The theory of thermodynamics, commonly associated with the steam engines of the 19th century, is a universal set of laws that governs everything from black holes to the evolution of life. But with modern technologies miniaturizing circuits to the atomic scale, thermodynamics has to be put to the test in a completely new realm. In this realm, quantum rather than classical laws apply. In the same way that thermodynamics was key to building classical steam engines, the emergence of quantum circuits is forcing us to reimagine this theory in the quantum case.