Resolving Lattice Oxygen Atoms

777 Thinking Coherently About the Second Law The efficiency of heat engines has been limited by the Carnot cycle, which states that the efficiency cannot exceed 1 – Tc/Th, where Tc and Th are the absolute temperatures of the cold and hot reservoirs feeding the engine. Scully et al. (p. 862; see the Perspective by Linke) show how this limiting efficiency can be beaten with a coherent heat source in which the atoms in the heat bath have an associated phase f. Such an engine can even produce net work when Tc = Th. However, the Second Law of Thermodynamics still holds because an outside energy source, such as a microwave field, is needed to create the initial coherence.