  Synchronization manifests itself in oscillators adjusting their frequencies
and phases with respect to an external signal or another oscillator. In the
quantum case, new features appear such as destructive interferences that can
result in the suppression of phase locking. A three-level (spin-1) oscillator
with equal gain and damping rates and subject to an external drive does not
exhibit any 1:1 phase locking but 2:1 phase locking, i.e., its phase
distribution features two maxima. This bistable locking at two opposite phases
is a signature of the quantum interference synchronization blockade. An
analogous behavior was found for two identical coupled spin-1 oscillators. In
this work, we consider two coupled spin-1 oscillators and a drive applied to
the first spin. This leads to two interference blockades between the drive and
the first spin as well as between both spins. Although both interference
blockades persist for strong drive and coupling strengths, remarkably, the
undriven spin does show a 1:1 phase locking to the external drive. The
magnitude of the locking is proportional to the drive strength if the drive
strength is small. In other words, the undriven oscillator synchronizes to the
external drive through both interference blockades while the blockades persist.
For a chain of three coupled spin-1 oscillators, we find synchronization
between the first and third spins mediated via the blockaded, second spin.
