  In the last twenty years there has been significant progress in our
understanding of quantum transport far from equilibrium and a conceptual
framework has emerged through a combination of the Landauer approach with the
non-equilibrium Green function (NEGF) method, which is now being widely used in
the analysis and design of nanoscale devices. It provides a unified description
for all kinds of devices from molecular conductors to carbon nanotubes to
silicon transistors covering different transport regimes from the ballistic to
the diffusive limit. In this talk I use a simple version of this model to
analyze a specially designed device that could be called an electronic
Maxwell's demon, one that lets electrons go preferentially in one direction
over another. My objective is to illustrate the fundamental role of contacts
and demons in transport and energy conversion. The discussion is kept at an
academic level steering clear of real world details, but the illustrative
devices we use are very much within the capabilities of present-day technology.
For example, recent experiments on thermoelectric effects in molecular
conductors agree well with the predictions from our model. The Maxwell's demon
device itself is very similar to the pentalayer spin-torque device which has
been studied by a number of groups though we are not aware of any discussion of
the possibility of using the device as a nanoscale heat engine or as a
refrigerator as proposed here. However, my objective is not to evaluate
possible practical applications. Rather it is to introduce a simple transparent
model showing how out-of-equibrium demons suitably incorporated into
nanodevices can achieve energy conversion.
