  We investigate the dynamics of interacting quantum planar rotors as the
building blocks of gear trains and nano-machinery operating in the quantum
regime. Contrary to a classical hard-gear scenario of rigidly interlocked
teeth, we consider the coherent contact-less coupling through a finite
interlocking potential and study the transmission of motion from one externally
driven gear to the next as a function of the coupling parameters and gear
profile. The transmission is assessed in terms of transferred angular momentum
and transferred mechanical work. We highlight the quantum features of the model
such as quantum state revivals in the interlocked rotation and
interference-enhanced transmission, which could be observed in prospective
rotational optomechanics experiments.
