Ken Sekimoto
Yukawa Institute for Theoretical Physics,
Kyoto University, Kyoto 606-8502 Japan
e-mail: sekimoto@yukawa.kyoto-u.ac.jp
Recently the author has explored with his
colleagues the framework of energetics of
fluctuating systems (called stochastic energetics).
This framework was motivated by the recent
development of nano-scale experiments and
numerical simulation and then naturally urges
us to reconsider apparently clear distinctions
such as work {\it vs.} heat, signal {\it
vs.} noise, system {\it vs.} its environment,
or macroscopic {\it vs.} microscopic quantities.
In the present paper we will explore the
control and sensing in the fluctuating systems,
taking their energetics into account.
First we discuss the irreversibility and
the cost related to external control and
sensing. As concrete examples we will discuss
microscopic Carnot cycles and its counterpart
of an open environment with particle exchanges.
Also we give a general consideration about
the observation of thermodynamic functions.
Then we discuss automatic control of fluctuating
systems surrounded by thermal and open environments.
After a brief survey of automatic mechanisms
of Feynman's ratchet and of B\"uttiker's
model, we will explore the mechanisms with
more accurate sensing and control, which
will be relevant to the bio-molecular pumps
and motors. Through concrete models we will
show how a kind of self-reference is established
within the system.
Designing and implementation of control and
sensing within a fluctuating system seem
to be of fundamental and conceptual interest,
besides of practical and technical interest,
and are related to the physics of computation
and that of observation.