975 research outputs found
Entanglement between charge qubit states and coherent states of nanomechanical resonator generated by ac Josephson effect
We considered a nanoelectromechanical system consisting of a movable Cooper-pair box qubit, which is subject to an electrostatic field, and coupled to the two bulk superconductors via tunneling processes. We suggest that qubit dynamics is related to that of a quantum oscillator and demonstrate that a bias voltage applied between superconductors generates states represented by the entanglement of qubit states and coherent states of the oscillator if certain resonant conditions are fulfilled. It is shown that a structure of this entanglement may be controlled by the bias voltage in a way that gives rise to the entanglement incorporating so-called cat-states—the superposition of coherent states. We characterize the formation and development of such states analyzing the entropy of entanglement and corresponding Wigner function. The experimentally feasible detection of the effect by measuring the average current is also considered
Umklapp-Assisted Electron Transport Oscillations in Metal Superlattices
We consider a superlattice of parallel metal tunnel junctions with a
spatially non-homogeneous probability for electrons to tunnel. In such
structures tunneling can be accompanied by electron scattering that conserves
energy but not momentum. In the special case of a tunneling probability that
varies periodically with period in the longitudinal direction, i.e.,
perpendicular to the junctions, electron tunneling is accompanied by "umklapp"
scattering, where the longitudinal momentum changes by a multiple of . We
predict that as a result a sequence of metal-insulator transitions can be
induced by an external electric- or magnetic field as the field strength is
increased.Comment: 5 pages, 3 figure
Цивільно-правове регулювання конфіденційної інформації
Кулініч О. О. Цивільно-правове регулювання конфіденційної інформації / О. О. Кулініч // Актуальні проблеми держави і права : зб. наук. пр. / редкол.: С. В. Ківалов (голов. ред.), Ю. М. Оборотов (заст. голов. ред.), Л. Р. Біла (відп. секр.) [та ін.] ; ОНЮА. – Одеса : Юрид. л-ра, 2005. – Вип. 25. – С. 257-260
Joule Heating and Current-Induced Instabilities in Magnetic Nanocontacts
We consider the electrical current through a magnetic point contact in the
limit of a strong inelastic scattering of electrons. In this limit local Joule
heating of the contact region plays a decisive role in determining the
transport properties of the point contact. We show that if an applied constant
bias voltage exceeds a critical value, the stationary state of the system is
unstable, and that periodic, non-harmonic oscillations in time of both the
electrical current through the contact and the local temperature in the contact
region develop spontaneously. Our estimations show that the necessary
experimental conditions for observing such oscillations with characteristic
frequencies in the range Hz can easily be met. We also show a
possibility to manipulate upon the magnetization direction of a magnetic grain
coupled through a point contact to a bulk ferromagnetic by exciting the
above-mentioned thermal-electric oscillations.Comment: 9 pages, 6 figures, submitted to Physical Review
Nanomechanics of a magnetic shuttle device
We show that self sustained mechanical vibrations in a model magnetic shuttle device can be driven by both the charge and the spin accumulated on the movable central island of the device. Different scenarios for how spin- and charge-induced shuttle instabilities may develop are discussed and shown to depend on whether there is a Coulomb blockade of tunneling or not. The crucial role of electronic spin flips in a magnetically driven shuttle is established and shown to cause giant magnetoresistance and dynamic magnetostriction effects
Large-scale structure formation in cosmology with classical and tachyonic scalar fields
The evolution of scalar perturbations is studied for 2-component
(non-relativistic matter and dark energy) cosmological models at the linear and
non-linear stages. The dark energy is assumed to be the scalar field with
either classical or tachyonic Lagrangian and constant equation-of-state
parameter w. The fields and potentials were reconstructed for the set of
cosmological parameters derived from observations. The comparison of the
calculated within these models and experimental large-scale structure
characteristics is made. It is shown that for w=const such analysis can't
remove the existing degeneracy of the dark energy models.Comment: 15 pages, 5 figures, text corrected, references added, accepted by
Kinematics and Physics of Celestial Bodie
Homotopy types of stabilizers and orbits of Morse functions on surfaces
Let be a smooth compact surface, orientable or not, with boundary or
without it, either the real line or the circle , and
the group of diffeomorphisms of acting on by the rule
, where and .
Let be a Morse function and be the orbit of under this
action. We prove that for , and
except for few cases. In particular, is aspherical, provided so is .
Moreover, is an extension of a finitely generated free abelian
group with a (finite) subgroup of the group of automorphisms of the Reeb graph
of .
We also give a complete proof of the fact that the orbit is tame
Frechet submanifold of of finite codimension, and that the
projection is a principal locally trivial -fibration.Comment: 49 pages, 8 figures. This version includes the proof of the fact that
the orbits of a finite codimension of tame action of tame Lie group on tame
Frechet manifold is a tame Frechet manifold itsel
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