1,323 research outputs found
Quantum trajectory approach to stochastically-induced quantum interference effects in coherently-driven two-level atoms
Stochastic perturbation of two-level atoms strongly driven by a coherent
light field is analyzed by the quantum trajectory method. A new method is
developed for calculating the resonance fluorescence spectra from numerical
simulations. It is shown that in the case of dominant incoherent perturbation,
the stochastic noise can unexpectedly create phase correlation between the
neighboring atomic dressed states. This phase correlation is responsible for
quantum interference between the related transitions resulting in anomalous
modifications of the resonance fluorescence spectra.Comment: paper accepted for publicatio
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Effect of Second-Phase Doping on Laser Deposited Al2O3 Ceramics
Direct fabrication of engineering ceramic components by additive manufacturing (AM) is a
relatively new method for producing complex mechanical structures. This study investigates how
a second-phase doping may affect Al2O3 ceramic parts deposited by AM with a laser engineered
net shaping (LENS) system. In this study, ZrO2 and Y2O3 powders are respectively doped into
Al2O3 powders at the eutectic ratio as second-phases to improve the quality of a deposited part.
The deposited Al2O3, Al2O3/ZrO2 and Al2O3/YAG (yttrium aluminum garnet) parts are examined
for their micro-structures and micro-hardness, as well as defects. The results show that doping of
ZrO2 or Y2O3 as a second-phase performs a significant role in suppressing cracks and in refining
grains of the laser deposited parts. The micro-hardness investigation reveals that the
second-phase doping does not result in much hardness reduction in Al2O3 and the two eutectic
ceramics are both harder than 1500 Hv. The study concludes that the second-phase doping is
good for improving laser deposited ceramic parts.Mechanical Engineerin
Cavity implementation of quantum interference in a -type atom
A scheme for engineering quantum interference in a -type atom
coupled to a frequency-tunable, single-mode cavity field with a pre-selected
polarization at finite temperature is proposed. Interference-assisted
population trapping, population inversions and probe gain at one sideband of
the Autler-Townes spectrum are predicted for certain cavity resonant
frequencies.Comment: 2 postscript figures are adde
Interference-induced gain in Autler-Townes doublet of a V-type atom in a cavity
We study the Autler-Townes spectrum of a V-type atom coupled to a
single-mode, frequency-tunable cavity field at finite termperature, with a
pre-selected polarization in the bad cavity limit, and show that, when the mean
number of thermal photons and the excited sublevel splitting is very
large (the same order as the cavity linewidth), the probe gain may occur at
either sideband of the doublet, depending on the cavity frequency, due to the
cavity-induced interference.Comment: Minor changes are mad
Strong Influence of Phonons on the Electron Dynamics of Bi2212
The sudden change of the velocity, so-called "kink," of the dispersing peak
in angle resolved photoelectron spectroscopy is a well-known feature in the
high temperature superconducting cuprates. Currently, the origin of the kink is
being much debated, but a consensus has not emerged yet. Here, we present a
study of the momentum evolution of the kink structure from the nodal region
towards the anti-nodal region, for optimally doped Bi2212 sample. We show that
the observed temperature dependence of the kink structure in both regions of
the momentum space is consistent with a scenario in which phonons contribute
strongly to the kink
Onsager Relations and Hydrodynamic Balance Equations in 2D Quantum Wells
In this letter we clarify the role of heat flux in the hydrodynamic balance
equations in 2D quantum wells, facilitating the formulation of an Onsager
relation within the framework of this theory. We find that the Onsager relation
is satisfied within the framework of the 2D hydrodynamic balance equation
transport theory at sufficiently high density. The condition of high density is
consonant with the requirement of strong electron-electron interactions for the
validity of our balance equation formulation.Comment: 11 pages, RevTex, 4 postscript figures are avaliable upon reques
Synthesis and characterization of atomically-thin graphite films on a silicon carbide substrate
This paper reports the synthesis and detailed characterization of graphite
thin films produced by thermal decomposition of the (0001) face of a 6H-SiC
wafer, demonstrating the successful growth of single crystalline films down to
approximately one graphene layer. The growth and characterization were carried
out in ultrahigh vacuum (UHV) conditions. The growth process and sample quality
were monitored by low-energy electron diffraction, and the thickness of the
sample was determined by core level x-ray photoelectron spectroscopy.
High-resolution angle-resolved photoemission spectroscopy shows constant energy
map patterns, which are very sharp and fully momentum-resolved, but nonetheless
not resolution limited. We discuss the implications of this observation in
connection with scanning electron microscopy data, as well as with previous
studies
Low energy excitations in graphite: The role of dimensionality and lattice defects
In this paper, we present a high resolution angle resolved photoemission
spectroscopy (ARPES) study of the electronic properties of graphite. We found
that the nature of the low energy excitations in graphite is particularly
sensitive to interlayer coupling as well as lattice disorder. As a consequence
of the interlayer coupling, we observed for the first time the splitting of the
bands by 0.7 eV near the Brillouin zone corner K. At low
binding energy, we observed signatures of massless Dirac fermions with linear
dispersion (as in the case of graphene), coexisting with quasiparticles
characterized by parabolic dispersion and finite effective mass. We also report
the first ARPES signatures of electron-phonon interaction in graphite: a kink
in the dispersion and a sudden increase in the scattering rate. Moreover, the
lattice disorder strongly affects the low energy excitations, giving rise to
new localized states near the Fermi level. These results provide new insights
on the unusual nature of the electronic and transport properties of graphite.Comment: 10 pages, 15 figure
Quantum-classical transition of the escape rate of uniaxial antiferromagnetic particles in an arbitrarily directed field
Quantum-classical escape rate transition has been studied for uniaxial
antiferromagnetic particles with an arbitrarily directed magnetic field. In the
case that the transverse and longitudinal fileds coexist, we calculate the
phase boundary line between first- and second-order transitions, from which
phase diagrams can be obtained. It is shown that the effects of the applied
longitudinal magnetic field on quantum-classical transition vary greatly for
different relative magnitudes of the non-compensation.Comment: to be appeared in Phys. Rev.
Synthesis and pinning properties of the infinite-layer superconductor Sr0.9La0.1CuO
We report the high-pressure synthesis of the electron-doped infinite-layer
superconductor Sr0.9La0.1CuO2 and its superconducting properties. A Rietveld
analysis of X-ray powder diffraction data showed that, within the resolution of
the measurement, the sample had purely an infinite-layer structure without any
discernible impurities. The superconducting volume fraction and the transition
width were greatly improved compared to those in previous reports. The
irreversibility field line and the intragranular critical current density were
much higher than those of La1.85Sr0.15CuO4 and Nd1.85Ce0.15CuO4. The stronger
pinning behaviors are consistent with the strong interlayer coupling due to the
short distance between CuO2 planes.Comment: Physica C (in press) 5 pages, 4 figur
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