15,657 research outputs found
Bright tripartite entanglement in triply concurrent parametric oscillation
We show that a novel optical parametric oscillator, based on concurrent
nonlinearities, can produce, above threshold, bright output beams
of macroscopic intensities which exhibit strong tripartite continuous-variable
entanglement. We also show that there are {\em two} ways that the system can
exhibit a new three-mode form of the Einstein-Podolsky-Rosen paradox, and
calculate the extra-cavity fluctuation spectra that may be measured to verify
our predictions.Comment: title change, expanded intro and discussion of experimental aspects,
1 new figure. Conclusions unaltere
Coulomb corrections to bremsstrahlung in electric field of heavy atom at high energies
The differential and partially integrated cross sections are considered for
bremsstrahlung from high-energy electrons in atomic field with the exact
account of this field. The consideration exploits the quasiclassical electron
Green's function and wave functions in an external electric field. It is shown
that the Coulomb corrections to the differential cross section are very
susceptible to screening. Nevertheless, the Coulomb corrections to the cross
section summed up over the final-electron states are independent of screening
in the leading approximation over a small parameter ( is
a screening radius, is the electron mass, ). Bremsstrahlung from
an electron beam of the finite size on heavy nucleus is considered as well.
Again, the Coulomb corrections to the differential probability are very
susceptible to the beam shape, while those to the probability integrated over
momentum transfer are independent of it, apart from the trivial factor, which
is the electron-beam density at zero impact parameter. For the Coulomb
corrections to the bremsstrahlung spectrum, the next-to-leading terms with
respect to the parameters ( is the electron energy) and
are obtained.Comment: 13 pages, 4 figure
A separability criterion for density operators
We give a necessary and sufficient condition for a mixed quantum mechanical
state to be separable. The criterion is formulated as a boundedness condition
in terms of the greatest cross norm on the tensor product of trace class
operators.Comment: REVTeX, 5 page
Quadripartite continuous-variable entanglement via quadruply concurrent downconversion
We investigate an intra-cavity coupled down-conversion scheme to generate
quadripartite entanglement using concurrently resonant nonlinearities. We
verify that quadripartite entanglement is present in this system by calculating
the output fluctuation spectra and then considering violations of optimized
inequalities of the van Loock-Furusawa type. The entanglement characteristics
both above and below the oscillation threshold are considered. We also present
analytic solutions for the quadrature operators and the van Loock-Furusawa
correlations in the undepleted pump approximation.Comment: 9 pages, 5 figure
DE 1 RIMS operational characteristics
The Retarding Ion Mass Spectrometer (RIMS) on the Dynamics Explorer 1 spacecraft observes both the thermal and superthermal (50 eV) ions of the ionosphere and inner magnetosphere. It is capable of measuring the detailed species distribution function of these ions in many cases. It was equipped with an integral electrometer to permit in-flight calibration of the detector sensitivities and variations thereof. A guide to understanding the RIMS data set is given. The reduction process from count rates to physical quantities is discussed in some detail. The procedure used to establish in-flight calibration is described, and results of a comparison with densities from plasma wave measurements are provided. Finally, a discussion is provided of various anomalies in the data set, including changes of channeltron efficiency with time, spin modulation of the axial sensor heads, apparent potential differences between the sensor heads, and failures of the radial head retarding potential sweep and of the -Z axial head aperture plane bias. Studies of the RIMS data set should be conducted only with a thorough awareness of the material presented here, or in collaboration with one of the scientists actively involved with RIMS data analysis
Analysis of a continuous-variable quadripartite cluster state from a single optical parametric oscillator
We examine the feasibility of generating continuous-variable multipartite
entanglement in an intra-cavity quadruply concurrent downconversion scheme that
has been proposed for the generation of cluster states by Menicucci \textit{et
al.} [Physical Review Letters \textbf{101}, 130501 (2008)]. By calculating
optimized versions of the van Loock-Furusawa correlations we demonstrate
genuine quadripartite entanglement and investigate the degree of entanglement
present. Above the oscillation threshold the basic cluster state geometry under
consideration suffers from phase diffusion. We alleviate this problem by
incorporating a small injected signal into our analysis. Finally, we
investigate squeezed joint operators. While the squeezed joint operators
approach zero in the undepleted regime, we find that this is not the case when
we consider the full interaction Hamiltonian and the presence of a cavity. In
fact, we find that the decay of these operators is minimal in a cavity, and
even depletion alone inhibits cluster state formation.Comment: 26 pages, 12 figure
Gluon Polarization in
We calculate the linear polarization of gluons radiated off top quarks
produced in e^+e^- annihilations. For typical top pair production energies at
the Next-Linear-Collider (NLC) the degree of linear polarization remains close
to its soft gluon value of 100% over almost the whole energy spectrum of the
gluon. The massive quark results are compared with the corresponding results
for the massless quark case.Comment: 9 pages, 2 postscript figures, shortened and revised versio
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