12,103 research outputs found
Quantum Computational Gates with Radiation Free Couplings
We examine a generic three state mechanism which realizes all fundamental
single and double qubit quantum logic gates operating under the effect of
adiabatically controllable static (radiation free) bias couplings between the
states. At the instant of time that the gate operations are defined the third
level is unoccupied which, in a certain sense, derives analogy with the
recently suggested dissipation free qubit subspaces. The physical
implementation of the mechanism is tentatively suggested in a form of the
Aharonov-Bohm persistent current loop in crossed electric and magnetic fields,
with the output of the loop read out by a (quantum) Hall effect aided
mechanism.Comment: 21 pages including 7 figures, revte
Observation of a New Fluxon Resonant Mechanism in Annular Josephson Tunnel Structures
A novel dynamical state has been observed in the dynamics of a perdurbed
sine-Gordon system. This resonant state, has been experimentally observed as a
singularity in the dc current voltage characteristic of an annular Josephson
tunnel junction, excited in the presence of a magnetic field. With this
respect, it can be assimilated to self-resonances known as Fiske steps.
Differently from these, however, we demonstrate, on the basis of numerical
simulations, that its detailed dynamics involves rotating fluxon pairs, a
mechanism associated, so far, to self-resonances known as zero-field steps.Comment: 4 pages, 2 figures, submitted to Physical Review Letter
Macroscopic quantum tunneling in "small" Josephson junctions in magnetic field
We study the phenomenon of macroscopic quantum tunneling (MQT) in small
Josephson junctions (JJ) with an externally applied magnetic field. The latter
results in the appearance of the Fraunhofer type modulation of the current
density along the barrier. The problem of MQT for a point-like JJ is reduced to
the motion of the quantum particle in the washboard potential. In the case of a
finite size JJ under consideration, this problem corresponds to a MQT in
potential which itself, besides the phase, depends on space variables. Finally,
the general expression for the crossover temperature T_0 between thermally
activated and macroscopic quantum tunneling regimes and the escaping time
tau_esc have been calculated
Superconductive pumping of nanomechanical vibrations
We demonstrate that a supercurrent can pump energy from a battery that
provides a voltage bias into nanomechanical vibrations. Using a device
containing a nanowire Josephson weak link as an example we show that a
nonlinear coupling between the supercurrent and a static external magnetic
field leads to a Lorentz force that excites bending vibrations of the wire at
resonance conditions. We also demonstrate the possibility to achieve more than
one regime of stationary nonlinear vibrations and how to detect them via the
associated dc Josephson currents and we discuss possible applications of such a
multistable nanoelectromechanical dynamics.Comment: 4 pages, 5 figure
Magnetic field of Josephson vortices outside superconductors
We consider the structure of Josephson vortices approaching the junction
boundary with vacuum in large area Josephson junctions with the Josephson
length large relative to the London penetration depth .
Using the stability argument for one-dimentional solitons with respect to 2D
perturbations, it is shown that on the scale the Josephson vortices
do not spread near the boundary in the direction of the junction. %, which is
in a striking difference with behavior of Abrikosov vortices exiting
superconductors. The field distribution in vacuum due to the Josephson vortex
is evaluated, the information needed for the Scanning SQUID Microscopy.Comment: 5 RevTeX pages, 3 eps figures. The second version includes more
detailed explanations and corrections, and slightly modified figure
Nonlinear response of a thin metamaterial film containing Josephson junctions
An interaction of electromagnetic field with metamaterial thin film
containing split-ring resonators with Josephson junctions is considered. It is
shown that dynamical self-inductance in a split rings results in reduction of
magnetic flux through a ring and this reduction is proportional to a time
derivative of split ring magnetization. Evolution of thin film magnetization
taking into account dynamical self-inductance is studied. New mechanism for
excitation of waves in one dimensional array of split-ring resonators with
Josephson junctions is proposed. Nonlinear magnetic susceptibility of such thin
films is obtained in the weak amplitude approximation.Comment: 6 figure
Charged currents, color dipoles and xF_3 at small x
We develop the light-cone color dipole description of highly asymmetric
diffractive interactions of left-handed and right-handed electroweak bosons. We
identify the origin and estimate the strength of the left-right asymmetry
effect in terms of the light-cone wave functions. We report an evaluation of
the small-x neutrino-nucleon DIS structure functions xF_3 and 2xF_1 and present
comparison with experimental data.Comment: 11 pages, 3 figures, misprints correcte
Study of sequential semileptonic decays of b hadrons produced at the Tevatron
We present a study of rates and kinematical properties of lepton pairs
contained in central jets with transverse energy E_T > 15 GeV that are produced
at the Fermilab Tevatron collider. We compare the data to a QCD prediction
based on the HERWIG and QQ Monte Carlo generator programs.We find that the data
are poorly described by the simulation, in which sequential semileptonic decays
of single b quarks (b --> l c X with c --> l s X) are the major source of such
lepton pairs.Comment: 25 pages, 8 figures. Some typos were fixed in the text and
bibliography. Submitted to Phys. Rev.
Diffractive photoproduction of opposite-charge pseudoscalar meson pairs at high energies
We calculate the cross section for diffractive photoproduction of
opposite-charge pseudoscalar meson pairs , ,
and in a broad range of center-of-mass energies relevant
for GlueX/Hall D, FOCUS, COMPASS and HERA experiments. In the case of
production we find that the interference of the resonance
and the two-pion continuum leads to a considerable deformation of the shape of
in agreement with the data from the ZEUS collaboration. We also
discuss the spectral shape of the as a function of the momentum
transfer and the contribution of higher partial waves to the mass
spectrum. We predict a sizeable energy-dependent forward-backward asymmetry in
the Gottfried-Jackson frame. For the heavy meson production we find that the
cross section for diffractive production increases much slower than the one for
open charm or bottom production. We discuss lower and upper limits for the
cross sections for diffractive production of and pairs,
which we find can be as large as 10% of the open flavor production.Comment: 14 pages, 19 figure
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