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2002-07-09
|
Optical phase-space reconstruction of mirror position at the attometer level
|
We describe an experiment in which the quadratures of the position of an
harmonically-bound mirror are observed at the attometer level. We have studied
the Brownian motion of the mirror, both in the free regime and in the
cold-damped regime when an external viscous force is applied by radiation
pressure. We have also studied the thermal-noise squeezing when the external
force is parametrically modulated. We have observed both the 50% theoretical
limit of squeezing at low gain and the parametric oscillation of the mirror for
a large gain.
|
0207049v2
|
2002-07-10
|
Error prevention scheme with two pairs of qubits
|
A scheme is presented for protecting one-qubit quantum information against
decoherence due to a general environment and local exchange interactions. The
scheme operates essentially by distributing information over two pairs of
qubits and through error prevention procedures. In the scheme, quantum
information is encoded through a decoherence-free subspace for collective phase
errors and exchange errors affecting the qubits in pairs; leakage out of the
encoding space due to amplitude damping is reduced by quantum Zeno effect. In
addition, how to construct decoherence-free states for n-qubit information
against phase and exchange errors is discussed.
|
0207063v1
|
2002-08-05
|
Path Integrals and Their Application to Dissipative Quantum Systems
|
Introduction
Path Integrals
- Introduction
- Propagator
- Free Particle
- Path Integral Representation of Quantum Mechanics
- Particle on a Ring
- Particle in a Box
- Driven Harmonic Oscillator
- Semiclassical Approximation
- Imaginary Time Path Integral
Dissipative Systems
- Introduction
- Environment as Collection of Harmonic Oscillators
- Effective Action
Damped Harmonic Oscillator
- Partition Function
- Ground State Energy and Density of States
- Position Autocorrelation Function
|
0208026v1
|
2002-11-25
|
Robust Entanglement in Atomic Systems via Lambda-Type Processes
|
It is shown that the system of two three-level atoms in $\Lambda$
configuration in a cavity can evolve to a long-lived maximum entangled state if
the Stokes photons vanish from the cavity by means of either leakage or
damping. The difference in evolution picture corresponding to the general model
and effective model with two-photon process in two-level system is discussed.
|
0211157v1
|
2003-04-29
|
Stability of stationary solutions of the Schrodinger-Langevin equation
|
The stability properties of a class of dissipative quantum mechanical systems
are investigated. The nonlinear stability and asymptotic stability of
stationary states (with zero and nonzero dissipation respectively) is
investigated by Liapunov's direct method. The results are demonstrated by
numerical calculations on the example of the damped harmonic oscillator.
|
0304190v3
|
2003-07-09
|
Teleportation in a noisy environment: a quantum trajectories approach
|
We study the fidelity of quantum teleportation for the situation in which
quantum logic gates are used to provide the long distance entanglement required
in the protocol, and where the effect of a noisy environment is modeled by
means of a generalized amplitude damping channel. Our results demonstrate the
effectiveness of the quantum trajectories approach, which allows the simulation
of open systems with a large number of qubits (up to 24). This shows that the
method is suitable for modeling quantum information protocols in realistic
environments.
|
0307065v1
|
2003-07-30
|
Maser and Laser Action with One Atom
|
We present a theory which can explain the micromaser as well as its optical
counterpart, the microlaser, for appropriate values of dissipative parameters.
We show that, in both the the cases, the cavity radiation fields can have
sub-Poissonian photon statistics. We further analyse if it is possible to
attain a Fock state of the radiation field. The microlaser is precluded for
such analysics due to the damping of its lasing levels making transitions at
optical frequencies. Hence, we focus our attention on the micromaser and our
exact simulation of the dynamics shows that it is not possible to generate a
Fock state of the cavity radiation field.
|
0307226v1
|
2003-08-25
|
Single Atom Cooling by Superfluid Immersion: A Non-Destructive Method for Qubits
|
We present a scheme to cool the motional state of neutral atoms confined in
sites of an optical lattice by immersing the system in a superfluid. The motion
of the atoms is damped by the generation of excitations in the superfluid, and
under appropriate conditions the internal state of the atom remains unchanged.
This scheme can thus be used to cool atoms used to encode a series of entangled
qubits non-destructively. Within realisable parameter ranges, the rate of
cooling to the ground state is found to be sufficiently large to be useful in
experiments.
|
0308129v1
|
2003-11-08
|
Cavity-induced damping and level shifts in a wide aperture spherical resonator
|
We calculate explicitly the space dependence of the radiative relaxation
rates and associated level shifts for a dipole placed in the vicinity of the
center of a spherical cavity with a large numerical aperture and a relatively
low finesse. In particular, we give simple and useful analytic formulas for
these quantities, that can be used with arbitrary mirrors transmissions. The
vacuum field in the vicinity of the center of the cavity is actually equivalent
to the one obtained in a microcavity, and this scheme allows one to predict
significant cavity QED effects.
|
0311047v2
|
2003-12-17
|
Quantum dynamics in single spin measurement
|
We study the quantum dynamics of a model for the single-spin measurement in
magnetic-resonance force microscopy. We consider an oscillating driven
cantilever coupled with the magnetic moment of the sample. Then, the cantilever
is damped through an external bath and its readout is provided by a radiation
field. Conditions for reliable measurements will be discussed.
|
0312147v2
|
2004-01-28
|
The Semiclassical Regime of the Chaotic Quantum-Classical Transition
|
An analysis of the semiclassical regime of the quantum-classical transition
is given for open, bounded, one dimensional chaotic dynamical systems.
Environmental fluctuations -- characteristic of all realistic dynamical systems
-- suppress the development of fine structure in classical phase space and damp
nonlocal contributions to the semiclassical Wigner function which would
otherwise invalidate the approximation. This dual regularization of the
singular nature of the semiclassical limit is demonstrated by a numerical
investigation of the chaotic Duffing oscillator.
|
0401174v4
|
2004-03-02
|
Completely-Positive Non-Markovian Decoherence
|
We propose an effective Hamiltonian approach to investigate decoherence of a
quantum system in a non-Markovian reservoir, naturally imposing the complete
positivity on the reduced dynamics of the system. The formalism is based on the
notion of an effective reservoir, i.e., certain collective degrees of freedom
in the reservoir that are responsible for the decoherence. As examples for
completely positive decoherence, we present three typical decoherence processes
for a qubit such as dephasing, depolarizing, and amplitude-damping. The effects
of the non-Markovian decoherence are compared to the Markovian decoherence.
|
0403018v1
|
2004-03-23
|
Optimal probabilistic cloning and purification of quantum states
|
We investigate the probabilistic cloning and purification of quantum states.
The performance of these probabilistic operations is quantified by the average
fidelity between the ideal and actual output states. We provide a simple
formula for the maximal achievable average fidelity and we explictly show how
to construct a probabilistic operation that achieves this fidelity. We
illustrate our method on several examples such as the phase covariant cloning
of qubits, cloning of coherent states, and purification of qubits transmitted
via depolarizing channel and amplitude damping channel. Our examples reveal
that the probabilistic cloner may yield higher fidelity than the best
deterministic cloner even when the states that should be cloned are linearly
dependent and are drawn from a continuous set.
|
0403165v1
|
2004-05-19
|
Information-capacity description of spin-chain correlations
|
Information capacities achievable in the multi-parallel-use scenarios are
employed to characterize the quantum correlations in unmodulated spin chains.
By studying the qubit amplitude damping channel, we calculate the quantum
capacity $Q$, the entanglement assisted capacity $C_E$, and the classical
capacity $C_1$ of a spin chain with ferromagnetic Heisenberg interactions.
|
0405110v3
|
2004-06-11
|
Optimal estimation of one parameter quantum channels
|
We explore the task of optimal quantum channel identification, and in
particular the estimation of a general one parameter quantum process. We derive
new characterizations of optimality and apply the results to several examples
including the qubit depolarizing channel and the harmonic oscillator damping
channel. We also discuss the geometry of the problem and illustrate the
usefulness of using entanglement in process estimation.
|
0406070v3
|
2004-12-02
|
Transient dynamics of linear quantum amplifiers
|
The transient dynamics of a quantum linear amplifier during the transition
from damping to amplification regime is studied. The master equation for the
quantized mode of the field is solved, and the solution is used to describe the
statistics of the output field. The conditions under which a nonclassical input
field may retain nonclassical features at the output of the amplifier are
analyzed and compared to the results of earlier theories. As an application we
give a dynamical description of the departure of the system from thermal
equilibrium.
|
0412018v2
|
2005-02-13
|
A minimal coupling method for investigating one dimensional dissipative quantum systems
|
Quantum mechanics of a general one dimensional dissipative system
investigated by it's coupling to a Klein-Gordon field as the environment using
a minimal coupling method. Heisenberg equation for such a dissipative system
containing a dissipative term proportional to velocity obtained. As an example,
quantum dynamics of a damped harmonic oscillator as the prototype of some
important one dimensional dissipative models investigated consistently. Some
transition probabilities indicating the way energy flows between the subsystems
obtained.
|
0502076v2
|
2005-02-22
|
Minimal coupling method and the dissipative scalar field theory
|
Quantum field theory of a damped vibrating string as the simplest dissipative
scalar field investigated by its coupling with an infinit number of
Klein-Gordon fields as the environment by introducing a minimal coupling
method. Heisenberg equation containing a dissipative term proportional to
velocity obtained for a special choice of coupling function and quantum
dynamics for such a dissipative system investigated. Some kinematical relations
calculated by tracing out the environment degrees of freedom. The rate of
energy flowing between the system and it's environment obtained.
|
0502134v2
|
2005-04-29
|
Stationary state entanglement and total correlation of two qubits or qutrits
|
We investigate the mutual information and entanglement of stationary state of
two locally driven qubits under the influence of collective dephasing. It is
shown that both the mutual information and the entanglement of two qubits in
the stationary state exhibit damped oscillation with the scaled action time
$\gamma{T}$ of the local external driving field. It means that we can control
both the entanglement and total correlation of the stationary state of two
qubits by adjusting the action time of the driving field. We also consider the
influence of collective dephasing on entanglement of two qutrits and obtain the
sufficient condition that the stationary state is entangled.
|
0504228v1
|
2005-05-22
|
Fast SWAP gate by adiabatic passage
|
We present a process for the construction of a SWAP gate which does not
require a composition of elementary gates from a universal set. We propose to
employ direct techniques adapted to the preparation of this specific gate. The
mechanism, based on adiabatic passage, constitutes a decoherence-free method in
the sense that spontaneous emission and cavity damping are avoided.
|
0505163v2
|
2005-08-15
|
Quantum electromdynamics in a linear absorbing dielectric medium
|
The eletromagnetic field in a linear absorptive dielectric medium, is
quantized in the framework of the damped polarization model. A Hamiltonian
containing a reservoir with continuous degrees of freedom, is proposed. The
reservoir minimally interacts with the dielectric polarization and the
electromagnetic field. The Lagevin-Schrodinger equation is obtained as the
equation of motion of the polarization field. The radiation reaction
electromagnetic field is considered. For a homogeneous medium, the equations of
motion are solved using the Laplace transformation method.
|
0508107v1
|
2005-08-18
|
The harmonic oscillator with dissipation within the theory of open quantum systems
|
Time evolution of the expectation values of various dynamical operators of
the harmonic oscillator with dissipation is analitically obtained within the
framework of the Lindblad theory for open quantum systems. We deduce the
density matrix of the damped harmonic oscillator from the solution of the
Fokker-Planck equation for the coherent state representation, obtained from the
master equation for the density operator. The Fokker-Planck equation for the
Wigner distribution function, subject to either the Gaussian type or the
$\delta$-function type of initial conditions, is also solved by using the
Wang-Uhlenbeck method. The obtained Wigner functions are two-dimensional
Gaussians with different widths.
|
0508140v1
|
2005-09-02
|
A dynamical model for quantum memory channels
|
A dynamical model for quantum channel is introduced which allows one to pass
continuously from the memoryless case to the case in which memory effects are
present. The quantum and classical communication rates of the model are defined
and explicit expression are provided in some limiting case. In this context we
introduce noise attenuation strategies where part of the signals are sacrificed
to modify the channel environment. The case of qubit channel with phase damping
noise is analyzed in details.
|
0509016v2
|
2005-09-19
|
Feedback cooling of a single trapped ion
|
Based on a real-time measurement of the motion of a single ion in a Paul
trap, we demonstrate its electro-mechanical cooling below the Doppler limit by
homodyne feedback control (cold damping). The feedback cooling results are well
described by a model based on a quantum mechanical Master Equation.
|
0509125v1
|
2005-09-27
|
CNOT gate by adiabatic passage with an optical cavity
|
We propose a scheme for the construction of a CNOT gate by adiabatic passage
in an optical cavity. In opposition to a previously proposed method, the
technique is not based on fractional adiabatic passage, which requires the
control of the ratio of two pulse amplitudes. Moreover, the technique
constitutes a decoherence-free method in the sense that spontaneous emission
and cavity damping are avoided since the dynamics follows dark states.
|
0509187v1
|
2005-12-12
|
Decoherence-free manipulation of photonic memories for quantum computation
|
We present a protocol to construct an arbitrary quantum circuit. The quantum
bits (qubits) are encoded in polarisation states of single photons. They are
stored in spatially separated dense media deposed in an optical cavity.
Specific sequences of pulses address individually the storage media to encode
the qubits and to implement a universal set of gates. The proposed protocol is
decoherence-free in the sense that spontaneous emission and cavity damping are
avoided. We discuss a coupling scheme for experimental implementation in Neon
atoms.
|
0512084v1
|
2006-01-23
|
Detuned Electromagnetically Induced Transparency in an $N$-type Atom
|
The electromagnetically induced transparency (EIT) in an $N$ configuration is
studied under both resonant and off-resonant conditions. In a certain
off-resonant condition the dark state of the four level system, which is almost
the same as the resonant dark state in $\Lambda$ configuration, is rebuilt. The
actual system with damping is examined using optical Bloch equation, both
numerically and analytically. Based on this detuned dark state, some new
applications with frequency shifts can be realized.
|
0601153v2
|
2006-04-28
|
Purity of states in the theory of open quantum systems
|
The condition of purity of states for a damped harmonic oscillator is
considered in the framework of Lindblad theory for open quantum systems. For a
special choice of the environment coefficients, the correlated coherent states
are shown to be the only states which remain pure all the time during the
evolution of the considered system. These states are also the most stable under
evolution in the presence of the environment.
|
0604212v1
|
2006-05-23
|
Continuous observation of a squeezed coherent state
|
The main aim of the paper is to present the analytical solution of the
Belavkin quantum filtering equation for damped harmonic oscillator being
initially in the squeezed coherent state for diffusion observation with complex
white noise. The comparison of the a priori and a posteriori mean value of the
optical quadrature operators and the photon number operator is given.
|
0605200v2
|
2006-06-27
|
Quantum decoherence of the damped harmonic oscillator
|
In the framework of the Lindblad theory for open quantum systems, we
determine the degree of quantum decoherence of a harmonic oscillator
interacting with a thermal bath. It is found that the system manifests a
quantum decoherence which is more and more significant in time. We also
calculate the decoherence time and show that it has the same scale as the time
after which thermal fluctuations become comparable with quantum fluctuations.
|
0606222v1
|
2006-08-16
|
Characterization of unwanted noise in realistic cavities
|
The problem of the description of absorption and scattering losses in high-Q
cavities is studied. The considerations are based on quantum noise theories,
hence the unwanted noise associated with scattering and absorption is taken
into account by introduction of additional damping and noise terms in the
quantum Langevin equations and input--output relations. Completeness conditions
for the description of the cavity models obtained in this way are studied and
corresponding replacement schemes are discussed.
|
0608126v1
|
2006-10-27
|
Quantum-limited force measurement with an optomechanical device
|
We study the detection of weak coherent forces by means of an optomechanical
device formed by a highly reflecting isolated mirror shined by an intense and
highly monochromatic laser field. Radiation pressure excites a vibrational mode
of the mirror, inducing sidebands of the incident field, which are then
measured by heterodyne detection. We determine the sensitivity of such a scheme
and show that the use of an entangled input state of the two sideband modes
improves the detection, even in the presence of damping and noise acting on the
mechanical mode.
|
0610236v1
|
2006-11-08
|
Quantum superchemistry in an output coupler of coherent matter waves
|
We investigate the quantum superchemistry or Bose-enhanced atom-molecule
conversions in a coherent output coupler of matter waves, as a simple
generalization of the two-color photo-association. The stimulated effects of
molecular output step and atomic revivals are exhibited by steering the rf
output couplings. The quantum noise-induced molecular damping occurs near a
total conversion in a levitation trap. This suggests a feasible two-trap scheme
to make a stable coherent molecular beam.
|
0611088v1
|
2007-02-01
|
Field quantization in inhomogeneous anisotropic dielectrics with spatio-temporal dispersion
|
A quantum damped-polariton model is constructed for an inhomogeneous
anisotropic linear dielectric with arbitrary dispersion in space and time. The
model Hamiltonian is completely diagonalized by determining the creation and
annihilation operators for the fundamental polariton modes as specific linear
combinations of the basic dynamical variables. Explicit expressions are derived
for the time-dependent operators describing the electromagnetic field, the
dielectric polarization and the noise term in the latter. It is shown how to
identify bath variables that generate the dissipative dynamics of the medium.
|
0702010v2
|
2007-02-15
|
Quantum Mechanics with Complex Time : A Comment to the Paper by Rajeev
|
In (quant-ph/0701141) Rajeev studied quantization of the damped simple
harmonic oscillator and introduced a complex-valued Hamiltonian (which is
normal). In this note we point out that the quantization is interpreted as a
quantum mechanics with {\bf complex time}. We also present a problem on
quantization of classical control systems.
|
0702148v1
|
2007-03-18
|
Lindblad master equation for the damped harmonic oscillator with deformed dissipation
|
In the framework of the Lindblad theory for open quantum systems, a master
equation for the quantum harmonic oscillator interacting with a dissipative
environment, in particular with a thermal bath, is derived for the case when
the interaction is based on deformed algebra. The equations of motion for
observables strongly depend on the deformation function. The expectation values
of the number operator and squared number operator are calculated in the limit
of a small deformation parameter for the case of zero temperature of the
thermal bath. The steady state solution of the equation for the density matrix
in the number representation is obtained and its independence of the
deformation is shown.
|
0703165v1
|
2007-04-06
|
Bremsstrahlung Radiation At a Vacuum Bubble Wall
|
When charged particles collide with a vacuum bubble, they can radiate strong
electromagnetic waves due to rapid deceleration. Owing to the energy loss of
the particles by this bremsstrahlung radiation, there is a non-negligible
damping pressure acting on the bubble wall even when thermal equilibrium is
maintained. In the non-relativistic region, this pressure is proportional to
the velocity of the wall and could have influenced the bubble dynamics in the
early universe.
|
0704.0837v1
|
2007-04-11
|
Effects of atomic interactions on Quantum Accelerator Modes
|
We consider the influence of the inclusion of interatomic interactions on the
delta-kicked accelerator model. Our analysis concerns in particular quantum
accelerator modes, namely quantum ballistic transport near quantal resonances.
The atomic interaction is modelled by a Gross-Pitaevskii cubic nonlinearity,
and we address both attractive (focusing) and repulsive (defocusing) cases. The
most remarkable effect is enhancement or damping of the accelerator modes,
depending on the sign of the nonlinear parameter. We provide arguments showing
that the effect persists beyond mean-field description, and lies within the
experimentally accessible parameter range.
|
0704.1382v1
|
2007-04-17
|
Dissipation in graphene and nanotube resonators
|
Different damping mechanisms in graphene nanoresonators are studied: charges
in the substrate, ohmic losses in the substrate and the graphene sheet,
breaking and healing of surface bonds (Velcro effect), two level systems,
attachment losses, and thermoelastic losses. We find that, for realistic
structures and contrary to semiconductor resonators, dissipation is dominated
by ohmic losses in the graphene layer and metallic gate. An extension of this
study to carbon nanotube-based resonators is presented.
|
0704.2225v3
|
2007-04-19
|
Substrate temperature changes during MBE growth of GaMnAs
|
Remarkably big increase of the substrate temperature during the
low-temperature MBE growth of GaMnAs layers is observed by means of band gap
spectroscopy. It is explained and simulated in terms of changes in the
absorption/emission characteristics of the growing layer. Options for the
temperature variation damping are discussed.
|
0704.2485v1
|
2007-04-29
|
Effect of Decoherence on the Dynamics of Bose-Einstein Condensates in a Double-well Potential
|
We study the dynamics of a Bose-Einstein condensate in a double-well
potential in the mean-field approximation. Decoherence effects are considered
by analyzing the couplings of the condensate to environments. Two kinds of
coupling are taken into account. With the first kind of coupling dominated, the
decoherence can enhance the self-trapping by increasing the damping of the
oscillations in the dynamics, while the decoherence from the second kind of
condensate-environment coupling leads to spoiling of the quantum tunneling and
self-trapping.
|
0704.3823v1
|
2007-05-08
|
Theoretical Analysis of Subthreshold Oscillatory Behaviors in Nonlinear Autonomous Systems
|
We have developed a linearization method to investigate the subthreshold
oscillatory behaviors in nonlinear autonomous systems. By considering firstly
the neuronal system as an example, we show that this theoretical approach can
predict quantitatively the subthreshold oscillatory activities, including the
damping coefficients and the oscillatory frequencies which are in good
agreement with those observed in experiments. Then we generalize the
linearization method to an arbitrary autonomous nonlinear system. The detailed
extension of this theoretical approach is also presented and further discussed.
|
0705.1019v1
|
2007-05-08
|
Supersymmetric methods in the traveling variable: inside neurons and at the brain scale
|
We apply the mathematical technique of factorization of differential
operators to two different problems. First we review our results related to the
supersymmetry of the Montroll kinks moving onto the microtubule walls as well
as mentioning the sine-Gordon model for the microtubule nonlinear excitations.
Second, we find analytic expressions for a class of one-parameter solutions of
a sort of diffusion equation of Bessel type that is obtained by supersymmetry
from the homogeneous form of a simple damped wave equations derived in the
works of P.A. Robinson and collaborators for the corticothalamic system. We
also present a possible interpretation of the diffusion equation in the brain
context
|
0705.1134v1
|
2007-05-11
|
Kerr quasinormal modes and Hod's time-temperature bound
|
We give an explicit expression for the frequencies of slowly damped
quasinormal modes of near-extreme Kerr black holes. It follows from this
expression that the near-extreme Kerr holes obey the Hod's bound: in the limit
of maximal rotation, $\lim \sup \omega_{IS}/T\leq \pi / \hbar$, where $\omega
_{IS}$ is the decay rate of the slowest decaying quasinormal mode, $T$ is the
black hole temperature. On the other hand, the bound is not saturated in the
sense that $\lim \inf \omega_{IS}/T< \pi /\hbar$ is a strict inequality. {\it
It remains unclear} whether the bound is saturated in the sense that $\lim \sup
\omega_{IS}/T= \pi /\hbar$.
|
0705.1725v1
|
2007-05-14
|
X-ray emission from magnetic dissipation in the magnetar magnetosphere
|
Magnetic dissipation through decay of Alfven waves in the magnetar
magnetosphere is discussed. Transport of magnetic fields in the star leads to
dissipation of the magnetic energy through either direct internal heating or
transferring of the energy in waves that decay in the magnetar magnetosphere.
In the latter case, the Alfven waves are excited by crust dislocations or
elastic waves underneath the star's surface. It is suggested that these Alfven
waves can decay into ion sound waves which can be effectively damped leading to
strong plasma heating. Hot plasmas expand producing transient X-rays.
|
0705.1859v1
|
2007-05-14
|
Effects of dissipation on a quantum critical point with disorder
|
We study the effects of dissipation on a disordered quantum phase transition
with O$(N)$ order parameter symmetry by applying a strong-disorder
renormalization group to the Landau-Ginzburg-Wilson field theory of the
problem. We find that Ohmic dissipation results in a non-perturbative
infinite-randomness critical point with unconventional activated dynamical
scaling while superohmic damping leads to conventional behavior. We discuss
applications to the superconductor-metal transition in nanowires and to Hertz'
theory of the itinerant antiferromagnetic transition.
|
0705.1865v3
|
2007-05-20
|
Heat transfer in sound propagation and attenuation through gas-liquid polyhedral foams
|
A cell method is developed, which takes into account the bubble geometry of
polyhedral foams, and provides for the generalized Rayleigh-Plesset equation
that contains the non-local in time term corresponding to heat relaxation. The
Rayleigh-Plesset equation together with the equations of mass and momentum
balances for an effective single-phase inviscid fluid yield a model for foam
acoustics. The present calculations reconcile observed sound velocity and
attenuation with those predicted using the assumption that thermal dissipation
is the dominant damping mechanism in a range of foam expansions and sound
excitation frequencies.
|
0705.2894v1
|
2007-05-28
|
Ground state of the time-independent Gross-Pitaevskii equation
|
We present a suite of programs to determine the ground state of the
time-independent Gross-Pitaevskii equation, used in the simulation of
Bose-Einstein condensates. The calculation is based on the Optimal Damping
Algorithm, ensuring a fast convergence to the true ground state. Versions are
given for the one-, two-, and three-dimensional equation, using either a
spectral method, well suited for harmonic trapping potentials, or a spatial
grid.
|
0705.4024v2
|
2007-05-29
|
Fresnel-transform's quantum correspondence and quantum optical ABCD Law
|
Corresponding to Fresnel transform there exists a unitary operator in quantum
optics theory, which could be named Fresnel operator (FO). We show that the
multiplication rule of FO naturally leads to the quantum optical ABCD law. The
canonical operator methods as mapping of ray-transfer ABCD matrix is explicitly
shown by FO's normally ordered expansion through the coherent state
representation and the technique of integration within an ordered product of
operators. We show that time evolution of the damping oscillator embodies the
quantum optical ABCD law.
|
0705.4184v1
|
2007-06-07
|
Lagrangians Galore
|
Searching for a Lagrangian may seem either a trivial endeavour or an
impossible task. In this paper we show that the Jacobi last multiplier
associated with the Lie symmetries admitted by simple models of classical
mechanics produces (too?) many Lagrangians in a simple way. We exemplify the
method by such a classic as the simple harmonic oscillator, the harmonic
oscillator in disguise [H Goldstein, {\it Classical Mechanics}, 2nd edition
(Addison-Wesley, Reading, 1980)] and the damped harmonic oscillator. This is
the first paper in a series dedicated to this subject.
|
0706.1008v1
|
2007-06-12
|
Theory of the Pseudospin Resonance in Semiconductor Bilayers
|
The pseudospin degree of freedom in a semiconductor bilayer gives rise to a
collective mode analogous to the ferromagnetic resonance mode of a ferromagnet.
We present a theory of the dependence of the energy and the damping of this
mode on layer separation $d$. Based on these results, we discuss the
possibility of realizing transport-current driven pseudospin-transfer
oscillators in semiconductors.
|
0706.1702v1
|
2007-06-19
|
Evidence for Growth of Eccentricity and Mass Clearing in a Disc Interior to a Planet
|
We present computational results showing eccentricity growth in the inner
portions of a protoplanetary disc. We attribute this to the evolving surface
density of the disc. The planet creates a gap, which adjusts the balance
between the 3:1 (eccentricity exciting) and 2:1 (eccentricity damping)
resonances. The eccentricity of the inner disc can rise as high as 0.3, which
is sufficient to cause it to be accreted onto the star. This offers an
alternative mechanism for producing the large holes observed in the discs of
CoKu Tau/4, GM Aur and DM Tau.
|
0706.2801v1
|
2007-06-23
|
Incoherent mid-infrared charge excitation and the high energy anomaly in the photoemission spectra of cuprates
|
On the basis of a semi-phenomenological model, it is argued that the high
energy anomaly observed in recent photoemission experiments on cuprates is
caused by interaction with an overdamped bosonic mode in the mid-infrared
region of the spectrum. Analysis of optical conductivity allows to connect this
excitation to the incoherent charge response reported for the majority of high
Tc materials and some other perovskites. We show that its large damping is an
essential feature responsible for the "waterfall" dispersion and linewidth of
the spectral weight.
|
0706.3449v1
|
2007-07-05
|
Magnetic-order induced phonon splitting in MnO from far-infrared spectroscopy
|
Detailed far-infrared spectra of the optical phonons are reported for
antiferromagnetic MnO. Eigenfrequencies, phonon damping and effective plasma
frequencies are studied as a function of temperature. Special attention is paid
to the phonon splitting at the antiferromagnetic phase transition. The results
are compared to recent experimental and theoretical studies of the spin-phonon
coupling in frustrated magnets, which are explained in terms of a spin-driven
Jahn-Teller effect, and to ab initio and model calculations, which predict
phonon splitting induced by magnetic order.
|
0707.0820v2
|
2007-07-12
|
Generalised Inverse-Cowling Approximation for Polar $w$-mode Oscillations of Neutron Stars
|
Adopting the Lindblom-Detweiler formalism for polar oscillations of neutron
stars, we study the $w$-mode oscillation and find that the Lagrangian change in
pressure, measured by the physical quantity $X$, is negligibly small. Based on
this observation, we develop the generalised inverse-Cowling approximation
(GICA) with the approximation $X=X'=0$, where $X'$ is the derivative of $X$
with respect to the circumferential radius, for $w$-mode oscillations of
neutron stars. Under GICA, $w$-mode oscillations are described by a
second-order differential system, which can yield accurate frequencies and
damping rates of quasi-normal modes.
|
0707.1727v1
|
2007-08-07
|
Experimental Demonstration of Decoherence-Free One-Way Information Transfer
|
We report the experimental demonstration of a one-way quantum protocol
reliably operating in the presence of decoherence. Information is protected by
designing an appropriate decoherence-free subspace for a cluster state
resource. We demonstrate our scheme in an all-optical setup, encoding the
information into the polarization states of four photons. A measurement-based
one-way information-transfer protocol is performed with the photons exposed to
severe symmetric phase-damping noise. Remarkable protection of information is
accomplished, delivering nearly ideal outcomes.
|
0708.0960v2
|
2007-08-10
|
Qualitative properties of coupled parabolic systems of evolution equations
|
We apply functional analytical and variational methods in order to study
well-posedness and qualitative properties of evolution equations on product
Hilbert spaces. To this aim we introduce an algebraic formalism for matrices of
sesquilinear mappings. We apply our results to parabolic problems of different
nature: a coupled diffusive system arising in neurobiology, a strongly damped
wave equation, a heat equation with dynamic boundary conditions, and a general
semilinear Hodgkin--Huxley sytem.
|
0708.1428v2
|
2007-09-06
|
Nonequilibrium Electron Interactions in Metal Films
|
Ultrafast relaxation dynamics of an athermal electron distribution is
investigated in silver films using a femtosecond pump-probe technique with 18
fs pulses in off-resonant conditions. The results yield evidence for an
increase with time of the electron-gas energy loss rate to the lattice and of
the free electron damping during the early stages of the electron-gas
thermalization. These effects are attributed to transient alterations of the
electron average scattering processes due to the athermal nature of the
electron gas, in agreement with numerical simulations.
|
0709.0815v1
|
2007-09-24
|
Quasinormal Modes and Late-Time Tails of Canonical Acoustic Black Holes
|
In this paper, we investigate the evolution of classical wave propagation in
the canonical acoustic black hole by numerical method and discuss the details
of tail phenomenon. The oscillating frequency and damping time scale both
increase with the angular momentum $l$. For the lower $l$, numerical results
show the lowest WKB approximation gives the most reliable result. We also find
that time scale of the interim region from ringing to tail is not affected
obviously by changing $l$.
|
0709.3714v1
|
2007-10-03
|
Grain Boundary Diffusion in a Peierls-Nabarro Potential
|
We investigate the diffusion of a grain boundary in a crystalline material.
We consider in particular the case of a regularly spaced low-angle grain
boundary schematized as an array of dislocations that interact with each other
through long-range stress fields and with the crystalline Peierls-Nabarro
potential. The methodology employed to analyze the dynamics of the center of
mass of the grain boundary and its spatio-temporal fluctuations is based on
over-damped Langevin equations. The generality and the efficiency of this
technique is proved by the agreement with molecular dynamics simulations.
|
0710.0807v1
|
2007-10-04
|
Effect of Impurity Scattering on the Nonlinear Microwave Response in High-Tc Superconductors
|
We theoretically investigate intermodulation distortion in high-Tc
superconductors. We study the effect of nonmagnetic impurities on the real and
imaginary parts of nonlinear conductivity. The nonlinear conductivity is
proportional to the inverse of temperature owing to the dependence of the
damping effect on energy, which arises from the phase shift deviating from the
unitary limit. It is shown that the final-states interaction makes the real
part predominant over the imaginary part. These effects have not been included
in previous theories based on the two-fluid model, enabling a consistent
explanation for the experiments with the rf and dc fields.
|
0710.0934v1
|
2007-10-15
|
Ferromagnetic resonance study of polycrystalline Fe_{1-x}V_x alloy thin films
|
Ferromagnetic resonance has been used to study the magnetic properties and
magnetization dynamics of polycrystalline Fe$_{1-x}$V$_{x}$ alloy films with
$0\leq x < 0.7$. Films were produced by co-sputtering from separate Fe and V
targets, leading to a composition gradient across a Si substrate. FMR studies
were conducted at room temperature with a broadband coplanar waveguide at
frequencies up to 50 GHz using the flip-chip method. The effective
demagnetization field $4 \pi M_{\mathrm{eff}}$ and the Gilbert damping
parameter $\alpha$ have been determined as a function of V concentration. The
results are compared to those of epitaxial FeV films.
|
0710.2826v2
|
2007-10-20
|
Khasminskii--Whitham averaging for randomly perturbed KdV equation
|
We consider the damped-driven KdV equation $$ \dot
u-\nu{u_{xx}}+u_{xxx}-6uu_x=\sqrt\nu \eta(t,x), x\in S^1, \int u dx\equiv
\int\eta dx\equiv0, $$ where $0<\nu\le1$ and the random process $\eta$ is
smooth in $x$ and white in $t$. For any periodic function $u(x)$ let $
I=(I_1,I_2,...) $ be the vector, formed by the KdV integrals of motion,
calculated for the potential $u(x)$. We prove that if $u(t,x)$ is a solution of
the equation above, then for $0\le t\lesssim\nu^{-1}$ and $\nu\to0$ the vector
$ I(t)=(I_1(u(t,\cdot)),I_2(u(t,\cdot)),...) $ satisfies the (Whitham) averaged
equation.
|
0710.3869v1
|
2007-10-25
|
Casimir energy and entropy between dissipative mirrors
|
We discuss the Casimir effect between two identical, parallel slabs,
emphasizing the role of dissipation and temperature. Starting from quite
general assumptions, we analyze the behavior of the Casimir entropy in the
limit T->0 and link it to the behavior of the slab's reflection coefficients at
low frequencies. We also derive a formula in terms of a sum over modes, valid
for dissipative slabs that can be interpreted in terms of a damped quantum
oscillator.
|
0710.4915v2
|
2007-10-29
|
Nonlinear damping of slab modes and cosmic ray transport
|
By applying recent results for the slab correlation time scale onto cosmic
ray scattering theory, we compute cosmic ray parallel mean free paths within
the quasilinear limit. By employing these results onto charged particle
transport in the solar system, we demonstrate that much larger parallel mean
free paths can be obtained in comparison to previous results. A comparison with
solar wind observations is also presented to show that the new theoretical
results are much closer to the observations than the previous results.
|
0710.5418v1
|
2007-10-30
|
Dynamics of a 1-D model for the emergence of the plasma edge shear flow layer with momentum conserving Reynolds stress
|
A one-dimensional version of the second-order transition model based on the
sheared flow amplification by Reynolds stress and turbulence supression by
shearing is presented. The model discussed in this paper includes a form of the
Reynolds stress which explicitly conserves momentum. A linear stability
analysis of the critical point is performed. Then, it is shown that the
dynamics of weakly unstable states is determined by a reduced equation for the
shear flow. In the case in which the flow damping term is diffusive, the
stationary solutions are those of the real Ginzburg-Landau equation.
|
0710.5612v1
|
2007-11-10
|
A magnetization equation for non-equilibrium spin systems
|
A magnetization equation for a system of spins evolving non-adiabatically and
out of equilibrium is derived without specifying the internal interactions. For
relaxation processes, this equation provides a general form of magnetization
damping. A special case of the spin-spin exchange interaction is considered.
|
0711.1576v1
|
2007-11-13
|
Non-local dynamics of Bell states in separate cavities
|
We present non-local dynamics of Bell states in separate cavities. It is
demonstrated that (i) the entanglement damping speed will saturate when the
cavity leakage rate $\gamma\geq 0.4$; (ii) the synchronism relationship between
the fidelity and the concurrence depends on the initial state; (iii) if the
initial state is $1/\sqrt{2}(|01>+|10>)$, the dynamics of entropy is opposite
to that of fidelity.
|
0711.1923v1
|
2007-11-14
|
Isolated large amplitude periodic motions of towed rigid wheels
|
This study investigates a low degree-of-freedom (DoF) mechanical model of
shimmying wheels. The model is studied using bifurcation theory and numerical
continuation. Self-excited vibrations, that is, stable and unstable periodic
motions of the wheel, are detected with the help of Hopf bifurcation
calculations. These oscillations are then followed over a large parameter range
for different damping values by means of the software package AUTO97. For
certain parameter regions, the branches representing large amplitude stable and
unstable periodic motions become isolated following an isola birth. These
regions are extremely dangerous from an engineering view-point if they are not
identified and avoided at the design stage.
|
0711.2228v1
|
2007-11-21
|
Power Processing Circuits for Mems Inertial Energy Scavengers
|
Inertial energy scavengers are self-contained devices which generate power
from ambient motion, by electrically damping the internal motion of a suspended
proof mass. There are significant challenges in converting the power generated
from such devices to useable form, particularly in micro-engineered variants.
This paper presents approaches to this power conversion requirement, with
emphasis on the cases of electromagnetic and electrostatic transduction.
|
0711.3311v1
|
2007-11-21
|
Scaling Effects for Electromagnetic Vibrational Power Generators
|
This paper investigates how the power generated by electromagnetic based
vibrational power generators scales with the dimension of the generator. The
effects of scaling on the magnetic fields, the coil parameters and the
electromagnetic damping are presented. An analysis is presented for both
wire-wound coil technology and micro-fabricated coils.
|
0711.3316v1
|
2007-11-30
|
Large voltage from spin pumping in magnetic tunnel junctions
|
We studied the response of a ferromagnet-insulator-normal metal tunnel
structure under an external oscillating radio frequency (R.F.) magnetic field.
The D. C. voltage across the junction is calculated and is found not to
decrease despite the high resistance of the junction; instead, it is of the
order of $\mu V$ to $100\mu V$, much larger than the experimentally observed
value (100 nano-V) in the "strong coupled" ohmic ferromagnet-normal metal
bilayers. This is consistent with recent experimental results in tunnel
structures, where the voltage is larger than $\mu V$s. The damping and loss of
an external RF field in this structure is calculated.
|
0711.4939v1
|
2007-12-01
|
Description of current-driven torques in magnetic tunnel junctions
|
A free electron description of spin-dependent tranport in magnetic tunnel
junctions with non collinear magnetizations is presented. We investigate the
origin of transverse spin density in tunnelling transport and the quantum
interferences which give rise to oscillatory torques on the local
magnetization. Spin transfer torque is also analyzed and an important bias
asymmetry is found as well as a damped oscillatory behaviour. Furthermore, we
investigate the influence of the s-d exchange coupling on torque in particular
in the case of half-metallic MTJ in which the spin transfer torque is due to
interfacial spin-dependent reflections.
|
0712.0055v1
|
2007-12-10
|
Pathways through interstellar matter: - From the closest stars to the most distant quasars
|
Observations of quasar absorption systems relevant for studies of star
formation at redshift 2 </= z </= 4 are briefly reviewed. Emphasis is given on
the role played by dust in our understanding of the star formation history of
galaxies detected as absorption systems. Local interstellar studies are used as
a reference for understanding the properties of high redshift interstellar
media. An example is shown of the potential effects of dust extinction on the
metallicity-N(HI) distribution obtained from magnitude-limited surveys of
damped lyman alpha absorbers.
|
0712.1418v1
|
2007-12-17
|
Exact time-average distribution for a stationary non-Markovian massive Brownian particle coupled to two heat baths
|
Using a time-averaging technique we obtain exactly the probability
distribution for position and velocity of a Brownian particle under the
influence of two heat baths at different temperatures. These baths are
expressed by a white noise term, representing the fast dynamics, and a colored
noise term, representing the slow dynamics. Our exact solution scheme accounts
for inertial effects, that are not present in approaches that assume the
Brownian particle in the over-damped limit. We are also able to obtain the
contribution associated with the fast noise that are usually neglected by other
approaches.
|
0712.2839v1
|
2007-12-19
|
Hyperon bulk viscosity in the presence of antikaon condensate
|
We investigate the hyperon bulk viscosity due to the non-leptonic process $n
+ p \rightleftharpoons p + \Lambda $ in $K^-$ condensed matter and its effect
on the r-mode instability in neutron stars. We find that the hyperon bulk
viscosity coefficient in the presence of antikaon condensate is suppressed
compared with the case without the condensate. The suppressed hyperon bulk
viscosity in the superconducting phase is still an efficient mechanism to damp
the r-mode instability in neutron stars.
|
0712.3171v2
|
2007-12-31
|
Exact Solution of the Landau-Lifshitz Equations for a Radiating Charged Particle in The Coulomb Potential
|
We solve exactly the classical non-relativistic Landau-Lifshitz equations of
motion for a charged particle moving in a Coulomb potential, including
radiation damping. The general solution involves the Painleve transcendent of
type II. It confirms our physical intuition that a negatively charged classical
particle will spiral into the nucleus, supporting the the validity of the
Landau-Lifshitz equation.
|
0801.0238v2
|
2008-01-16
|
Charge and Spin Currents Generated by Dynamical Spins
|
We demonstrate theoretically that a charge current and a spin current are
generated by spin dynamics in the presence of spin-orbit interaction in the
perturbative regime. We consider a general spin-orbit interaction including the
spatially inhomogeneous case. Spin current due to spin damping is identified as
one origin of generated charge current, but other contributions exist, such as
the one due to an induced conservative field and the one arising from the
inhomogeneity of spin-orbit interaction.
|
0801.2466v2
|
2008-01-16
|
Dynamic stabilization of non-spherical bodies against unlimited collapse
|
We solve equations, describing in a simplified way the newtonian dynamics of
a selfgravitating nonrotating spheroidal body after loss of stability. We find
that contraction to a singularity happens only in a pure spherical collapse,
and deviations from the spherical symmetry stop the contraction by the
stabilising action of nonlinear nonspherical oscillations. A real collapse
happens after damping of the oscillations due to energy losses, shock wave
formation or viscosity. Detailed analysis of the nonlinear oscillations is
performed using a Poincar\'{e} map construction. Regions of regular and chaotic
oscillations are localized on this map.
|
0801.2538v1
|
2008-01-30
|
Effective theory of fluctuating circulating currents in high-Tc cuprates
|
We derive an effective dissipative quantum field theory for fluctuating
orbital currents in clean $CuO_2$ sheets of high-$T_c$ cuprates, based on a
three-band model. The Coulomb repulsion term between $Cu$- and $O$-sites is
decoupled in terms of current operators representing horizontal and vertical
parts of circulating currents within each $CuO_2$ unit cell of the lattice. The
model has ordering of currents at finite temperatures. The dissipative kernel
in the model is of the form $|\omega|/|{\bf q}|$, indicating Landau damping.
Applications of the effective theory to other models are also discussed.
|
0801.4611v1
|
2008-02-04
|
Nodal quasiparticles and the onset of spin density wave order in the cuprates
|
We present a theory for the onset of spin density wave order in the
superconducting ground state of the cuprates. We compute the scaling dimensions
of allowed perturbations of a `relativistic' fixed point with O(4)xO(3)
symmetry, including those associated with the fermionic nodal Bogoliubov
quasiparticles. Analyses of up to six loops show that all perturbations with
square lattice symmetry are likely irrelevant. We demonstrate that the fermion
spectral functions are primarily damped by the coupling to fluctuations of a
composite field with Ising nematic order. We also discuss the influence of
quenched disorder.
|
0802.0199v1
|
2008-02-08
|
Rate of decoherence for an electron weakly coupled to a phonon gas
|
We study the dynamics of an electron weakly coupled to a phonon gas. The
initial state of the electron is the superposition of two spatially localized
distant bumps moving towards each other, and the phonons are in a thermal
state. We investigate the dynamics of the system in the kinetic regime and show
that the time evolution makes the non-diagonal terms of the density matrix of
the electron decay, destroying the interference between the two bumps. We show
that such a damping effect is exponential in time, and the related decay rate
is proportional to the total scattering cross section of the electron-phonon
interaction.
|
0802.1229v1
|
2008-02-11
|
Massive Charged Scalar Quasinormal Modes of Reissner-Nördstrom Black Hole Surrounded by Quintessence
|
We evaluate the complex frequencies of the normal modes for the massive
charged scalar field perturbations around a Reissner-N\"ordstrom black hole
surrounded by a static and spherically symmetric quintessence using third order
WKB approximation approach. Due to the presence of quintessence, quasinormal
frequencies damp more slowly. We studied the variation of quasinormal
frequencies with charge of the black bole, mass and charge of perturbating
scalar field and the quintessential state parameter.
|
0802.1397v1
|
2008-02-22
|
Algebraic Structure of a Master Equation with Generalized Lindblad Form
|
The quantum damped harmonic oscillator is described by the master equation
with usual Lindblad form. The equation has been solved completely by us in
arXiv : 0710.2724 [quant-ph]. To construct the general solution a few facts of
representation theory based on the Lie algebra $su(1,1)$ were used.
In this paper we treat a general model described by a master equation with
generalized Lindblad form. Then we examine the algebraic structure related to
some Lie algebras and construct the interesting approximate solution.
|
0802.3252v1
|
2008-02-22
|
Environmental limits on the non-resonant cosmic-ray current-driven instability
|
We investigate the so-called non-resonant cosmic-ray streaming instability,
first discussed by Bell (2004). The extent to which thermal damping and
ion-neutral collisions reduce the growth of this instability is calculated.
Limits on the growth of the non-resonant mode in SN1006 and RX J1713.7-3946 are
presented.
|
0802.3322v1
|
2008-03-04
|
The decreasing property of relative entropy and the strong superadditivity of quantum channels
|
We argue that a fundamental (conjectured) property of memoryless quantum
channels, namely the strong superadditivity, is intimately related to the
decreasing property of the quantum relative entropy. Using the latter we first
give, for a wide class of input states, an estimation of the output entropy for
phase damping channels and some Weyl quantum channels. Then we prove, without
any input restriction, the strong superadditivity for several quantum channels,
including depolarizing quantum channels, quantum-classical channels and quantum
erasure channels.
|
0803.0452v2
|
2008-03-08
|
The Impact of Stochastic Primordial Magnetic Fields on the Scalar Contribution to Cosmic Microwave Background Anisotropies
|
We study the impact of a stochastic background of primordial magnetic fields
on the scalar contribution of CMB anisotropies and on the matter power
spectrum. We give the correct initial conditions for cosmological perturbations
and the exact expressions for the energy density and Lorentz force associated
to the stochastic background of primordial magnetic fields, given a power-law
for their spectra cut at a damping scale. The dependence of the CMB temperature
and polarization spectra on the relevant parameters of the primordial magnetic
fields is illustrated.
|
0803.1246v1
|
2008-03-13
|
Dynamical density functional theory with hydrodynamic interactions and colloids in unstable traps
|
A density functional theory for colloidal dynamics is presented which
includes hydrodynamic interactions between the colloidal particles. The theory
is applied to the dynamics of colloidal particles in an optical trap which
switches periodically in time from a stable to unstable confining potential. In
the absence of hydrodynamic interactions, the resulting density breathing mode,
exhibits huge oscillations in the trap center which are almost completely
damped by hydrodynamic interactions. The predicted dynamical density fields are
in good agreement with Brownian dynamics computer simulations.
|
0803.2009v1
|
2008-03-26
|
Damping of Type I X-ray Burst Oscillations by Convection
|
I construct a simple model of the convective burning layer during a type I
X-ray burst to investigate the effects convection has on the stability of the
layer to nonradial oscillations. A linear perturbation analysis demonstrates
that the region is stable to nonradial oscillations when energy transport is
convection-dominated, but it is unstable when energy transport is
radiation-dominated. Thus, efficient convection always dampens oscillations.
These results may explain the nondetection of oscillations during the peak of
some X-ray bursts.
|
0803.3814v2
|
2008-03-28
|
Dipole Oscillations of a Bose-Einstein Condensate in Presence of Defects and Disorder
|
We consider dipole oscillations of a trapped dilute Bose-Einstein condensate
in the presence of a scattering potential consisting either in a localized
defect or in an extended disordered potential. In both cases the breaking of
superfluidity and the damping of the oscillations are shown to be related to
the appearance of a nonlinear dissipative flow. At supersonic velocities the
flow becomes asymptotically dissipationless.
|
0803.4116v1
|
2008-03-28
|
Atomic Zitterbewegung
|
Ultra-cold atoms which are subject to ultra-relativistic dynamics are
investigated. By using optically induced gauge potentials we show that the
dynamics of the atoms is governed by a Dirac type equation. To illustrate this
we study the trembling motion of the centre of mass for an effective two level
system, historically called Zitterbewegung. Its origin is described in detail,
where in particular the role of the finite width of the atomic wave packets is
seen to induce a damping of both the centre of mass dynamics and the dynamics
of the populations of the two levels.
|
0803.4189v2
|
2008-04-01
|
Passive Convection of Density Fluctuations in the Local Interstellar Medium
|
We have developed a time-dependent three-dimensional model of isotropic,
adiabatic, and compressible magnetohydrodynamic plasma to understand nonlinear
cascades of density fluctuations in local interstellar medium. Our simulations,
describing evolution of initial supersonic, super Alfv\'enic plasma modes,
indicate that nonlinear interactions lead to damping of plasma motion. During
the process, turbulent cascades are governed predominantly by the Alfv\'enic
modes and velocity field fluctuations evolve towards a state charachterized by
near incompressibility. Consequently, density field is advected passively by
the velocity field. Our findings thus demonstrate that the observed density
fluctuations in the interstellar medium are the structures passively convected
by the background velocity field.
|
0804.0045v1
|
2008-04-02
|
Anomalous quantum reflection as a quasi-dynamical damping effect
|
We develop a quasi-analytical theory for the quantum reflection amplitude of
Bose-Einstein condensates. We derive and calculate the decay-width of a
Bose-Einstein condensate. A general relation between the time-dependent
decay-law of the system and its quantum reflection amplitude allows us to
explain the quantum reflection anomaly of Bose-Einstein condensates present in
BEC-surface systems as a direct consequence of the repulsive particle
interaction.
|
0804.0367v2
|
2008-04-10
|
Colliding solitons for the nonlinear Schrodinger equation
|
We study the collision of two fast solitons for the nonlinear Schr\"odinger
equation in the presence of a spatially adiabatic external potential. For a
high initial relative speed $\|v\|$ of the solitons, we show that, up to times
of order $\log\|v\|$ after the collision, the solitons preserve their shape (in
$L^2$-norm), and the dynamics of the centers of mass of the solitons is
approximately determined by the external potential, plus error terms due to
radiation damping and the extended nature of the solitons. We remark on how to
obtain longer time scales under stronger assumptions on the initial condition
and the external potential.
|
0804.1608v1
|
2008-04-10
|
Statistical correlations of an anyon liquid at low temperatures
|
Using a proposed generalization of the pair distribution function for a gas
of non-interacting particles obeying fractional exclusion statistics in
arbitrary dimensionality, we derive the statistical correlations in the
asymptotic limit of vanishing or low temperature. While Friedel-like
oscillations are present in nearly all non-bosonic cases at T=0, they are
characterized by exponential damping at low temperature. We discuss the
dependence of these features on dimensionality and on the value of the
statistical parameter alpha.
|
0804.1691v1
|
2008-04-11
|
Collisional Properties of a Polarized Fermi Gas with Resonant Interactions
|
Highly polarized mixtures of atomic Fermi gases constitute a novel Fermi
liquid. We demonstrate how information on thermodynamic properties may be used
to calculate quasiparticle scattering amplitudes even when the interaction is
resonant and apply the results to evaluate the damping of the spin dipole mode.
We estimate that under current experimental conditions, the mode would be
intermediate between the hydrodynamic and collisionless limits.
|
0804.1885v2
|
2008-04-25
|
Impurity induced coherent current oscillations in one-dimensional conductors
|
We study theoretically the electronic transport through a single impurity in
a repulsive Luttinger liquid (LL), and find that above a threshold voltage
related to a strength of the impurity potential the DC current $\bar I$ is
accompanied by coherent oscillations with frequency $f = \bar I/e$. There is an
analogy with Josephson junctions: the well-known regime of power-law I-V curves
in the LL corresponds to damping of the Josephson current below the critical
one, while the oscillatory regime in the LL can be compared with the Josephson
oscillations above the critical current.
|
0804.4113v1
|
2008-05-06
|
Wave Decay in MHD Turbulence
|
We present a model for nonlinear decay of the weak wave in three-dimensional
incompressible magnetohydrodynamic (MHD) turbulence. We show that the decay
rate is different for parallel and perpendicular waves. We provide a general
formula for arbitrarily directed waves and discuss particular limiting cases
known in the literature. We test our predictions with direct numerical
simulations of wave decay in three-dimensional MHD turbulence, and discuss the
influence of turbulent damping on the development of linear instabilities in
the interstellar medium and on other important astrophysical processes.
|
0805.0630v1
|
2008-05-07
|
A piecewise-linear reduced-order model of squeeze-film damping for deformable structures including large displacement effects
|
This paper presents a reduced-order model for the Reynolds equation for
deformable structure and large displacements. It is based on the model
established in [11] which is piece-wise linearized using two different methods.
The advantages and drawbacks of each method are pointed out. The pull-in time
of a microswitch is determined and compared to experimental and other
simulation data.
|
0805.0894v1
|
2008-05-14
|
Signal propagation through dense granular systems
|
The manner in which signals propagate through dense granular systems in both
space and time is not well understood. In order to learn more about this
process, we carry out discrete element simulations of the system response to
excitations where we control the driving frequency and wavelength
independently. Fourier analysis shows that properties of the signal depend
strongly on the spatial and temporal scales introduced by the perturbation. The
features of the response provide a test-bed for any continuum theory attempting
to predict signal properties. We illustrate this connection between micro-scale
physics and macro-scale behavior by comparing the system response to a simple
elastic model with damping.
|
0805.2051v1
|
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