2,137 research outputs found
R-matrix Approach to Quantum Superalgebras su_{q}(m|n)
Quantum superalgebras are studied in the framework of
-matrix formalism. Explicit parametrization of and
matrices in terms of generators are presented. We also show
that quantum deformation of nonsimple superalgebra requires its
extension to .Comment: 14 page
Theory of elastic interaction between colloidal particles in the nematic cell in the presence of the external electric or magnetic field
The Green function method developed in Ref.[S. B. Chernyshuk and B. I. Lev,
Phys. Rev. E \textbf{81}, 041707 (2010)] is used to describe elastic
interactions between axially symmetric colloidal particles in the nematic cell
in the presence of the external electric or magnetic field. General formulas
for dipole-dipole, dipole-quadrupole and quadrupole-quadrupole interactions in
the homeotropic and planar nematic cells with parallel and perpendicular field
orientations are obtained. A set of new results has been predicted: 1)
\textit{Deconfinement effect} for dipole particles in the homeotropic nematic
cell with negative dielectric anisotropy and perpendicular
to the cell electric field, when electric field is approaching it's Frederiks
threshold value . This means cancellation of the
confinement effect found in Ref. [M.Vilfan et al. Phys.Rev.Lett. {\bf 101},
237801, (2008)] for dipole particles near the Frederiks transition while it
remains for quadrupole particles. 2) New effect of \textit{attraction and
stabilization} of the particles along the electric field parallel to the cell
planes in the homeotropic nematic cell with . The minimun
distance between two particles depends on the strength of the field and can be
ordinary for . 3) Attraction and repulsion zones for all elastic interactions
are changed dramatically under the action of the external field.Comment: 15 pages, 17 figure
Elastic interaction between colloidal particles in confined nematic liquid crystals
The theory of elastic interaction of micron size axially symmetric colloidal
particles immersed into confined nematic liquid crystal has been proposed.
General formulas are obtained for the self energy of one colloidal particle and
interaction energy between two particles in arbitrary confined NLC with strong
anchoring condition on the bounding surface. Particular cases of dipole-dipole
interaction in the homeotropic and planar nematic cell with thickness are
considered and found to be exponentially screened on far distances with decay
length . It is predicted that bounding surfaces in
the planar cell crucially change the attraction and repulsion zones of usual
dipole-dipole interaction. As well it is predicted that \textit{the decay
length} in quadrupolar interaction is \textit{two times smaller} than for the
dipolar case.Comment: 4 pages,2 figure
Nonclassicality of noisy quantum states
Nonclassicality conditions for an oscillator-like system interacting with a
hot thermal bath are considered. Nonclassical properties of quantum states can
be conserved up to a certain temperature threshold only. In this case,
affection of the thermal noise can be compensated via transformation of an
observable, which tests the nonclassicality (witness function). Possibilities
for experimental implementations based on unbalanced homodyning are discussed.
At the same time, we demonstrate that the scheme based on balanced homodyning
cannot be improved for noisy states with proposed technique and should be
applied directly.Comment: 15 pages, 3 figure
Peculiarities of the Weyl - Wigner - Moyal formalism for scalar charged particles
A description of scalar charged particles, based on the Feshbach-Villars
formalism, is proposed. Particles are described by an object that is a Wigner
function in usual coordinates and momenta and a density matrix in the charge
variable. It is possible to introduce the usual Wigner function for a large
class of dynamical variables. Such an approach explicitly contains a measuring
device frame. From our point of view it corresponds to the Copenhagen
interpretation of quantum mechanics. It is shown how physical properties of
such particles depend on the definition of the coordinate operator. The
evolution equation for the Wigner function of a single-charge state in the
classical limit coincides with the Liouville equation. Localization
peculiarities manifest themselves in specific constraints on possible initial
conditions.Comment: 16 pages, 2 figure
Ordered droplet structures at the liquid crystal surface and elastic-capillary colloidal interactions
We demonstrate a variety of ordered patterns, including hexagonal structures
and chains, formed by colloidal particles (droplets) at the free surface of a
nematic liquid crystal (LC). The surface placement introduces a new type of
particle interaction as compared to particles entirely in the LC bulk. Namely,
director deformations caused by the particle lead to distortions of the
interface and thus to capillary attraction. The elastic-capillary coupling is
strong enough to remain relevant even at the micron scale when its
buoyancy-capillary counterpart becomes irrelevant.Comment: 10 pages, 3 figures, to be published in Physical Review Letter
Non-equilibrium statistical mechanics of classical nuclei interacting with the quantum electron gas
Kinetic equations governing time evolution of positions and momenta of atoms
in extended systems are derived using quantum-classical ensembles within the
Non-Equilibrium Statistical Operator Method (NESOM). Ions are treated
classically, while their electrons quantum mechanically; however, the
statistical operator is not factorised in any way and no simplifying
assumptions are made concerning the electronic subsystem. Using this method, we
derive kinetic equations of motion for the classical degrees of freedom (atoms)
which account fully for the interaction and energy exchange with the quantum
variables (electrons). Our equations, alongside the usual Newtonian-like terms
normally associated with the Ehrenfest dynamics, contain additional terms,
proportional to the atoms velocities, which can be associated with the
electronic friction. Possible ways of calculating the friction forces which are
shown to be given via complicated non-equilibrium correlation functions, are
discussed. In particular, we demonstrate that the correlation functions are
directly related to the thermodynamic Matsubara Green's functions, and this
relationship allows for the diagrammatic methods to be used in treating
electron-electron interaction perturbatively when calculating the correlation
functions. This work also generalises previous attempts, mostly based on model
systems, of introducing the electronic friction into Molecular Dynamics
equations of atoms.Comment: 18 page
Cavity QED in a molecular ion trap
We propose an approach for studying quantum information and performing high
resolution spectroscopy of rotational states of trapped molecular ions using an
on-chip superconducting microwave resonator. Molecular ions have several
advantages over neutral molecules. Ions can be loaded into deep (1 eV) RF traps
and are trapped independent of the electric dipole moment of their rotational
transition. Their charge protects them from motional dephasing and prevents
collisional loss, allowing 1 s coherence times when used as a quantum memory,
with detection of single molecules possible in <10 ms. An analysis of the
detection efficiency and coherence properties of the molecules is presented.Comment: 9 pages, 1 figur
Spectroscopy of a narrow-line laser cooling transition in atomic dysprosium
The laser cooling and trapping of ultracold neutral dysprosium has been
recently demonstrated using the broad, open 421-nm cycling transition.
Narrow-line magneto-optical trapping of Dy on longer wavelength transitions
would enable the preparation of ultracold Dy samples suitable for loading
optical dipole traps and subsequent evaporative cooling. We have identified the
closed 741-nm cycling transition as a candidate for the narrow-line cooling of
Dy. We present experimental data on the isotope shifts, the hyperfine constants
A and B, and the decay rate of the 741-nm transition. In addition, we report a
measurement of the 421-nm transition's linewidth, which agrees with previous
measurements. We summarize the laser cooling characteristics of these
transitions as well as other narrow cycling transitions that may prove useful
for cooling Dy.Comment: 6+ pages, 5 figures, 5 table
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