10,526 research outputs found
The Topological Structure of the Space-Time Disclination
The space-time disclination is studied by making use of the decomposition
theory of gauge potential in terms of antisymmetric tensor field and
-mapping method. It is shown that the self-dual and anti-self-dual parts
of the curvature compose the space-time disclinations which are classified in
terms of topological invariants--winding number. The projection of space-time
disclination density along an antisymmetric tensor field is quantized
topologically and characterized by Brouwer degree and Hopf index.Comment: 18 pages, Revte
Reflection asymmetric relativistic mean field approach and its application to the octupole deformed nucleus Ra
A Reflection ASymmetric Relativistic Mean Field (RAS-RMF) approach is
developed by expanding the equations of motion for both the nucleons and the
mesons on the eigenfunctions of the two-center harmonic-oscillator potential.
The efficiency and reliability of the RAS-RMF approach are demonstrated in its
application to the well-known octupole deformed nucleus Ra and the
available data, including the binding energy and the deformation parameters,
are well reproduced.Comment: 4 pages, 2 figures, and 2 tables, to appear in Chinese Physics
Letter
Light trapping in high-density ultracold atomic gases for quantum memory applications
High-density and ultracold atomic gases have emerged as promising media for
storage of individual photons for quantum memory applications. In this paper we
provide an overview of our theoretical and experimental efforts in this
direction, with particular attention paid to manipulation of light storage (a)
through complex recurrent optical scattering processes in very high density
gases (b) by an external control field in a characteristic electromagnetically
induced transparency configuration.Comment: Submitted to Journal of Modern Optics, Special 2010 PQE Issu
Gaussian approximation and single-spin measurement in OSCAR MRFM with spin noise
A promising technique for measuring single electron spins is magnetic
resonance force microscopy (MRFM), in which a microcantilever with a permanent
magnetic tip is resonantly driven by a single oscillating spin. If the quality
factor of the cantilever is high enough, this signal will be amplified over
time to the point that it can be detected by optical or other techniques. An
important requirement, however, is that this measurement process occur on a
time scale short compared to any noise which disturbs the orientation of the
measured spin. We describe a model of spin noise for the MRFM system, and show
how this noise is transformed to become time-dependent in going to the usual
rotating frame. We simplify the description of the cantilever-spin system by
approximating the cantilever wavefunction as a Gaussian wavepacket, and show
that the resulting approximation closely matches the full quantum behavior. We
then examine the problem of detecting the signal for a cantilever with thermal
noise and spin with spin noise, deriving a condition for this to be a useful
measurement.Comment: 12 pages, 8 figures in EPS format, RevTeX 4.
S-Matrix Poles Close to Thresholds in Confined Geometries
We have studied the behavior of the S-matrix poles near threshold for quantum
waveguides coupled to a cavity with a defect. We emphasize the occurrence of
both dominant and shadow poles on the various sheets of the energy Riemann
surface, and show that the changes of the total conductivity near threshold as
the cavity's width changes can be explained in terms of dominant to shadow pole
transitions.Comment: 10 pages, 5 figure
Atomistic theory of electronic and optical properties of InAs/InP self-assembled quantum dots on patterned substrates
We report on a atomistic theory of electronic structure and optical
properties of a single InAs quantum dot grown on InP patterned substrate. The
spatial positioning of individual dots using InP nano-templates results in a
quantum dot embedded in InP pyramid. The strain distribution of a quantum dot
in InP pyramid is calculated using the continuum elasticity theory. The
electron and valence hole single-particle states are calculated using atomistic
effective-bond-orbital model with second nearest-neighbor interactions, coupled
to strain via Bir-Pikus Hamiltonian. The optical properties are determined by
solving many-exciton Hamiltonian for interacting electron and hole complexes
using the configuration-interaction method. The effect of positioning of
quantum dots using nanotemplate on their optical spectra is determined by a
comparison with dots on unpatterned substrates, and with experimental results.
The possibility of tuning the quantum dot properties with varying the
nano-template is explored.Comment: 9 pages, 12 figure
Intriguing Heat Conduction of a Polymer Chain
We study heat conduction in a one-dimensional chain of particles with
longitudinal as well as transverse motions. The particles are connected by
two-dimensional harmonic springs together with bending angle interactions.
Using equilibrium and nonequilibrium molecular dynamics, three types of thermal
conducting behaviors are found: a logarithmic divergence with system sizes for
large transverse coupling, 1/3 power-law at intermediate coupling, and 2/5
power-law at low temperatures and weak coupling. The results are consistent
with a simple mode-coupling analysis of the same model. The 1/3 power-law
divergence should be a generic feature for models with transverse motions.Comment: 4 page
Coherent inelastic backscattering of intense laser light by cold atoms
We present a nonperturbative treatment of coherent backscattering of intense
laser light from cold atoms, and predict a nonvanishing backscattering signal
even at very large intensities, due to the constructive (self-)interference of
inelastically scattered photons.Comment: minor change
Large adiabatic temperature and magnetic entropy changes in EuTiO3
We have investigated the magnetocaloric effect in single and polycrystalline
samples of quantum paraelectric EuTiO3 by magnetization and heat capacity
measurements. Single crystalline EuTiO3 shows antiferromagnetic ordering due to
Eu2+ magnetic moments below TN = 5.6 K. This compound shows a giant
magnetocaloric effect around its Neel temperature. The isothermal magnetic
entropy change is 49 Jkg-1K-1, the adiabatic temperature change is 21 K and the
refrigeration capacity is 500 JKg-1 for a field change of 7 T at TN. The single
crystal and polycrystalline samples show similar values of the magnetic entropy
change and adiabatic temperature changes. The large magnetocaloric effect is
due to suppression of the spin entropy associated with localized 4f moment of
Eu2+ ions. The giant magnetocaloric effect together with negligible hysteresis,
suggest that EuTiO3 could be a potential material for magnetic refrigeration
below 20 K.Comment: 12 pages, 4 figure
Diffusive transport of light in two-dimensional granular materials
We study photon diffusion in a two-dimensional random packing of monodisperse
disks as a simple model of granular material. We apply ray optics approximation
to set up a persistent random walk for the photons. We employ Fresnel's
intensity reflectance with its rich dependence on the incidence angle and
polarization state of the light. We present an analytic expression for the
transport-mean-free path in terms of the refractive indices of grains and host
medium, grain radius, and packing fraction. We perform numerical simulations to
examine our analytical result.Comment: 9 pages, 3 figure
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