2,170 research outputs found
A Scalar Wigner Theory for Polarized Light in Nonlinear Kerr Media
A scalar Wigner distribution function for describing polarized light is
proposed in analogy with the treatment of spin variables in quantum kinetic
theory. The formalism is applied to the propagation of circularly polarized
light in nonlinear Kerr media and an extended phase space evolution equation is
derived along with invariant quantities. We further consider modulation
instability as well as the extension to partially coherent fields.Comment: 6 page
Broadband, unpolarized repumping and clearout light sources for Sr single-ion clocks
Future transportable optical clocks require compact and reliable light
sources. Here, broadband, unpolarized repumper and state clearout sources for
Sr+ single-ion optical clocks are reported. These turn-key devices require no
frequency stabilization nor external modulators. They are fiber based,
inexpensive, and compact. Key characteristics for clock operation are
presented, including optical spectra, induced light shifts and required
extinction ratios. Tests with an operating single-ion standard show a clearout
efficiency of 100%. Compared to a laser-based repumper, the achievable
fluorescence rates for ion detection are a few tens of per cent lower. The
resulting ion kinetic temperature is 1--1.5 mK, near the Doppler limit of the
ion system. Similar repumper light sources could be made for Ca+ (866 nm) and
Ba+ (650 nm) using semiconductor gain media.Comment: 4 pages, 6 figure
The Effect of Columnar Disorder on the Superconducting Transition of a Type-II Superconductor in Zero Applied Magnetic Field
We investigate the effect of random columnar disorder on the superconducting
phase transition of a type-II superconductor in zero applied magnetic field
using numerical simulations of three dimensional XY and vortex loop models. We
consider both an unscreened model, in which the bare magnetic penetration
length is approximated as infinite, and a strongly screened model, in which the
magnetic penetration length is of order the vortex core radius. We consider
both equilibrium and dynamic critical exponents. We show that, as in the
disorder free case, the equilibrium transitions of the unscreened and strongly
screened models lie in the same universality class, however scaling is now
anisotropic. We find for the correlation length exponent , and
for the anisotropy exponent . We find different dynamic
critical exponents for the unscreened and strongly screened models.Comment: 30 pages 12 ps figure
Conformation of a Polyelectrolyte Complexed to a Like-Charged Colloid
We report results from a molecular dynamics (MD) simulation on the
conformations of a long flexible polyelectrolyte complexed to a charged sphere,
\textit{both negatively charged}, in the presence of neutralizing counterions
in the strong Coulomb coupling regime. The structure of this complex is very
sensitive to the charge density of the polyelectrolyte. For a fully charged
polyelectrolyte the polymer forms a dense two-dimensional "disk", whereas for a
partially charged polyelectrolyte the monomers are spread over the colloidal
surface. A mechanism involving the \textit{overcharging} of the polyelectrolyte
by counterions is proposed to explain the observed conformations.Comment: 4 pages, 4 figures (6 EPS files
Vortex glass transition in a random pinning model
We study the vortex glass transition in disordered high temperature
superconductors using Monte Carlo simulations. We use a random pinning model
with strong point-correlated quenched disorder, a net applied magnetic field,
longrange vortex interactions, and periodic boundary conditions. From a finite
size scaling study of the helicity modulus, the RMS current, and the
resistivity, we obtain critical exponents at the phase transition. The new
exponents differ substantially from those of the gauge glass model, but are
consistent with those of the pure three-dimensional XY model.Comment: 7 pages RevTeX, 4 eps figure
Superfluid, Mott-Insulator, and Mass-Density-Wave Phases in the One-Dimensional Extended Bose-Hubbard Model
We use the finite-size density-matrix-renormalization-group (FSDMRG) method
to obtain the phase diagram of the one-dimensional () extended
Bose-Hubbard model for density in the plane, where and
are, respectively, onsite and nearest-neighbor interactions. The phase diagram
comprises three phases: Superfluid (SF), Mott Insulator (MI) and Mass Density
Wave (MDW). For small values of and , we get a reentrant SF-MI-SF phase
transition. For intermediate values of interactions the SF phase is sandwiched
between MI and MDW phases with continuous SF-MI and SF-MDW transitions. We
show, by a detailed finite-size scaling analysis, that the MI-SF transition is
of Kosterlitz-Thouless (KT) type whereas the MDW-SF transition has both KT and
two-dimensional-Ising characters. For large values of and we get a
direct, first-order, MI-MDW transition. The MI-SF, MDW-SF and MI-MDW phase
boundaries join at a bicritical point at (.Comment: 10 pages, 15 figure
Quantum simulations of the superfluid-insulator transition for two-dimensional, disordered, hard-core bosons
We introduce two novel quantum Monte Carlo methods and employ them to study
the superfluid-insulator transition in a two-dimensional system of hard-core
bosons. One of the methods is appropriate for zero temperature and is based
upon Green's function Monte Carlo; the other is a finite-temperature world-line
cluster algorithm. In each case we find that the dynamical exponent is
consistent with the theoretical prediction of by Fisher and co-workers.Comment: Revtex, 10 pages, 3 figures (postscript files attached at end,
separated by %%%%%% Fig # %%%%%, where # is 1-3). LA-UR-94-270
Mean Field Theory of the Localization Transition
A mean field theory of the localization transition for bosonic systems is
developed. Localization is shown to be sensitive to the distribution of the
random site energies. It occurs in the presence of a triangular distribution,
but not a uniform one. The inverse participation ratio, the single site Green's
function, the superfluid order parameter and the corresponding susceptibility
are calculated, and the appropriate exponents determined. All of these
quantities indicate the presence of a new phase, which can be identified as the
{\it Bose-glass}.Comment: 4 pages, Revtex, 2 figures appende
A model of inversion of DNA charge by a positive polymer: fractionization of the polymer charge
Charge inversion of a DNA double helix by an oppositely charged flexible
polyelectrolyte (PE) is considered. We assume that, in the neutral state of the
DNA-PE complex, each of the DNA charges is locally compensated by a PE charge.
When an additional PE molecule is adsorbed by DNA, its charge gets fractionized
into monomer charges of defects (tails and arches) on the background of the
perfectly neutralized DNA. These charges spread all over the DNA eliminating
the self-energy of PE. This fractionization mechanism leads to a substantial
inversion of the DNA charge, a phenomenon which is widely used for gene
delivery.Comment: 4 pages, 2 figures. Improved figures and various corrections to tex
Spin Bose Glass Phase in Bilayer Quantum Hall Systems at
We develop an effective spin theory to describe magnetic properties of the
Quantum Hall bilayer systems. In the absence of disorder this theory
gives quantitative agreement with the results of microscopic Hartree-Fock
calculations, and for finite disorder it predicts the existence of a novel spin
Bose glass phase. The Bose glass is characterized by the presence of domains of
canted antiferromagnetic phase with zero average antiferromagnetic order and
short range mean antiferromagnetic correlations. It has infinite
antiferromagnetic transverse susceptibility, finite longitudinal spin
susceptibility and specific heat linear in temperature. Transition from the
canted antiferromagnet phase to the spin Bose glass phase is characterized by a
universal value of the longitudinal spin conductance.Comment: 4 pages, 4 eps figure
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