987 research outputs found
Topological and Entanglement Properties of Resonating Valence Bond wavefunctions
We examine in details the connections between topological and entanglement
properties of short-range resonating valence bond (RVB) wave functions using
Projected Entangled Pair States (PEPS) on kagome and square lattices on
(quasi-)infinite cylinders with generalized boundary conditions (and perimeters
with up to 20 lattice spacings). Making use of disconnected topological sectors
in the space of dimer lattice coverings, we explicitly derive (orthogonal)
"minimally entangled" PEPS RVB states. For the kagome lattice, we obtain, using
the quantum Heisenberg antiferromagnet as a reference model, the finite size
scaling of the energy separations between these states. In particular, we
extract two separate (vanishing) energy scales corresponding (i) to insert a
vison line between the two ends of the cylinder and (ii) to pull out and freeze
a spin at either end. We also investigate the relations between bulk and
boundary properties and show that, for a bipartition of the cylinder, the
boundary Hamiltonian defined on the edge can be written as a product of a
highly non-local projector with an emergent (local) su(2)-invariant
one-dimensional (superfluid) t--J Hamiltonian, which arises due to the symmetry
properties of the auxiliary spins at the edge. This multiplicative structure, a
consequence of the disconnected topological sectors in the space of dimer
lattice coverings, is characteristic of the topological nature of the states.
For minimally entangled RVB states, it is shown that the entanglement spectrum,
which reflects the properties of the edge modes, is a subset (half for kagome
RVB) of the spectrum of the local Hamiltonian, providing e.g. a simple argument
on the origin of the topological entanglement entropy S0=-ln 2 of Z2 spin
liquids. We propose to use these features to probe topological phases in
microscopic Hamiltonians and some results are compared to existing DMRG data.Comment: 15 pages, 19 figures. Large extension of the paper. Finite size
scaling of the (topological) ground state energy splittings added (for the
Kagome quantum antiferromagnet
Resonating valence bond states in the PEPS formalism
We study resonating valence bond (RVB) states in the Projected Entangled Pair
States (PEPS) formalism. Based on symmetries in the PEPS description, we
establish relations between the toric code state, the orthogonal dimer state,
and the SU(2) singlet RVB state on the kagome lattice: We prove the equivalence
of toric code and dimer state, and devise an interpolation between the dimer
state and the RVB state. This interpolation corresponds to a continuous path in
Hamiltonian space, proving that the RVB state is the four-fold degenerate
ground state of a local Hamiltonian on the (finite) kagome lattice. We
investigate this interpolation using numerical PEPS methods, studying the decay
of correlation functions, the change of overlap, and the entanglement spectrum,
none of which exhibits signs of a phase transition.Comment: 11+9 pages, 28 figures. v2: More numerical results, and a few minor
improvements. v3: Accepted version (minor changes relative to v2),
Journal-Ref adde
Quantum entanglement theory in the presence of superselection rules
Superselection rules severly constrain the operations which can be
implemented on a distributed quantum system. While the restriction to local
operations and classical communication gives rise to entanglement as a nonlocal
resource, particle number conservation additionally confines the possible
operations and should give rise to a new resource. In [Phys. Rev. Lett. 92,
087904 (2004), quant-ph/0310124] we showed that this resource can be quantified
by a single additional number, the superselection induced variance (SiV)
without changing the concept of entanglement. In this paper, we give the
results on pure states in greater detail; additionally, we provide a discussion
of mixed state nonlocality with superselection rules where we consider both
formation and distillation. Finally, we demonstrate that SiV is indeed a
resource, i.e., that it captures how well a state can be used to overcome the
restrictions imposed by the superselection rule.Comment: 16 pages, 5 figure
Matrix Product State and mean field solutions for one-dimensional systems can be found efficiently
We consider the problem of approximating ground states of one-dimensional
quantum systems within the two most common variational ansatzes, namely the
mean field ansatz and Matrix Product States. We show that both for mean field
and for Matrix Product States of fixed bond dimension, the optimal solutions
can be found in a way which is provably efficient (i.e., scales polynomially).
This implies that the corresponding variational methods can be in principle
recast in a way which scales provably polynomially. Moreover, our findings
imply that ground states of one-dimensional commuting Hamiltonians can be found
efficiently.Comment: 5 pages; v2: accepted version, Journal-ref adde
Xcompact3D: An open-source framework for solving turbulence problems on a Cartesian mesh
Xcompact3D is a Fortran 90–95 open-source framework designed for fast and accurate simulations of turbulent flows, targeting CPU-based supercomputers. It is an evolution of the flow solver Incompact3D which was initially designed in France in the mid-90’s for serial processors to solve the incompressible Navier–Stokes equations. Incompact3D was then ported to parallel High Performance Computing (HPC) systems in the early 2010’s. Very recently the capabilities of Incompact3D have been extended so that it can now tackle more flow regimes (from incompressible flows to compressible flows at low Mach numbers), resulting in the design of a new user-friendly framework called Xcompact3D. The present manuscript presents an overview of Xcompact3D with a particular focus on its functionalities, its ready-to-run simulations and a few case studies to demonstrate its impact
Projection, Spatial Correlations, and Anisotropies in a Large and Complete Sample of Abell Clusters
An analysis of R >= 1 Abell clusters is presented for samples containing
recent redshifts from the MX Northern Abell Cluster Survey. The newly obtained
redshifts from the MX Survey as well as those from the ESO Nearby Abell Cluster
Survey (ENACS) provide the necessary data for the largest magnitude-limited
correlation analysis of rich clusters in the entire sky (excluding the galactic
plane) to date. We find 19.4 <= r_0 <= 23.3 h^-1Mpc, -1.92 <= gamma <= -1.83
for four different subsets of Abell/ACO clusters, including a large sample
(N=104) of cD clusters. We have used this dataset to look for line-of-sight
anisotropies within the Abell/ACO catalogs. We show that the strong
anisotropies present in previously studied Abell cluster datasets are not
present in our R >= 1 samples. There are, however, indications of residual
anisotropies which we show are the result of two elongated superclusters, Ursa
Majoris and Corona Borealis, whose axes lie near the line-of-sight. After
rotating these superclusters so that their semi-major axes are prependicular to
the line-of-sight, we find no anisotropies as indicated by the correlation
function. The amplitude and slope of the two-point correlation function remain
the same before and after these rotations. We also remove a subset of R = 1
Abell/ACO clusters that show sizable foreground/background galaxy contamination
and again find no change in the amplitude or slope of the correlation function.
We conclude that the correlation length of R >= 1 Abell clusters is not
artificially enhanced by line-of-sight anisotropies.Comment: 37 pages, 8 figures, AASTeX Accepted for publication in Ap
Enhanced dielectronic recombination of lithium-like Ti19+ ions in external ExB fields
Dielectronic recombination(DR) of lithium-like Ti19+(1s2 2s) ions via 2s->2p
core excitations has been measured at the Heidelberg heavy ion storage ring
TSR. We find that not only external electric fields (0 <= Ey <= 280 V/cm) but
also crossed magnetic fields (30 mT <= Bz <= 80 mT) influence the DR via high-n
(2p_j nl)-Rydberg resonances. This result confirms our previous finding for
isoelectronic Cl14+ ions [Bartsch T et al, PRL 82, 3779 (1999)] that
experimentally established the sensitivity of DR to ExB fields. In the present
investigation the larger 2p_{1/2}-2p_{3/2} fine structure splitting of Ti19+
allowed us to study separately the influence of external fields via the two
series of Rydberg DR resonances attached to the 2s -> 2p_{1/2} and 2s ->
2p_{3/2} excitations of the Li-like core, extracting initial slopes and
saturation fields of the enhancement. We find that for Ey > 80 V/cm the field
induced enhancement is about 1.8 times stronger for the 2p_{3/2} series than
for the 2p_{1/2} series.Comment: 10 pages, 3 figures, to be published in Journal of Physics B, see
also http://www.strz.uni-giessen.de/~k
Experimental Test of Higher-Order Electron-Capture Processes in Collisions of Fast Protons with Atomic Hydrogen
We present measurements of the angular distribution of fast hydrogen atoms formed by electron capture of 2.8- and 5.0-MeV protons in atomic hydrogen. In the angular region of the Thomas peak (0.47 mrad) the experimental results obtained with this pure three-body collision system are in reasonable agreement with a strong-potential Born calculation and the impulse approximation, but not with other higher-order theories
Coherent states of a charged particle in a uniform magnetic field
The coherent states are constructed for a charged particle in a uniform
magnetic field based on coherent states for the circular motion which have
recently been introduced by the authors.Comment: 2 eps figure
Extracts of Tagetes minuta L. front of bacteria regarding bovine mastites.
Bovine mastitis is a problem in the context of animal health. However medicinal plants are a management strategy in agroecological production systems. In this context, the plant Tagetes minuta L. plays a leading role, due to its recognition in the popular pharmacopeia. Thus, the objective of this work was to assess the effect of hydroalcoholic extracts of T. minuta from different collection sites compared to ten bacteria related to bovine mastitis. The antimicrobial evaluation was done through the microdilution technique in syrup, in 96 well microplates in triplicate, for the determination of Minimal Bacterial Concentration (MBC) (%). In the microplates, the extracts of T. minuta and the inoculums of the bacteria were placed in addition to the growth control of the bacteria and the control of the extracts, which were incubated for 72 hours at 37°C in an oven. After this time, aliquots of 5?L of each orifice were transferred to plates containing 5% equine defibrinated blood agar and maintained in incubation for 24 hours at the same previous temperature. With this, the growth readings were performed, with the subsequent interpretation of the results by the geometric mean of the MBC (%). The results indicate that there is a difference in sensitivity to microorganisms by the extracts as a function of the collection sites and both present antimicrobial action
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