The new quantum technology combines free electrons and photons

Faster computers, contactless communication, better car sensors – quantum technologies have the potential to revolutionize our lives, just as the invention of computers or the Internet once did. Experts around the world are trying to apply findings from basic research to quantum technologies. To that end, they often look for individual particles, such as photons—the elementary particles of light—with tailored properties.

However, obtaining individual particles is complicated and requires complicated methods. In a study recently published in the journal scienceresearchers now present a new method that simultaneously generates two individual particles in the form of a pair.

Fundamental quantum physics in electron microscopes

The international team from the Göttingen Max Planck Institute (MPI) for Multidisciplinary Sciences, the University of Göttingen and the Swiss Federal Institute of Technology in Lausanne (EPFL) succeeded in coupling free electrons and single photons in an electron microscope. In the Göttingen experiment, the beam from an electron microscope passes through an integrated optical chip fabricated by the Swiss team. The chip consists of a fiber-optic coupling and a ring-shaped resonator that stores light by keeping photons moving in a circular path.

“When an electron is scattered in the initially empty resonator, a photon is generated,” explains Armin Feist, scientist at MPI and one of the first authors of the study. “In the process, the electron loses exactly the amount of energy that the photon requires to be created from virtually nothing in the resonator. As a result, the two particles come together through their interaction and form a pair.” With an improved method of measurement, physicists could precisely detect the individual particles involved and their simultaneous manifestation.

Future quantum technology with free electrons

“With the electron-photon pair, we only need to measure one particle to get information about the energy content and temporal pattern of the second particle,” says Germaine Arend, a Ph.D. candidate at MPI and also the first author of the study. This allows researchers to use one quantum particle in an experiment while, at the same time, confirming its presence by detecting the other particle, in a so-called alarm scheme. Such a feature is necessary for many applications in quantum technology.

Max Planck director Claus Ropers sees electron-photon pairs as a new opportunity for quantum research. “The method opens up fascinating new possibilities in electron microscopy. In the field of quantum optics, entangled photon pairs already enhance imaging. With our work, such concepts can now be explored with electrons,” says Roper.

Tobias Kippenberg, professor at EPFL, adds, “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 pave the way for a new class of hybrid quantum technologies. .”