15,454 research outputs found
Topology of Knotted Optical Vortices
Optical vortices as topological objects exist ubiquitously in nature. In this
paper, by making use of the -mapping topological current theory, we
investigate the topology in the closed and knotted optical vortices. The
topological inner structure of the optical vortices are obtained, and the
linking of the knotted optical vortices is also given.Comment: 11 pages, no figures, accepted by Commun. Theor. Phys. (Beijing, P.
R. China
A QM/MM equation-of-motion coupled-cluster approach for predicting semiconductor color-center structure and emission frequencies
Valence excitation spectra are computed for all deep-center silicon-vacancy
defect types in 3C, 4H, and 6H silicon carbide (SiC) and comparisons are made
with literature photoluminescence measurements. Nuclear geometries surrounding
the defect centers are optimized within a Gaussian basis-set framework using
many-body perturbation theory or density functional theory (DFT) methods, with
computational expenses minimized by a QM/MM technique called SIMOMM. Vertical
excitation energies are subsequently obtained by applying excitation-energy,
electron-attached, and ionized equation-of-motion coupled-cluster (EOMCC)
methods, where appropriate, as well as time-dependent (TD) DFT, to small models
including only a few atoms adjacent to the defect center. We consider the
relative quality of various EOMCC and TD-DFT methods for (i) energy-ordering
potential ground states differing incrementally in charge and multiplicity,
(ii) accurately reproducing experimentally measured photoluminescence peaks,
and (iii) energy-ordering defects of different types occurring within a given
polytype. The extensibility of this approach to transition-metal defects is
also tested by applying it to silicon-substitutional chromium defects in SiC
and comparing with measurements. It is demonstrated that, when used in
conjunction with SIMOMM-optimized geometries, EOMCC-based methods can provide a
reliable prediction of the ground-state charge and multiplicity, while also
giving a quantitative description of the photoluminescence spectra, accurate to
within 0.1 eV of measurement in all cases considered.Comment: 13 pages, 4 figures, 6 tables, 5 equations, 100 reference
Comment on "Quantum Phase Slips and Transport in Ultrathin Superconducting Wires"
In a recent Letter (Phys. Rev. Lett.78, 1552 (1997) ), Zaikin, Golubev, van
Otterlo, and Zimanyi criticized the phenomenological time-dependent
Ginzburg-Laudau model which I used to study the quantum phase-slippage rate for
superconducting wires. They claimed that they developed a "microscopic" model,
made qualitative improvement on my overestimate of the tunnelling barrier due
to electromagnetic field. In this comment, I want to point out that, i), ZGVZ's
result on EM barrier is expected in my paper; ii), their work is also
phenomenological; iii), their renormalization scheme is fundamentally flawed;
iv), they underestimated the barrier for ultrathin wires; v), their comparison
with experiments is incorrect.Comment: Substantial changes made. Zaikin et al's main result was expected
from my work. They underestimated tunneling barrier for ultrathin wires by
one order of magnitude in the exponen
Superfluidity of fermions with repulsive on-site interaction in an anisotropic optical lattice near a Feshbach resonance
We present a numerical study on ground state properties of a one-dimensional
(1D) general Hubbard model (GHM) with particle-assisted tunnelling rates and
repulsive on-site interaction (positive-U), which describes fermionic atoms in
an anisotropic optical lattice near a wide Feshbach resonance. For our
calculation, we utilize the time evolving block decimation (TEBD) algorithm,
which is an extension of the density matrix renormalization group and provides
a well-controlled method for 1D systems. We show that the positive-U GHM, when
hole-doped from half-filling, exhibits a phase with coexistence of
quasi-long-range superfluid and charge-density-wave orders. This feature is
different from the property of the conventional Hubbard model with positive-U,
indicating the particle-assisted tunnelling mechanism in GHM brings in
qualitatively new physics.Comment: updated with published version
Efficient engineering of multi-atom entanglement through single-photon detections
We propose an efficient scheme to engineer multi-atom entanglement by
detecting cavity decay through single-photon detectors. In the special case of
two atoms, this scheme is much more efficient than previous probabilistic
schemes, and insensitive to randomness in the atom's position. More generally,
the scheme can be used to prepare arbitrary superpositions of multi-atom Dicke
states without the requirements of high-efficiency detection and separate
addressing of different atoms.Comment: 5 pages, 2 figure
Entangling many atomic ensembles through laser manipulation
We propose an experimentally feasible scheme to generate
Greenberger-Horne-Zeilinger (GHZ) type of maximal entanglement between many
atomic ensembles based on laser manipulation and single-photon detection. The
scheme, with inherent fault tolerance to the dominant noise and efficient
scaling of the efficiency with the number of ensembles, allows to maximally
entangle many atomic ensemble within the reach of current technology. Such a
maximum entanglement of many ensembles has wide applications in demonstration
of quantum nonlocality, high-precision spectroscopy, and quantum information
processing.Comment: 4 pages, 1 figur
The extraction of nuclear sea quark distribution and energy loss effect in Drell-Yan experiment
The next-to-leading order and leading order analysis are performed on the
differential cross section ratio from Drell-Yan process. It is found that the
effect of next-to-leading order corrections can be negligible on the
differential cross section ratios as a function of the quark momentum fraction
in the beam proton and the target nuclei for the current Fermilab and future
lower beam proton energy. The nuclear Drell-Yan reaction is an ideal tool to
study the energy loss of the fast quark moving through cold nuclei. In the
leading order analysis, the theoretical results with quark energy loss are in
good agreement with the Fermilab E866 experimental data on the Drell-Yan
differential cross section ratios as a function of the momentum fraction of the
target parton. It is shown that the quark energy loss effect has significant
impact on the Drell-Yan differential cross section ratios. The nuclear
Drell-Yan experiment at current Fermilab and future lower energy proton beam
can not provide us with more information on the nuclear sea quark distribution.Comment: 17 pages, 4 figure
Fermionic zero modes in gauge and gravity backgrounds On
In this note we study fermionic zero modes in gauge and gravity backgrounds
taking a two dimensional compact manifold as extra dimensions. The result
is that there exist massless Dirac fermions which have normalizable zero modes
under quite general assumptions about these backgrounds on the bulk. Several
special cases of gauge background on the torus are discussed and some simple
fermionic zero modes are obtained.Comment: 8 pages, no figures, v2: more references, accepted by Mod.Phys.Lett.
Neutrino spin oscillations in gravitational fields
We study neutrino spin oscillations in black hole backgrounds. In the case of
a charged black hole, the maximum frequency of oscillations is a monotonically
increasing function of the charge. For a rotating black hole, the maximum
frequency decreases with increasing the angular momentum. In both cases, the
frequency of spin oscillations decreases as the distance from the black hole
grows. As a phenomenological application of our results, we study simple
bipolar neutrino system which is an interesting example of collective neutrino
oscillations. We show that the precession frequency of the flavor pendulum as a
function of the neutrino number density will be higher for a
charged/non-rotating black hole compared with a neutral/rotating black hole
respectively.Comment: Replaced with the version accepted for publication in Gravitation and
Cosmology, Springer. 10 pages. 4 figure
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