2,569 research outputs found
Tensor networks for Lattice Gauge Theories and Atomic Quantum Simulation
We show that gauge invariant quantum link models, Abelian and non-Abelian,
can be exactly described in terms of tensor networks states. Quantum link
models represent an ideal bridge between high-energy to cold atom physics, as
they can be used in cold-atoms in optical lattices to study lattice gauge
theories. In this framework, we characterize the phase diagram of a (1+1)-d
quantum link version of the Schwinger model in an external classical background
electric field: the quantum phase transition from a charge and parity ordered
phase with non-zero electric flux to a disordered one with a net zero electric
flux configuration is described by the Ising universality class.Comment: 9 pages, 9 figures. Published versio
Real-time Dynamics in U(1) Lattice Gauge Theories with Tensor Networks
Tensor network algorithms provide a suitable route for tackling real-time
dependent problems in lattice gauge theories, enabling the investigation of
out-of-equilibrium dynamics. We analyze a U(1) lattice gauge theory in (1+1)
dimensions in the presence of dynamical matter for different mass and electric
field couplings, a theory akin to quantum-electrodynamics in one-dimension,
which displays string-breaking: the confining string between charges can
spontaneously break during quench experiments, giving rise to charge-anticharge
pairs according to the Schwinger mechanism. We study the real-time spreading of
excitations in the system by means of electric field and particle fluctuations:
we determine a dynamical state diagram for string breaking and quantitatively
evaluate the time-scales for mass production. We also show that the time
evolution of the quantum correlations can be detected via bipartite von Neumann
entropies, thus demonstrating that the Schwinger mechanism is tightly linked to
entanglement spreading. To present the variety of possible applications of this
simulation platform, we show how one could follow the real-time scattering
processes between mesons and the creation of entanglement during scattering
processes. Finally, we test the quality of quantum simulations of these
dynamics, quantifying the role of possible imperfections in cold atoms, trapped
ions, and superconducting circuit systems. Our results demonstrate how
entanglement properties can be used to deepen our understanding of basic
phenomena in the real-time dynamics of gauge theories such as string breaking
and collisions.Comment: 15 pages, 25 figures. Published versio
Differential vulnerability to hurricanes in Cuba, Haiti, and the Dominican Republic: the contribution of education
The possible impacts of the level of formal education on different aspects of disaster management, prevention, alarm, emergency, or postdisaster activities, were studied in a comparative perspective for three countries with a comparable exposure to hurricane hazards but different capacities for preventing harm. The study focused on the role of formal education in reducing vulnerability operating through a long-term learning process and put particular emphasis on the education of women. The comparative statistical analysis of the three countries was complemented through qualitative studies in Cuba and the Dominican Republic collected in 2010-2011. We also analyzed to what degree targeted efforts to reduce vulnerability were interconnected with other policy domains, including education and science, health, national defense, regional development, and cultural factors. We found that better education in the population had clear short-term effects on reducing vulnerability through awareness about crucial information, faster and more efficient responses to alerts, and better postdisaster recuperation. However, there were also important longer term effects of educational efforts to reduce social networks for mutual assistance creating a general culture of safety and preparedness. Not surprisingly, took an intermediate position
The tractability frontier of well-designed SPARQL queries
We study the complexity of query evaluation of SPARQL queries. We focus on
the fundamental fragment of well-designed SPARQL restricted to the AND,
OPTIONAL and UNION operators. Our main result is a structural characterisation
of the classes of well-designed queries that can be evaluated in polynomial
time. In particular, we introduce a new notion of width called domination
width, which relies on the well-known notion of treewidth. We show that, under
some complexity theoretic assumptions, the classes of well-designed queries
that can be evaluated in polynomial time are precisely those of bounded
domination width
Dressed, noise- or disorder- resilient optical lattices
External noise is inherent in any quantum system, and can have especially
strong effects for systems exhibiting sensitive many-body phenomena. We show
how a dressed lattice scheme can provide control over certain types of noise
for atomic quantum gases in the lowest band of an optical lattice, removing the
effects of lattice amplitude noise to first order for particular choices of the
dressing field parameters. We investigate the non-equilibrium many-body
dynamics for bosons and fermions induced by noise away from this parameter
regime, and also show how the same technique can be used to reduce spatial
disorder in projected lattice potentials.Comment: 4+ Pages, 4 Figure
Topological Quantum Optics in Two-Dimensional Atomic Arrays
We demonstrate that two-dimensional atomic emitter arrays with subwavelength
spacing constitute topologically protected quantum optical systems where the
photon propagation is robust against large imperfections while losses
associated with free space emission are strongly suppressed. Breaking
time-reversal symmetry with a magnetic field results in gapped photonic bands
with non-trivial Chern numbers and topologically protected, long-lived edge
states. Due to the inherent nonlinearity of constituent emitters, such systems
provide a platform for exploring quantum optical analogues of interacting
topological systems.Comment: 11 pages and 9 figures; paper updated to match published versio
Quantum Hall Physics with Cold Atoms in Cylindrical Optical Lattices
We propose and study various realizations of a Hofstadter-Hubbard model on a
cylinder geometry with fermionic cold atoms in optical lattices. The
cylindrical optical lattice is created by copropagating Laguerre-Gauss beams,
i.e.~light beams carrying orbital angular momentum. By strong focusing of the
light beams we create a real space optical lattice in the form of rings, which
are offset in energy. A second set of Laguerre-Gauss beams then induces a
Raman-hopping between these rings, imprinting phases corresponding to a
synthetic magnetic field (artificial gauge field). In addition, by rotating the
lattice potential, we achieve a slowly varying flux through the hole of the
cylinder, which allows us to probe the Hall response of the system as a
realization of Laughlin's thought experiment. We study how in the presence of
interactions fractional quantum Hall physics could be observed in this setup.Comment: 10 pages, 9 figure
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