Evidence of Feshbach resonances between as


A team led by Prof. Dr. Tobias Schätz, Professor of Atomic and Quantum Physics at the Physics Institute of the University of Freiburg, Dr. Pascal alarm clock, Fabian Thielemann and colleagues show magnetic Feshbach resonances between a single barium ion and lithium atoms at a temperature close to absolute zero. The researchers found that the expansion of the ion and the atoms can be controlled depending on the strength of the external magnetic field. “At these ultra-cold temperatures, the collisions between the particles reveal their quantum mechanical nature,” explains Schätz. “Our research has shown that we are learning a little more about the possibilities of controlling the quantum mechanical properties of the wave-particle duality.” The group published its results in the journal nature.

Quantum effects dominate at ultra-low temperatures

In classical physics, the molecular formation of atoms and ions usually slows down as the temperature drops, until it finally becomes so cold that the individual particles stop and no collision or reaction can take place. The laws of quantum physics predict, however, that at ultra-low temperatures, quantum effects dominate rather than classical laws and that the collision of atoms and ions suddenly follows different rules. In the quantum range, where the so-called wave-particle dualism prevails, an ultra-cold temperature – just above absolute zero of -273.15 degrees Celsius – leads to an increase in collision rates. Because the particles can no longer be described as colliding spheres, but as wave packets that overlap, reinforce or cancel each other like water waves.

Feshbach resonances despite stronger interaction

The superimposition of the waves creates resonances, which the Freiburg researchers investigated. “Among other things, we found Feshbach resonances between barium ions and lithium atoms by controlling their interaction processes with the help of a magnetic field,” says Schätz. Feshbach resonances have already been demonstrated when slow atoms collide. However, the research group succeeded in doing this in a significantly different regime of the strong interaction that prevails due to the charge of the ion. In addition to magnetic fields, the scientists used ultra-high vacuum and light cages in their laboratory to isolate the laser-cooled atoms and ions.

“Basic research on quantum mechanics is increasingly leaving the laboratory and entering the real world. By studying the effects under idealized conditions in the laboratory, we can better understand them and use them in a targeted and extensive manner – from curiosity and the perspective of controlling and increasing the efficiency of chemical reactions to the search for new ways of charge flow in solids, ”says Schätz.

Quantum Science and Technologies on the European Campus”

Prof. Dr. Tobias Schätz is a member of the steering committee of the international doctoral college “Quantum Science and Technologies at the European Campus”, or QUSTEC for short. In spring 2019, the European Commission approved the application for funding the program in quantum science on the European Campus (EUCOR). In addition to Freiburg, the universities of Basel and Strasbourg, the Karlsruhe Institute of Technology (KIT) and the research department of the IT group IBM in Zurich are involved. The program funds a doctorate for 40 quantum researchers; the universities involved will offer a further 40 doctoral positions. It runs for five years and is funded with 9.1 million euros. 4.2 million come from the EU, the rest from partners and other donors.

Original publication

Weckesser, P., Thielemann, F., Wiater, D., Wojciechowska, A., Karpa, L., Jachymski, K., Tomza, M., Walker, T., Schaetz T. (2021): Observation of Feshbach Resonances between a single ion and ultra-cold atoms. In: nature. DOI: 10.1038 / s41586-021-04112-y


Prof. Dr. Tobias Schätz
Institute for Physics
University of Freiburg
Tel .: 0761 / 203-5815
E-mail: [email protected]

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