Title  Nonlocal propagation of correlations in longrange interacting quantum systems

Publication Type  Journal Article 
Year of Publication  2014 
Authors  Richerme, P, Gong, ZX, Lee, A, Senko, C, Smith, J, FossFeig, M, Michalakis, S, Gorshkov, AV, Monroe, C 
Journal  Nature 
Volume  511 
Issue  7508 
Pages  198  201 
Date Published  2014/7/9 
Abstract  The maximum speed with which information can propagate in a quantum manybody
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 shortrange interactions, Lieb and Robinson derived a
constantvelocity bound that limits correlations to within a linear effective
light cone. However, little is known about the propagation speed in systems
with longrange interactions, since the best longrange bound is too loose to
give the correct lightcone shape for any known spin model and since analytic
solutions rarely exist. In this work, we experimentally determine the spatial
and timedependent correlations of a farfromequilibrium quantum manybody
system evolving under a longrange Ising or XYmodel 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
LiebRobinson prediction, and in one instance cannot be explained by any
existing theory. Our results demonstrate that even modestlysized quantum
simulators are wellpoised for studying complicated manybody systems that are
intractable to classical computation.

URL  http://arxiv.org/abs/1401.5088v1 
DOI  10.1038/nature13450 
Short Title  Nature 