212 research outputs found
Chaos and isospin symmetry breaking in rotational nuclei
For nuclei with N = Z, the isospin degree of freedom is important and, for
deformed systems, rotational bands of different isospin may be expected at low
excitation energies. We have investigated, in a simple model space, the
influence of the isospin-breaking Coulomb interaction on the degree of
chaoticity of these rotational bands. The statistical measures used rely on an
analysis of level-spacing distributions, which are extremely difficult to
measure experimentally. We show, however, that the overlap intergrals between
states of similar frequency reflect well the degree of chaoticity. This
quantity is closely related to the experimentally more accessible gamma-decay
``spreading width''.Comment: 13 pages, 9 figures, Elsevie
Projected shell model study for the yrast-band structure of the proton-rich mass-80 nuclei
A systematic study of the yrast-band structure for the proton-rich, even-even
mass-80 nuclei is carried out using projected shell model approach. We describe
the the energy spectra, transition quadrupole moments and gyromagnetic factors.
The observed variations in energy spectra and transition quadrupole moments in
this mass region are discussed in terms of the configuration mixing of the
projected deformed Nilsson states as a function of shell filling.Comment: 22 pages, 7 figure
Partitioned trace distances
New quantum distance is introduced as a half-sum of several singular values
of difference between two density operators. This is, up to factor, the metric
induced by so-called Ky Fan norm. The partitioned trace distances enjoy similar
properties to the standard trace distance, including the unitary invariance,
the strong convexity and the close relations to the classical distances. The
partitioned distances cannot increase under quantum operations of certain kind
including bistochastic maps. All the basic properties are re-formulated as
majorization relations. Possible applications to quantum information processing
are briefly discussed.Comment: 8 pages, no figures. Significant changes are made. New section on
majorization is added. Theorem 4.1 is extended. The bibliography is enlarged
Membranes for Topological M-Theory
We formulate a theory of topological membranes on manifolds with G_2
holonomy. The BRST charges of the theories are the superspace Killing vectors
(the generators of global supersymmetry) on the background with reduced
holonomy G_2. In the absence of spinning formulations of supermembranes, the
starting point is an N=2 target space supersymmetric membrane in seven
euclidean dimensions. The reduction of the holonomy group implies a twisting of
the rotations in the tangent bundle of the branes with ``R-symmetry'' rotations
in the normal bundle, in contrast to the ordinary spinning formulation of
topological strings, where twisting is performed with internal U(1) currents of
the N=(2,2) superconformal algebra. The double dimensional reduction on a
circle of the topological membrane gives the strings of the topological A-model
(a by-product of this reduction is a Green-Schwarz formulation of topological
strings). We conclude that the action is BRST-exact modulo topological terms
and fermionic equations of motion. We discuss the role of topological membranes
in topological M-theory and the relation of our work to recent work by Hitchin
and by Dijkgraaf et al.Comment: 22 pp, plain tex. v2: refs. adde
Anomalous rotational-alignment in N=Z nuclei and residual neutron-proton interaction
Recent experiments have demonstrated that the rotational-alignment for the
nuclei in the mass-80 region is considerably delayed as compared to the
neighboring nuclei. We investigate whether this observation can be
understood by a known component of nuclear residual interactions. It is shown
that the quadrupole-pairing interaction, which explains many of the delays
known in rare-earth nuclei, does not produce the substantial delay observed for
these nuclei. However, the residual neutron-proton interaction which is
conjectured to be relevant for nuclei is shown to be quite important in
explaining the new experimental data.Comment: 4 pages, 3 figures, final version accepted by Phys. Rev. C as a Rapid
Communicatio
Experimentally feasible measures of distance between quantum operations
We present two measures of distance between quantum processes based on the
superfidelity, introduced recently to provide an upper bound for quantum
fidelity. We show that the introduced measures partially fulfill the
requirements for distance measure between quantum processes. We also argue that
they can be especially useful as diagnostic measures to get preliminary
knowledge about imperfections in an experimental setup. In particular we
provide quantum circuit which can be used to measure the superfidelity between
quantum processes.
As the behavior of the superfidelity between quantum processes is crucial for
the properties of the introduced measures, we study its behavior for several
families of quantum channels. We calculate superfidelity between arbitrary
one-qubit channels using affine parametrization and superfidelity between
generalized Pauli channels in arbitrary dimensions. Statistical behavior of the
proposed quantities for the ensembles of quantum operations in low dimensions
indicates that the proposed measures can be indeed used to distinguish quantum
processes.Comment: 9 pages, 4 figure
Multi-Phonon -Vibrational Bands and the Triaxial Projected Shell Model
We present a fully quantum-mechanical, microscopic, unified treatment of
ground-state band and multi-phonon -vibrational bands using shell model
diagonalization with the triaxial projected shell model. The results agree very
well with data on the g- and -band spectra in Er, as well
as with recently measured 2-phonon -bandhead energies in
Er and Er. Multi-phonon -excitation energies are
predicted.Comment: 4 pages, 4 figures, submitted to Phys. Lett.
Notes on entropic characteristics of quantum channels
One of most important issues in quantum information theory concerns
transmission of information through noisy quantum channels. We discuss few
channel characteristics expressed by means of generalized entropies. Such
characteristics can often be dealt in line with more usual treatment based on
the von Neumann entropies. For any channel, we show that the -average output
entropy of degree is bounded from above by the -entropy of the
input density matrix. Concavity properties of the -entropy exchange are
considered. Fano type quantum bounds on the -entropy exchange are
derived. We also give upper bounds on the map -entropies in terms of the
output entropy, corresponding to the completely mixed input.Comment: 10 pages, no figures. The statement of Proposition 1 is explicitly
illustrated with the depolarizing channel. The bibliography is extended and
updated. More explanations. To be published in Cent. Eur. J. Phy
Chern-Simons Vortices in Supergravity
We study supersymmetric vortex solutions in three-dimensional abelian gauged
supergravity. First, we construct the general U(1)-gauged D=3, N=2 supergravity
whose scalar sector is an arbitrary Kahler manifold with U(1) isometry. This
construction clarifies the connection between local supersymmetry and the
specific forms of some scalar potentials previously found in the literature --
in particular, it provides the locally supersymmetric embedding of the abelian
Chern-Simons Higgs model. We show that the Killing spinor equations admit
rotationally symmetric vortex solutions with asymptotically conical geometry
which preserve half of the supersymmetry.Comment: 26 pages, LaTeX2
The Seven-sphere and its Kac-Moody Algebra
We investigate the seven-sphere as a group-like manifold and its extension to
a Kac-Moody-like algebra. Covariance properties and tensorial composition of
spinors under are defined. The relation to Malcev algebras is
established. The consequences for octonionic projective spaces are examined.
Current algebras are formulated and their anomalies are derived, and shown to
be unique (even regarding numerical coefficients) up to redefinitions of the
currents. Nilpotency of the BRST operator is consistent with one particular
expression in the class of (field-dependent) anomalies. A Sugawara construction
is given.Comment: 22 pages. Macropackages used: phyzzx, epsf. Three epsf figure files
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