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Simulating Quantum Computation by Contracting Tensor Networks

2008/01/01 by Igor L. Markov, Yaoyun Shi · 48 citations
Computer Science · #Quantum Computing Algorithms and Architecture #Stochastic Gradient Optimization Techniques #Complexity and Algorithms in Graphs

paper · doi:10.1137/050644756

Abstract

The treewidth of a graph is a useful combinatorial measure of how close the graph is to a tree. We prove that a quantum circuit with T gates whose underlying graph has treewidth d can be simulated classically in poly(T)*exp(O(d)) time, which, in particular, is polynomial in T if d = O(logT). Among many implications, we show efficient simulations for quantum formulas, defined and studied by Yao (Proceedings of the 34th Annual Symposium on Foundations of Computer Science, 352-361, 1993), and for log-depth circuits whose gates apply to nearby qubits only, a natural constraint satisfied by most physical implementations. We also extend the result to show that one-way quantum computation of Raussendorf and Briegel (Physical Review Letters, 86:5188-5191, 2001), a universal quantum computation scheme very promising for its physical implementation, can be efficiently simulated by a randomized algorithm if its quantum resource is derived from a small-treewidth graph.

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