Radiation released by electrons is an ancient phenomena that has been studied for more than 100 years and has been absorbed into technology for a very long period, with the home microwave oven being one example. The belief that classical physics had adequately characterised this type of radiation for many years since it seemed that we had learned everything there was to know about electron radiation. The experimental setup we constructed makes it possible to demonstrate the quantum character of electron radiation, which stands in stark contrast to this idea.

"The recently reported experimental experiment investigates the quantum-photonic properties of electron radiation. The experiment is a part of a paradigm change in how we think about this radiation and, in a broader sense, how electrons interact with the radiation they generate. For instance, we now know that free electrons may interact with the photons they release to form entangled states. The experiment has revealed intriguing and unexpected aspects of this phenomena."

Says Shai Tsesses "In Yuval Adiv's latest experiment, we compelled the electrons to pass close to a photonic-plasmonic surface that I designed using a method used in Prof. Guy Bartal's group. In order to get a strong coupling, more than that typically attained when coupling is to radiation in three dimensions, the electron velocity was precisely regulated. We detect the spontaneous quantum character of radiation emission, which is produced in discrete energy packets known as photons, at the core of the process. The experiment provides fresh insight into the quantum nature of photons in this way."

Under the terms of a Creative Commons licence, this article has been taken from PHYSOORG. Go here to read the original article.