1,158 research outputs found
Other incarnations of the Gross-Pitaevskii dark soliton
We show that the dark soliton of the Gross-Pitaevskii equation (GPE) that
describes the Bose-Einstein condensate (BEC) density of a system of weakly
repulsive bosons, also describes that of a system of strongly repulsive hard
core bosons at half filling. As a consequence of this, the GPE soliton gets
related to the magnetic soliton in an easy-plane ferromagnet, where it
describes the square of the in-plane magnetization of the system. These
relationships are shown to be useful in understanding various characteristics
of solitons in these distinct many-body systems
Coherent pairing states for the Hubbard model
We consider the Hubbard model and its extensions on bipartite lattices. We
define a dynamical group based on the -pairing operators introduced by
C.N.Yang, and define coherent pairing states, which are combinations of
eigenfunctions of -operators. These states permit exact calculations of
numerous physical properties of the system, including energy, various
fluctuations and correlation functions, including pairing ODLRO to all orders.
This approach is complementary to BCS, in that these are superconducting
coherent states associated with the exact model, although they are not
eigenstates of the Hamiltonian.Comment: 5 pages, RevTe
The Mannose Receptor Mediates Dengue Virus Infection of Macrophages
Macrophages (MĂ) and mononuclear phagocytes are major targets of infection by dengue virus (DV), a mosquito-borne flavivirus that can cause haemorrhagic fever in humans. To our knowledge, we show for the first time that the MĂ mannose receptor (MR) binds to all four serotypes of DV and specifically to the envelope glycoprotein. Glycan analysis, ELISA, and blot overlay assays demonstrate that MR binds via its carbohydrate recognition domains to mosquito and human cellâproduced DV antigen. This binding is abrogated by deglycosylation of the DV envelope glycoprotein. Surface expression of recombinant MR on NIH3T3 cells confers DV binding. Furthermore, DV infection of primary human MĂ can be blocked by anti-MR antibodies. MR is a prototypic marker of alternatively activated MĂ, and pre-treatment of human monocytes or MĂ with type 2 cytokines (IL-4 or IL-13) enhances their susceptibility to productive DV infection. Our findings indicate a new functional role for the MR in DV infection
Semiclassical description of Heisenberg models via spin-coherent states
We use spin-coherent states as a time-dependent variational ansatz for a
semiclassical description of a large family of Heisenberg models. In addition
to common approaches we also evaluate the square variance of the Hamiltonian in
terms of coherent states. This quantity turns out to have a natural
interpretation with respect to time-dependent solutions of the equations of
motion and allows for an estimate of quantum fluctuations in a semiclassical
regime. The general results are applied to solitons, instantons and vortices in
several one- and two-dimensional models.Comment: 14 page
Field-Dependent Tilt and Birefringence of Electroclinic Liquid Crystals: Theory and Experiment
An unresolved issue in the theory of liquid crystals is the molecular basis
of the electroclinic effect in the smectic-A phase. Recent x-ray scattering
experiments suggest that, in a class of siloxane-containing liquid crystals, an
electric field changes a state of disordered molecular tilt in random
directions into a state of ordered tilt in one direction. To investigate this
issue, we measure the optical tilt and birefringence of these liquid crystals
as functions of field and temperature, and we develop a theory for the
distribution of molecular orientations under a field. Comparison of theory and
experiment confirms that these materials have a disordered distribution of
molecular tilt directions that is aligned by an electric field, giving a large
electroclinic effect. It also shows that the net dipole moment of a correlated
volume of molecules, a key parameter in the theory, scales as a power law near
the smectic-A--smectic-C transition.Comment: 18 pages, including 9 postscript figures, uses REVTeX 3.0 and
epsf.st
f-Oscillators and Nonlinear Coherent States
The notion of f-oscillators generalizing q-oscillators is introduced. For
classical and quantum cases, an interpretation of the f-oscillator is provided
as corresponding to a special nonlinearity of vibration for which the frequency
of oscillation depends on the energy. The f-coherent states (nonlinear coherent
states) generalizing q-coherent states are constructed. Applied to quantum
optics, photon distribution function, photon number means, and dispersions are
calculated for the f-coherent states as well as the Wigner function and
Q-function. As an example, it is shown how this nonlinearity may affect the
Planck distribution formula.Comment: Latex, 32 pages, accepted by Physica Script
Scalar quantum kinetic theory for spin-1/2 particles: mean field theory
Starting from the Pauli Hamiltonian operator, we derive a scalar quantum
kinetic equations for spin-1/2 systems. Here the regular Wigner two-state
matrix is replaced by a scalar distribution function in extended phase space.
Apart from being a formulation of principal interest, such scalar quantum
kinetic equation makes the comparison to classical kinetic theory
straightforward, and lends itself naturally to currently available numerical
Vlasov and Boltzmann schemes. Moreover, while the quasi-distribution is a
Wigner function in regular phase space, it is given by a Q-function in spin
space. As such, nonlinear and dynamical quantum plasma problems are readily
handled. Moreover, the issue of gauge invariance is treated. Applications (e.g.
ultra-dense laser compressed targets and their diagnostics), possible
extensions, and future improvements of the presented quantum statistical model
are discussed.Comment: 21 pages, 2 figure
Supercoherent States, Super K\"ahler Geometry and Geometric Quantization
Generalized coherent states provide a means of connecting square integrable
representations of a semi-simple Lie group with the symplectic geometry of some
of its homogeneous spaces. In the first part of the present work this point of
view is extended to the supersymmetric context, through the study of the
OSp(2/2) coherent states. These are explicitly constructed starting from the
known abstract typical and atypical representations of osp(2/2). Their
underlying geometries turn out to be those of supersymplectic OSp(2/2)
homogeneous spaces. Moment maps identifying the latter with coadjoint orbits of
OSp(2/2) are exhibited via Berezin's symbols. When considered within
Rothstein's general paradigm, these results lead to a natural general
definition of a super K\"ahler supermanifold, the supergeometry of which is
determined in terms of the usual geometry of holomorphic Hermitian vector
bundles over K\"ahler manifolds. In particular, the supergeometry of the above
orbits is interpreted in terms of the geometry of Einstein-Hermitian vector
bundles. In the second part, an extension of the full geometric quantization
procedure is applied to the same coadjoint orbits. Thanks to the super K\"ahler
character of the latter, this procedure leads to explicit super unitary
irreducible representations of OSp(2/2) in super Hilbert spaces of
superholomorphic sections of prequantum bundles of the Kostant type. This work
lays the foundations of a program aimed at classifying Lie supergroups'
coadjoint orbits and their associated irreducible representations, ultimately
leading to harmonic superanalysis. For this purpose a set of consistent
conventions is exhibited.Comment: 53 pages, AMS-LaTeX (or LaTeX+AMSfonts
Geometric Entanglement of Symmetric States and the Majorana Representation
Permutation-symmetric quantum states appear in a variety of physical
situations, and they have been proposed for quantum information tasks. This
article builds upon the results of [New J. Phys. 12, 073025 (2010)], where the
maximally entangled symmetric states of up to twelve qubits were explored, and
their amount of geometric entanglement determined by numeric and analytic
means. For this the Majorana representation, a generalization of the Bloch
sphere representation, can be employed to represent symmetric n qubit states by
n points on the surface of a unit sphere. Symmetries of this point distribution
simplify the determination of the entanglement, and enable the study of quantum
states in novel ways. Here it is shown that the duality relationship of
Platonic solids has a counterpart in the Majorana representation, and that in
general maximally entangled symmetric states neither correspond to anticoherent
spin states nor to spherical designs. The usability of symmetric states as
resources for measurement-based quantum computing is also discussed.Comment: 10 pages, 8 figures; submitted to Lecture Notes in Computer Science
(LNCS
Coherent States Measurement Entropy
Coherent states (CS) quantum entropy can be split into two components. The
dynamical entropy is linked with the dynamical properties of a quantum system.
The measurement entropy, which tends to zero in the semiclassical limit,
describes the unpredictability induced by the process of a quantum approximate
measurement. We study the CS--measurement entropy for spin coherent states
defined on the sphere discussing different methods dealing with the time limit
. In particular we propose an effective technique of computing
the entropy by iterated function systems. The dependence of CS--measurement
entropy on the character of the partition of the phase space is analysed.Comment: revtex, 22 pages, 14 figures available upon request (e-mail:
[email protected]). Submitted to J.Phys.
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