First observation of Cherenkov radiation phenomenon in 2D space

First observation of Cherenkov radiation phenomenon in 2D space

A single free electron propagates above the special layered structure the researchers designed, just a few tens of nanometers above it. During its motion, the electron emits discrete packets of radiation called “photons”. Between the electron and the photons it emits, a bond of “quantum entanglement” is formed. Credit: Ella Maru Studio

Researchers from the Andrew and Erna Viterbi Faculty of Electrical and Computer Engineering at the Technion-Israel Institute of Technology have presented the first experimental observation of Cherenkov radiation confined in two dimensions. The results represent a new record in electron-radiation coupling strength, revealing the quantum properties of radiation.

Cherenkov radiation is a unique physical phenomenon that has for many years been used in medical imaging and particle detection applications, as well as in laser-driven electron accelerators. The discovery by the Technion researchers links this phenomenon to future applications of photonic quantum computing and free-electron quantum light sources.

The study, which was published in Physical analysis X, was led by Ph.D. students Yuval Adiv and Shai Tsesses from the Technion, along with Hao Hu from Nanyang Technological University in Singapore (now a professor at Nanjing University in China). It was supervised by Prof. Ido Kaminer and Prof. Guy Bartal from the Technion, in collaboration with colleagues from China: Prof. Hongsheng Chen and Prof. Xiao Lin from Zhejiang University.

The interaction of free electrons with light underlies many known radiation phenomena and has led to numerous applications in science and industry. One of the most important of these interaction effects is Cherenkov radiation—the electromagnetic radiation emitted when a charged particle, such as an electron, travels through a medium at a speed greater than the phase speed of light in that specific medium. It is the optical equivalent of a supersonic boom, which occurs, for example, when a jet travels faster than the speed of sound. Consequently, Cherenkov radiation is sometimes called an “optical shock wave”. The phenomenon was discovered in 1934. In 1958, the scientists who discovered it received the Nobel Prize in Physics.

Since then, over 80 years of research, the investigation of Cherenkov radiation has led to the development of a multitude of applications, mostly for particle identification detectors and medical imaging. However, despite the intense concern with the phenomenon, most theoretical research and all experimental demonstrations have focused on Cherenkov radiation in three-dimensional space and based their description on classical electromagnetism.

Now, Technion researchers present the first experimental observation of 2D Cherenkov radiation, demonstrating that in two-dimensional space, the radiation behaves in a completely different way – for the first time, the quantum description of light is essential to explain the results of the experiment.

The researchers designed a special multilayer structure that allows interaction between free electrons and light waves traveling along a surface. Clever engineering of the structure enabled a first measurement of 2D Cherenkov radiation. The low size of the effect allowed a glimpse into the quantum nature of the process of radiation emission from free electrons: a count of the number of photons (quantum particles of light) emitted from a single electron and indirect evidence of electron strain. with the light waves they emit.

In this context, “entanglement” means the correlation between the properties of the electron and those of the emitted light, so that measuring one provides information about the other. It is worth noting that the 2022 Nobel Prize in Physics was awarded for conducting a series of experiments demonstrating the effects of quantum entanglement (in systems other than those demonstrated in the present research).

Yuval Adiv says: “The result of the study that surprised us the most concerns the efficiency of electron radiation emission in the experiment: while the most advanced experiments that preceded the present one achieved a regime in which approximately only one electron in a hundred emitted. radiation, here we were able to achieve an interaction regime in which each electron emitted radiation. In other words, we were able to demonstrate an improvement of more than two orders of magnitude in the interaction efficiency (also called the coupling strength). This result helps promote modern developments of efficient electron-driven radiation sources’.

Prof. Kaminer says: “The radiation emitted by electrons is an ancient phenomenon that has been researched for over 100 years and was assimilated into technology a long time ago, an example being the home microwave oven. For many years, it seemed that we had already discovered everything there was to know about electronic radiation, and thus the idea that this type of radiation had already been fully described by classical physics took root. In striking contrast to this concept, the experimental apparatus we have constructed allows for the quantum nature of electron radiation. to be revealed.

“The new experiment that has now been published explores the quantum-photonic nature of electron radiation. The experiment is part of a paradigm shift in how we understand this radiation and, more broadly, the relationship between electrons and the radiation they emit. For example, we now understand that free electrons can become entangled with the photons they emit. It is both surprising and interesting to see signs of this phenomenon in the experiment.”

Shai Tsesses says: “In Yuval Adiv’s new experiment, we forced electrons to travel near a photonic-plasmonic surface that we planned based on a technique developed in Professor Guy Bartal’s lab. The speed of the electron has been precisely set to achieve a high coupling strength, higher than that obtained in normal situations, where the coupling is to radiation in three dimensions. At the heart of the process, we observe the spontaneous quantum nature of the radiation emission, obtained in discrete packets of energy called photons. In this way, the experiment sheds new light on the quantum nature of photons.”

More information:
Yuval Adiv et al, Observation of 2D Cherenkov radiation, Physical analysis X (2023). DOI: 10.1103/PhysRevX.13.011002

Provided by Technion – Israel Institute of Technology

Citation: First observation of Cherenkov radiation phenomenon in 2D space (2023, January 18) Retrieved January 18, 2023 from

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