Maximally efficient quantum thermal machines: The basic principles

Following the result by Skrzypczyk et al., arXiv:1009.0865, that certain self-contained quantum thermal machines can reach Carnot efficiency, we discuss the functioning of self-contained quantum thermal machines and show, in a very general case, that they can reach the Carnot efficiency limit. Most importantly, the full analytical solution for the functioning of the machines is not required; the efficiency can be deduced from a very small number of fundamental and highly intuitive equations which capture the core of the problem.