5,671 research outputs found
Matrix Product States with long-range Localizable Entanglement
We derive a criterion to determine when a translationally invariant matrix
product state (MPS) has long-range localizable entanglement, where that
quantity remains finite in the thermodynamic limit. We give examples fulfilling
this criterion and eventually use it to obtain all such MPS with bond dimension
2 and 3.Comment: 8 pages, 1 figur
Wetland restoration and nitrate reduction: the example of the periurban wetland of Vitoria-Gasteiz (Basque Country, North Spain)
Changes in land use and agricultural intensification caused wetlands on the quaternary aquifer of Vitoria-Gasteiz (Basque Country) to disappear some years ago and nitrate concentration in groundwaters increased very quickly. The Basque Government recently declared the East Sector of this aquifer a Vulnerable Zone according to the 91/676/CEE European Directive. Recently, the wetlands have been restored through the closure of the main drainage ditches, the consequent elevation of the water table and the abondonment of agricultural practices near the wetlands. This is the case of the Zurbano wetland. Restoration has allowed the recovery of its biogeochemical function, which has reduced nitrate concentrations in waters. Nitrate concentrations which exceed 50 mg lâ1 in groundwaters entering into the wetland are less than 10 mg lâ1 at the outlet. Conditions in the wetland are conducive to the loss of nitrates: organic matter rich wetted soils, clay presence allowing a local semiconfined flow and very low hydraulic gradient. Water quality monitoring at several points around the wetland showed the processes involved in nitrate loss, although some aspects still remain unresolved. However, during storm events, the wetland effectively reduces the nitrate concentration entering the Alegria River, the most important river on the quaternary aquifer
Transformation Optics Approach to Plasmon-Exciton Strong Coupling in Nanocavities
We investigate the conditions yielding plasmon-exciton strong coupling at the
single emitter level in the gap between two metal nanoparticles. A
quasi-analytical transformation optics approach is developed that makes
possible a thorough exploration of this hybrid system incorporating the full
richness of its plasmonic spectrum. This allows us to reveal that by placing
the emitter away from the cavity center, its coupling to multipolar dark modes
of both even and odd parity increases remarkably. This way, reversible dynamics
in the population of the quantum emitter takes place in feasible
implementations of this archetypal nanocavity.Comment: 5 pages, 4 figure
Effect of long range spatial correlations on the lifetime statistics of an emitter in a two-dimensional disordered lattice
The effect of spatial correlations on the Purcell effect in a bidimensional
dispersion of resonant nanoparticles is analyzed. We perform extensive
calculations on the fluorescence decay rate of a point emitter embedded in a
system of nanoparticles statistically distributed according to a simple 2D
lattice-gas model near the critical point. For short-range correlations (high
temperature thermalization) the Purcell factors present a long-tailed statistic
which evolves towards a bimodal distribution when approaching the critical
point where the spatial correlation length diverges. Our results suggest
long-range correlations as a possible origin of the large fluctuations of
experimental decay rates in disordered metal films.Comment: 6 pages, 5 figure
Matrix Product States: Symmetries and Two-Body Hamiltonians
We characterize the conditions under which a translationally invariant matrix
product state (MPS) is invariant under local transformations. This allows us to
relate the symmetry group of a given state to the symmetry group of a simple
tensor. We exploit this result in order to prove and extend a version of the
Lieb-Schultz-Mattis theorem, one of the basic results in many-body physics, in
the context of MPS. We illustrate the results with an exhaustive search of
SU(2)--invariant two-body Hamiltonians which have such MPS as exact ground
states or excitations.Comment: PDFLatex, 12 pages and 6 figure
Violation of area-law scaling for the entanglement entropy in spin 1/2 chains
Entanglement entropy obeys area law scaling for typical physical quantum
systems. This may naively be argued to follow from locality of interactions. We
show that this is not the case by constructing an explicit simple spin chain
Hamiltonian with nearest neighbor interactions that presents an entanglement
volume scaling law. This non-translational model is contrived to have couplings
that force the accumulation of singlet bonds across the half chain. Our result
is complementary to the known relation between non-translational invariant,
nearest neighbor interacting Hamiltonians and QMA complete problems.Comment: 9 pages, 4 figure
String order and symmetries in quantum spin lattices
We show that the existence of string order in a given quantum state is
intimately related to the presence of a local symmetry by proving that both
concepts are equivalent within the framework of finitely correlated states.
Once this connection is established, we provide a complete characterization of
local symmetries in these states. The results allow to understand in a
straightforward way many of the properties of string order parameters, like
their robustness/fragility under perturbations and their typical disappearance
beyond strictly one-dimensional lattices. We propose and discuss an alternative
definition, ideally suited for detecting phase transitions, and generalizations
to two and more spatial dimensions.Comment: 5 pages, 1 figur
Present and future of the OTELO project
OTELO is an emission-line object survey carried out with the red tunable
filter of the instrument OSIRIS at the GTC, whose aim is to become the deepest
emission-line object survey to date. With 100% of the data of the first
pointing finally obtained in June 2014, we present here some aspects of the
processing of the data and the very first results of the OTELO survey. We also
explain the next steps to be followed in the near future.Comment: Oral contribution presented in the XI Scientific Meeting of the
Spanish Astronomical Society held on September 8-12, in Teruel, Spain (7
pages, 2 figures, 1 table). To appear in Highlights of Spanish Astrophysics
VIII, Proceedings of the XI Scientific Meeting of the Spanish Astronomical
Society. Eds. A. J. Cenarro, F. Figueras, C. Hern\'andez-Monteagudo, J.
Trujillo, L. Valdiviels
Neutrino mean free paths in spin-polarized neutron Fermi liquids
Neutrino mean free paths in magnetized neutron matter are calculated using
the Hartree-Fock approximation with effective Skyrme and Gogny forces in the
framework of the Landau Fermi Liquid Theory. It is shown that describing
nuclear interaction with Skyrme forces and for magnetic field strengths
, the neutrino mean free paths stay almost unchanged
at intermediate densities but they largely increase at high densities when they
are compared to the field-free case results. However the description with Gogny
forces differs from the previous and mean free paths stay almonst unchanged or
decrease at densities . This different behaviour can be explained
due to the combination of common mild variation of the Landau parameters with
both types of forces and the values of the nucleon effective mass and induced
magnetization of matter under presence of a strong magnetic field as described
with the two parametrizations of the nuclear interaction.Comment: 9 pages, 3 figure
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