  Dynamics of a simple system, such as a two-state (dimer) model, are
dramatically changed in the presence of interactions and external driving, and
the resultant unitary dynamics show both regular and chaotic regions. We
investigate the non-unitary dynamics of such a dimer in the presence of
balanced gain and loss for the two states, i.e. a $\mathcal{PT}$ symmetric
dimer. We find that at low and high driving frequencies, the
$\mathcal{PT}$-symmetric dimer motion continues to be regular, and the system
is in the $\mathcal{PT}$-symmetric state. On that other hand, for intermediate
driving frequency, the system shows chaotic motion, and is usually in the
$\mathcal{PT}$-symmetry broken state. Our results elucidate the interplay
between the $\mathcal{PT}$-symmetry breaking transitions and regular-chaotic
transitions in an experimentally accessible toy model.
