Tiny quantum engines reveal useful energy hiding in “waste heat”

What counts as heat, and what qualifies as useful work when a machine is made from only an atom and particles of light? In emerging quantum technologies, questions like this bring together two branches of physics that were developed for very different purposes. Researchers at the University of Basel in Switzerland have now introduced a theoretical framework designed to make thermodynamics and quantum physics work consistently in the same setting.

Thermodynamics emerged in the 19th century largely to explain how large machines such as steam engines convert and transfer energy. Quantum physics, developed in the early 20th century, instead focuses on atoms and subatomic particles. Today, however, the two fields increasingly overlap. Tiny systems built from atoms and light particles (photons) can take in energy, transform it, and release it, allowing them to function as microscopic quantum machines.