First observation of the phenomenon of Cherenkov radiation in 2D space

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

cherenkov radiation it is a unique physical phenomenon, which for many years has been used in medical imaging and particle detection applications, as well as in laser-driven electron accelerators. The breakthrough made 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 exam X, was in charge of the Ph.D. Technion students Yuval Adiv and Shai Tsesses, along with Hao Hu from Nanyang Technological University in Singapore (now a professor at Nanjing University in China). He 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 is the basis of many known radiation phenomena and has given rise to numerous applications in science and industry. One of the most important interaction effects is Cherenkov radiation:electromagnetic radiation Emitted when a charged particle, such as an electron, travels through a medium at a speed greater than the phase velocity of light in that specific medium. It is the optical equivalent of a supersonic boom, which occurs, for example, when an airplane travels faster than the speed of sound. Consequently, Cherenkov radiation is sometimes called “optical shock wave”. The phenomenon was discovered in 1934. In 1958, the scientists who discovered it received the Nobel Prize in Physics.

Since then, during more than 80 years of research, Cherenkov radiation research has led to the development of a large number of applications, most of them for particle identification detectors and medical imaging. However, despite the intense concern about the phenomenon, most of the theoretical research and all the experimental demonstrations concerned 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, showing that in two-dimensional space, the radiation behaves in a completely different way: for the first time, a 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 allowed a first measurement of 2D Cherenkov radiation. The low dimensionality of the effect allowed a glimpse of the quantum nature of the free electron radiation emission process: a count of the number of photons (quantum particles of light) emitted by a single electron and indirect evidence of the entanglement of electrons with the light waves they emit.

In this context, “entanglement” means correlation between the properties of the electron and those of the emitted light, such that measuring one provides information about the other. It should be noted that the 2022 Nobel Prize in Physics was awarded for carrying out a series of experiments that demonstrated the effects of quantum entanglement (in systems other than those demonstrated in the present investigation).

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

Prof. Kaminer says: “Radiation emitted by electrons is an ancient phenomenon that has been investigated for over 100 years and was assimilated into technology long ago, an example being the household microwave oven. For many years, it seemed that we had already discovered all there was to know about electron radiation, and thus the idea that this type of radiation had already been fully described by classical physics took hold.In stark contrast to this concept, the apparatus experimental we built allows 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 the way we understand this radiation and, more broadly, the relationship between electrons and radiation that “They emit. For example, we now understand that free electrons can become entangled with the photons they emit. It’s surprising and exciting to see signs of this phenomenon in experiment.”

Shai Tsesses says: “In Yuval Adiv’s new experiment, we force electrons to travel close to a photonic-plasmonic surface that I mapped out based on a technique developed in Professor Guy Bartal’s lab. The speed of the electrons was established with precision to obtain a large coupling strength, greater 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 some ways, the experiment sheds new light on the quantum nature of photons.”