New Quantum Technology Connects Free Electrons And Photons

Researchers from Göttingen and Switzerland have succeeded for the first time in generating controlled electron-photon pairs in an electron microscope. Using a new measurement method, they were able to precisely identify the particles involved. The findings of the study expand the toolbox of quantum technology.

Faster computers, tap-proof communication, better sensors in cars - quantum technologies have the potential to revolutionize our lives just like the invention of computers or the Internet once did. Experts around the world are working on translating findings from basic research into quantum technologies. In order for this to succeed, they sometimes need individual particles, such as photons – the elementary particles of light – with special properties. Obtaining exactly individual particles, however, is laborious and requires complex methods. In a study recently published in the journal Science , researchers are now presenting a new process that creates two different individual particles in the form of a pair.

Basic quantum physics in the electron microscope
Scientists from the Max Planck Institute (MPI) for Multidisciplinary Natural Sciences in Göttingen, the University of Göttingen and the Swiss École Polytechnique Fédérale de Lausanne (EPFL)succeeded in coupling individual free electrons and photons together in an electron microscope. In the Göttingen experiment, the beam from an electron microscope passes through an integrated optical chip made by the Swiss team. This chip consists of a fiber optic coupling and a ring-shaped memory - a so-called resonator - that keeps moving light particles on a circular path. "When an electron interacts with the initially empty resonator, a photon is generated," explains Armin Feist, scientist at the MPI and one of the first authors of the study. "In doing so, the electron loses exactly the amount of energy that the photon needs to emerge from virtually nothing in the resonator: the two particles are connected to one another through their interaction and form an electron-photon pair.

Future quantum technology with free electrons
"What is special about the electron-photon pairs is that only one particle has to be measured in order to obtain information about the energy content and temporal occurrence of the second one," emphasizes Germaine Arend, PhD student at the MPI and also first author of the study. The researchers can use one quantum particle in an experiment and measure the other as a control at the same time. This is necessary for many applications in quantum technology.

Max Planck Director Claus Ropers sees a new opportunity for quantum research in the electron-photon pairs: “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 also be explored with electrons.” Tobias Kippenberg , Professor at EPFL, adds: “For the first time, we are bringing free electrons into the toolbox of quantum information science. In a broader sense, the coupling of free electrons and light using integrated photonics could open the way to a new class of hybrid quantum technologies.”