  Interaction in quantum systems can spread initially localized quantum
information into the many degrees of freedom of the entire system.
Understanding this process, known as quantum scrambling, is the key to
resolving various conundrums in physics. Here, by measuring the time-dependent
evolution and fluctuation of out-of-time-order correlators, we experimentally
investigate the dynamics of quantum scrambling on a 53-qubit quantum processor.
We engineer quantum circuits that distinguish the two mechanisms associated
with quantum scrambling, operator spreading and operator entanglement, and
experimentally observe their respective signatures. We show that while operator
spreading is captured by an efficient classical model, operator entanglement
requires exponentially scaled computational resources to simulate. These
results open the path to studying complex and practically relevant physical
observables with near-term quantum processors.
