The theoretical notion of a 'quantum heat engine' has been around for several decades. It was first introduced around sixty years ago by Scovil and Schulz-DuBois, two physicists at Bell Labs who drew an analogy between three-level masers and thermal machines. In the years that followed, other researchers have developed a variety of theories building on the ideas of Scovil and Schulz-DuBois, introducing proposals of thermodynamic cycles at the quantum scale. Very recently, physicists have started testing some of these theories in experimental settings. One of these experiments was carried out by a team of researchers at the University of...