3,770 research outputs found
Quantum decay of dark solitons in one dimensional Bose systems
Unless protected by the exact integrability, solitons are subject to
dissipative forces, originating from a thermally fluctuating background. At low
enough temperatures background fluctuations should be considered as being
quantized which enables us to calculate finite lifetime of the solitons
. We also find that the coherent nature of the quantum
fluctuations leads to long-range interactions between the solitons mediated by
the superradiation. Our results are of relevance to current experiments with
ultracold atoms, while the approach may be extended to solitons in other media.Comment: 5 pages, 1 figure. Accepted for publication in PRL
Spin Torque Dynamics with Noise in Magnetic Nano-System
We investigate the role of equilibrium and nonequilibrium noise in the
magnetization dynamics on mono-domain ferromagnets. Starting from a microscopic
model we present a detailed derivation of the spin shot noise correlator. We
investigate the ramifications of the nonequilibrium noise on the spin torque
dynamics, both in the steady state precessional regime and the spin switching
regime. In the latter case we apply a generalized Fokker-Planck approach to
spin switching, which models the switching by an Arrhenius law with an
effective elevated temperature. We calculate the renormalization of the
effective temperature due to spin shot noise and show that the nonequilibrium
noise leads to the creation of cold and hot spot with respect to the noise
intensity.Comment: 10 pages, 7 figure
Symmetry of Quantum Phase Space in a Degenerate Hamiltonian System
Using Husimi function approach, we study the ``quantum phase space'' of a
harmonic oscillator interacting with a plane monochromatic wave. We show that
in the regime of weak chaos, the quantum system has the same symmetry as the
classical system. Analytical results agree with the results of numerical
calculations.Comment: 11 pages LaTex, including 2 Postscript figure
Weak Charge Quantization as an Instanton of Interacting sigma-model
Coulomb blockade in a quantum dot attached to a diffusive conductor is
considered in the framework of the non-linear sigma-model. It is shown that the
weak charge quantization on the dot is associated with instanton configurations
of the Q-field in the conductor. The instantons have a finite action and are
replica non--symmetric. It is argued that such instantons may play a role in
the transition regime to the interacting insulator.Comment: 4 pages. The 2D case substantially modifie
Spin-torque shot noise in magnetic tunnel junctions
Spin polarized current may transfer angular momentum to a ferromagnet,
resulting in a spin-torque phenomenon. At the same time the shot noise,
associated with the current, leads to a non-equilibrium stochastic force acting
on the ferromagnet. We derive stochastic version of Landau-Lifshitz-Gilbert
equation for a magnetization of a ''free'' ferromagnetic layer in contact with
a ''fixed'' ferromagnet. We solve the corresponding Fokker-Planck equation and
show that the non-equilibrium noise yields to a non-monotonous dependence of
the precession spectrum linewidth on the current.Comment: 5 pages, 2 figure
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