  We consider the basic, thermodynamic properties of an elementary
micro-machine operating at colloidal length scales. In particular, we track and
analyse the driven stochastic motion of a carefully designed micro-propeller
rotating unevenly in an optical tweezers, in water. In this intermediate
regime, the second law of macroscopic thermodynamics is satisfied only as an
ensemble average, and individual trajectories can be temporarily associated
with decreases in entropy. We show that our light driven micro-propeller
satisfies an appropriate fluctuation theorem that constrains the probability
with which these apparent violations of the second law occur. Implications for
the development of more complex micro-machines are discussed.
