



@article {1202,
	title = {Non-local propagation of correlations in long-range interacting quantum  systems
},
	journal = {Nature},
	volume = {511},
	year = {2014},
	month = {2014/7/9},
	pages = {198 - 201},
	abstract = {  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.
},
	doi = {10.1038/nature13450},
	url = {http://arxiv.org/abs/1401.5088v1},
	author = {Philip Richerme and Zhe-Xuan Gong and Aaron Lee and Crystal Senko and Jacob Smith and Michael Foss-Feig and Spyridon Michalakis and Alexey V. Gorshkov and Christopher Monroe}
}
@article {1176,
	title = {Persistence of locality in systems with power-law interactions},
	journal = {Physical Review Letters},
	volume = {113},
	year = {2014},
	month = {2014/7/16},
	abstract = {  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.
},
	doi = {10.1103/PhysRevLett.113.030602},
	url = {http://arxiv.org/abs/1401.6174v2},
	author = {Zhe-Xuan Gong and Michael Foss-Feig and Spyridon Michalakis and Alexey V. Gorshkov}
}
