  From synthetic active devices such as self-propelling Janus colloids to
micro-organisms like bacteria, micro-algae, living cells in tissues, active
fluctuations are ubiquitous. Thermodynamics of small systems involving thermal
as well as active fluctuations are of immense importance. They can be employed
to extract thermodynamic work. Here we propose a simple model system that can
produce thermodynamic work exploiting active fluctuations. We consider a
Brownian particle, trapped by an externally controlled harmonic confinement
which time-periodically contracts and expands by modulating its spring constant
e.g an optical tweezer. The system produces work by being alternately connected
to two baths one passive and other active, modeled as exponentially correlated
noise which breaks the fluctuation dissipation theorem. The average efficiency
of the system is calculated exactly in quasistatic limit. Nonquasistatic regime
is explored by numerics. Comparing with its passive counterpart, we also show
that the active micro heat engine can be more efficient depending on the chosen
parameter space. We also believe that our model can be realized experimentally
with the help of bacterial baths.
