Observation of saturation of fidelity decay with an atom interferometer.

We use an atom interferometer to investigate the dynamics of matter waves in a periodically pulsed optical standing wave: an atom optics realization of the quantum kicked rotor that exhibits chaotic classical dynamics. We experimentally show that a measure of the coherence between the interferometer diffraction orders can revive after a quick initial loss, and can approach a finite asymptote as the number of kicks increases. This observation demonstrates that quantum fidelity of a classically chaotic system can survive strong perturbations over long times without decay.