Contrary to a driven classical system that exhibits chaos phenomena and diffusive energy growth, a driven quantum system can exhibit dynamical localization that features energy saturation. However, the evolution of the dynamically localized state in the presence of many-body interactions has for long remained an open question. Here we realize a many-body quantum kicked rotor with a 1D ultracold gas periodically kicked by a pulsed optical lattice, and observe the interaction-driven emergence of dynamical delocalization. The dynamics feature a sub-diffusive energy growth which is manifest over a broad parameter range of interaction strengths and kick strengths. This observed onset of many-body quantum chaos and its characterization by the accompanying theoretical modeling introduce new tools to study many-body localization-delocalization phenomena in the synthetic momentum space.
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