6,063 research outputs found
Theory of Fano-Kondo effect of transport properties through quantum dots
The Fano-Kondo effect in zero-bias conductance is investigated based on a
theoretical model for the T-shaped quantum dot. The conductance as a function
of the gate voltage is generally characterized by a Fano asymmetric parameter
q. With varying temperature the conductance shows a crossover between the high
and low temperature regions compared with the Kondo temperature T_K: two Fano
asymmetric peaks at high temperatures and the Fano-Kondo plateau inside a Fano
peak at low temperatures. Temperature dependence of conductance is calculated
numerically by the Finite temperature density matrix renormalization group
method (FT-DMRG).Comment: 8 pages, 7 figure
Efficient magneto-optical trapping of Yb atoms with a violet laser diode
We report the first efficient trapping of rare-earth Yb atoms with a
high-power violet laser diode (LD). An injection-locked violet LD with a 25 mW
frequency-stabilized output was used for the magneto-optical trapping (MOT) of
fermionic as well as bosonic Yb isotopes. A typical number of
atoms for Yb with a trap density of cm was
obtained. A 10 mW violet external-cavity LD (ECLD) was used for the
one-dimensional (1D) slowing of an effusive Yb atomic beam without a Zeeman
slower resulting in a 35-fold increase in the number of trapped atoms. The
overall characteristics of our compact violet MOT, e.g., the loss time of 1 s,
the loading time of 400 ms, and the cloud temperature of 0.7 mK, are comparable
to those in previously reported violet Yb MOTs, yet with a greatly reduced cost
and complexity of the experiment.Comment: 5 pages, 3 figures, 1 table, Phys. Rev. A (to be published
Critical review of [K- ppn] bound states
We make a thorough study of the process of three body kaon absorption in
nuclei, in connection with a recent FINUDA experiment which claims the
existence of a deeply bound kaonic state from the observation of a peak in the
Lambda d invariant mass distribution following K- absorption on Li6. We show
that the peak is naturally explained in terms of K- absorption from three
nucleons leaving the rest as spectators. We can also reproduce all the other
observables measured in the same experiment and used to support the hypothesis
of the deeply bound kaon state. Our study also reveals interesting aspects of
kaon absorption in nuclei, a process that must be understood in order to make
progress in the search for K- deeply bound states in nuclei.Comment: 8 pages, 7 figures. New section "Empirical qualitative discussion of
the strength of the reaction" with one new figure is added. Published in PR
The Heavy Photon Search beamline and its performance
The Heavy Photon Search (HPS) is an experiment to search for a hidden sector
photon, aka a heavy photon or dark photon, in fixed target electroproduction at
the Thomas Jefferson National Accelerator Facility (JLab). The HPS experiment
searches for the ee decay of the heavy photon with bump hunt and
detached vertex strategies using a compact, large acceptance forward
spectrometer, consisting of a silicon microstrip detector (SVT) for tracking
and vertexing, and a PbWO electromagnetic calorimeter for energy
measurement and fast triggering. To achieve large acceptance and good vertexing
resolution, the first layer of silicon detectors is placed just 10 cm
downstream of the target with the sensor edges only 500 m above and below
the beam. Placing the SVT in such close proximity to the beam puts stringent
requirements on the beam profile and beam position stability. As part of an
approved engineering run, HPS took data in 2015 and 2016 at 1.05 GeV and 2.3
GeV beam energies, respectively. This paper describes the beam line and its
performance during that data taking
Solutions of the Strominger System via Stable Bundles on Calabi-Yau Threefolds
We prove that a given Calabi-Yau threefold with a stable holomorphic vector
bundle can be perturbed to a solution of the Strominger system provided that
the second Chern class of the vector bundle is equal to the second Chern class
of the tangent bundle. If the Calabi-Yau threefold has strict SU(3) holonomy
then the equations of motion derived from the heterotic string effective action
are also satisfied by the solutions we obtain.Comment: 19 pages, late
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Higher order parametric x-ray spectra in mosaic graphite and single silicon crystals
We have observed up to eight orders (n) in the spectra of parametric x-radiation, in the range 5-40 keV, produced by interaction of a 90-MeV electron beam with mosaic graphite and 90 and 35 MeV beams with single Si crystals, Measured yields and intensity ratios, I(n{ge}2)/I(n=1), in graphite are not in agreement with PXR theory for mosaic crystals. In comparison, yield and ratios of intensities in Si are close to preductions for perfect crystals. Bandwidths of spectral lines measured in both Si and graphite are in good agreement with theory and are determined by the angular field of view of the detector
Formation of Organic Color Centers in Air-Suspended Carbon Nanotubes Using Vapor-Phase Reaction
Organic color centers in single-walled carbon nanotubes have demonstrated
exceptional ability to generate single photons at room temperature in the
telecom range. Combining the color centers with pristine air-suspended tubes
would be desirable for improved performance, but all current synthetic methods
occur in solution which makes them incompatible. Here we demonstrate formation
of color centers in air-suspended nanotubes using vapor-phase reaction.
Functionalization is directly verified on the same nanotubes by
photoluminescence spectroscopy, with unambiguous statistics from more than a
few thousand individual nanotubes. The color centers show a strong
diameter-dependent emission intensity, which can be explained with a
theoretical model for chemical reactivity taking into account strain along the
tube curvature. We are also able to estimate the defect density by comparing
the experiments with simulations based on a one-dimensional diffusion equation,
whereas the analysis of diameter dependent peak energies gives insight to the
nature of the dopant states. Time-resolved measurements show a longer lifetime
for color center emission compared to E exciton states. Our results
highlight the influence of the tube structure on vapor-phase reactivity and
emission properties, providing guidelines for development of high-performance
near-infrared quantum light sources.Comment: 8 pages, 6 figure
Sudden switch of generalized Lieb-Robinson velocity in a transverse field Ising spin chain
The Lieb-Robinson theorem states that the speed at which the correlations
between two distant nodes in a spin network can be built through local
interactions has an upper bound, which is called the Lieb-Robinson velocity.
Our central aim is to demonstrate how to observe the Lieb-Robinson velocity in
an Ising spin chain with a strong transverse field. We adopt and compare four
correlation measures for characterizing different types of correlations, which
include correlation function, mutual information, quantum discord, and
entanglement of formation. We prove that one of correlation functions shows a
special behavior depending on the parity of the spin number. All the
information-theoretical correlation measures demonstrate the existence of the
Lieb-Robinson velocity. In particular, we find that there is a sudden switch of
the Lieb-Robinson speed with the increasing of the number of spin
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