
arXiv: 1607.06700
Consider a graph having quantum systems lying at each node. Suppose that the whole thing evolves in discrete time steps, according to a global, unitary causal operator. By causal we mean that information can only propagate at a bounded speed, with respect to the distance given by the graph. Suppose, moreover, that the graph itself is subject to the evolution, and may be driven to be in a quantum superposition of graphs---in accordance to the superposition principle. We show that these unitary causal operators must decompose as a finite-depth circuit of local unitary gates. This unifies a result on Quantum Cellular Automata with another on Reversible Causal Graph Dynamics. Along the way 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. Keywords: Quantum Lattice Gas Automata, Block-representation, Curtis-Hedlund-Lyndon, No-signalling, Localizability, Quantum Gravity, Quantum Graphity, Causal Dynamical Triangulations, Spin Networks, Dynamical networks, Graph Rewriting.
8 pages, 1 figure
Quantum Gravity, FOS: Computer and information sciences, causality, Quantum Graphity, Discrete Mathematics (cs.DM), Block-representation, No-signalling, Curtis-Hedlund-Lyndon, FOS: Physical sciences, triangulation, General Relativity and Quantum Cosmology (gr-qc), [INFO.INFO-DM]Computer Science [cs]/Discrete Mathematics [cs.DM], [INFO] Computer Science [cs], spin, General Relativity and Quantum Cosmology, [PHYS.QPHY]Physics [physics]/Quantum Physics [quant-ph], Dynamical networks, Localizability, gas, gate, unitarity, Causal Dynamical Triangulations, time, [PHYS.QPHY] Physics [physics]/Quantum Physics [quant-ph], Graph Rewriting, lattice, Quantum Physics, [PHYS.GRQC] Physics [physics]/General Relativity and Quantum Cosmology [gr-qc], superposition, F.1.1; F.1.2, Quantum Lattice Gas Automata, 004, [INFO.INFO-DM] Computer Science [cs]/Discrete Mathematics [cs.DM], quantum gravity, network, [PHYS.GRQC]Physics [physics]/General Relativity and Quantum Cosmology [gr-qc], discrete, time dependence, Spin Networks, F.1.2, Quantum Physics (quant-ph), F.1.1, Computer Science - Discrete Mathematics
Quantum Gravity, FOS: Computer and information sciences, causality, Quantum Graphity, Discrete Mathematics (cs.DM), Block-representation, No-signalling, Curtis-Hedlund-Lyndon, FOS: Physical sciences, triangulation, General Relativity and Quantum Cosmology (gr-qc), [INFO.INFO-DM]Computer Science [cs]/Discrete Mathematics [cs.DM], [INFO] Computer Science [cs], spin, General Relativity and Quantum Cosmology, [PHYS.QPHY]Physics [physics]/Quantum Physics [quant-ph], Dynamical networks, Localizability, gas, gate, unitarity, Causal Dynamical Triangulations, time, [PHYS.QPHY] Physics [physics]/Quantum Physics [quant-ph], Graph Rewriting, lattice, Quantum Physics, [PHYS.GRQC] Physics [physics]/General Relativity and Quantum Cosmology [gr-qc], superposition, F.1.1; F.1.2, Quantum Lattice Gas Automata, 004, [INFO.INFO-DM] Computer Science [cs]/Discrete Mathematics [cs.DM], quantum gravity, network, [PHYS.GRQC]Physics [physics]/General Relativity and Quantum Cosmology [gr-qc], discrete, time dependence, Spin Networks, F.1.2, Quantum Physics (quant-ph), F.1.1, Computer Science - Discrete Mathematics
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