  We experimentally investigate the effect of atomic $\delta$-kicked rotor
potentials on the mutual coherence between wavepackets in an atom
interferometer. The differential action of the kicked rotor degrades the mutual
coherence, leading to a reduction of the interferometry fringe visibility;
however, when the repetition rate of the kicked rotor is at or near the quantum
resonance, we observe revival of matter-wave coherence as the number of kicks
increases, resulting in non-vanishing coherence in the large kick number limit.
This coherence saturation effect reflects a saturation of fidelity decay due to
momentum displacements in deep quantum regime. The saturation effect is
accompanied with an invariant distribution of matter-wave coherence under the
kicked rotor perturbations.
