  We report on a new class of Ising Machines (IMs) that rely on coupled
parametric frequency dividers (PFDs) as macroscopic artificial spins. Unlike
the IM counterparts based on subharmonic injection locking (SHIL), PFD IMs do
not require strong injected continuous wave signals or applied DC voltages.
Therefore, they show a significantly lower power consumption per spin compared
to SHIL based IMs, making it feasible to accurately solve large scale
combinatorial optimization problems (COPs) that are hard or even impossible to
solve by using the current von Neumann computing architectures. Furthermore,
using high quality (Q) factor resonators in the PFD design makes PFD IMs able
to exhibit a nanoWatt level power per spin. Also, it remarkably allows a speed
up of the phase synchronization among the PFDs, resulting in shorter time to
solution and lower energy to solution despite the resonators' longer relaxation
time. As a proof of concept, a 4 node PFD IM has been demonstrated. This IM
correctly solves a set of MaxCut problems while consuming just 600 nanoWatts
per spin. This power consumption is two orders of magnitude lower than the
power per spin of state of the art SHIL based IMs operating at the same
frequency.
