  Coupled parametric oscillators were recently employed as simulators of
artificial Ising networks, with the potential to solve computationally hard
minimization problems. We demonstrate a new dynamical regime within the
simplest network - two coupled parametric oscillators, where the oscillators
never reach a steady state, but show persistent, full-scale, coherent beats,
whose frequency reflects the coupling properties and strength. We present a
detailed theoretical and experimental study and show that this new dynamical
regime appears over a wide range of parameters near the oscillation threshold
and depends on the nature of the coupling (dissipative or energy preserving).
Thus, a system of coupled parametric oscillators transcends the Ising
description and manifests unique coherent dynamics, which may have important
implications for coherent computation machines.
