Locality Preserving Unitaries Beyond QCA

Carolyn Zhang describes a three-dimensional locality-preserving unitary that transports a Chern insulator to a boundary. It differs from a quantum cellular automaton because local operators acquire exponentially decaying tails. Although no local single-particle Hamiltonian generates it, an interacting fermionic implementation becomes possible when particle-number symmetry is broken. The talk identifies an integer topological invariant and related even-order discrete-symmetry examples, establishing a class of symmetry-protected locality-preserving operations beyond quantum cellular automata.