Quantum physics deals with the laws of nature in the atomic and subatomic range. The knowledge gained from this has enabled the development of computer chips, nuclear magnetic resonance tomographs and navigation systems, for example. At the Rhineland-Palatinate University of Kaiserslautern-Landau, Professor Dr. Artur Widera and his research group are conducting research into quantum physics. In a current research project, they present a quantum motor that cannot be described in the classical sense using thermodynamic principles. The motor is driven by quantum mechanics, not by heat transfer. The corresponding paper has been published in the journal Nature.
Classic engines are heat engines and follow the laws of thermodynamics. They convert the heat energy released when fuel is burned into mechanical energy or kinetic energy via compression in a piston. The idea of transferring an engine to the quantum world is not new. Professor Artur Widera had already shown in a previous research project that it is possible to operate a quantum heat engine stably and efficiently. Now, together with colleagues from the University of Stuttgart and the Okinawa Institute of Science and Technology in Japan, he and his research group have succeeded in developing a quantum motor that uses a different, purely quantum mechanical phenomenon as a drive.
Energy difference as a drive
"In the quantum world, or at the atomic level, we distinguish between two classes of particles: Bosons and fermions," explains Jennifer Koch, research associate in the working group and first author of the study. "These differ in one property, namely their intrinsic angular momentum or spin." When a large number of bosons and fermions come together in a so-called atom trap in an ultracold environment (in which thermal effects play no role), the following happens: "If the bosons are not guided by thermal energy, they remain energetically in their ground state and join each other," explains the physicist. "The fermions, on the other hand, follow the Pauli principle." The Pauli principle states that two identical fermions cannot be in the same energy state. Instead, they move away from each other and assume different excitation states or increasing energy levels. The crucial point for research: "The total energy of the fermion ensemble is higher," summarizes Koch.
In order to tap into the energy difference between the different particle ensembles, the research team took advantage of the fact that fermions are readily convertible under suitable experimental conditions. The physicist explains: "We combined the fermions in pairs - this created bosons. We have thus created a quantum mechanical alternative to igniting a fuel that can be used to operate our quantum engine."
Thermodynamics - yes or no?
The proof of concept has therefore been successful. What will happen with the findings? "At the moment, we are still a long way from a concrete application because our development only works under special test conditions. However, I am convinced that there is valuable potential in our basic research that can provide inspiration for new applications in solid-state physics, for example in superconductors, where fermionic electrons also conduct electricity as pairs without loss," Widera sums up. "Our motor already had a good performance compared to a standard machine. And the more particles the ensembles contain, the higher energy levels and therefore energy yields can be achieved," says Widera. Professor Eric Lutz, one of the co-authors of the study, adds another aspect: "The topic is extremely exciting from the point of view of the scientific community. We are initiating a discussion about how the experimental results should be classified from a scientific point of view. Can we use the laws of thermodynamics? If not, how do we describe the processes that make our engine run?" And Professor Thomas Busch, whose team from Japan was involved in the theoretical modeling, adds: "These questions help to advance our knowledge of the world of the smallest particles and to understand how we can use their properties for further technical innovations."
Together to success
The Kaiserslautern research team, which was responsible for managing the project, included Professor Artur Widera, Jennifer Koch and Sian Barbosa. The project partners included researchers from the Okinawa Institute of Science and Technology (OIST) in Japan - Professor Thomas Busch, Eloisa Cuestas, Keerthy Menon and Thomas Fogarty. They provided the theoretical models for the experimental approach. Also involved was Professor Eric Lutz from the University of Stuttgart (Theoretical Physics), who contributed his expertise in thermodynamics.
The study "A quantum engine in the BEC-BCS crossover" can be viewed in the renowned scientific journal Nature: https://www.nature.com/articles/s41586-023-06469-8
Bibliographic information on the published study:
A quantum engine in the BEC-BCS crossover
Jennifer Koch, Keerthy Menon, Eloisa Cuestas, Sian Barbosa, Eric Lutz, Thomas Fogarty, Thomas Busch, and Artur Widera
Nature, Volume 621 Issue 7980, September 28, 2023
DOI: 10.1038/s41586-023-06469-8
Answer questions:
Dipl.-Phys. Jennifer Koch
Phone: 0631 205 5272
E-Mail: jekoch@rptu.de
Prof. Dr. Artur Widera
Phone: 0631 205-4130
E-Mail: widera@rptu.de
About the RPTU
Since January 1, 2023, the Technical University of Kaiserslautern and the University of Landau together form the Rhineland-Palatinate Technical University of Kaiserslautern-Landau. With over 20,000 students and more than 300 professors, RPTU is the second largest academic institution in the state. As a place of top international research and an academic talent factory for business and science, RPTU offers excellent study and research conditions as well as a cosmopolitan environment. RPTU is also an innovation and transfer partner for politics, business and society. Anyone who studies, learns, researches or works at RPTU is part of a vibrant university community and shapes the world of tomorrow.