  We describe a single-level quantum dot in contact with two leads as a
nanoscale finite-time thermodynamic machine. The dot is driven by an external
stochastic force that switches its energy between two values. In the isothermal
regime, it can operate as a rechargeable battery by generating an electric
current against the applied bias in response to the stochastic driving, and
re-delivering work in the reverse cycle. This behavior is reminiscent of the
Parrondo paradox. If there is a thermal gradient the device can function as a
work-generating thermal engine, or as a refrigerator that extracts heat from
the cold reservoir via the work input of the stochastic driving. The efficiency
of the machine at maximum power output is investigated for each mode of
operation, and universal features are identified.
