  Open-dissipative systems obeying parity-time ($\mathcal{PT}$) symmetry are
capable of demonstrating oscillatory dynamics akin to the conservative systems.
In contrast to limit cycle solutions characteristic of nonlinear systems, the
$\mathcal{PT}$-symmetric oscillations form a continuum of non-isolated orbits.
However, precise sculpturing of the real potential and the gain-loss spatial
profiles required for establishing of the $\mathcal{PT}$-symmetry is
practically challenging. The optical devices, such as lasers, exhibit
relaxation dynamics and do not operate as the $\mathcal{PT}$-symmetric systems.
Here we demonstrate how these constraints can be overcome. We predict that a
pair of optically trapped polariton condensates (a polariton dimer) can be
excited and operated in the oscillating regime typical of the isolated systems.
This regime can be realized in the presence of both dissipative and
conservative coupling between the condensates and can be maintained at an
arbitrary external pump intensity. Every orbit is characterised by a frequency
comb appearing in the spectrum of a dimer in the presence of the conservative
nonlinearity. Our results pave the way for the creation of the optical
computing devices operating under the constant-wave external pumping.
