563 research outputs found

### Fast magnetization reversal of nanoclusters in resonator

An effective method for ultrafast magnetization reversal of nanoclusters is
suggested. The method is based on coupling a nanocluster to a resonant electric
circuit. This coupling causes the appearance of a magnetic feedback field
acting on the cluster, which drastically shortens the magnetization reversal
time. The influence of the resonator properties, nanocluster parameters, and
external fields on the magnetization dynamics and reversal time is analyzed.
The magnetization reversal time can be made many orders shorter than the
natural relaxation time. The reversal is studied for both the cases of a single
nanocluster as well as for the system of many nanoclusters interacting through
dipole forces.Comment: latex file, 21 pages, 7 figure

### Entanglement production in quantum decision making

The quantum decision theory introduced recently is formulated as a quantum
theory of measurement. It describes prospect states represented by complex
vectors of a Hilbert space over a prospect lattice. The prospect operators,
acting in this space, form an involutive bijective algebra. A measure is
defined for quantifying the entanglement produced by the action of prospect
operators. This measure characterizes the level of complexity of prospects
involved in decision making. An explicit expression is found for the maximal
entanglement produced by the operators of multimode prospects.Comment: Latex file, 7 page

### Entanglement production with multimode Bose-Einstein condensates in optical lattices

Deep optical lattices are considered, in each site of which there are many
Bose-condensed atoms. By the resonant modulation of trapping potentials it is
possible to transfer a macroscopic portion of atoms to the collective nonlinear
states corresponding to topological coherent modes. Entanglement can be
generated between these modes. By varying the resonant modulating field it is
possible to effectively regulate entanglement production in this multimode
multitrap system of Bose condensates.Comment: Latex file, 16 pages, 7 figure

### Collective spin dynamics in magnetic nanomaterials

Magnetic nanomaterials are considered, formed by magnetic nanomolecules with
high spins. The problem of spin reversal in these materials is analyzed, which
is of interest for the possible use of such materials for quantum information
processing and quantum computing. The fastest spin reversal can be achieved by
coupling the spin sample to a resonant electric circuit and by an appropriate
choice of the system parameters. A principal point is to choose these
parameters so that to organize coherent spin motion. Dynamics of collective
motion is modelled by computer simulations, which confirm the high level of
dynamical coherence of molecular spins in the process of spin reversal.Comment: Latex file, 7 pages, 4 figure

### Possibility of Turbulent Crystals

The possibility for the occurrence in crystals of a phenomenon, resembling
turbulence, is discussed. This phenomenon, called {\it heterophase turbulence},
is manifested by the fluctuational appearance inside a crystalline sample of
disordered regions randomly distributed in space. The averaged picture for such
a turbulent solid is exemplified by an exactly solvable lattice-gas model. The
origin of heterophase turbulence is connected with stochastic instability of
quasi-isolated systems.Comment: Latex file, 20 pages, no figure

### Atomic Squeezing under Collective Emission

Atomic squeezing is studied for the case of large systems of radiating atoms,
when collective effects are well developed. All temporal stages are analyzed,
starting with the quantum stage of spontaneous emission, passing through the
coherent stage of superradiant emission, and going to the relaxation stage
ending with stationary solutions. A method of governing the temporal behaviour
of the squeezing factor is suggested. The influence of a squeezed effective
vacuum on the characteristics of collective emission is also investigated.Comment: Latex file, 21 page, 9 figure

### Nonlinear Dynamics of Nuclear-Electronic Spin Processes in Ferromagnets

Spin dynamics is considered in ferromagnets consisting of electron and
nuclear subsystems interacting with each other through hyperfine forces. In
addition, the ferromagnetic sample is coupled with a resonance electric
circuit. Under these conditions, spin relaxation from a strongly nonequilibrium
initial state displays several peculiarities absent for the standard set-up in
studying spin relaxation. The main feature of the nonlinear spin dynamics
considered in this communication is the appearance of ultrafast coherent
relaxation, with characteristic relaxation times several orders shorter than
the transverse relaxation time $T_2$. This type of coherent spin relaxation can
be used for extracting additional information on the intrinsic properties of
ferromagnetic materials and also can be employed for different technical
applications.Comment: 1 file, 4 pages, RevTex, no figure

### Spin superradiance versus atomic superradiance

A comparative analysis is given of spin superradiance and atomic
superradiance. Their similarities and distinctions are emphasized. It is shown
that, despite a close analogy, these phenomena are fundamentally different. In
atomic systems, superradiance is a self-organized process, in which both the
initial cause, being spontaneous emission, as well as the collectivizing
mechanism of their interactions through the common radiation field, are of the
same physical nature. Contrary to this, in actual spin systems with dipole
interactions, the latter are the major reason for spin motion. Electromagnetic
spin interactions through radiation are negligible and can never produce
collective effects. The possibility of realizing superradiance in molecular
magnets by coupling them to a resonant circuit is discussed.Comment: Latex file, 12 pages, no figure

### Extrapolation of power series by self-similar factor and root approximants

The problem of extrapolating the series in powers of small variables to the
region of large variables is addressed. Such a problem is typical of quantum
theory and statistical physics. A method of extrapolation is developed based on
self-similar factor and root approximants, suggested earlier by the authors. It
is shown that these approximants and their combinations can effectively
extrapolate power series to the region of large variables, even up to infinity.
Several examples from quantum and statistical mechanics are analysed,
illustrating the approach.Comment: 21 pages, Latex fil

### Resummation Methods for Analyzing Time Series

An approach is suggested for analyzing time series by means of resummation
techniques of theoretical physics. A particular form of such an analysis, based
on the algebraic self-similar renormalization, is developed and illustrated by
several examples from the stock market time series.Comment: Corrections are made to match the published versio

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