  Advantages of quantum effects in several technologies, such as computation
and communication, have already been well appreciated, and some devices, such
as quantum computers and communication links, exhibiting superiority to their
classical counterparts have been demonstrated. The close relationship between
information and energy motivates us to explore if similar quantum benefits can
be found in energy technologies. Investigation of performance limits for a
broader class of information-energy machines is the subject of the rapidly
emerging field of quantum thermodynamics. Extension of classical
thermodynamical laws to the quantum realm is far from trivial. This short
review presents some of the recent efforts in this fundamental direction and
focuses on quantum heat engines and their efficiency bounds when harnessing
energy from non-thermal resources, specifically those containing quantum
coherence and correlations.
