Study: RPTU researchers develop motor with quantum mechanical drive

Quantum physics deals with the laws of nature in the atomic and subatomic range. Findings gained from this research have, for example, enabled the development of computer chips, nuclear magnetic resonance tomographs or navigation systems. At the University of Kaiserslautern-Landau (RPTU), Professor Dr. Artur Widera and his research group do research on quantum physics. In a current research paper, they present a quantum motor that cannot be described in the classical sense with thermodynamic principles. The drive is based on quantum mechanics, not on heat transfer. The associated paper has been published in the journal “Nature”.  

Classical engines are heat engines and follow the laws of thermodynamics. They convert thermal energy released during the combustion of fuel into mechanical or kinetic energy through combustion in a piston. The idea of bringing an engine into the quantum world is not new. Professor Artur Widera had already shown in a past research paper that it is possible to operate a quantum heat engine in a stable and efficient manner. 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 its drive.

Energy difference as a drive
“In the quantum world, or at the atomic level, we distinguish between two categories of particles: Bosons and fermions,” explains Jennifer Koch, a research associate in the group and first author of the study. “They differ in one characteristic and that is their intrinsic angular momentum or spin.” When a large number of bosons and fermions each gather in a so-called atom trap in an ultra-cold environment (where thermal effects do not play a role), the following happens: “If the bosons are not directed by thermal energy, they remain energetically in the ground state and join each other,” the physicist explains. “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, adopting different excited states or increasing energy levels. The crucial key point for the research as follows: “The total energy of the fermion ensemble is higher,” Koch sums up.

In order to exploit the energy difference between the different particle ensembles, the research team benefited from the fact that fermions are transformative under suitable experimental conditions. The physicist explains as follows: “We united the fermions in pairs in each case - thereby creating bosons. In this way, we have created a quantum mechanical alternative to igniting a fuel, which can be used to operate our quantum engine.”

Thermodynamics - yes or no?
The proof of concept has thus been successful. But what about the findings? “At the moment, we are still far away from a specific application, because our development only works under special experimental conditions. But I am convinced that there is valuable potential in our basic research that can provide ideas for new applications in solid-state physics, for example in superconductors, where fermionic electrons as pairs also conduct the current without loss,” Widera sums up. “Our engine already had a good performance compared to a standard machine. And the more particles the ensembles contain, the higher energy levels and thus energy yields can be achieved,” Widera says. Professor Eric Lutz, one of the co-authors of the study, elaborates on another aspect: “The topic is extremely exciting from the perspective of the scientific community. We are thus initiating a discussion about how the experimental results are to be classified from a scientific point of view at all. Can we use the laws of thermodynamics? And if not, how do we describe the processes that make our engine run?” And Professor Thomas Busch, whose research group from Japan was involved in the theoretical modelling, adds: “These questions help to advance knowledge of the world of the smallest particles and to understand how we can use their characteristics for further technical innovations.”

Working together to succeed
Besides Professor Artur Widera and Jennifer Koch, the Kaiserslautern research team, which was in charge of the project, also included 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 has been published in the journal Nature: www.nature.com/articles/s41586-023-06469-8

Full bibliographic information of the paper:
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, 28 September 2023
DOI: 10.1038/s41586-023-06469-8

Questions can be directed to:
Dipl.-Phys. Jennifer Koch
Phone: +49 631 205 5272
Mail: jekoch@rptu.de
Prof. Dr. Artur Widera
Phone: +49 631 205-4130
Mail: widera@rptu.de