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 $\sim 170$ 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 $(10 -- 20) h^{-1}$ 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