  Certain solutions of Einstein's equations in anti-de Sitter spacetime can be
engineered, using extended gravitational thermodynamics, to yield `holographic
heat engines', devices that turn heat into useful mechanical work. On the other
hand, there are constructions (both experimental and theoretical) where a
series of operations is performed on a small quantum system, defining what are
known as `quantum heat engines'. We propose that certain holographic heat
engines can be considered models of quantum heat engines, and the possible
fruitfulness of this connection is discussed. Motivated by features of quantum
heat engines that take a quantum system through analogues of certain classic
thermodynamic cycles, some black hole Otto and Diesel cycles are presented and
explored for the first time. In the expected regime of overlap, our Otto
efficiency formulae are of the form exhibited by quantum and classical heat
engines.
