  We consider quantum heat engines that operate between nonequilibrium
stationary reservoirs. We evaluate their maximum efficiency from the positivity
of the entropy production and show that it can be expressed in terms of an
effective temperature that depends on the nature of the reservoirs. We further
compute the efficiency at maximum power for different kinds of engineered
reservoirs and derive a nonequilibrium generalization of the Clausius statement
of the second law.

Quantum Physics;Statistical Mechanics