9,709 research outputs found
RPA puzzle in C(12) weak decay processes
We explain the origin of the difficulties that appear in a straightforward
application of the QRPA in C(12), and we demonstrate that it is imperative to
use the projected QRPA (PQRPA). Satisfactory results, not only for the weak
processes among the ground states of the triad B(12),C(12),N(12), but also for
the inclusive ones are obtained. We sketch as well a new formalism for the
neutrino-nucleus interaction that furnishes very simple final formulae for the
muon capture rate and neutrino induced cross sections.Comment: 14 pages in LaTex, changes are included in the text, to appear in PL
Frames of subspaces and operators
We study the relationship between operators, orthonormal basis of subspaces
and frames of subspaces (also called fusion frames) for a separable Hilbert
space . We get sufficient conditions on an orthonormal basis of
subspaces of a Hilbert space
and a surjective in order that
is a frame of subspaces with respect to a computable
sequence of weights. We also obtain generalizations of results in [J. A.
Antezana, G. Corach, M. Ruiz and D. Stojanoff, Oblique projections and frames.
Proc. Amer. Math. Soc. 134 (2006), 1031-1037], which related frames of
subspaces (including the computation of their weights) and oblique projections.
The notion of refinament of a fusion frame is defined and used to obtain
results about the excess of such frames. We study the set of admissible weights
for a generating sequence of subspaces. Several examples are given.Comment: 21 pages, LaTeX; added references and comments about fusion frame
Mesoscopic interference
We analyze a double-slit experiment when the interfering particle is
"mesoscopic" and one endeavors to obtain Welcher Weg information by shining
light on it. We derive a compact expression for the visibility of the
interference pattern: coherence depends on both the spatial and temporal
features of the wave function during its travel to the screen. We set a bound
on the temperature of the mesoscopic particle in order that its quantum
mechanical coherence be maintained.Comment: 16 pages, 14 figure
Wigner function and coherence properties of cold and thermal neutrons
We analyze the coherence properties of a cold or a thermal neutron by
utilizing the Wigner quasidistribution function. We look in particular at a
recent experiment performed by Badurek {\em et al.}, in which a polarized
neutron crosses a magnetic field that is orthogonal to its spin, producing
highly non-classical states. The quantal coherence is extremely sensitive to
the field fluctuation at high neutron momenta. A "decoherence parameter" is
introduced in order to get quantitative estimates of the losses of coherence.Comment: 6 pages, 3 figures. Contribution to the Sixth Central-European
Workshop on Quantum Optics, Chudobin near Olomouc, Czech Republic, April-May
199
Decoherence vs entropy in neutron interferometry
We analyze the coherence properties of polarized neutrons, after they have
interacted with a magnetic field or a phase shifter undergoing different kinds
of statistical fluctuations. We endeavor to probe the degree of disorder of the
distribution of the phase shifts by means of the loss of quantum mechanical
coherence of the neutron. We find that the notion of entropy of the shifts and
that of decoherence of the neutron do not necessarily agree. In some cases the
neutron wave function is more coherent, even though it has interacted with a
more disordered medium.Comment: 13 pages, 5 figure
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