  Quantization of energy is a quintessential characteristic of quantum systems.
Here we analyze its effects on the operation of Otto cycle heat machines and
show that energy quantization alone may alter and increase machine performance
in terms of output power, efficiency, and even operation mode. Our results
demonstrate that quantum thermodynamics enable the realization of classically
inconceivable Otto machines, such as those with an incompressible working
fluid. We propose to measure these effects experimentally using a laser-cooled
trapped ion as a microscopic heat machine.
