%0 Journal Article %J Nature %D 2014 %T Non-local propagation of correlations in long-range interacting quantum systems %A Philip Richerme %A Zhe-Xuan Gong %A Aaron Lee %A Crystal Senko %A Jacob Smith %A Michael Foss-Feig %A Spyridon Michalakis %A Alexey V. Gorshkov %A Christopher Monroe %X The maximum speed with which information can propagate in a quantum many-body system directly affects how quickly disparate parts of the system can become correlated and how difficult the system will be to describe numerically. For systems with only short-range interactions, Lieb and Robinson derived a constant-velocity bound that limits correlations to within a linear effective light cone. However, little is known about the propagation speed in systems with long-range interactions, since the best long-range bound is too loose to give the correct light-cone shape for any known spin model and since analytic solutions rarely exist. In this work, we experimentally determine the spatial and time-dependent correlations of a far-from-equilibrium quantum many-body system evolving under a long-range Ising- or XY-model Hamiltonian. For several different interaction ranges, we extract the shape of the light cone and measure the velocity with which correlations propagate through the system. In many cases we find increasing propagation velocities, which violate the Lieb-Robinson prediction, and in one instance cannot be explained by any existing theory. Our results demonstrate that even modestly-sized quantum simulators are well-poised for studying complicated many-body systems that are intractable to classical computation. %B Nature %V 511 %P 198 - 201 %8 2014/7/9 %G eng %U http://arxiv.org/abs/1401.5088v1 %N 7508 %! Nature %R 10.1038/nature13450 %0 Journal Article %J Physical Review Letters %D 2014 %T Persistence of locality in systems with power-law interactions %A Zhe-Xuan Gong %A Michael Foss-Feig %A Spyridon Michalakis %A Alexey V. Gorshkov %X Motivated by recent experiments with ultra-cold matter, we derive a new bound on the propagation of information in $D$-dimensional lattice models exhibiting $1/r^{\alpha}$ interactions with $\alpha>D$. The bound contains two terms: One accounts for the short-ranged part of the interactions, giving rise to a bounded velocity and reflecting the persistence of locality out to intermediate distances, while the other contributes a power-law decay at longer distances. We demonstrate that these two contributions not only bound but, except at long times, \emph{qualitatively reproduce} the short- and long-distance dynamical behavior following a local quench in an $XY$ chain and a transverse-field Ising chain. In addition to describing dynamics in numerous intractable long-range interacting lattice models, our results can be experimentally verified in a variety of ultracold-atomic and solid-state systems. %B Physical Review Letters %V 113 %8 2014/7/16 %G eng %U http://arxiv.org/abs/1401.6174v2 %N 3 %! Phys. Rev. Lett. %R 10.1103/PhysRevLett.113.030602