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Changing interactions between the smallest particles at the touch of a button: Quantum researchers at RPTU have developed a new tool that makes this possible. The new approach—a temporally oscillating magnetic field—has the potential to significantly expand fundamental knowledge in the field of quantum physics. It also opens completely new perspectives on the development of new materials.
Computer chips, imaging techniques such as magnetic resonance imaging, laser printers, transistors, and navigation systems: many milestones in our modern everyday world would not have been possible without the discoveries of quantum physics. What is remarkable is that it was only about a hundred years ago that physicists discovered that the world at the smallest scales cannot be explained by the laws of classical physics. Atoms and their components, protons, neutrons, and electrons – but also light particles – sometimes exhibit physical behaviors that are unknown in the macroscopic world. To this day, the quantum world therefore holds unclear and surprising phenomena that – once understood and controllable – could revolutionize future technologies.
Researchers at RPTU are at the forefront when it comes to expanding this fundamental knowledge in the field of quantum physics. Among other things, they are working on the question of how individual atoms can be controlled in a targeted manner. To do this, they use ultracold gases, among other things, to study atoms and their quantum mechanical behavior.
In a recent study, the researchers discovered how the interactions between atoms in an ultracold gas can be precisely controlled by “driving” them periodically over time. Professor Artur Widera, who researches and teaches quantum physics at RPTU, explains: “Normally, so-called Feshbach scattering resonances are used in such systems.” This means that an external magnetic field can cause the atoms to interact in ways ranging from barely measurable to extremely strong attraction or repulsion.
What is new about the approach taken by the RPTU researchers is that they use a temporally oscillating magnetic field to generate additional Floquet scattering resonances. These Floquet scattering resonances occur in addition to Feshbach scattering resonances, but their properties can be controlled over a very wide range by the strength and frequency of the magnetic field oscillation used. This means that the interaction of quantum mechanical systems can now be adjusted in situations where the experiment was previously fixed at a single value.
Another recently published paper provides the corresponding theoretical foundation: In it, the RPTU researchers prove that the observed resonances are based on dynamically generated bound states. “These states exist only thanks to temporal modulation and can dramatically change the scattering behavior of the atoms,” says Professor Sebastian Eggert, who researches and teaches the fundamentals of solid-state and many-body systems at RPTU.
Tailoring resonances and interactions
In summary, both experimental and theoretical work show that resonances and interactions can be tailored using the new tool. Artur Widera: “We can control quantum gases in experiments to achieve previously unattainable states. And we can do this for as long as we want.” Researchers can now specifically control whether particles repel each other or not: “At the push of a button, our neutral particles can suddenly interact in a completely different way; if they had a charge, we could adjust the charge continuously, so to speak. Matter suddenly takes on different interaction properties. With the new tool, all this is possible”, emphasizes Widera.
The new development opens numerous perspectives for quantum physics – both in terms of basic research and with a view to possible applications: Not only could exotic states of matter that we do not yet know about be explored in this way, for example. Solid-state systems can be simulated, and states of matter can be changed in a simulation at the touch of a button. This tool could also open completely new perspectives in the development of new materials.
Prof. Dr. Artur Widera
Individual Quantum Systems
Department of Physics
Email: widera[at]physik.uni-kl.de
Prof. Dr. Sebastian Eggert
Fundamentals of Solid State and Many-Body Systems
Department of Physics
Email: eggert[at]physik.uni-kl.de
Understanding Floquet Resonances in Ultracold Quantum Gas Scattering, July 2025, Physical Review Letters 135(3):033402, DOI:10.1103/47xs-223h
Floquet engineering of Feshbach resonances in ultracold gases, October 2025, Science Advances 11(40), DOI:10.1126/sciadv.adw3856
RPTU researchers expand knowledge in the field of quantum physics: Prof. Dr. Artur Widera, doctoral ...
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RPTU researchers expand knowledge in the field of quantum physics: Prof. Dr. Artur Widera, doctoral ...
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