8,536 research outputs found
Dipole anisotropies of IRAS galaxies and the contribution of a large-scale local void
Recent observations of dipole anisotropies show that the velocity of the
Local Group (\Vec v_{\rm G}) induced by the clustering of IRAS galax ies has
an amplitude and direction similar to those of the velocity of Cosmic Microwave
Background dipole anisotropy (\Vec v_{\rm CMB}), but the difference | \Vec
v_{\rm G} - \Vec v_{\rm CMB} | is still km/s, which is about 28% of
|\Vec v_{\rm CMB} |. Here we consider the possibility that the origin of this
difference comes from a hypothetical large-scale local void, with which we can
account for the accelerating behavior of type Ia supernovae due to the spatial
inhomogeneity of the Hubble constant without dark energies and derive the
constraint to the model parameters of the local void. It is found as a result
that the distance between the Local Group and the center of the void must be
Mpc, whose accurate value depends on the background model
parameters.Comment: 13 pages, 1 figure, to be published in ApJ 584, No.2 (2003
Gravitational Lens Statistics and The Density Profile of Dark Halos
We investigate the influence of the inner profile of lens objects on
gravitational lens statistics taking into account of the effect of
magnification bias and both the evolution and the scatter of halo profiles. We
take the dark halos as the lens objects and consider the following three models
for the density profile of dark halos; SIS (singular isothermal sphere), the
NFW (Navarro Frenk White) profile, and the generalized NFW profile which has a
different slope at smaller radii. The mass function of dark halos is assumed to
be given by the Press-Schechter function. We find that magnification bias for
the NFW profile is order of magnitude larger than that for SIS. We estimate the
sensitivity of the lensing probability of distant sources to the inner profile
of lenses and to the cosmological parameters. It turns out that the lensing
probability is strongly dependent on the inner density profile as well as on
the cosmological constant. We compare the predictions with the largest
observational sample, the Cosmic Lens All-Sky Survey. The absence or presence
of large splitting events in larger surveys currently underway such as the 2dF
and SDSS could set constraints on the inner density profile of dark halos.Comment: 22 pages, minor changes and references added, accepted for
publication in Ap
Remote preparation of arbitrary ensembles and quantum bit commitment
The Hughston-Jozsa-Wootters theorem shows that any finite ensemble of quantum
states can be prepared "at a distance", and it has been used to demonstrate the
insecurity of all bit commitment protocols based on finite quantum systems
without superselection rules. In this paper, we prove a generalized HJW theorem
for arbitrary ensembles of states on a C*-algebra. We then use this result to
demonstrate the insecurity of bit commitment protocols based on infinite
quantum systems, and quantum systems with Abelian superselection rules.Comment: 21 pages, LaTeX. Version 2: Proofs expanded and made more
self-contained; added an example of a bit commitment protocol with continuous
ensemble
Quantum information with Gaussian states
Quantum optical Gaussian states are a type of important robust quantum states
which are manipulatable by the existing technologies. So far, most of the
important quantum information experiments are done with such states, including
bright Gaussian light and weak Gaussian light. Extending the existing results
of quantum information with discrete quantum states to the case of continuous
variable quantum states is an interesting theoretical job. The quantum Gaussian
states play a central role in such a case. We review the properties and
applications of Gaussian states in quantum information with emphasis on the
fundamental concepts, the calculation techniques and the effects of
imperfections of the real-life experimental setups.
Topics here include the elementary properties of Gaussian states and relevant
quantum information device, entanglement-based quantum tasks such as quantum
teleportation, quantum cryptography with weak and strong Gaussian states and
the quantum channel capacity, mathematical theory of quantum entanglement and
state estimation for Gaussian states.Comment: 170 pages. Minors of the published version are corrected and listed
in the Acknowledgement part of this versio
Influence of pure-dephasing by phonons on exciton-photon interfaces: Quantum microscopic theory
We have developed a full quantum microscopic theory to analyze the time
evolution of transversal and longitudinal components of an exciton-single
photon system coupled to bulk acoustic phonons. These components are subjected
to two decay processes. One is radiative relaxation and the other is
pure-dephasing due to exciton-phonon interaction. The former results in a decay
with an exponent linear to time, while the latter causes a faster initial decay
than the radiative decay. We analyzed the dependence of the components on the
duration of the input one-photon pulse, temperature, and radiative relaxation
rates. Such a quantitative analysis is important for the developments of
atom-photon interfaces which enable coherent transfer of quantum information
between photons and atomic systems. We found that, for a GaAs spherical quantum
dot in which the exciton interacts with bulk phonons, the maximal probability
of the excited state can be increased up to 75 %. This probability can be
considered as the efficiency for quantum information transfer from photon to
exciton.Comment: 9pages, 5figure
Context-Free Path Querying with Structural Representation of Result
Graph data model and graph databases are very popular in various areas such
as bioinformatics, semantic web, and social networks. One specific problem in
the area is a path querying with constraints formulated in terms of formal
grammars. The query in this approach is written as grammar, and paths querying
is graph parsing with respect to given grammar. There are several solutions to
it, but how to provide structural representation of query result which is
practical for answer processing and debugging is still an open problem. In this
paper we propose a graph parsing technique which allows one to build such
representation with respect to given grammar in polynomial time and space for
arbitrary context-free grammar and graph. Proposed algorithm is based on
generalized LL parsing algorithm, while previous solutions are based mostly on
CYK or Earley algorithms, which reduces time complexity in some cases.Comment: Evaluation extende
- …