From The Swiss Federal Institute of Technology in Lausanne [EPFL-École Polytechnique Fédérale de Lausanne] (CH): “New quantum technology combines free electrons and photons”

From The Swiss Federal Institute of Technology in Lausanne [EPFL-École Polytechnique Fédérale de Lausanne] (CH)

Andrea Testa
Guanhao Huang

Scientists from EPFL, the Max Planck Institute for Multidisciplinary Sciences and the University of Göttingen have successfully created electron-photon pairs for the first time in a controlled way, using integrated photonic circuits on a chip. Using a new technique, they could precisely detect the involved particles. The findings of the study expand the toolbox of quantum technology.

Faster computers, tap-proof communication, sensors beyond standard quantum limit – quantum technologies have the potential to revolutionize our lives just as once the invention of computers or the internet. Experts worldwide are trying to implement findings from basic research into quantum technologies.

To this end, they sometimes require individual particles, such as photons – the elementary particles of light – with special properties. However, obtaining individual particles is complicated and requires complex methods. Various applications already use free electrons to generate light, such as the case in X-ray tubes.

In a new study, recently published in the journal Science [below], scientists from EPFL’s Laboratory of Photonics and Quantum Measurement, Göttingen Max Planck Institute for Multidisciplinary Sciences (MPI-NAT) and the University of Göttingen demonstrate a novel method for generating cavity-photons using free electrons, in a form of pair states. To do so, they used chip-based photonic integrated circuits in an electron microscope.

An optical chip with ring-shaped light storage, called a microring resonator, and a fiber-optic coupling. The chip is only three millimeters wide, and the ring resonator at its tip has a radius of 0.114 millimeters. © Armin Feist / Max Planck Institute for Multidisciplinary Sciences.

Fundamental Particle Physics in Electron Microscopes

In the experiment, the beam of an electron microscope passes on a built-in integrated photonic chip, consisting of a micro-ring resonator and optical fiber output ports. This new approach, using photonic structures fabricated at EPFL for transmission electron microscope (TEM) experiments performed at MPI-NAT, was established in a recent study [Nature (below)].

Whenever an electron interacts with the vacuum evanescent field of the ring resonator a photon can be generated. In this process, obeying the laws of energy and momentum conservation, the electron loses the energy quantum of a single photon. Through this interaction, the system evolves into a pair state. Thanks to a newly developed measurement method, the scientists could precisely detect simultaneously both electron energy and generated photons, revealing the underlying electron-photon pair states.

Future quantum technology with free electrons

Besides observing this process for the first time at the single particle level, these findings implement a novel concept for generating single-photon or electron. Specifically, the measurement of the pair state enables heralded particle sources, where the detection of one particle signals the generation of the other. This is necessary for many applications in quantum technology and adds to its growing toolset.

“The method opens up fascinating new possibilities in electron microscopy. In the field of quantum optics, entangled photon pairs already improve imaging. With our work, such concepts can now be explored with electrons,” explains Claus Ropers, MPI-NAT Director.

In the first proof-of-principle experiment, the researchers make use of the generated correlated electron-photon pairs for photonic mode imaging, achieving a three-orders of magnitude contrast enhancement. Dr. Yujia Yang, a postdoc at EPFL and a co-lead author of the study, adds: “We believe our work has a substantial impact on the future development in electron microscopy by harnessing the power of quantum technology.”

A particular challenge for future quantum technology is how to interface different physical systems. “For the first time, we bring free electrons into the toolbox of quantum information science. More broadly, coupling free electrons and light using integrated photonics could open the way to a new class of hybrid quantum technologies,” says Tobias Kippenberg, professor at EPFL and head of the Laboratory of Photonics and Quantum Measurement.

The work from the collaboration between the two teams contributes to the currently emerging field of free-electron quantum optics, and demonstrates a powerful experimental platform for event-based and photon-gated electron spectroscopy and imaging. “Our work represents a critical step to utilize quantum optics concepts in electron microscopy. We plan to further explore future directions like electron-heralded exotic photonic states, and noise reduction in electron microscopy,” says Guanhao Huang, PhD student at EPFL and co-lead author of the study.

Science papers:
Nature 2021

See the full article here .


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The Swiss Federal Institute of Technology in Lausanne [EPFL-École Polytechnique Fédérale de Lausanne] (CH) is a research institute and university in Lausanne, Switzerland, that specializes in natural sciences and engineering. It is one of the two Swiss Federal Institutes of Technology, and it has three main missions: education, research and technology transfer.

The QS World University Rankings ranks EPFL(CH) 14th in the world across all fields in their 2020/2021 ranking, whereas Times Higher Education World University Rankings ranks EPFL(CH) as the world’s 19th best school for Engineering and Technology in 2020.

EPFL(CH) is located in the French-speaking part of Switzerland; the sister institution in the German-speaking part of Switzerland is The Swiss Federal Institute of Technology ETH Zürich [Eidgenössische Technische Hochschule Zürich] (CH). Associated with several specialized research institutes, the two universities form The Domain of the Swiss Federal Institutes of Technology (ETH Domain) [ETH-Bereich; Domaine des Écoles Polytechniques Fédérales] (CH) which is directly dependent on the Federal Department of Economic Affairs, Education and Research. In connection with research and teaching activities, EPFL(CH) operates a nuclear reactor CROCUS; a Tokamak Fusion reactor; a Blue Gene/Q Supercomputer; and P3 bio-hazard facilities.

ETH Zürich, EPFL (Swiss Federal Institute of Technology in Lausanne) [École Polytechnique Fédérale de Lausanne](CH), and four associated research institutes form The Domain of the Swiss Federal Institutes of Technology (ETH Domain) [ETH-Bereich; Domaine des Écoles polytechniques fédérales] (CH) with the aim of collaborating on scientific projects.

The roots of modern-day EPFL(CH) can be traced back to the foundation of a private school under the name École Spéciale de Lausanne in 1853 at the initiative of Lois Rivier, a graduate of the École Centrale Paris (FR) and John Gay the then professor and rector of the Académie de Lausanne. At its inception it had only 11 students and the offices were located at Rue du Valentin in Lausanne. In 1869, it became the technical department of the public Académie de Lausanne. When the Académie was reorganized and acquired the status of a university in 1890, the technical faculty changed its name to École d’Ingénieurs de l’Université de Lausanne. In 1946, it was renamed the École polytechnique de l’Université de Lausanne (EPUL). In 1969, the EPUL was separated from the rest of the University of Lausanne and became a federal institute under its current name. EPFL(CH), like ETH Zürich (CH), is thus directly controlled by the Swiss federal government. In contrast, all other universities in Switzerland are controlled by their respective cantonal governments. Following the nomination of Patrick Aebischer as president in 2000, EPFL(CH) has started to develop into the field of life sciences. It absorbed the Swiss Institute for Experimental Cancer Research (ISREC) in 2008.

In 1946, there were 360 students. In 1969, EPFL(CH) had 1,400 students and 55 professors. In the past two decades the university has grown rapidly and as of 2012 roughly 14,000 people study or work on campus, about 9,300 of these being Bachelor, Master or PhD students. The environment at modern day EPFL(CH) is highly international with the school attracting students and researchers from all over the world. More than 125 countries are represented on the campus and the university has two official languages, French and English.


EPFL is organized into eight schools, themselves formed of institutes that group research units (laboratories or chairs) around common themes:

School of Basic Sciences
Institute of Mathematics
Institute of Chemical Sciences and Engineering
Institute of Physics
European Centre of Atomic and Molecular Computations
Bernoulli Center
Biomedical Imaging Research Center
Interdisciplinary Center for Electron Microscopy
MPG-EPFL Centre for Molecular Nanosciences and Technology
Swiss Plasma Center
Laboratory of Astrophysics

School of Engineering

Institute of Electrical Engineering
Institute of Mechanical Engineering
Institute of Materials
Institute of Microengineering
Institute of Bioengineering

School of Architecture, Civil and Environmental Engineering

Institute of Architecture
Civil Engineering Institute
Institute of Urban and Regional Sciences
Environmental Engineering Institute

School of Computer and Communication Sciences

Algorithms & Theoretical Computer Science
Artificial Intelligence & Machine Learning
Computational Biology
Computer Architecture & Integrated Systems
Data Management & Information Retrieval
Graphics & Vision
Human-Computer Interaction
Information & Communication Theory
Programming Languages & Formal Methods
Security & Cryptography
Signal & Image Processing

School of Life Sciences

Bachelor-Master Teaching Section in Life Sciences and Technologies
Brain Mind Institute
Institute of Bioengineering
Swiss Institute for Experimental Cancer Research
Global Health Institute
Ten Technology Platforms & Core Facilities (PTECH)
Center for Phenogenomics
NCCR Synaptic Bases of Mental Diseases

College of Management of Technology

Swiss Finance Institute at EPFL
Section of Management of Technology and Entrepreneurship
Institute of Technology and Public Policy
Institute of Management of Technology and Entrepreneurship
Section of Financial Engineering

College of Humanities

Human and social sciences teaching program

EPFL Middle East

Section of Energy Management and Sustainability

In addition to the eight schools there are seven closely related institutions

Swiss Cancer Centre
Center for Biomedical Imaging (CIBM)
Centre for Advanced Modelling Science (CADMOS)
École Cantonale d’art de Lausanne (ECAL)
Campus Biotech
Wyss Center for Bio- and Neuro-engineering
Swiss National Supercomputing Centre