TY - JOUR T1 - The computational power of matchgates and the XY interaction on arbitrary graphs JF - Quantum Information and Computation Y1 - 2014 A1 - Daniel J. Brod A1 - Andrew M. Childs AB - Matchgates are a restricted set of two-qubit gates known to be classically simulable when acting on nearest-neighbor qubits on a path, but universal for quantum computation when the qubits are arranged on certain other graphs. Here we characterize the power of matchgates acting on arbitrary graphs. Specifically, we show that they are universal on any connected graph other than a path or a cycle, and that they are classically simulable on a cycle. We also prove the same dichotomy for the XY interaction, a proper subset of matchgates related to some implementations of quantum computing. VL - 14 U4 - 901-916 UR - http://arxiv.org/abs/1308.1463v1 CP - 11-12 J1 - Quantum Information and Computation 14 ER -