Fast-Scrambling and Operator Confinement Using an Auxiliary Qubit*

We study a locally interacting spin-1/2 system coupled to a single, central qubit. All spins develop effective all-to-all interactions through shared interaction with the auxiliary qubit, where stronger coupling continuously degrades any sense of locality. We obtain the operator and entanglement dynamics in a nonintegrable ring-star, spin-1/2 Ising model with tunable ancilla coupling. As the interaction with the central spin increases across all sites, we find a surprising transition from super-ballistic scrambling and information growth to continuously restricted sub-ballistic entanglement and increasingly inhibited operator growth. We provide exact dynamics of small systems working with non-equilibrium and effective infinite temperature states, and additionally contribute analytic early-time expansions that support the observed rapid scrambling to quantum-zeno transition.