  The interaction between magnons and mechanical vibrations dynamically modify
the properties of the mechanical oscillator, such as its frequency and decay
rate. Known as dynamical backaction, this effect is the basis for many
theoretical protocols, such as entanglement generation or mechanical
ground-state cooling. However, dynamical backaction is also detrimental for
specific applications. Here, we demonstrate the implementation of a cavity
magnomechanical measurement that fully evades dynamical backaction effects.
Through careful engineering, the magnomechanical scattering rate into the
hybrid magnon-photon modes can be precisely matched, eliminating dynamical
backaction damping. Backaction evasion is confirmed via the measurement of a
drive-power-independent mechanical linewidth.
