Thermodynamics with Feedback: Extracting Work from Information

The laws of thermodynamics restrict the maximum efficiency with which
a thermodynamic engine can convert heat into useful work. This limit,
however, can be exceeded with the use of feedback – that is by
altering the operational protocol of the engine in response to
information about its microscopic state. The reason being that the
information acquired through feedback can itself be converted into
work. In this talk, I will discuss recent results detailing how
information enters into the thermodynamics of a system driven away
from equilibrium by feedback, such as a thermodynamic engine. In
particular, I will prove and analyze the second law of thermodynamics
with discrete feedback, which relates information to heat, work, and
irreversibility. We will see that optimal feedback processes that
convert all the information into work are feedback reversible – they
are indistinguishable from their time reverse. Finally, building on
the intuition gained from examining the second law with feedback, I
will introduce a method for designing optimal thermodynamic engines
with feedback, which I will illustrate with an N-particle Szilard
engine.

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