1,401 research outputs found
Measurements, quantum discord and parity in spin 1 systems
We consider the evaluation of the quantum discord and other related measures
of quantum correlations in a system formed by a spin 1 and a complementary spin
system. A characterization of general projective measurements in such system in
terms of spin averages is thereby introduced, which allows to easily visualize
their deviation from standard spin measurements. It is shown that the
measurement optimizing these measures corresponds in general to a non-spin
measurement. The important case of states that commute with the total
spin parity is discussed in detail, and the general stationary measurements for
such states (parity preserving measurements) are identified. Numerical and
analytical results for the quantum discord, the geometric discord and the one
way information deficit in the relevant case of a mixture of two aligned spin 1
states are also presented.Comment: 6 pages, 2 figures, References adde
Generalized mean field description of entanglement in dimerized spin systems
We discuss a generalized self-consistent mean field (MF) treatment, based on
the selection of an arbitrary subset of operators for representing the system
density matrix, and its application to the problem of entanglement evaluation
in composite quantum systems. As a specific example, we examine in detail a
pair MF approach to the ground state (GS) of dimerized spin 1/2 systems with
anisotropic ferromagnetic-type XY and XYZ couplings in a transverse field,
including chains and arrays with first neighbor and also longer range
couplings. The approach is fully analytic and able to capture the main features
of the GS of these systems, in contrast with the conventional single spin MF.
Its phase diagram differs significantly from that of the latter, exhibiting
(Sz) parity breaking just in a finite field window if the coupling between
pairs is sufficiently weak, together with a fully dimerized phase below this
window and a partially aligned phase above it. It is then shown that through
symmetry restoration, the approach is able to correctly predict not only the
concurrence of a pair, but also its entanglement with the rest of the chain,
which shows a pronounced peak in the parity breaking window. Perturbative
corrections allow to reproduce more subtle observables like the entanglement
between weakly coupled spins and the low lying energy spectrum. All predictions
are tested against exact results for finite systems.Comment: 13 pages, 9 figures. Final versio
Factorization and entanglement in general XYZ spin arrays in non-uniform transverse fields
We determine the conditions for the existence of a pair of degenerate parity
breaking separable eigenstates in general arrays of arbitrary spins connected
through couplings of arbitrary range and placed in a transverse field,
not necessarily uniform. Sufficient conditions under which they are ground
states are also provided. It is then shown that in finite chains, the
associated definite parity states, which represent the actual ground state in
the immediate vicinity of separability, can exhibit entanglement between any
two spins regardless of the coupling range or separation, with the reduced
state of any two subsystems equivalent to that of pair of qubits in an
entangled mixed state. The corresponding concurrences and negativities are
exactly determined. The same properties persist in the mixture of both definite
parity states. These effects become specially relevant in systems close to the
limit. The possibility of field induced alternating separable solutions
with controllable entanglement side limits is also discussed. Illustrative
numerical results for the negativity between the first and the
spin in an open spin chain for different values of and are as well
provided.Comment: 6 pages, figures adde
Thermal entanglement in fully connected spin systems and its RPA description
We examine the thermal pairwise entanglement in a symmetric system of
spins fully connected through anisotropic -type couplings embedded in a
transverse magnetic field. We consider both the exact evaluation together with
that obtained with the static path + random phase approximation (RPA) and the
ensuing mean field + RPA. The latter is shown to provide an accurate analytic
description of both the parallel and antiparallel thermal concurrence in large
systems. We also analyze the limit temperature for pairwise entanglement, which
is shown to increase for large fields and to decrease logarithmically with
increasing . Special finite size effects are as well discussed.Comment: 9 pages, 5 figure
Description of thermal entanglement with the static path plus random-phase approximation
We discuss the application of the static path plus random phase approximation
(SPA+RPA) and the ensuing mean field+RPA treatment to the evaluation of
entanglement in composite quantum systems at finite temperature. These methods
involve just local diagonalizations and the determination of the generalized
collective vibrational frequencies. As illustration, we evaluate the pairwise
entanglement in a fully connected XXZ chain of spins at finite temperature
in a transverse magnetic field . It is shown that already the mean field+RPA
provides an accurate analytic description of the concurrence below the mean
field critical region (), exact for large , whereas the full
SPA+RPA is able to improve results for finite systems in the critical region.
It is proved as well that for weak entanglement also arises when the
ground state is separable (), with the limit temperature for pairwise
entanglement exhibiting quite distinct regimes for .Comment: 20 pages, 5 figure
Plant Essential Oils as Healthy Functional Ingredients of Nutraceuticals and Diet Supplements: A Review
Essential oils (EOs) are mixtures of volatile molecules endowed with health-promoting biological activities that go beyond their role as aromas and natural preservatives and can be exploited to develop functional foods and diet supplements. Their composition is briefly addressed along with regulatory aspects. The potential health benefit of human diet supplementation with EOs is outlined through a review of the recent literature on available clinical trials and preclinical research concerning EOs activity towards: (1) irritable bowel syndrome; (2) inflammatory bowel disease; (3) regulation of microbiota; (4) gastroprotection; (5) hepatoprotection; (6) protection of the urinary tract and diuresis; (7) management of metabolic disorders including hyperglycemia and hyperlipidemia; (8) anti-inflammatory and pain control; (9) immunomodulation and protection from influenza; and (10) neuroprotection and modulation of mood and cognitive performance. The emerging potential in such activities of selected EOs is given focus, particularly green and black cumin, bergamot, orange, myrtle, peppermint, sage, eucalyptus, lavender, thyme, lemon balm, ginger, and garlic
RNA-mediated interaction of Cajal bodies and U2 snRNA genes
Cajal bodies (CBs) are nuclear structures involved in RNA metabolism that accumulate high concentrations of small nuclear ribonucleoproteins (snRNPs). Notably, CBs preferentially associate with specific genomic loci in interphase human cells, including several snRNA and histone gene clusters. To uncover functional elements involved in the interaction of genes and CBs, we analyzed the expression and subcellular localization of stably transfected artificial arrays of U2 snRNA genes. Although promoter substitution arrays colocalized with CBs, constructs containing intragenic deletions did not. Additional experiments identified factors within CBs that are important for association with the native U2 genes. Inhibition of nuclear export or targeted degradation of U2 snRNPs caused a marked decrease in the levels of U2 snRNA in CBs and strongly disrupted the interaction with U2 genes. Together, the results illustrate a specific requirement for both the snRNA transcripts as well as the presence of snRNPs (or snRNP proteins) within CBs. Our data thus provide significant insight into the mechanism of CB interaction with snRNA loci, strengthening the putative role for this nuclear suborganelle in snRNP biogenesis
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