8,337 research outputs found
Time delays and energy transport velocities in three dimensional ideal cloaking
We obtained the energy transport velocity distribution for a three
dimensional ideal cloak explicitly. Near the operation frequency, the energy
transport velocity has rather peculiar distribution. The velocity along a line
joining the origin of the cloak is a constant, while the velocity approaches
zero at the inner boundary of the cloak. A ray pointing right into the origin
of the cloak will experience abrupt changes of velocities when it impinges on
the inner surface of the cloak. This peculiar distribution causes infinite time
delays for the ideal cloak within a geometric optics description.Comment: A scaling factor is added to convert the parameter \tau into the
physical tim
Magnitude and crystalline anisotropy of hole magnetization in (Ga,Mn)As
Theory of hole magnetization Mc in zinc-blende diluted ferromagnetic
semiconductors is developed relaxing the spherical approximation of earlier
approaches. The theory is employed to determine Mc for (Ga,Mn)As over a wide
range of hole concentrations and a number of crystallographic orientations of
Mn magnetization. It is found that anisotropy of Mc is practically negligible
but the obtained magnitude of Mc is significantly greater than that determined
in the spherical approximation. Its sign and value compares favorably with the
results of available magnetization measurements and ferromagnetic resonance
studies.Comment: 5 pages, 3 figure
Analysis of pion elliptic flows and HBT interferometry in a granular quark-gluon plasma droplet model
In many simulations of high-energy heavy-ion collisions on an event-by-event
analysis, it is known that the initial energy density distribution in the
transverse plane is highly fluctuating. Subsequent longitudinal expansion will
lead to many longitudinal tubes of quark-gluon plasma which have tendencies to
break up into many spherical droplets because of sausage instabilities. We are
therefore motivated to use a model of quark-gluon plasma granular droplets that
evolve hydrodynamically to investigate pion elliptic flows and
Hanbury-Brown-Twiss interferometry. We find that the data of pion transverse
momentum spectra, elliptic flows, and HBT radii in \sqrt{s_{NN}}=200 GeV Au +
Au collisions at RHIC can be described well by an expanding source of granular
droplets with an anisotropic velocity distribution.Comment: 9 pages, 6 figures, in Late
Viscoelastic Behavior of Solid He
Over the last five years several experimental groups have reported anomalies
in the temperature dependence of the period and amplitude of a torsional
oscillator containing solid He. We model these experiments by assuming that
He is a viscoelastic solid--a solid with frequency dependent internal
friction. We find that while our model can provide a quantitative account of
the dissipation observed in the torsional oscillator experiments, it only
accounts for about 10% of the observed period shift, leaving open the
possibility that the remaining period shift is due to the onset of
superfluidity in the sample.Comment: 4 pages, 3 figure
Monte Carlo simulations of , a classical Heisenberg antiferromagnet in two-dimensions with dipolar interaction
We study the phase diagram of a quasi-two dimensional magnetic system with Monte Carlo simulations of a classical Heisenberg spin
Hamiltonian which includes the dipolar interactions between
spins. Our simulations reveal an Ising-like antiferromagnetic phase at low
magnetic fields and an XY phase at high magnetic fields. The boundary between
Ising and XY phases is analyzed with a recently proposed finite size scaling
technique and found to be consistent with a bicritical point at T=0. We discuss
the computational techniques used to handle the weak dipolar interaction and
the difference between our phase diagram and the experimental results.Comment: 13 pages 18 figure
Parametric resonance and spin-charge separation in 1D fermionic systems
We show that the periodic modulation of the Hamiltonian parameters for 1D
correlated fermionic systems can be used to parametrically amplify their
bosonic collective modes. Treating the problem within the Luttinger liquid
picture, we show how charge and spin density waves with different momenta are
simultaneously amplified. We discuss the implementation of our predictions for
cold atoms in 1D modulated optical lattices, showing that the fermionic
momentum distribution directly provides a clear signature of spin-charge
separation.Comment: 6 pages, 3 figures, published versio
Creation of entangled states in coupled quantum dots via adiabatic rapid passage
Quantum state preparation through external control is fundamental to
established methods in quantum information processing and in studies of
dynamics. In this respect, excitons in semiconductor quantum dots (QDs) are of
particular interest since their coupling to light allows them to be driven into
a specified state using the coherent interaction with a tuned optical field
such as an external laser pulse. We propose a protocol, based on adiabatic
rapid passage, for the creation of entangled states in an ensemble of pairwise
coupled two-level systems, such as an ensemble of QD molecules. We show by
quantitative analysis using realistic parameters for semiconductor QDs that
this method is feasible where other approaches are unavailable. Furthermore,
this scheme can be generically transferred to some other physical systems
including circuit QED, nuclear and electron spins in solid-state environments,
and photonic coupled cavities.Comment: 10 pages, 2 figures. Added reference, minor changes. Discussion,
results and conclusions unchange
Stationary wave patterns generated by an impurity moving with supersonic velocity through a Bose-Einstein condensate
Formation of stationary 3D wave patterns generated by a small point-like
impurity moving through a Bose-Einstein condensate with supersonic velocity is
studied. Asymptotic formulae for a stationary far-field density distribution
are obtained. Comparison with three-dimensional numerical simulations
demonstrates that these formulae are accurate enough already at distances from
the obstacle equal to a few wavelengths.Comment: 7 pages, 3 figure
On the relation between Unruh and Sokolov--Ternov effects
We show that the Sokolov--Ternov effect -- the depolarization of particles in
storage rings coming from synchrotron radiation due to spin flip transitions --
is physically equivalent to the Unruh effect for circular acceleration if one
uses a spin 1/2 particle as the Unruh--DeWitt detector. It is shown that for
the electron, with gyromagnetic number , the exponential
contribution to the polarization, which usually characterizes the Unruh effect,
is "hidden" in the standard Sokolov-Ternov effect making it hard to observe.
Thus, our conclusions are different in detail from previous work.Comment: 23 pages, no figure
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