  We propose and analyze a simple mesoscopic quantum heat engine that exhibits
both high-power and high-efficiency. The system consists of a biased Josephson
junction coupled to two microwave cavities, with each cavity coupled to a
thermal bath. Resonant Cooper pair tunneling occurs with the exchange of
photons between cavities, and a temperature difference between the baths can
naturally lead to a current against the voltage, and hence work. As a
consequence of the unique properties of Cooper-pair tunneling, the heat current
is completely separated from the charge current. This combined with the strong
energy-selectivity of the process leads to an extremely high efficiency.
