9,831 research outputs found
Bidirectional imperfect quantum teleportation with a single Bell state
We present a bidirectional modification of the standard one-qubit
teleportation protocol, where both Alice and Bob transfer noisy versions of
their qubit states to each other by using single Bell state and auxiliary
(trigger) qubits. Three schemes are considered: the first where the actions of
parties are governed by two independent quantum random triggers, the second
with single random trigger, and the third as a mixture of the first two. We
calculate the fidelities of teleportation for all schemes and find a condition
on correlation between trigger qubits in the mixed scheme which allows us to
overcome the classical fidelity boundary of 2/3. We apply the Choi-Jamiolkowski
isomorphism to the quantum channels obtained in order to investigate an
interplay between their ability to transfer the information,
entanglement-breaking property, and auxiliary classical communication needed to
form correlations between trigger qubits. The suggested scheme for
bidirectional teleportation can be realized by using current experimental
tools.Comment: 8 pages, 4 figures; published versio
Information processing using three-qubit and qubit-qutrit encodings of noncomposite quantum systems
We study quantum information properties of a seven-level system realized by a
particle in an one-dimensional square-well trap. Features of encodings of
seven-level systems in a form of three-qubit or qubit-qutrit systems are
discussed. We use the three-qubit encoding of the system in order to
investigate subadditivity and strong subadditivity conditions for the thermal
state of the particle. The qubit-qutrit encoding is employed to suggest a
single qudit algorithm for calculation of parity of a bit string. Obtained
results indicate on the potential resource of multilevel systems for
realization of quantum information processing.Comment: 6 pages, 3 figures; published versio
Non-Abelian Vortices, Super-Yang-Mills Theory and Spin(7)-Instantons
We consider a complex vector bundle E endowed with a connection A over the
eight-dimensional manifold R^2 x G/H, where G/H = SU(3)/U(1)xU(1) is a
homogeneous space provided with a never integrable almost complex structure and
a family of SU(3)-structures. We establish an equivalence between G-invariant
solutions A of the Spin(7)-instanton equations on R^2 x G/H and general
solutions of non-Abelian coupled vortex equations on R^2. These vortices are
BPS solitons in a d=4 gauge theory obtained from N=1 supersymmetric Yang-Mills
theory in ten dimensions compactified on the coset space G/H with an
SU(3)-structure. The novelty of the obtained vortex equations lies in the fact
that Higgs fields, defining morphisms of vector bundles over R^2, are not
holomorphic in the generic case. Finally, we introduce BPS vortex equations in
N=4 super Yang-Mills theory and show that they have the same feature.Comment: 14 pages; v2: typos fixed, published versio
Momentum Space Integral Equations for Three Charged Particles: Diagonal Kernels
It has been a long-standing question whether momentum space integral
equations of the Faddeev type are applicable to reactions of three charged
particles, in particular above the three-body threshold. For, the presence of
long-range Coulomb forces has been thought to give rise to such severe
singularities in their kernels that the latter may lack the compactness
property known to exist in the case of purely short-range interactions.
Employing the rigorously equivalent formulation in terms of an
effective-two-body theory we have proved in a preceding paper [Phys. Rev. C
{\bf 61}, 064006 (2000)] that, for all energies, the nondiagonal kernels
occurring in the integral equations which determine the transition amplitudes
for all binary collision processes, possess on and off the energy shell only
integrable singularities, provided all three particles have charges of the same
sign, i.e., all Coulomb interactions are repulsive. In the present paper we
prove that, for particles with charges of equal sign, the diagonal kernels, in
contrast, possess one, but only one, nonintegrable singularity. The latter can,
however, be isolated explicitly and dealt with in a well-defined manner. Taken
together these results imply that modified integral equations can be
formulated, with kernels that become compact after a few iterations. This
concludes the proof that standard solution methods can be used for the
calculation of all binary (i.e., (in-)elastic and rearrangement) amplitudes by
means of momentum space integral equations of the effective-two-body type.Comment: 36 pages, 2 figures, accepted for publication in Phys. Rev.
Effects of Sequence Disorder on DNA Looping and Cyclization
Effects of sequence disorder on looping and cyclization of the
double-stranded DNA are studied theoretically. Both random intrinsic curvature
and inhomogeneous bending rigidity are found to result in a remarkably wide
distribution of cyclization probabilities. For short DNA segments, the range of
the distribution reaches several orders of magnitude for even completely random
sequences. The ensemble averaged values of the cyclization probability are also
calculated, and the connection to the recent experiments is discussed.Comment: 8 pages, 4 figures, LaTeX; accepted to Physical Review E; v2: a
substantially revised version; v3: references added, conclusions expanded,
minor editorial corrections to the text; v4: a substantially revised and
expanded version (total number of pages doubled); v5: new Figure 4, captions
expanded, minor editorial improvements to the tex
Statistical properties of one dimensional Bose gas
Monte Carlo method within, so called, classical fields approximation is
applied to one dimensional weakly interacting repulsive Bose gas trapped in a
harmonic potential. Equilibrium statistical properties of the condensate are
calculated within a canonical ensemble. We also calculate experimentally
relevant low order correlation functions of the whole gas
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Using Structured Assurance Case Approach to Analyse Security and Reliability of Critical Infrastructures
The evaluation of the security, reliability and resilience of critical infrastruc-tures (CI) faces a wide range of challenges ranging from the scale and tempo of attacks to the need to address complex and interdependent systems of sys-tems. Model-based approaches and probabilistic design are fundamental to the evaluation of CI and we need to know whether we can trust these mod-els. This paper presents an approach we are developing to justify the models used to assure CI using structured assurance cases based on Claims, Argu-ments and Evidence (CAE). The modelling and quantitative evaluation of the properties are supported by the Preliminary Interdependency Analysis (PIA) method and platform applied to a case study – a reference power transmission network enhanced with an industrial distributed system of monitoring, protection and control. We discuss the usefulness of the model-ling and assurance case structuring approaches, some findings from the case study, and outline the directions of further work
Affine spherical homogeneous spaces with good quotient by a maximal unipotent subgroup
For an affine spherical homogeneous space G/H of a connected semisimple
algebraic group G, we consider the factorization morphism by the action on G/H
of a maximal unipotent subgroup of G. We prove that this morphism is
equidimensional if and only if the weight semigroup of G/H satisfies some
simple condition.Comment: v2: title and abstract changed; v3: 16 pages, minor correction
On Explicit Point Multi-Monopoles in SU(2) Gauge Theory
It is well known that the Dirac monopole solution with the U(1) gauge group
embedded into the group SU(2) is equivalent to the SU(2) Wu-Yang point monopole
solution having no Dirac string singularity. We consider a multi-center
configuration of m Dirac monopoles and n anti-monopoles and its embedding into
SU(2) gauge theory. Using geometric methods, we construct an explicit solution
of the SU(2) Yang-Mills equations which generalizes the Wu-Yang solution to the
case of m monopoles and n anti-monopoles located at arbitrary points in R^3.Comment: 1+7 pages, LaTe
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