77,751 research outputs found
Spontaneous Spin Polarization in Quantum Wires
A number of recent experiments report spin polarization in quantum wires in
the absence of magnetic fields. These observations are in apparent
contradiction with the Lieb-Mattis theorem, which forbids spontaneous spin
polarization in one dimension. We show that sufficiently strong interactions
between electrons induce deviations from the strictly one-dimensional geometry
and indeed give rise to a ferromagnetic ground state in a certain range of
electron densities.Comment: 4 pages, 4 figure
Linear response in infinite nuclear matter as a tool to reveal finite size instabilities
Nuclear effective interactions are often modelled by simple analytical
expressions such as the Skyrme zero-range force. This effective interaction
depends on a limited number of parameters that are usually fitted using
experimental data obtained from doubly magic nuclei. It was recently shown that
many Skyrme functionals lead to the appearance of instabilities, in particular
when symmetries are broken, for example unphysical polarization of odd-even or
rotating nuclei. In this article, we show how the formalism of the linear
response in infinite nuclear matter can be used to predict and avoid the
regions of parameters that are responsible for these unphysical instabilities.Comment: Based on talk presented at 18th Nuclear Physics Workshop "Maria and
Pierre Curie", 2011, Kazimierz, Polan
Quantum lattice gases and their invariants
The one particle sector of the simplest one dimensional quantum lattice gas
automaton has been observed to simulate both the (relativistic) Dirac and
(nonrelativistic) Schroedinger equations, in different continuum limits. By
analyzing the discrete analogues of plane waves in this sector we find
conserved quantities corresponding to energy and momentum. We show that the
Klein paradox obtains so that in some regimes the model must be considered to
be relativistic and the negative energy modes interpreted as positive energy
modes of antiparticles. With a formally similar approach--the Bethe ansatz--we
find the evolution eigenfunctions in the two particle sector of the quantum
lattice gas automaton and conclude by discussing consequences of these
calculations and their extension to more particles, additional velocities, and
higher dimensions.Comment: 19 pages, plain TeX, 11 PostScript figures included with epsf.tex
(ignore the under/overfull \vbox error messages
Quantum Chinos Game: winning strategies through quantum fluctuations
We apply several quantization schemes to simple versions of the Chinos game.
Classically, for two players with one coin each, there is a symmetric stable
strategy that allows each player to win half of the times on average. A partial
quantization of the game (semiclassical) allows us to find a winning strategy
for the second player, but it is unstable w.r.t. the classical strategy.
However, in a fully quantum version of the game we find a winning strategy for
the first player that is optimal: the symmetric classical situation is broken
at the quantum level.Comment: REVTEX4.b4 file, 3 table
Localization of Two-Dimensional Quantum Walks
The Grover walk, which is related to the Grover's search algorithm on a
quantum computer, is one of the typical discrete time quantum walks. However, a
localization of the two-dimensional Grover walk starting from a fixed point is
striking different from other types of quantum walks. The present paper
explains the reason why the walker who moves according to the degree-four
Grover's operator can remain at the starting point with a high probability. It
is shown that the key factor for the localization is due to the degeneration of
eigenvalues of the time evolution operator. In fact, the global time evolution
of the quantum walk on a large lattice is mainly determined by the degree of
degeneration. The dependence of the localization on the initial state is also
considered by calculating the wave function analytically.Comment: 21 pages RevTeX, 4 figures ep
The energy spectra of solar flare electrons
A survey of 50 electron energy spectra from .1 to 100 MeV originating from solar flares was made by the combination of data from two spectrometers onboard the International Sun Earth Explorer-3 spacecraft. The observed spectral shapes of flare events can be divided into two classes through the criteria of fit to an acceleration model. This standard two step acceleration model, which fits the spectral shape of the first class of flares, involves an impulsive step that accelerates particles up to 100 keV and a second step that further accelerates these particles up to 100 MeV by a single shock. This fit fails for the second class of flares that can be characterized as having excessively hard spectra above 1 MeV relative to the predictions of the model. Correlations with soft X-ray and meter radio observations imply that the acceleration of the high energy particles in the second class of flares is dominated by the impulsive phase of the flares
Formation of defects in multirow Wigner crystals
We study the structural properties of a quasi-one-dimensional classical
Wigner crystal, confined in the transverse direction by a parabolic potential.
With increasing density, the one-dimensional crystal first splits into a zigzag
crystal before progressively more rows appear. While up to four rows the ground
state possesses a regular structure, five-row crystals exhibit defects in a
certain density regime. We identify two phases with different types of defects.
Furthermore, using a simplified model, we show that beyond nine rows no stable
regular structures exist.Comment: 11 pages, 8 figure
Ferromagnetism within the periodic Anderson model: A new approximation scheme
We introduce a new approach to the periodic Anderson model (PAM) that allows
a detailed investigation of the magnetic properties in the Kondo as well as the
intermediate valence regime. Our method is based on an exact mapping of the PAM
onto an effective medium strong-coupling Hubbard model. For the latter, the
so-called spectral density approach (SDA) is rather well motivated since it is
based on exact results in the strong coupling limit. Besides the T=0 phase
diagram, magnetization curves and Curie temperatures are presented and
discussed with help of temperature-dependent quasiparticle densities of state.
In the intermediate valence regime, the hybridization gap plays a major role in
determining the magnetic behaviour. Furthermore, our results indicate that
ferromagnetism in this parameter regime is not induced by an effective
spin-spin interaction between the localized levels mediated by conduction
electrons as it is the case in the Kondo regime. The magnetic ordering is
rather a single band effect within an effective f-band.Comment: 13 pages, 16 figures, Phys. Stat. Sol. in pres
- …