Since time immemorial, looking up at the night sky has sparked a magical fascination and longing. Today, modern space probes and satellites provide ever higher resolution images and information of celestial bodies and galaxies, constantly expanding our knowledge of the universe. Nevertheless, central questions about the origin and development of the universe are still unanswered, which researchers want to decipher using innovative technologies.

“Numerous astronomical observations and realistic models of the origin of the universe suggest that the directly observable part of the universe represents only a fraction of the entire cosmos, and that a large part consists of unknown, invisible, so-called dark matter,” explains Dr. Theo Scholtes, head of the Quantum Magnetometry Group from the ­Quantum Systems Research Department at Leibniz IPHT. “While the existence of this dark matter is widely accepted in science, its nature remains unclear. Therefore, it is being searched for in numerous and very different experiments worldwide.”

A physically well-motivated ­hypothesis is that dark matter particles are so-called axions, or axion-like particles, particles with very small masses that may be able to form structures, such as axion walls or stars, and interact with the spins of “conventional” atoms. With the “Global Network of Optical Magnetometers for the Search for Exotic Physics” (GNOME), researchers are currently searching for signatures of such exotic objects.

To this end, GNOME currently connects up to 17 stations around the globe with highly sensitive optical ­magnetometers. One of these ­stations is operated by ­Leibniz IPHT at the Moxa Geodynamic ­Observatory of the Friedrich Schiller University Jena. “I developed the first version of the setup as a postdoctoral researcher at the University of Fribourg (Switzerland) and was able to continue the work seamlessly when I returned to Leibniz IPHT. I am very grateful to both sides for this,” says Dr. Theo Scholtes.

If the earth passes through a structure of exotic matter, it can interact with the atomic gas contained in the GNOME magnetometers. The changing optical properties of the atoms in the synchronized sensors are detected by laser light. The search for correlations in the data from the stations allows the detection of cosmic events, and thus to draw conclusions about dark matter.

In first comprehensive long-term measurements, no exotic cosmic events could be observed yet, but free parameters of some dark matter models could already be constrained. The collaboration is currently working on making the magnetometers even more sensitive to exotic interactions. In this way, the search for dark matter will be further advanced in the future, and its nature clarified.

In addition to the search for dark matter, optically pumped magnetome­ters also support ­biomedical applications, and can ­detect the smallest magnetic signals, such as heart and brain activity.

In the picture:
The atoms are located in a special glass vapor cell that tracks signals from the exotic matter in a magnetically very well-shielded setup.
©Sven Döring