22,870 research outputs found
The Wess-Zumino term and quantum tunneling
The significance of the Wess--Zumino term in spin tunneling is explored, and
a formula is established for the splitting of energy levels of a particle with
large fermionic spin as an applied magnetic field is switched on.Comment: Latex, 7 page
Enhancement of Quantum Tunneling for Excited States in Ferromagnetic Particles
A formula suitable for a quantitative evaluation of the tunneling effect in a
ferromagnetic particle is derived with the help of the instanton method. The
tunneling between n-th degenerate states of neighboring wells is dominated by a
periodic pseudoparticle configuration. The low-lying level-splitting previously
obtained with the LSZ method in field theory in which the tunneling is viewed
as the transition of n bosons induced by the usual (vacuum) instanton is
recovered. The observation made with our new result is that the tunneling
effect increases at excited states. The results should be useful in analyzing
results of experimental tests of macroscopic quantum coherence in ferromagnetic
particles.Comment: 18 pages, LaTex, 1 figur
Winding number transitions at finite temperature in the Abelian-Higgs model
Following our earlier investigations we examine the quantum-classical winding
number transition in the Abelian-Higgs system. It is demonstrated that the
sphaleron transition in this system is of the smooth second order type in the
full range of parameter space. Comparison of the action of classical vortices
with that of the sphaleron supports our finding.Comment: final version, to appear in J. Phys.
Vacuum induced Berry phases in single-mode Jaynes-Cummings models
Motivated by the work [Phys. Rev. Lett. 89, 220404 (2002)] for detecting the
vacuum-induced Berry phases with two-mode Jaynes-Cummings models (JCMs), we
show here that, for a parameter-dependent single-mode JCM, certain atom-field
states also acquire the photon-number-dependent Berry phases after the
parameter slowly changed and eventually returned to its initial value. This
geometric effect related to the field quantization still exists, even the filed
is kept in its vacuum state. Specifically, a feasible Ramsey interference
experiment with cavity quantum electrodynamics (QED) system is designed to
detect the vacuum-induced Berry phase.Comment: 10 pages, 4 figures
Periodic instanton method and macroscopic quantum tunneling between two weakly-linked Bose-Einstein condensates
A new method is used to investigate the tunneling between two weakly-linked
Bose-Einstein condensates confined in double-well potential traps. The
nonlinear interaction between the atoms in each well contributes to a finite
chemical potential, which, with consideration of periodic instantons, leads to
a remarkably high tunneling frequency. This result can be used to interpret the
newly found Macroscopic Quantum Self Trapping (MQST) effect. Also a new kind of
first-order crossover between different regions is predicted.Comment: 4 pages, 2 eps figures, final version to appear in Phys. Rev.
Hyperon polarization in e^-p --> e^-HK with polarized electron beams
We apply the picture proposed in a recent Letter for transverse hyperon
polarization in unpolarized hadron-hadron collisions to the exclusive process
e^-p --> e^-HK such as e^-p-->e^-\Lambda K^+, e^-p --> e^-\Sigma^+ K^0, or
e^-p--> e^-\Sigma^0 K^+, or the similar process e^-p\to e^-n\pi^+ with
longitudinally polarized electron beams. We present the predictions for the
longitudinal polarizations of the hyperons or neutron in these reactions, which
can be used as further tests of the picture.Comment: 15 pages, 2 figures. submitted to Phys. Rev.
Spin Current and Shot Noise in Single-Molecule Quantum Dots with a Phonon Mode
In this paper we investigate the spin-current and its shot-noise spectrum in
a single-molecule quantum dot coupled with a local phonon mode. We pay special
attention on the effect of phonon on the quantum transport property. The
spin-polarization dependent current is generated by a rotating magnetic filed
applied in the quantum dot. Our results show the remarkable influence of phonon
mode on the zero-frequency shot noise. The electron-phonon interaction leads to
sideband peaks which are located exactly on the integer number of the phonon
frequency and moreover the peak-height is sensitive to the electron-phonon
coupling.Comment: 17 pages,5 figure
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