Suppose that an entire graph evolves quantum mechanically and gets driven into superpositions of graphs of different connectivities and node populations. Suppose moreover that the evolution is causal, meaning that information can only propagate at a bounded speed, with respect to graph distance. We show that this quantum evolution must decompose into small, local unitary rewritings of graph disks. This unifies a result on Quantum Cellular Automata with another on Reversible Causal Graph Dynamics. To reach the result we formalize a notion of causality which is valid in the context of quantum superpositions of time-varying graphs, and has a number of good properties.
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