2,146 research outputs found
Augmentation of nucleon-nucleus scattering by information entropy
Quantum information entropy is calculated from the nucleon nucleus forward
scattering amplitudes. Using a representative set of nuclei, from He to
Pb, and energies, \,[GeV], we establish a linear
dependence of quantum information entropy as functions of logarithm nuclear
mass and logarithm projectile energy .Comment: 5 pages, 2 figure
Incomplete quantum process tomography and principle of maximal entropy
The main goal of this paper is to extend and apply the principle of maximum
entropy (MaxEnt) to incomplete quantum process estimation tasks. We will define
a so-called process entropy function being the von Neumann entropy of the state
associated with the quantum process via Choi-Jamiolkowski isomorphism. It will
be shown that an arbitrary process estimation experiment can be reformulated in
a unified framework and MaxEnt principle can be consistently exploited. We will
argue that the suggested choice for the process entropy satisfies natural list
of properties and it reduces to the state MaxEnt principle, if applied to
preparator devices.Comment: 8 pages, comments welcome, references adde
Configuration mixing in Pb : band structure and electromagnetic properties
In the present paper, we carry out a detailed analysis of the presence and
mixing of various families of collective bands in Pb. Making use of the
interacting boson model, we construct a particular intermediate basis that can
be associated with the unperturbed bands used in more phenomenological studies.
We use the E2 decay to construct a set of collective bands and discuss in
detail the B(E2)-values. We also perform an analysis of these theoretical
results (Q, B(E2)) to deduce an intrinsic quadrupole moment and the associated
quadrupole deformation parameter, using an axially deformed rotor model.Comment: submitted to pr
Shannon dimensionality of quantum channels and its application to photon entanglement
We introduce the concept of Shannon dimensionality D as a new way to quantify
bipartite entanglement as measured in an experiment. This is applied to
orbital-angular-momentum entanglement of two photons, using two state analyzers
composed of a rotatable angular-sector phase plate that is lens-coupled to a
single-mode fiber. We can deduce the value of D directly from the observed
two-photon coincidence fringe. In our experiment, D varies between 2 and 6,
depending on the experimental conditions. We predict how the Shannon
dimensionality evolves when the number of angular sectors imprinted in the
phase plate is increased and anticipate that D = 50 is experimentally within
reach.Comment: 4 pages, 3 figures, accepted for Physical Review Letter
`Classical' quantum states
We show that several classes of mixed quantum states in finite-dimensional
Hilbert spaces which can be characterized as being, in some respect, 'most
classical' can be described and analyzed in a unified way. Among the states we
consider are separable states of distinguishable particles, uncorrelated states
of indistinguishable fermions and bosons, as well as mixed spin states
decomposable into probabilistic mixtures of pure coherent states. The latter
were the subject of the recent paper by Giraud et. al., who showed that in the
lowest-dimensional, nontrivial case of spin 1, each such state can be
decomposed into a mixture of eight pure states. Using our method we prove that
in fact four pure states always suffice.Comment: revtex, 17 page
Positrons from particle dark-matter annihilation in the Galactic halo: propagation Green's functions
We have made a calculation of the propagation of positrons from dark-matter
particle annihilation in the Galactic halo in different models of the dark
matter halo distribution using our 3D code, and present fits to our numerical
propagation Green's functions. We show that the Green's functions are not very
sensitive to the dark matter distribution for the same local dark matter energy
density. We compare our predictions with computed cosmic ray positron spectra
(``background'') for the ``conventional'' CR nucleon spectrum which matches the
local measurements, and a modified spectrum which respects the limits imposed
by measurements of diffuse Galactic gamma-rays, antiprotons, and positrons. We
conclude that significant detection of a dark matter signal requires favourable
conditions and precise measurements unless the dark matter is clumpy which
would produce a stronger signal. Although our conclusion qualitatively agrees
with that of previous authors, it is based on a more realistic model of
particle propagation and thus reduces the scope for future speculations.
Reliable background evaluation requires new accurate positron measurements and
further developments in modelling production and propagation of cosmic ray
species in the Galaxy.Comment: 8 pages, 6 ps-figures, 3 tables, uses revtex. Accepted for
publication in Physical Review D. More details can be found at
http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm
The Geroch group in the Ashtekar formulation
We study the Geroch group in the framework of the Ashtekar formulation. In
the case of the one-Killing-vector reduction, it turns out that the third
column of the Ashtekar connection is essentially the gradient of the Ernst
potential, which implies that the both quantities are based on the ``same''
complexification. In the two-Killing-vector reduction, we demonstrate Ehlers'
and Matzner-Misner's SL(2,R) symmetries, respectively, by constructing two sets
of canonical variables that realize either of the symmetries canonically, in
terms of the Ashtekar variables. The conserved charges associated with these
symmetries are explicitly obtained. We show that the gl(2,R) loop algebra
constructed previously in the loop representation is not the Lie algebra of the
Geroch group itself. We also point out that the recent argument on the
equivalence to a chiral model is based on a gauge-choice which cannot be
achieved generically.Comment: 40 pages, revte
Duality in a fermion-like formulation for the electromagnetic field
We employ the Dirac-like equation for the gauge field proposed by Majorana to
obtain an action that is symmetric under duality transformation. We also use
the equivalence between duality and chiral symmetry in this fermion-like
formulation to show how the Maxwell action can be seen as a mass term.Comment: 4 pages. Revtex. Final version to be published in Phys. Rev.
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
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