8,783 research outputs found
The reduction of the closest disentangled states
We study the closest disentangled state to a given entangled state in any
system (multi-party with any dimension). We obtain the set of equations the
closest disentangled state must satisfy, and show that its reduction is
strongly related to the extremal condition of the local filtering on each
party. Although the equations we obtain are not still tractable, we find some
sufficient conditions for which the closest disentangled state has the same
reduction as the given entangled state. Further, we suggest a prescription to
obtain a tight upper bound of the relative entropy of entanglement in two-qubit
systems.Comment: a crucial error was correcte
Incoherent pion photoproduction on the deuteron in the first resonance region
Incoherent pion photoproduction on the deuteron is studied in the first
resonance region. The unpolarized cross section, the beam asymmetry, and the
vector and tensor target asymmetries are calculated in the framework of a
diagrammatic approach. Pole diagrams and one-loop diagrams with scattering
in the final state are taken into account. An elementary operator for pion
photoproduction on the nucleon is taken in various on-shell forms and
calculated using the SAID and MAID multipole analyses. Model dependence of the
obtained results is discussed in some detail. A comparison with predictions of
other works is given. Although a reasonable description of many available
experimental data on the unpolarized total and differential cross sections and
photon asymmetry has been achieved, in some cases a significant disagreement
between the theory and experiment has been found. Invoking known information on
the reactions and we predict the total
photoabsorption cross section for deuterium. We find that our values strongly
overestimate experimental data in the vicinity of the peak.Comment: 22 pages, 23 figure
Quantum Copying: Beyond the No-Cloning Theorem
We analyze to what extent it is possible to copy arbitrary states of a
two-level quantum system. We show that there exists a "universal quantum
copying machine", which approximately copies quantum mechanical states in such
a way that the quality of its output does not depend on the input. We also
examine a machine which combines a unitary transformation with a selective
measurement to produce good copies of states in a neighborhood of a particular
state. We discuss the problem of measurement of the output states.Comment: RevTex, 26 pages, to appear in Physical Review
Robust single-parameter quantized charge pumping
This paper investigates a scheme for quantized charge pumping based on
single-parameter modulation. The device was realized in an AlGaAs-GaAs gated
nanowire. We find a remarkable robustness of the quantized regime against
variations in the driving signal, which increases with applied rf power. This
feature together with its simple configuration makes this device a potential
module for a scalable source of quantized current.Comment: Submitted to Appl. Phys. Let
Observation of the Higgs Boson of strong interaction via Compton scattering by the nucleon
It is shown that the Quark-Level Linear Model (QLLM) leads
to a prediction for the diamagnetic term of the polarizabilities of the nucleon
which is in excellent agreement with the experimental data. The bare mass of
the meson is predicted to be MeV and the two-photon
width keV. It is argued that the
mass predicted by the QLLM corresponds to the reaction, i.e. to a -channel pole of the reaction.
Large -angle Compton scattering experiments revealing effects of the
meson in the differential cross section are discussed. Arguments are presented
that these findings may be understood as an observation of the Higgs boson of
strong interaction while being part of the constituent quark.Comment: 17 pages, 6 figure
Cloud microphysical effects of turbulent mixing and entrainment
Turbulent mixing and entrainment at the boundary of a cloud is studied by
means of direct numerical simulations that couple the Eulerian description of
the turbulent velocity and water vapor fields with a Lagrangian ensemble of
cloud water droplets that can grow and shrink by condensation and evaporation,
respectively. The focus is on detailed analysis of the relaxation process of
the droplet ensemble during the entrainment of subsaturated air, in particular
the dependence on turbulence time scales, droplet number density, initial
droplet radius and particle inertia. We find that the droplet evolution during
the entrainment process is captured best by a phase relaxation time that is
based on the droplet number density with respect to the entire simulation
domain and the initial droplet radius. Even under conditions favoring
homogeneous mixing, the probability density function of supersaturation at
droplet locations exhibits initially strong negative skewness, consistent with
droplets near the cloud boundary being suddenly mixed into clear air, but
rapidly approaches a narrower, symmetric shape. The droplet size distribution,
which is initialized as perfectly monodisperse, broadens and also becomes
somewhat negatively skewed. Particle inertia and gravitational settling lead to
a more rapid initial evaporation, but ultimately only to slight depletion of
both tails of the droplet size distribution. The Reynolds number dependence of
the mixing process remained weak over the parameter range studied, most
probably due to the fact that the inhomogeneous mixing regime could not be
fully accessed when phase relaxation times based on global number density are
considered.Comment: 17 pages, 10 Postscript figures (figures 3,4,6,7,8 and 10 are in
reduced quality), to appear in Theoretical Computational Fluid Dynamic
Single-parameter non-adiabatic quantized charge pumping
Controlled charge pumping in an AlGaAs/GaAs gated nanowire by
single-parameter modulation is studied experimentally and theoretically.
Transfer of integral multiples of the elementary charge per modulation cycle is
clearly demonstrated. A simple theoretical model shows that such a quantized
current can be generated via loading and unloading of a dynamic quasi-bound
state. It demonstrates that non-adiabatic blockade of unwanted tunnel events
can obliterate the requirement of having at least two phase-shifted periodic
signals to realize quantized pumping. The simple configuration without multiple
pumping signals might find wide application in metrological experiments and
quantum electronics.Comment: 4 pages, 4 figure
Evolution of structure and local magnetic fields during crystallization of HITPERM glassy alloys studied by in situ diffraction and nuclear forward scattering of synchrotron radiation
Evolution of structure and local magnetic fields in Fe1 xCox 76Mo8Cu1B15 HITPERM metallic glass ribbons with various amounts of Co x 0, 0.25, 0.5 were studied in situ using diffraction and nuclear forward scattering of synchrotron radiation. It was found that crystallization for all three glasses proceeds in two stages. In the first stage, bcc Fe,Co nanocrystals are formed, while in the second stage additional crystalline phases evolve. For all three glasses, the crystallization temperatures at the wheel side were found to be lower than at the air side of the ribbon. The crystallization temperatures were found to decrease with increasing Co content. The lattice parameters of the bcc nanocrystals decrease up to about 550 C and then increase pointing to squeezing Mo atoms out of the nanograins or to interface effects between the nanocrystals and the glassy matrix. Nuclear forward scattering enabled separate evaluation of the contributions that stem from structurally different regions within the investigated samples including the newly formed nanocrystals and the residual amorphous matrix. Even minor Co content x 0.25 has a substantial effect not only upon the magnetic behaviour of the alloy but also upon its structure. Making use of hyperfine magnetic fields, it was possible to unveil structurally diverse positions of Fe atoms that reside in a nanocrystalline lattice with different number of Co nearest neighbour
Nucleon polarizabilities in the perturbative chiral quark model
The nucleon polarizabilities alpha(E) and beta(M) are studied in the context
of the perturbative chiral quark model. We demonstrate that meson cloud effects
are sufficient to explain the electric polarizability of nucleon. Contributions
of excite quark states to the paramagnetic polarizability are dominant and
cancel the diamagnetic polarizability arising from the chiral field. The
obtained results are compared to data and other theoretical predictions.Comment: 25 pages, 18 figures, 2 table
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