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2009-12-24
|
A resonance model with magnetic connection for 3:2 HFQPO pairs in black hole binaries
|
We apply epicyclic resonances to the magnetic connection (MC) of a black hole
(BH) with a relativistic accretion disc, interpreting the high frequency
quasi-periodic oscillations (HFQPOs) with 3:2 pairs observed in three BH X-ray
binaries. It turns out that the 3:2 HFQPO pairs are associated with the steep
power-law states, and the severe damping can be overcome by transferring energy
and angular momentum from a spinning BH to the inner disc in the MC process.
|
0912.4776v1
|
2010-01-03
|
Stabilities for Euler-Poisson Equations with Repulsive Forces in R^N
|
This article extends the previous paper in "M.W. Yuen, \textit{Stabilities
for Euler-Poisson Equations in Some Special Dimensions}, J. Math. Anal. Appl.
\textbf{344} (2008), no. 1, 145--156.", from the Euler-Poisson equations for
attractive forces to the repulsive ones in $R^{N}$ $(N\geq2)$. The similar
stabilities of the system are studied. Additionally, we explain that it is
impossible to have the density collapsing solutions with compact support to the
system with repulsive forces for $\gamma>1$.
|
1001.0385v1
|
2010-01-10
|
Production of entanglement in Raman three-level systems using feedback
|
We examine the theoretical limits of the generation of entanglement in a
damped coupled ion-cavity system using jump-based feedback. Using Raman
transitions to produce entanglement between ground states reduces the necessary
feedback bandwidth, but does not improve the overall effect of the spontaneous
emission on the final entanglement. We find that the fidelity of the resulting
entanglement will be limited by the asymmetries produced by vibrations in the
trap, but that the concurrence remains above 0.88 for realistic ion trap sizes.
|
1001.1567v1
|
2010-01-15
|
Coulomb screening and collective excitations in biased bilayer graphene
|
We have investigated the Coulomb screening properties and plasmon spectrum in
a bilayer graphene under a perpendicular electric bias. The bias voltage
applied between the two graphene layers opens a gap in the single particle
energy spectrum and modifies the many-body correlations and collective
excitations. The energy gap can soften the plasmon modes and lead to a
crossover of the plasmons from a Landau damped mode to being undamped. Plasmon
modes of long lifetime may be observable in experiments and may have potentials
for device applications.
|
1001.2762v1
|
2010-01-18
|
Quiet sigma delta quantization, and global convergence for a class of asymmetric piecewise affine maps
|
In this paper, we introduce a family of second-order sigma delta quantization
schemes for analog-to-digital conversion which are `quiet' : quantization
output is guaranteed to fall to zero at the onset of vanishing input. In the
process, we prove that the origin is a globally attractive fixed point for the
related family of asymmetrically-damped piecewise affine maps. Our proof of
convergence is twofold: first, we construct a trapping set using a
Lyapunov-type argument; we then take advantage of the asymmetric structure of
the maps under consideration to prove convergence to the origin from within
this trapping set.
|
1001.2955v2
|
2010-01-20
|
Non-Markovian dynamics of a damped driven two-state system
|
We study a driven two-state system interacting with a structured environment.
We introduce the non-Markovian master equation ruling the system dynamics, and
we derive its analytic solution for general reservoir spectra. We compare the
non-Markovian dynamics of the Bloch vector for two classes of reservoir
spectra: the Ohmic and the Lorentzian reservoir. Finally, we derive the
analytic conditions for complete positivity with and without the secular
approximation. Interestingly, the complete positivity conditions have a
transparent physical interpretation in terms of the characteristic timescales
of phase diffusion and relaxation processes.
|
1001.3564v2
|
2010-01-26
|
Non-Markovian reservoir-dependent squeezing
|
The squeezing dynamics of a damped harmonic oscillator are studied for
different types of environment without making the Markovian approximation. The
squeezing dynamics of a coherent state depend on the reservoir spectrum in a
unique way that can, in the weak coupling approximation, be analyzed
analytically. Comparison of squeezing dynamics for Ohmic, sub-Ohmic and
super-Ohmic environments is done showing a clear connection between the
squeezing--non-squeezing oscillations and reservoir structure. Understanding
the effects occurring due to structured reservoirs is important both from a
purely theoretical point of view and in connection with evolving experimental
techniques and future quantum computing applications.
|
1001.4669v1
|
2010-02-01
|
Non linear diffusion and wave damped propagation : weak solutions and statistical turbulence behavior
|
We present mathematical proofs on the existence and uniqueness of weak
solutions for a special class of non linear parabolic and hyperbolic equations
of mathematical physics subject to colored noise (structured turbulence) as
random- initial conditions
|
1002.0165v2
|
2010-02-04
|
Sudden violation of the CHSH inequality in a two qubits system
|
I study the dynamics of the violation of the CHSH inequality for two qubits
interacting with a common zero-temperature non-Markovian environment. I
demonstrate sudden violation of the inequality for two qubits initially
prepared in a factorized state. Due to the strong coupling between the qubits
and the reservoir, the dynamics is characterized by numerous sharp revivals.
Furthermore I focus on a more realistic physical system in which the
spontaneous emission for the qubits is taken into account. When including
spontaneous emission even for small decay parameters, revivals in the violation
are heavily damped out. If the decay rates exceed a certain threshold, the
inequality turns out to be always satisfied.
|
1002.1000v1
|
2010-02-08
|
Backward Raman compression of x-rays in metals and warm dense matters
|
Experimentally observed decay rate of the long wavelength Langmuir wave in
metals and dense plasmas is orders of magnitude larger than the prediction of
the prevalent Landau damping theory. The discrepancy is explored, and the
existence of a regime where the forward Raman scattering is stable and the
backward Raman scattering is unstable is examined. The amplification of an
x-ray pulse in this regime, via the backward Raman compression, is
computationally demonstrated, and the optimal pulse duration and intensity is
estimated.
|
1002.1735v2
|
2010-02-09
|
The pulse and monochromatic light stimulation of semiconductor quantum wells
|
The light reflectance and absorbance are calculated for a quantum well (QW)
the width of which is comparable with the light wave length. The difference of
the refraction coefficients of the quantum well and barriers is taken into
account. The stimulating pulse form is arbitrary. An existence of two closely
situated discrete excitation energy levels is supposed. Such energy level pare
may correspond to two magnetopolaron states in a quantizing magnetic field
perpendicular to the QW plane. The relationship of the radiative and
non-radiative damping is arbitrary. The final results does not use the
approximation of the weak Coulomb interaction of electrons and holes.
|
1002.1780v1
|
2010-02-09
|
Asymptotical photon distributions in the dissipative Dynamical Casimir Effect
|
Asymptotical formulas for the photon distribution function of a quantum
oscillator with time-dependent frequency and damping coefficients, interacting
with a thermal reservoir, are derived in the case of a large mean number of
quanta. Different regimes of excitation of an initial thermal state with an
arbitrary temperature are considered. New formulas are used to predict the
statistical properties of the electromagnetic field created in the experiments
on the Dynamical Casimir Effect which are now under preparation.
|
1002.1861v1
|
2010-02-16
|
Dynamical Unbinding Transition in a Periodically Driven Mott Insulator
|
We study the double occupancy in a fermionic Mott insulator at half-filling
generated via a dynamical periodic modulation of the hopping amplitude. Tuning
the modulation amplitude, we describe a crossover in the nature of
doublon-holon excitations from a Fermi Golden Rule regime to damped Rabi
oscillations. The decay time of excited states diverges at a critical
modulation strength, signaling the transition to a dynamically bound
non-equilibrium state of doublon-holon pairs. A setup using a fermionic quantum
gas should allow to study the critical exponents.
|
1002.3085v1
|
2010-02-19
|
Observation of magnetocoriolis waves in a liquid metal Taylor-Couette experiment
|
The first observation of fast and slow magnetocoriolis (MC) waves in a
laboratory experiment is reported. Rotating nonaxisymmetric modes arising from
a magnetized turbulent Taylor-Couette flow of liquid metal are identified as
the fast and slow MC waves by the dependence of the rotation frequency on the
applied field strength. The observed slow MC wave is damped but the observation
provides a means for predicting the onset of the Magnetorotational Instability.
|
1002.3791v1
|
2010-03-11
|
Exact quasinormal modes for a special class of black holes
|
Analytic exact expressions for the quasinormal modes of scalar and
electromagnetic perturbations around a special class of black holes are found
in d\ge3 dimensions. It is shown that, the size of the black hole provides a
bound for the angular momentum of the perturbation. Quasinormal modes appear
when this bound is fulfilled, otherwise the excitations become purely damped.
|
1003.2256v1
|
2010-03-12
|
Symmetry Analysis of 2+1 dimensional Burgers equation with variable damping
|
The symmetry classification of the two dimensional Burgers equation with
variable coefficient is considered. Symmetry algebra is found and a
classification of its subalgebras, up to conjugacy, is obtained. Similarity
reductions are performed for each class.
|
1003.2511v1
|
2010-03-16
|
Driven Dirac-like Equation via Mirror Oscillation: Controlled Cold-Atom Zitterbewegung
|
By considering mirror oscillation in a "tripod-scheme" laser-atom system, we
advocate explorative studies of driven Dirac-like equations. Both analytical
and numerical studies show that mirror oscillation can be used to drive an
effective spin-orbit interaction and hence control the amplitude, the
frequency, and the damping of the cold-atom Zitterbewegung oscillation. Our
results demonstrate an interesting coupling between the mirror mechanical
motion and a fundamental quantum coherent oscillation, opening up new means of
matter wave manipulation.
|
1003.3074v1
|
2010-03-18
|
Stimulated Raman adiabatic passage in an open quantum system: Master equation approach
|
A master equation approach to the study of environmental effects in the
adiabatic population transfer in three-state systems is presented. A systematic
comparison with the non-Hermitian Hamiltonian approach [N. V. Vitanov and S.
Stenholm, Phys. Rev. A {\bf 56}, 1463 (1997)] shows that in the weak coupling
limit the two treatments lead to essentially the same results. Instead, in the
strong damping limit the predictions are quite different: in particular the
counterintuitive sequences in the STIRAP scheme turn out to be much more
efficient than expected before. This point is explained in terms of quantum
Zeno dynamics.
|
1003.3616v1
|
2010-03-19
|
Self-stimulated Emission of Undulator Radiation
|
We attract attention that interaction of particle in downstream undulator
with its own wavelet emitted in upstream undulator could be as strong as with
the frictional field in undulator itself. This phenomenon could be used for
enhancement of signal from pickup undulators in optical stochastic cooling
methods as well as for increase of damping.
|
1003.3747v1
|
2010-03-19
|
Dynamics of magnetization on the topological surface
|
We investigate theoretically the dynamics of magnetization coupled to the
surface Dirac fermions of a three dimensional topological insulator, by
deriving the Landau-Lifshitz-Gilbert (LLG) equation in the presence of charge
current. Both the inverse spin-Galvanic effect and the Gilbert damping
coefficient $\alpha$ are related to the two-dimensional diagonal conductivity
$\sigma_{xx}$ of the Dirac fermion, while the Berry phase of the ferromagnetic
moment to the Hall conductivity $\sigma_{xy}$. The spin transfer torque and the
so-called $\beta$-terms are shown to be negligibly small. Anomalous behaviors
in various phenomena including the ferromagnetic resonance are predicted in
terms of this LLG equation.
|
1003.3769v1
|
2010-03-23
|
Effect of extra dimensions on gravitational waves from cosmic strings
|
We show how taking into account the kinematical effect of extra dimensions
can have a significant impact on the gravity wave emission from cosmic strings.
Additional dimensions both round off cusps, as well as reduce the probability
of their formation. We recompute the cusp gravity wave burst with these factors
and find a significant dimension dependent damping of the gravity waves.
|
1003.4395v2
|
2010-03-31
|
Energy carriers in the Fermi-Pasta-Ulam $β$ lattice: Solitons or Phonons?
|
We investigate anomalous energy transport processes in the Fermi-Pasta-Ulam
$\beta$ lattice. They are determined by the maximum sound velocity of the
relevant weakly damped energy carriers. That velocity can be numerically
resolved by measuring the propagating fronts of the correlation functions of
energy/momentum fluctuations at different times. The numerical results are
compared with the predictions for solitons and effective (renormalized)
phonons, respectively. Excellent agreement has been found for the prediction of
effective long wavelength phonons, giving strong evidence that the energy
carriers should be effective phonons rather than solitons.
|
1003.6113v1
|
2010-04-07
|
Neutrino Flavor Ratio on Earth and at Astrophysical Sources
|
We present the reconstruction of neutrino flavor ratios at astrophysical
sources. For distinguishing the pion source and the muon-damped source to the
3$\sigma$ level, the neutrino flux ratios,
$R\equiv\phi(\nu_\mu)/(\phi(\nu_e)+\phi(\nu_\tau))$ and
$S\equiv\phi(\nu_e)/\phi(\nu_\tau)$, need to be measured in accuracies better
than 10%.
|
1004.1030v1
|
2010-04-08
|
Ab initio vibrations in nonequilibrium nanowires
|
We review recent results on electronic and thermal transport in two different
quasi one-dimensional systems: Silicon nanowires (SiNW) and atomic gold chains.
For SiNW's we compute the ballistic electronic and thermal transport properties
on equal footing, allowing us to make quantitative predictions for the
thermoelectric properties, while for the atomic gold chains we evaluate
microscopically the damping of the vibrations, due to the coupling of the chain
atoms to the modes in the bulk contacts. Both approaches are based on a
combination of density-functional theory, and nonequilibrium Green's functions.
|
1004.1312v1
|
2010-04-08
|
Spin-charge and spin-orbital coupling effects on spin dynamics in ferromagnetic manganites
|
Correlation-induced spin-charge and spin-orbital coupling effects on spin
dynamics in ferromagnetic manganites are calculated with realistic parameters
in order to provide a quantitative comparison with experimental results for
spin stiffness, magnon dispersion, magnon damping, anomalous zone-boundary
magnon softening, and Curie temperature. The role of orbital degeneracy,
orbital ordering, and orbital correlations on spin dynamics in different doping
regimes is highlighted.
|
1004.1352v2
|
2010-04-12
|
Existence and stability of steady states of a reaction convection diffusion equation modeling microtubule formation
|
We generalize the Dogterom-Leibler model for microtubule dynamics [DL] to the
case where the rates of elongation as well as the lifetimes of the elongating
and shortening phases are a function of GTP-tubulin concentration. We study
also the effect of nucleation rate in the form of a damping term which leads to
new steady-states. For this model, we study existence and stability of steady
states satisfying the boundary conditions at x = 0. Our stability analysis
introduces numerical and analytical Evans function computations as a new
mathematical tool in the study of microtubule dynamics.
|
1004.1866v1
|
2010-04-14
|
Non-equilibrium Effects in the Thermal Switching of Underdamped Josephson Junctions
|
We study the thermal escape problem in the low damping limit. We find that
finiteness of the barrier is crucial for explaining the thermal activation
results. In this regime low barrier non-equilibrium corrections to the usual
theories become necessary. We propose a simple theoretical extension accounting
for these non-equilibrium processes which agrees numerical results. We apply
our theory to the understanding of switching current curves in underdamped
Josephson junctions.
|
1004.2512v1
|
2010-04-18
|
Fundamental defect of the macroeconomic thinking as one of the main causes of the crisis endured
|
The main points of the first section of the article written by S.I.
Chernyshov, A.V. Voronin and S.A. Razumovsky arXiv:1003.4382), which deals with
the fundamental bases of the macroeconomic theory, have been analyzed. An
incorrectness of the Harrod's model of the economical growth in its generally
accepted interpretation was specifically considered. The inevitability of the
economic crisis has been shown to follow directly from the premises of this
model. At the same time there is an opportunity to realize the damping
strategies.
|
1004.3067v1
|
2010-04-19
|
Occurrence of superconductivity when the metal-insulator transition is inhibited in $1T$-TaS${_2}$
|
When a Mott metal-insulator transition is inhibited by a small amount of
disorder in the layered dichalcogenide 1T-TaS$_2$, an inhomogeneous
superconducting state arises below T=2.1 K, and coexists with a
nearly-commensurate charge-density-wave. By angle-resolved photoelectron
spectroscopy (ARPES) we show that it emerges from a bad metal state with
strongly damped quasiparticles. Superconductivity is almost entirely suppressed
by an external magnetic field of 0.1 T.
|
1004.3251v1
|
2010-05-06
|
A probability-conserving dissipative Schrödinger equation
|
Dissipative effects on a microscopic level are included in the Schr\"odinger
equation. When the decay between different local levels as a result of the
coupling to a bath, the Schr\"odinger equation no longer conserves energy, but
the probability of the states is conserved. The procedure is illustrated with
several examples that include direct electronic decay and damping of local
phonons (vibrational levels). This method significantly reduces the
calculational effort compared to conventional density matrix techniques.
|
1005.1079v1
|
2010-05-10
|
A New Approach to Non-Commutative U(N) Gauge Fields
|
Based on the recently introduced model of arXiv:0912.2634 for non-commutative
U(1) gauge fields, a generalized version of that action for U(N) gauge fields
is put forward. In this approach to non-commutative gauge field theories, UV/IR
mixing effects are circumvented by introducing additional 'soft breaking' terms
in the action which implement an IR damping mechanism. The techniques used are
similar to those of the well-known Gribov-Zwanziger approach to QCD.
|
1005.1578v2
|
2010-05-18
|
The effect of extra dimensions on gravity wave bursts from cosmic string cusps
|
We explore the kinematical effect of having extra dimensions on the gravity
wave emission from cosmic strings. Additional dimensions both round off cusps,
and reduce the probability of their formation. We recompute the gravity wave
burst, taking into account these two factors, and find a potentially
significant damping on the gravity waves of the strings.
|
1005.3220v2
|
2010-05-24
|
Direct observation of paramagnons in palladium
|
We report an inelastic neutron scattering study of the spin fluctuations in
the nearly-ferromagnetic element palladium. Dispersive over-damped collective
magnetic excitations or ``paramagnons'' are observed up to 128 meV. We analyze
our results in terms of a Moriya-Lonzarich-type spin fluctuation model and
estimate the contribution of the spin fluctuations to the low temperature heat
capacity. In spite of the paramagnon excitations being relatively strong, their
relaxation rates are large. This leads to a small contribution to the
low-temperature electronic specific heat.
|
1005.4402v1
|
2010-06-01
|
High Gradient Superconducting Cavity with Low Surface EM Fields and Well-Suppressed HOMS for the ILC
|
We present an optimized geometry for a 1.3 GHz superconducting cavity in
which the surface electromagnetic fields have been minimized and the bandwidth
of the fundamental mode has been maximized. We refer to this design as the New
Low Surface Field (NLSF) cavity. Earlier work focused on properties of the
fundamental mode. Here we additionally study higher order modes (HOMs), means
of damping them, and short range wake fields. A two-band circuit model is
employed in order to facilitate rapid characterization of cavity HOMs.
|
1006.0086v1
|
2010-06-14
|
Transport parameters in neutron stars from in-medium NN cross sections
|
We present a numerical study of shear viscosity and thermal conductivity of
symmetric nuclear matter, pure neutron matter and $\beta$-stable nuclear
matter, in the framework of the Brueckner theory. The calculation of in-medium
cross sections and nucleon effective masses is performed with a consistent two
and three body interaction. The investigation covers a wide baryon density
range as requested in the applications to neutron stars. The results for the
transport coefficients in $\beta$-stable nuclear matter are used to make
preliminary predictions on the damping time scales of non radial modes in
neutron stars.
|
1006.2656v1
|
2010-06-25
|
Perturbations of Mathieu equations with parametric excitation of large period
|
We consider a linear differential system of Mathieu equations with periodic
coefficients over periodic closed orbits and we prove that, arbitrarily close
to this system, there is a linear differential system of Hamiltonian damped
Mathieu equations with periodic coefficients over periodic closed orbits such
that, all but a finite number of closed periodic coefficients, have unstable
solutions. The perturbations will be peformed in the periodic coefficients.
|
1006.5025v1
|
2010-07-01
|
Instability of ion kinetic waves in a weakly ionized plasma
|
The fundamental higher-order Landau plasma modes are known to be generally
heavily damped. We show that these modes for the ion component in a weakly
ionized plasma can be substantially modified by ion-neutral collisions and a dc
electric field driving ion flow so that some of them can become unstable. This
instability is expected to naturally occur in presheaths of gas discharges at
sufficiently small pressures and thus affect sheaths and discharge structures.
|
1007.0142v3
|
2010-07-06
|
Temperature and Friction Accelerated Sampling of Boltzmann-Gibbs Distribution
|
This paper is concerned with tuning friction and temperature in Langevin
dynamics for fast sampling from the canonical ensemble. We show that
near-optimal acceleration is achieved by choosing friction so that the local
quadratic approximation of the Hamiltonian is a critical damped oscillator. The
system is also over-heated and cooled down to its final temperature. The
performances of different cooling schedules are analyzed as functions of total
simulation time.
|
1007.0995v1
|
2010-07-09
|
Purely electrical damping of vibrations in arbitrary PEM plates: a mixed non-conforming FEM-Runge-Kutta time evolution analysis
|
A new numerical code, based upon a mixed FEM-Runge-Kutta method, is used for
the analysis and design of plane 2-D smart structures. The code is applied to
the study of arbitrarily shaped PEM plates, based on a weak formulation of
their governing equations, [17]. The optimal parameters needed to synthesize
appropriate electric networks are computed, and the overall performances of
such plates are investigated. Two examples are studied: firstly, a simple case
is used to test the main features of the code; secondly, a more complex PEM
plate is designed and analyzed by means of the proposed numerical approach.
|
1007.1581v1
|
2010-08-02
|
Entanglement and teleportation via chaotic system
|
The dynamics of entangled state interacting with a single cavity mode is
investigated in the presence of a random parameter. We have shown that degree
of entanglement decays with time and rate of decay is defined by features of
random parameter. Quantum teleportation through dissipative channal and
teleportation fidelity as a function of damping rates has been studied. The
sensitivity of the fidelity with respect to random parameter is discussed. We
have evaluated the time interval during which one can perform the quantum
teleportation and send the information with reasonable fidelity, for a given
values of correlation length of random parameter.
|
1008.0323v1
|
2010-08-03
|
AMENDART in Markovian circuit QED
|
We study the cavity field's and atomic asymptotic mean excitation numbers due
to anti-rotating term (AMENDART) in the circuit Quantum Electrodynamics
(circuit QED) system, composed of a two-level atom and a single cavity field
mode, subject to Markovian damping and dephasing mechanisms. We show that the
AMENDART are above the thermal values, and their behavior is analyzed
analytically and numerically for typical parameters in circuit QED
implementations described by the Rabi Hamiltonian. We point out that "parasitic
elements", such as other cavity modes or eventual off-resonant atoms, also
contribute substantially to AMENDART.
|
1008.0564v2
|
2010-08-04
|
Quantum open systems approach to the dynamical Casimir effect
|
We analyze the introduction of dissipative effects in the study of the
dynamical Casimir effect. We consider a toy model for an electromagnetic cavity
that contains a semiconducting thin shell, which is irradiated with short laser
pulses in order to produce periodic oscillations of its conductivity. The
coupling between the quantum field in the cavity and the microscopic degrees of
freedom of the shell induces dissipation and noise in the dynamics of the
field. We argue that the photon creation process should be described in terms
of a damped oscillator with nonlocal dissipation and colored noise.
|
1008.0786v1
|
2010-08-16
|
The probability distribution of a trapped Brownian particle in plane shear flows
|
We investigate the statistical properties of an over-damped Brownian particle
that is trapped by a harmonic potential and simultaneously exposed to a linear
shear flow or to a plane Poiseuille flow. Its probability distribution is
determined via the corresponding Smoluchowski equation, which is solved
analytically for a linear shear flow. In the case of a plane Poiseuille flow,
analytical approximations for the distribution are obtained by a perturbation
analysis and they are substantiated by numerical results. There is a good
agreement between the two approaches for a wide range of parameters.
|
1008.2670v3
|
2010-09-04
|
Combined Influence of Off-diagonal System Tensors and Potential Valley Returning of the Optimal Path
|
The two-dimensional barrier passage is studied in the framework of Langevin
statistical reactive dynamics. The optimal incident angle for a particle
diffusing in the dissipative non-orthogonal environment with various strengths
of coupling between the two degrees of freedom is systematically calculated.
The optimal diffusion path of the particle in a non-Ohmic damping system is
revealed to have a probability to return to the potential valley under the
combined influence of the off-diagonal system tensors.
|
1009.0835v1
|
2010-09-11
|
Critical density of urban traffic
|
A modified version of the Intelligent Driver Model was used to simulate
traffic in the district of Afogados, in the city of Recife, Brazil, with the
objective to verify whether the complexity of the underlying street grid, with
multiple lane streets, crossings, and semaphores, is capable of exhibiting the
effect of critical density: appearance of a maximum in the vehicle flux versus
density curve. Numerical simulations demonstrate that this effect indeed is
observed on individual avenues, while the phase offset among the avenues
results in damping of this effect for the region as a whole.
|
1009.2180v1
|
2010-09-11
|
Nonlinear optical response of hole-trion systems in quantum dots in tilted magnetic fields
|
We discuss, from a theoretical point of view, the four wave mixing
spectroscopy on an ensemble of p-doped quantum dots in a magnetic field
slightly tilted from the in-plane configuration. We describe the system
evolution in the density matrix formalism. In the limit of coherent ultrafast
optical driving, we obtain analytical formulas for the single system dynamics
and for the response of an inhomogeneously broadened ensemble. The results are
compared to the previously studied time-resolved Kerr rotation spectroscopy on
the same system. We show that the Kerr rotation and four wave mixing spectra
yield complementary information on the spin dynamics (precession and damping).
|
1009.2202v1
|
2010-09-17
|
Linear response calculation using the canonical-basis TDHFB with a schematic pairing functional
|
A canonical-basis formulation of the time-dependent Hartree-Fock-Bogoliubov
(TDHFB) theory is obtained with an approximation that the pair potential is
assumed to be diagonal in the time-dependent canonical basis. The
canonical-basis formulation significantly reduces the computational cost. We
apply the method to linear-response calculations for even-even nuclei. E1
strength distributions for proton-rich Mg isotopes are systematically
calculated. The calculation suggests strong Landau damping of giant dipole
resonance for drip-line nuclei.
|
1009.3339v1
|
2010-10-14
|
Behavior of test particles in the plasma sheath upon local bias and plasma switching
|
Equilibrating gravitation by electric forces, microparticles can be confined
in the plasma sheath above suitably biased local electrodes.Their position
depends on the detailed structure of the plasma sheath and on the charge that
the particles acquire in the surrounding plasma, that is by the electron and
ion currents towards it. Bias switching experiments reveal how the charge and
equilibrium position of the microparticle change upon altered sheath
conditions. We observe similar particle behaviors also in the afterglow of the
discharge for a persisting bias voltage on the electrode: damped oscillation
into a new equilibrium or (accelerated) fall according to the bias.
|
1010.2862v1
|
2010-10-15
|
Anomalous diffusion in viscosity landscapes
|
Anomalous diffusion is predicted for Brownian particles in inhomogeneous
viscosity landscapes by means of scaling arguments, which are substantiated
through numerical simulations. Analytical solutions of the related
Fokker-Planck equation in limiting cases confirm our results. For an ensemble
of particles starting at a spatial minimum (maximum) of the viscous damping we
find subdiffusive (superdiffusive) motion. Superdiffusion occurs also for a
monotonically varying viscosity profile. We suggest different substances for
related experimental investigations.
|
1010.3115v1
|
2010-10-17
|
Coherent soft-mode phonon generation and detection in ultrathin SrTiO3 grown directly on silicon
|
Time-resolved two color pump-probe polarization spectroscopy was performed at
room temperature on SrTiO3 films grown directly on Si with film thickness
varying from 2 nm to 7.8 nm. The E soft mode with a characteristic frequency of
0.2 THz is impulsively generated and measured in these coherently strained
tetragonal phase SrTiO3 thin films. Another over-damped signal observed
indicates the possible relaxational hopping of Ti ion between double potential
wells. The dependence of the coherent phonon signal on pump and probe laser
polarization helps to identify the phonon modes.
|
1010.3443v1
|
2010-11-09
|
Hamiltonian formulation of the effective kinetic theory for superfluid Fermi liquids
|
We present in a local form the time dependent effective description of a
superfluid Fermi liquid which includes Landau damping effects at $T\neq 0$.
This is achieved by the introduction of an additional variable, the
quasiparticle distribution function, which obeys a simple kinetic equation. The
transport equation is coupled with first order equations for the Goldstone mode
and the particle density. We prove that a main feature of this formulation is
its Hamiltonian structure relative to a certain Poisson bracket. We construct
the Hamiltonian to quadratic order.
|
1011.2040v1
|
2010-11-15
|
Decoherence Strength of Multiple Non-Markovian Environments
|
It is known that one can characterize the decoherence strength of a Markovian
environment by the product of its temperature and induced damping, and order
the decoherence strength of multiple environments by this quantity. We show
that for non-Markovian environments in the weak coupling regime there also
exists a natural (albeit partial) ordering of environment-induced
irreversibility within a perturbative treatment. This measure can be applied to
both low-temperature and non-equilibrium environments.
|
1011.3286v3
|
2010-11-18
|
Stochastic Resonance in Periodic Potentials
|
The phenomenon of stochastic resonance (SR) is known to occur mostly in
bistable systems. However, the question of occurrence of SR in periodic
potential systems is not conclusively resolved. Our present numerical work
shows that the periodic potential system indeed exhibits SR in the high
frequency regime, where the linear response theory yields maximum frequency
dependent mobility as a function of noise strength. The existence of two (and
only two) distinct dynamical states of trajectories in this moderately
feebly-damped periodically driven noisy periodic potential system plays an
important role in the occurrence of SR.
|
1011.4198v2
|
2010-11-19
|
Spin waves in magnetic quantum wells with Coulomb interaction and $sd$ exchange coupling
|
We theoretically describe the spin excitation spectrum of a two dimensional
electron gas embedded in a quantum well with localized magnetic impurities.
Compared to the previous work, we introduce equations that allow to consider
the interplay between the Coulomb interaction of delocalized electrons and the
$sd$ exchange coupling between electrons and magnetic impurities. Strong
qualitative changes are found : mixed waves propagate below the single particle
continuum, an anticrossing gap is open at a specific wavevector and the kinetic
damping due to the electron motion strongly influences the coupling strength
between electrons and impurities spins.
|
1011.4422v1
|
2010-11-22
|
Global p-mode oscillations throughout the complete solar cycle 23 and the beginning of cycle 24
|
The parameters of the p-mode oscillations vary with solar activity. Such
temporal variations provide insights for the study of the structural and
dynamical changes occurring in the Sun's interior throughout the solar cycle.
We present here a complete picture of the temporal variations of the global
p-mode parameters (excitation, damping, frequency, peak asymmetry, and
rotational splitting) over the entire solar cycle 23 and the beginning of cycle
24 as observed by the space-based, Sun-as-a-star helioseismic GOLF and VIRGO
instruments onboard SoHO.
|
1011.4966v1
|
2010-11-24
|
Evolution equation of entanglement for multi-qubit systems
|
We discuss entanglement evolution of a multi-qubit system when one of its
qubits is subjected to a general noisy channel. For such a system, an evolution
equation of entanglement for a lower bound for multi-qubit concurrence is
derived. Using this evolution equation, the entanglement dynamics of an
initially mixed three-qubit state composed of a GHZ and a W state is analyzed
if one of the qubits is affected by a phase, an amplitude or a generalized
amplitude damping channel.
|
1011.5348v1
|
2010-12-06
|
Two Proposals for Robust PCA using Semidefinite Programming
|
The performance of principal component analysis (PCA) suffers badly in the
presence of outliers. This paper proposes two novel approaches for robust PCA
based on semidefinite programming. The first method, maximum mean absolute
deviation rounding (MDR), seeks directions of large spread in the data while
damping the effect of outliers. The second method produces a low-leverage
decomposition (LLD) of the data that attempts to form a low-rank model for the
data by separating out corrupted observations. This paper also presents
efficient computational methods for solving these SDPs. Numerical experiments
confirm the value of these new techniques.
|
1012.1086v3
|
2010-12-07
|
Cavity cooling of a mechanical resonator in the presence of two-level-system defects
|
Cavity cooling via quantum backaction force can extract thermal fluctuations
from a mechanical resonator to reach the quantum ground state. Surface or bulk
two-level-system (TLS) defects in a mechanical resonator can couple with the
mechanical mode via deformation potential and affect the cooling process
significantly. Here, we develop a theory to study the cavity cooling of a
mechanical mode in the presence of a TLS defect using the adiabatic elimination
technique. Our result shows that the cooling process depends strongly on the
resonance and the damping rate of the TLS.
|
1012.1380v2
|
2010-12-10
|
Spin-orbit driven ferromagnetic resonance: A nanoscale magnetic characterisation technique
|
We demonstrate a scalable new ferromagnetic resonance (FMR) technique based
on the spin-orbit interaction. An alternating current drives FMR in uniform
ferromagnetic structures patterned from the dilute magnetic semiconductors
(Ga,Mn)As and (Ga,Mn)(As,P). This allows the direct measurement of magnetic
anisotropy coefficients and damping parameters for individual nano-bars. By
analysing the ferromagnetic resonance lineshape, we perform vector magnetometry
on the current-induced driving field, observing contributions with symmetries
of both the Dresselhaus and Rashba spin-orbit interactions.
|
1012.2397v1
|
2010-12-12
|
Quasi-two-dimensional optomechanical crystals with a complete phononic bandgap
|
A fully planar two-dimensional optomechanical crystal formed in a silicon
microchip is used to create a structure devoid of phonons in the GHz frequency
range. A nanoscale photonic crystal cavity is placed inside the phononic
bandgap crystal in order to probe the properties of the localized acoustic
modes. By studying the trends in mechanical damping, mode density, and
optomechanical coupling strength of the acoustic resonances over an array of
structures with varying geometric properties, clear evidence of a complete
phononic bandgap is shown.
|
1012.2556v1
|
2010-12-22
|
Discovering author impact: A PageRank perspective
|
This article provides an alternative perspective for measuring author impact
by applying PageRank algorithm to a coauthorship network. A weighted PageRank
algorithm considering citation and coauthorship network topology is proposed.
We test this algorithm under different damping factors by evaluating author
impact in the informetrics research community. In addition, we also compare
this weighted PageRank with the h-index, citation, and program committee (PC)
membership of the International Society for Scientometrics and Informetrics
(ISSI) conferences. Findings show that this weighted PageRank algorithm
provides reliable results in measuring author impact.
|
1012.4870v1
|
2010-12-29
|
On sub-ideal causal smoothing filters
|
Smoothing causal linear time-invariant filters are studied for continuous
time processes. The paper suggests a family of causal filters with almost
exponential damping of the energy on the higher frequencies. These filters are
sub-ideal meaning that a faster decay of the frequency response would lead to
the loss of causality.
|
1012.5883v3
|
2011-01-06
|
Dissipative dynamics of a harmonically confined Bose-Einstein condensate
|
We study the dissipation of the centre of mass oscillation of a harmonically
confined condensate in the presence of a disorder potential. An extension of
the Generalized Harmonic Theorem allows one to formulate the dynamics from the
point of view of an oscillating disorder potential. This formulation leads to a
rigorous result for the damping rate in the limit of weak disorder.
|
1101.1332v2
|
2011-01-25
|
Magnetic field generated by r-modes in accreting quark stars
|
We show that the r-mode instability can generate strong toroidal fields in
the core of accreting millisecond quark stars by inducing differential
rotation. We follow the spin frequency evolution on a long time scale taking
into account the magnetic damping rate in the evolution equations of r-modes.
The maximum spin frequency of the star is only marginally smaller than in the
absence of the magnetic field. The late-time evolution of the stars which enter
the r-mode instability region is instead rather different if the generated
magnetic fields are taken into account: they leave the millisecond pulsar
region and they become radio pulsars.
|
1101.4875v1
|
2011-02-04
|
Long-Term Damped Dynamics of the Extensible Suspension Bridge
|
This work is focused on the doubly nonlinear equation, whose solutions
represent the bending motion of an extensible, elastic bridge suspended by
continuously distributed cables which are flexible and elastic with stiffness
k^2. When the ends are pinned, long-term dynamics is scrutinized for arbitrary
values of axial load p and stiffness k^2. For a general external source f, we
prove the existence of bounded absorbing sets.When f is timeindependent, the
related semigroup of solutions is shown to possess the global attractor of
optimal regularity and its characterization is given in terms of the steady
states of the problem.
|
1102.0877v1
|
2011-02-07
|
Experimental demonstration of decoherence suppression via quantum measurement reversal
|
Taming decoherence is essential in realizing quantum computation and quantum
communication. Here we experimentally demonstrate that decoherence due to
amplitude damping can be suppressed by exploiting quantum measurement reversal
in which a weak measurement and the reversing measurement are introduced before
and after the decoherence channel, respectively. We have also investigated the
trade-off relation between the degree of decoherence suppression and the
channel transmittance.
|
1102.1303v2
|
2011-02-11
|
Simple proof of the robustness of Gaussian entanglement in bosonic noisy channels
|
The extremality of Gaussian states is exploited to show that Gaussian states
are the most robust, among all possible bipartite continuous-variable states at
fixed energy, against disentanglement due to noisy evolutions in Markovian
Gaussian channels involving dissipation and thermal hopping. This proves a
conjecture raised recently in [M. Allegra, P. Giorda, and M. G. A. Paris, Phys.
Rev. Lett. {\bf 105}, 100503 (2010)], providing a rigorous validation of the
conclusions of that work. The problem of identifying continuous variable states
with maximum resilience to entanglement damping in more general bosonic open
system dynamical evolutions, possibly including correlated noise and
non-Markovian effects, remains open.
|
1102.2356v1
|
2011-02-25
|
First-principles calculations of magnetization relaxation in pure Fe, Co, and Ni with frozen thermal lattice disorder
|
The effect of the electron-phonon interaction on magnetization relaxation is
studied within the framework of first-principles scattering theory for Fe, Co,
and Ni by displacing atoms in the scattering region randomly with a thermal
distribution. This "frozen thermal lattice disorder" approach reproduces the
non-monotonic damping behaviour observed in ferromagnetic resonance
measurements and yields reasonable quantitative agreement between calculated
and experimental values. It can be readily applied to alloys and easily
extended by determining the atomic displacements from ab initio phonon spectra.
|
1102.5305v2
|
2011-02-26
|
Dynamics of Skyrmion Crystals in Metallic Thin Films
|
We study the collective dynamics of the Skyrmion crystal (SkX) in thin films
of ferromagnetic metals resulting from the nontrivial Skyrmion topology. We
show that the current-driven motion of the crystal reduces the topological Hall
effect and the Skyrmion trajectories bend away from the direction of the
electric current (the Skyrmion Hall effect). We find a new dissipation
mechanism in non-collinear spin textures that can lead to a much faster spin
relaxation than Gilbert damping, calculate the dispersion of phonons in the
SkX, and discuss effects of impurity pinning of Skyrmions.
|
1102.5384v2
|
2011-03-06
|
Rapid cooling of neutron star in Cassiopeia A and r-mode damping in the core
|
We proposed alternative explanation to the rapid cooling of neutron star in
Cas A. It is suggested that the star is experiencing the recovery period
following the r-mode heating process,assuming the star is differentially
rotating. Like the neutron-superfluidity-triggering model, our model predicts
the rapid cooling will continue for several decades. However, the behavior of
the two models has slight differences, and they might be distinguished by
observations in the near future.
|
1103.1092v3
|
2011-03-11
|
Dynamic Systems Model for Ionic Mem-Resistors based on Harmonic Oscillation
|
Memristive system models have previously been proposed to describe ionic
memory resistors. However, these models neglect the mass of ions and repulsive
forces between ions and are not well formulated in terms of semiconductor and
ionic physics. This article proposes an alternative dynamic systems model in
which the system state is derived from a second order differential equation in
the form of a driven damped harmonic oscillator. Application is made to
Schottky and tunneling barriers.
Keywords- mem-resistor, non-linear dynamic systems
|
1103.2190v4
|
2011-03-14
|
Conflicting coupling of the unpaired nucleons and the structure of collective bands in odd-odd nuclei
|
Conflicting coupling of unpaired nucleons in the odd-odd nuclei is discussed.
A very simple explanation is suggested for the damping of the energy spacing of
the lowest levels in the rotational bands in the odd-odd nuclei in the case of
a "conflicting" coupling of the odd proton and neutron comparative to those of
the bands based on the state of the strongly-coupled particle in the
neighbouring odd nuclei entering the "conflicting" configuration.
|
1103.2609v1
|
2011-03-20
|
Rational Design of Half-Metallic Heterostructures
|
We present a rational approach to the design of half-metallic
heterostructures which allows the design of an infinite number of half-metallic
heterostructures. The wide range of materials that can be made half-metallic
using our approach makes it possible to engineer materials with tunable
characteristic properties, for example low intrinsic magnetic damping, small
magnetic moment or perpendicular anisotropy. We demonstrate the proposed design
scheme for a series of transition metal heterostructures based on the B2
crystal structure.
|
1103.3855v1
|
2011-03-20
|
Uniform resolvent estimates for a non-dissipative Helmholtz equation
|
We study the high frequency limit for a non-dissipative Helmholtz equation.
We first prove the absence of eigenvalue on the upper half-plane and close to
an energy which satisfies a weak damping assumption on trapped trajectories.
Then we generalize to this setting the resolvent estimates of Robert-Tamura and
prove the limiting absorption principle. We finally study the semiclassical
measures of the solution when the source term concentrates on a bounded
submanifold of R^n.
|
1103.3868v1
|
2011-03-24
|
Effect of nonadiabatic spin transfer torque on domain wall resonance frequency and mass
|
The dynamics of a magnetic domain wall in a semi circular nanowire loop is
studied by an analytical model and micromagnetic simulations. We find a damped
sinusoidal oscillation of the domain wall for small displacement angles around
its equilibrium position under an external magnetic field in the absence of
currents. By studying the effect of current induced nonadiabatic spin transfer
torque on the magnetic domain wall resonance frequency and mass, a red shift is
found in the resonance frequency and domain wall mass increases by increasing
the ratio of nonadiabatic spin torque to adiabatic contribution above 1.
|
1103.4670v1
|
2011-03-25
|
Multipartite entanglement for open system in noninertial frames
|
Based on Greenberger-Horne-Zeilinger ($GHZ$) and $W$ initial states, the
tripartite entanglement of a fermionic system under the amplitude damping
channel and in depolarizing noise when two subsystems accelerated is
investigated. Unlike the case of two-qubit system in which sudden death occurs
easily, we find here that the sudden death never occurs even all subsystems are
under the noise environment. We note that both acceleration and environment can
destroy the symmetry between the subsystems, but the effect of environment is
much stronger than that of acceleration. We also show that an entanglement
rebound process will take place when $P>0.75$ in the depolarizing noise and the
larger acceleration will result in the weaker rebound process.
|
1103.4903v1
|
2011-04-08
|
Coherence and Instability in a Driven Bose-Einstein Condensate: A Fully Dynamical Number-Conserving Approach
|
We consider a Bose-Einstein condensate driven by periodic delta-kicks. In
contrast to first-order descriptions, which predict rapid, unbounded growth of
the noncondensate in resonant parameter regimes, the consistent treatment of
condensate depletion in our fully-time-dependent, second-order description acts
to damp this growth, leading to oscillations in the (non)condensate population
and the coherence of the system.
|
1104.1521v3
|
2011-04-25
|
Rotation of Comet Hartley 2 from Structures in the Coma
|
The CN coma structure of the EPOXI mission target, comet 103P/Hartley 2, was
observed during twenty nights from September to December 2010. These CN images
probe the rotational state of the comet's nucleus and provide a ground-based
observational context to complement the EPOXI observations. A dynamically
excited cometary nucleus with a changing rotational rate is observed, a
characteristic not seen in any comet in the past. The lack of rotational
damping during the four-month observing interval places constraints on the
interior structure of the nucleus.
|
1104.4672v1
|
2011-05-11
|
Dispersion and damping of multi-quantum well polaritons from resonant Brillouin scattering by folded acoustic modes
|
We report on confined exciton resonances of acoustic and folded acoustic
phonon light scattering in a GaAs/AlAs multi-quantum-well. Significant
variations of the line shifts and widths are observed across the resonance and
quantitatively reproduced in terms of the polariton dispersion. This high
resolution Brillouin study brings new unexpectedly detailed informations on the
polariton dynamics in confined systems.
|
1105.2229v1
|
2011-05-23
|
Radiative damping: a case study
|
We are interested in the motion of a classical charge coupled to the Maxwell
self-field and subject to a uniform external magnetic field, B. This is a
physically relevant, but difficult dynamical problem, to which contributions
range over more than one hundred years. Specifically, we will study the
Sommerfeld-Page approximation which assumes an extended charge distribution at
small velocities. The memory equation is then linear and many details become
available. We discuss how the friction equation arises in the limit of "small"
B and contrast this result with the standard Taylor expansion resulting in a
second order equation for the velocity of the charge.
|
1105.4470v1
|
2011-05-27
|
Creating quantum correlations through local non-unitary memoryless channels
|
We show that two qubits, initially in a fully classical state, can develop
significant quantum correlations as measured by the quantum discord (QD) under
the action of a local memoryless noise (specifically we consider the case of a
Markovian amplitude-damping channel). This is analytically proven after
deriving in a compact form the QD for the class of separable states involved in
such a process. We provide a picture in the Bloch sphere that unambiguously
highlights the physical mechanism behind the effect regardless of the specific
measure of QCs adopted.
|
1105.5551v3
|
2011-06-01
|
Indirect stabilization of weakly coupled systems with hybrid boundary conditions
|
We investigate stability properties of indirectly damped systems of evolution
equations in Hilbert spaces, under new compatibility assumptions. We prove
polynomial decay for the energy of solutions and optimize our results by
interpolation techniques, obtaining a full range of power-like decay rates. In
particular, we give explicit estimates with respect to the initial data. We
discuss several applications to hyperbolic systems with {\em hybrid} boundary
conditions, including the coupling of two wave equations subject to Dirichlet
and Robin type boundary conditions, respectively.
|
1106.0263v2
|
2011-06-02
|
Density response of a trapped Fermi gas: a crossover from the pair vibration mode to the Goldstone mode
|
We consider the density response of a trapped two-component Fermi gas.
Combining the Bogoliubov-deGennes method with the random phase approximation
allows the study of both collective and single particle excitations.
Calculating the density response across a wide range of interactions, we
observe a crossover from a weakly interacting pair vibration mode to a strongly
interacting Goldstone mode. The crossover is associated with a depressed
collective mode frequency and an increased damping rate, in agreement with
density response experiments performed in strongly interacting atomic gases.
|
1106.0430v2
|
2011-06-07
|
Electromagnetically induced transparency with Rydberg atoms
|
We present a theory of electromagnetically induced transparency in a cold
ensemble of strongly interacting Rydberg atoms. Long-range interactions between
the atoms constrain the medium to behave as a collection of superatoms, each
comprising a blockade volume that can accommodate at most one Rydberg
excitation. The propagation of a probe field is affected by its two-photon
correlations within the blockade distance, which are strongly damped due to low
saturation threshold of the superatoms. Our model is computationally very
efficient and is in quantitative agreement with the results of recent
experiment of Pritchard et al. [Phys. Rev. Lett. 105, 193603 (2010)].
|
1106.1360v2
|
2011-06-10
|
Discrete-time quadrature feedback cooling of a radio-frequency mechanical resonator
|
We have employed a feedback cooling scheme, which combines high-frequency
mixing with digital signal processing. The frequency and damping rate of a 2
MHz micromechanical resonator embedded in a dc SQUID are adjusted with the
feedback, and active cooling to a temperature of 14.3 mK is demonstrated. This
technique can be applied to GHz resonators and allows for flexible control
strategies.
|
1106.2106v1
|
2011-06-22
|
Magnetic excitations in iron pnictides
|
Spin wave dispersion and damping are investigated in the metallic SDW state
of different itinerant electron models including a small interlayer hopping.
Magnetic excitations in iron pnictides are shown to be well understood in terms
of physical mechanisms characteristic of metallic magnets, such as
carrier-induced ferromagnetic spin couplings, intra-band particle-hole
excitations, and the spin-charge coupling mechanism, which is also important in
ferromagnetic manganites.
|
1106.4421v1
|
2011-06-22
|
Storing light as a mechanical excitation in a silica optomechanical resonator
|
We report the experimental demonstration of optomechanical light storage in a
silica resonator. We use writing and readout laser pulses tuned to one
mechanical frequency below an optical cavity resonance to control the coupling
between the mechanical displacement and the optical field at the cavity
resonance. The writing pulse maps a signal pulse at the cavity resonance to a
mechanical excitation. The readout pulse later converts the mechanical
excitation back to an optical pulse. The light storage lifetime is determined
by the relatively long damping time of the mechanical excitation.
|
1106.4512v1
|
2011-07-18
|
Quantum gravity stability of isotropy in homogeneous cosmology
|
It has been shown that anisotropy of homogeneous spacetime described by the
general Kasner metric can be damped by quantum fluctuations coming from
perturbative quantum gravity in one-loop approximation. Also, a formal
argument, not limited to one-loop approximation, is put forward in favor of
stability of isotropy in the exactly isotropic case.
|
1107.3468v4
|
2011-07-19
|
Calculating a maximizer for quantum mutual information
|
We obtain a maximizer for the quantum mutual information for classical
information sent over the quantum qubit amplitude damping channel. This is
achieved by limiting the ensemble of input states to antipodal states, in the
calculation of the product-state capacity for the channel, the resulting
maximizing ensemble consisting of just two non-orthogonal states. We also
consider the product-state capacity of a convex combination of two memoryless
channels and demonstrate in particular that it is in general not given by the
minimum of the capacities of the respective memoryless channels.
|
1107.3741v1
|
2011-07-19
|
Damping of Bloch oscillations in the Hubbard model
|
Using nonequilibrium dynamical mean-field theory, we study the isolated
Hubbard model in a static electric field in the limit of weak interactions.
Linear response behavior is established at long times, but only if the
interaction exceeds a critical value, below which the system exhibits an
AC-type response with Bloch oscillations. The transition from AC to DC response
is defined in terms of the universal long-time behavior of the system, which
does not depend on the initial condition.
|
1107.3830v1
|
2011-07-20
|
Fractional Equations of Kicked Systems and Discrete Maps
|
Starting from kicked equations of motion with derivatives of non-integer
orders, we obtain "fractional" discrete maps. These maps are generalizations of
well-known universal, standard, dissipative, kicked damped rotator maps. The
main property of the suggested fractional maps is a long-term memory. The
memory effects in the fractional discrete maps mean that their present state
evolution depends on all past states with special forms of weights. These forms
are represented by combinations of power-law functions.
|
1107.3953v1
|
2011-07-21
|
Averaging approximation to singularly perturbed nonlinear stochastic wave equations
|
An averaging method is applied to derive effective approximation to the
following singularly perturbed nonlinear stochastic damped wave equation \nu
u_{tt}+u_t=\D u+f(u)+\nu^\alpha\dot{W} on an open bounded domain
$D\subset\R^n$\,, $1\leq n\leq 3$\,. Here $\nu>0$ is a small parameter
characterising the singular perturbation, and $\nu^\alpha$\,, $0\leq \alpha\leq
1/2$\,, parametrises the strength of the noise. Some scaling transformations
and the martingale representation theorem yield the following effective
approximation for small $\nu$, u_t=\D u+f(u)+\nu^\alpha\dot{W} to an error of
$\ord{\nu^\alpha}$\,.
|
1107.4184v1
|
2011-08-03
|
Parametric amplification of magnetoplasmons in semiconductor quantum dots
|
We show that the magnetoplasmon collective modes in quasi-two-dimensional
semiconductor quantum dots can be parametrically amplified by periodically
modulating the magnetic field perpendicular to the nanostructure. The two
magnetoplasmon modes are excited and amplified simultaneously, leading to an
exponential growth of the number of bosonic excitations in the system. We
further demonstrate that damping mechanisms as well as anharmonicities in the
confinement of the quantum dot lead to a saturation of the parametric
amplification. This work constitutes a first step towards parametric
amplification of collective modes in many-body fermionic systems beyond one
dimension.
|
1108.0891v3
|
2011-08-09
|
Beam-beam studies for the High-Energy LHC
|
LHC upgrades are being considered both towards higher luminosity (HL-LHC) and
towards higher energy (HE-LHC). In this paper we report initial studies of the
beam-beam effects in the HE-LHC [1]. The HE-LHC aims at beam energies of 16.5
TeV, where the transverse emittance decreases due to synchrotron radiation with
a 2-hour damping time. As a result of this emittance, shrinkage the beam-beam
parameter increases with time, during a physics store. The beam-beam limit in
the HE-LHC is explored using computer simulations.
|
1108.1871v1
|
2011-08-10
|
Protecting entangled states of two ions by engineering reservoir
|
We present a proposal for realizing local decoherence-free evolution of given
entangled states of two two-level (TL) ions. For two TL ions coupled to a
single heavily damped cavity, we can use engineering reservoir scheme to obtain
a decoherence-free subspace which can be nonadiabatically controlled by the
system and reservoir parameters. Then the local decoherence-free evolution of
the entangled states are achieved. And we also discuss the relation between the
geometric phases and the entanglement of the two ions under the nonadiabatic
coherent evolution.
|
1108.2186v1
|
2011-08-11
|
Weak Primordial Magnetic Fields and Anisotropies in the Cosmic Microwave Background Radiation
|
It is shown that small-scale magnetic fields present before recombination
induce baryonic density inhomogeneities of appreciable magnitude. The presence
of such inhomogeneities changes the ionization history of the Universe, which
in turn decreases the angular scale of the Doppler peaks and increases Silk
damping by photon diffusion. This unique signature could be used to (dis)prove
the existence of primordial magnetic fields of strength as small as B~10^(-11)
Gauss by upcoming cosmic microwave background observations.
|
1108.2517v1
|
2011-08-13
|
Demonstration of K-Kbar, B-Bbar, and D-Dbar Transitions with a Pair of Coupled Pendula
|
A setup of two coupled and damped pendula is used to demonstrate the main
features of transitions beween neutral K, D, B mesons and their respective
antiparticles, including CP violation in K Kbar transitions. The transitions
are described by two-state Schr\"odinger equations. Since the real parts of
their solutions obey the same differential equations as the pendula
coordinates, the pendulum motions can be used to represent the meson
transitions. Video clips of the motions are attached as supplementary material.
|
1108.2772v2
|
2011-08-15
|
Structural transitions in hypersphere fluids: predictions of Kirkwood's approximation
|
We use an analytic criterion for vanishing of exponential damping of
correlations developed previously (Piasecki et al, J. Chem. Phys., 133, 164507,
2010) to determine the threshold volume fractions for structural transitions in
hard sphere systems in dimensions D=3,4,5 and 6, proceeding from the YBG
hierarchy and using the Kirkwood superposition approximation. We conclude that
the theory does predict phase transitions in qualitative agreement with
numerical studies. We also derive, within the superposition approximation, the
asymptotic form of the analytic condition for occurence of a structural
transition in the D->Infinity limit .
|
1108.2919v1
|
2011-08-15
|
Directed transport in equilibrium : analysis of the dimer model with inertial terms
|
We have previously shown an analysis of our dimer model in the over-damped
regime to show directed transport in equilibrium. Here we analyze the full
model with inertial terms present to establish the same result. First we derive
the Fokker-Planck equation for the system following a Galilean transformation
to show that a uniformly translating equilibrium distribution is possible.
Then, we find out the velocity selection for the centre of mass motion using
that distribution on our model. We suggest generalization of our calculations
for soft collision potentials and indicate to interesting situation with
possibility of oscillatory non-equilibrium state within equilibrium.
|
1108.2927v1
|
2011-09-01
|
Double adiabatic theory of collisionless geodesic acoustic modes in tokamaks
|
Collisionless geodesic acoustic modes in tokamaks being supersonic for large
"safety factor" q, the CGL (G. Chew, M. Goldberger, F. Low, 1956)1
double-adiabatic fluid closure is applied to formulate a theory for these
modes. The basic linear normal mode is obtained. External means to drive these
modes at resonance, as has been proposed earlier, are explored. The external
drivers considered include external magnetic forces to effect flux surface
displacements, as well as non-axisymmetric ion heating. Finally, the damping of
these modes from collisional magnetic pumping is investigated using a model set
of CGL collision-corrected equations.
|
1109.0057v1
|
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