4,295 research outputs found
Limit quantum efficiency for violation of Clauser-Horne Inequality for qutrits
In this paper we present the results of numerical calculations about the
minimal value of detection efficiency for violating the Clauser - Horne
inequality for qutrits. Our results show how the use of non-maximally entangled
states largely improves this limit respect to maximally entangled ones. A
stronger resistance to noise is also found.Comment: Phys. Rev. A in pres
Experimental realization of a measurement conditional unitary operation at single photon level and application to detector characterization
Our last experimental results on the realization of a measurement-conditional
unitary operation at single photon level are presented. This gate operates by
rotating by the polarization of a photon produced by means of Type-II
Parametric Down Conversion conditional to a polarization measurement on the
correlated photon. We then propose a new scheme for measuring the quantum
efficiency of a single photon detection apparatus by using this set-up. We
present experimental results obtained with this scheme compared with {\it
traditional} biphoton calibration. Our results show the interesting
potentiality of the suggested scheme.Comment: to appear in Proc. of SPIE meeting, Denver august 200
Multiquark Systems in a Constituent Quark Model with Chiral Dynamics
We discuss the stability of multiquark systems within the recent model of
Glozman et al. where the chromomagnetic hyperfine interaction is replaced by
pseudoscalar-meson exchange. We find that such an interaction binds a heavy
tetraquark system ( and by GeV.
This is at variance with results of previous models where is
unstable.Comment: 6 pages, Plain Latex, Contribution to the Workshop''Quark Confinement
and the Hadron Spectrum II'', Como, Italy, June 26--29, 1996, to appear in
the Proceedings, ed. Nora Brambilla, World Scientifi
Heavy-Flavour Pentaquarks in a Chiral Constituent Quark Model
Within the chiral constituent quark model of Glozman and Riska, we discuss
the stability of heavy pentaquarks, i.e. hadrons containing four light quarks
and a heavy antiquark. The spin-dependent part of the Hamiltonian is dominated
by the short-range part of the Goldstone-boson-exchange interaction. We find
that these systems are not bound, having an energy above the lowest
dissociation threshold into a baryon and a meson.Comment: 10 pages + table
Quantum contextuality in N-boson systems
Quantum contextuality in systems of identical bosonic particles is explicitly
exhibited via the maximum violation of a suitable inequality of
Clauser-Horne-Shimony-Holt type. Unlike the approaches considered so far, which
make use of single-particle observables, our analysis involves collective
observables constructed using multi-boson operators. An exemplifying scheme to
test this violation with a quantum optical setup is also discussed.Comment: 4 pages, 1 figure, LaTe
Accurate Complex Scaling of Three Dimensional Numerical Potentials
The complex scaling method, which consists in continuing spatial coordinates
into the complex plane, is a well-established method that allows to compute
resonant eigenfunctions of the time-independent Schroedinger operator. Whenever
it is desirable to apply the complex scaling to investigate resonances in
physical systems defined on numerical discrete grids, the most direct approach
relies on the application of a similarity transformation to the original,
unscaled Hamiltonian. We show that such an approach can be conveniently
implemented in the Daubechies wavelet basis set, featuring a very promising
level of generality, high accuracy, and no need for artificial convergence
parameters. Complex scaling of three dimensional numerical potentials can be
efficiently and accurately performed. By carrying out an illustrative resonant
state computation in the case of a one-dimensional model potential, we then
show that our wavelet-based approach may disclose new exciting opportunities in
the field of computational non-Hermitian quantum mechanics.Comment: 11 pages, 8 figure
Bell measurements as a witness of a dualism in entanglement
We show how a property of dualism, which can exist in the entanglement of
identical particles, can be tested in the usual photonic Bell measurement
apparatus with minor modifications. Two different sets of coincidence
measurements on the same experimental setup consisting of a Hong-Ou-Mandel
interferometer demonstrate how the same two-photon state can emerge
entanglement in the polarization or the momentum degree of freedom depending on
the dynamical variables used for labeling the particles. Our experiment
demonstrates how the same source can be used as both a polarization entangled
state, as well as a dichotomic momentum entangled state shared between distant
users Alice and Bob in accordance to which sets of detectors they access. When
the particles become distinguishable by letting the information about one of
the variables to be imprinted in yet another (possibly inaccessible) system or
degree of freedom, the feature of dualism is expected to vanish. We verify this
feature by polarization decoherence (polarization information in environment)
or arrival time difference, which both respectively destroy one of the dual
forms of entanglement.Comment: 5 pages, 4 figure
Role of heat and mechanical treatments in the fabrication of superconducting Ba0.6K0.4Fe2As2 ex-situ Powder-In-Tube tapes
Among the recently discovered Fe-based superconducting compounds, the
(K,Ba)Fe2As2 phase is attracting large interest within the scientific community
interested in conductor developments. In fact, after some years of development,
critical current densities Jc of about 105 A/cm2 at fields up to more than 10 T
have been obtained in powder in tube (PIT) processed wires and tapes. Here we
explore the crucial points in the wire/tape fabrication by means of the ex-situ
PIT method. We focus on scaling up processes which are crucial for the
industrial fabrication. We analyzed the effects on the microstructure of the
different heat and mechanical treatments. By an extensive microstructural
analysis correlated with the transport properties we addressed the issues
concerning the phase purity, the internal porosity and crack formation in the
superconducting core region. Our best conductors with a filling factor of about
30 heat treated at 800 C exhibited Tc = 38 K the highest value measured in such
kind of superconducting tape. The microstructure analysis shows clean and well
connected grain boundaries but rather poor density: The measured Jc of about 3
x 10^4 A/cm2 in self-field is suppressed by less than a factor 7 at 7 T. Such
not yet optimized Jc values can be accounted for by the reduced density while
the moderate in-field suppression and a rather high n-factor confirm the high
homogeneity and uniformity of these tapes
The effect of ionization on the global minima of small and medium sized silicon and magnesium clusters
We re-examine the question of whether the geometrical ground state of neutral
and ionized clusters are identical. Using a well defined criterion for being
"identical" together, the extensive sampling methods on a potential energy
surface calculated by density functional theory, we show that the ground states
are in general different. This behavior is to be expected whenever there are
metastable configurations which are close in energy to the ground state, but it
disagrees with previous studies.Comment: 7 pages, 7 figure
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