Researchers at the University of Stuttgart have shown that the Carnot principle, a cornerstone of thermodynamics, does not fully hold for correlated particles at the atomic level. Their work reveals that quantum engines can surpass the traditional efficiency limit by harnessing quantum correlations. This discovery could pave the way for highly efficient nanoscale motors.
The Carnot principle, established nearly two centuries ago by French physicist Sadi Carnot, sets the theoretical maximum efficiency for heat engines based on temperature differences. It forms part of the second law of thermodynamics and applies to large-scale systems like steam turbines and internal combustion engines, which convert thermal energy into mechanical motion.
Advances in quantum mechanics have enabled the development of microscopic heat engines, shrinking them to atomic dimensions. Professor Eric Lutz and Dr. Milton Aguilar from the Institute for Theoretical Physics I at the University of Stuttgart have now demonstrated that this principle breaks down for strongly correlated systems at the atomic scale. In such setups, particles are physically linked, introducing quantum effects not accounted for in classical thermodynamics.
The researchers derived generalized thermodynamic laws that incorporate quantum correlations—subtle connections between particles in tiny systems. These correlations allow quantum engines to convert not only heat but also the correlations themselves into work, exceeding the Carnot limit. "Tiny motors, no larger than a single atom, could become a reality in the future," says Professor Lutz. He adds, "It is now also evident that these engines can achieve a higher maximum efficiency than larger heat engines."
Their mathematical proof was published in Science Advances under the title "Correlated quantum machines beyond the standard second law." This research refines fundamental physics and suggests applications in ultra-small quantum motors for tasks like powering medical nanobots or manipulating materials atom by atom. By expanding the understanding of efficiency at the nanoscale, the findings highlight how quantum effects can enhance energy conversion in future technologies.