  We propose a simple diatomic system trapped inside an optical cavity to
control the energy flow between two thermal baths. Through the action of the
baths the system is driven to a non- equilibrium steady state. Using the Large
Deviation theory we show that the number of photons flowing between the two
baths is dramatically different depending on the symmetry of the atomic states.
Here we present a deterministic scheme to prepare symmetric and antisymmetric
atomic states with the use of external driving fields, thus implementing an
atomic control switch for the energy flow.
