  Colloidal microspheres in optical tweezers are model systems for mesoscopic
particles in conservative harmonic potentials and are used to realize
micrometer-sized heat engines. While non-conservative forces and hydrodynamic
flows that dissipate energy input by them are known to exist, their effect on
the motion of the colloidal bead in an isolated optical trap has been shown to
be negligible. Here, we demonstrate that the same, however, is not true if
another particle is trapped in close proximity. The internal energy of the
adjacent trapped colloid gets enhanced by obstructing the flows generated by
non-conservative forces and in turn feeds it back to the microsphere. We
establish this specifically in the case of two colloidal beads trapped in close
separation and the synergy between them was observed predominantly along the
direction of laser propagation. Using parameters that tune the hydrodynamics,
we showed that the energy addition can in turn be controlled. Leveraging on
these results in a manner analogous to microswimmers that increase propulsion
velocity by collectively exploiting non-conservative flows, we operated two
micrometer-sized heat engines constructed from the colloidal microspheres and
showed that their performance can be similarly enhanced. The increased
performance was observed to arise by reusing the energy input otherwise
rejected into the hydrodynamic flows. While these results explore only the
simplest case of two engines, the underlying concepts should be considered
while designing larger collections. Nevertheless, our results mark the first
basic step towards constructing engines by a bottom-up architecture akin to
biological systems.
