832 research outputs found
Gap soliton dynamics in an optical lattice as a parametrically driven pendulum
A long wavelength optical lattice is generated in a two-level medium by
low-frequency contrapropagating beams. Then a short wave length gap soliton
generated by evanescent boundary instability (supratransmission) undergoes a
dynamics shown to obey the Newton equation of the parametrically driven
pendulum, hence presenting extremely rich, possibly chaotic, dynamical
behavior. The theory is sustained by numerical simulations and provides an
efficient tool to study soliton trajectories
Coherent spin relaxation in molecular magnets
Numerical modelling of coherent spin relaxation in nanomagnets, formed by
magnetic molecules of high spins, is accomplished. Such a coherent spin
dynamics can be realized in the presence of a resonant electric circuit coupled
to the magnet. Computer simulations for a system of a large number of
interacting spins is an efficient tool for studying the microscopic properties
of such systems. Coherent spin relaxation is an ultrafast process, with the
relaxation time that can be an order shorter than the transverse spin dephasing
time. The influence of different system parameters on the relaxation process is
analysed. The role of the sample geometry on the spin relaxation is
investigated.Comment: Latex file, 22 pages, 7 figure
Physical theory of the twentieth century and contemporary philosophy
It has been shown that the criticism of Pauli as well as of Susskind and
Glogover may be avoided if the standard quantum-mechanical mathematical model
has been suitably extended. There is not more any reason for Einstein's
citicism, either, if in addition to some new results concerning Bell's
inequalities and Belifante's argument are taken into account. The ensemble
interpretation of quantum mechanics (or the hidden-variable theory) should be
preferred, which is also supported by the already published results of
experiments with three polarizers. Greater space in the text has been devoted
also to the discussion of epistemological problems and some philosophical
consequences.Comment: 12 page
Three-dimensional harmonic oscillator and time evolution in quantum mechanics
The problem of defining time (or phase) operator for three-dimensional
harmonic oscillator has been analyzed. A new formula for this operator has been
derived. The results have been used to demonstrate a possibility of
representing quantum-mechanical time evolution in the framework of an extended
Hilbert space structure. Physical interpretation of the extended structure has
been discussed shortly, too.Comment: 14 pages; submitted to Phys Rev
Development of superconducting YBa2Cu3O(x) wires with low resistance electrical contacts
Materials exhibiting superconductivity above liquid nitrogen temperatures (77 K) will enable new applications of this phenomena. One of the first commercial applications of this technology will be superconducting magnets for medical imaging. However, a large number of aerospace applications of the high temperature superconducting materials have also been identified. These include magnetic suspension and balance of models in wind tunnels and resistanceless leads to anemometers. The development of superconducting wires fabricated from the ceramic materials is critical for these applications. The progress in application of a patented fiber process developed by Clemson University for the fabrication of superconducting wires is reviewed. The effect of particle size and heat treatment on the quality of materials is discussed. Recent advances made at Christopher Newport College in the development of micro-ohm resistance electrical contacts which are capable of carrying the highest reported direct current to this material is presented
Nonlinear spin relaxation in strongly nonequilibrium magnets
A general theory is developed for describing the nonlinear relaxation of spin
systems from a strongly nonequilibrium initial state, when, in addition, the
sample is coupled to a resonator. Such processes are characterized by nonlinear
stochastic differential equations. This makes these strongly nonequilibrium
processes principally different from the spin relaxation close to an
equilibrium state, which is represented by linear differential equations. The
consideration is based on a realistic microscopic Hamiltonian including the
Zeeman terms, dipole interactions, exchange interactions, and a single-site
anisotropy. The influence of cross correlations between several spin species is
investigated. The critically important function of coupling between the spin
system and a resonant electric circuit is emphasized. The role of all main
relaxation rates is analyzed. The phenomenon of self-organization of transition
coherence in spin motion, from the quantum chaotic stage of incoherent
fluctuations, is thoroughly described. Local spin fluctuations are found to be
the triggering cause for starting the spin relaxation from an incoherent
nonequilibrium state. The basic regimes of collective coherent spin relaxation
are studied.Comment: Latex file, 31 page
Integrating individual knowledge into innovation processes of R&D alliance
Integrating individual knowledge into innovation processes of R&D allianc
Local-field correction to one- and two-atom van der Waals interactions
Based on macroscopic quantum electrodynamics in linearly and causally
responding media, we study the local-field corrected van der Waals potentials
and forces for unpolarized ground-state atoms placed within a magnetoelectric
medium of arbitrary size and shape. We start from general expressions for the
van der Waals potentials in terms of the (classical) Green tensor of the
electromagnetic field and the atomic polarizability and incorporate the
local-field correction by means of the real-cavity model. In this context,
special emphasis is given to the decomposition of the Green tensor into a
medium part multiplied by a global local-field correction factor and, in the
single-atom case, a part that only depends on the cavity characteristics. The
result is used to derive general formulas for the local-field corrected van der
Waals potentials and forces. As an application, we calculate the van der Waals
potential between two ground-state atoms placed within magnetoelectric bulk
material.Comment: 9 pages, 2 figures, corrections according to erratu
Scattering of slow-light gap solitons with charges in a two-level medium
The Maxwell-Bloch system describes a quantum two-level medium interacting
with a classical electromagnetic field by mediation of the the population
density. This population density variation is a purely quantum effect which is
actually at the very origin of nonlinearity. The resulting nonlinear coupling
possesses particularly interesting consequences at the resonance (when the
frequency of the excitation is close to the transition frequency of the
two-level medium) as e.g. slow-light gap solitons that result from the
nonlinear instability of the evanescent wave at the boundary. As nonlinearity
couples the different polarizations of the electromagnetic field, the
slow-light gap soliton is shown to experience effective scattering whith
charges in the medium, allowing it for instance to be trapped or reflected.
This scattering process is understood qualitatively as being governed by a
nonlinear Schroedinger model in an external potential related to the charges
(the electrostatic permanent background component of the field).Comment: RevTex, 14 pages with 5 figures, to appear in J. Phys. A: Math. Theo
Origin of Pure Spin Superradiance
The question addressed in this paper is: What originates pure spin
superradiance in a polarized spin system placed inside a resonator? The term
"pure" means that no initial coherence is imposed on spins, and its appearance
manifests a purely self-organized collective effect. The consideration is based
on a microscopic model with dipole spin interactions. An accurate solution of
evolution equations is given. The results show that the resonator Nyquist noise
does not play, contrary to the common belief, any role in starting spin
superradiance, but the emergence of the latter is initiated by local spin
fluctuations. The decisive role of nonsecular dipole interactions is stressed.Comment: 1 file, 13 pages, RevTe
- …