Nanomechanical
resonances coupled to microwave cavities can be
excited, measured, and controlled simultaneously using electromechanical
back-action phenomena. Examples of these effects include sideband
cooling and amplification, which are commonly described through linear
equations of motion governed by an effective optomechanical Hamiltonian.
However, this linear approximation is invalid when the pump-induced
cavity microwave field is large enough to trigger optomechanical nonlinearities,
resulting in phenomena like frequency combs. Here, we employ a niobium-based
superconducting electromechanical device to explore the generation
of microwave frequency combs. We observe the formation of combs around
a microwave resonant frequency (3.78 GHz) with 8-MHz frequency spacing,
equal to the mechanical resonant frequency. We investigate their dynamics
for different optomechanical parameters, including detuning, pump
powers, and cavity decay rates. Our experimental results show excellent
agreement with numerical modeling. These electromechanical frequency
combs can be beneficial in nanomechanical sensing applications that
require precise electrical tracking of mechanical resonant frequencies.
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