Achieving Single-Electron–Single-Photon Interaction in a Transmission Electron Microscope Using 2D Cherenkov Radiation
Yuval Adiv a, Ido Kaminer a, Guy Bartal a, Shai Tsesses a, Raphael Dahan a, Kangpeng Wang a, Yaniv Kurman a, Hao Hu b, Xiao Lin c, Hongsheng Chen c, Alexey Gorlach a
a Technion - Israel Institute of Technology, Electrical Engineering Department, Haifa, Israel
b Novitas, Nanoelectronics Centre of Excellence, School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore, Singapore
c Interdisciplinary Center for Quantum Information, State Key Laboratory of Modern Optical Instrumentation, ZJU-Hangzhou Global Science and Technology Innovation Center
Proceedings of Electron Beam Spectroscopy for Nanooptics 2021 (EBSN2021)
Online, Spain, 2021 June 14th - 15th
Organizers: Mathieu Kociak and Nahid Talebi
Poster, Yuval Adiv, 031
Publication date: 8th June 2021

Over 80 years of research into free-electron radiation have not yet changed its popular description as a three-dimensional, classical electromagnetic wave1–5, best exemplified by the Cherenkov effect – the radiation of charged particles exceeding the speed of light in a medium1,6. Free-electron radiation was predicted to fundamentally change in reduced dimensionality7–9 and to exhibit novel phenomena due to the quantized nature of the electromagnetic field10–12. However, neither has been demonstrated experimentally.

Here, we present the first observation of the two-dimensional Cherenkov effect, wherein free electrons emit narrow-bandwidth surface polaritons and shift their energy following the Cherenkov condition. The dimensionality and bandwidth of the effect enable a quantum coupling strength over two orders of magnitude larger than in previous experiments13–20, leading to a single-electron–single-polariton interaction. This observation brings us to the regime of ultrastrong coupling between a free electron and a polariton, which is manifested by several quantized emission events in the electron energy loss spectrum (EELS).

To reach the regime of single-electron–single-photon interaction, we combined a dispersion-engineered structure21,22 supporting surface polariton modes, with the high electron beam quality of a transmission electron microscope. Our results show the first example of electromagnetic field quantization in a coherent cathodoluminescence process, where the EELS measurement is directly correlated to emission of a polariton Fock state.

As a future outlook our findings pave the way to discovering previously-unexplored phenomena in free-electron quantum optics12,23, facilitating the use of free electrons for quantum information applications24,25 and as bright quantum emitters for heralded single- and multi-photon states26–29.

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