5,631 research outputs found
Eavesdropping on the "ping-pong" quantum communication protocol
The proposed eavesdropping scheme reveals that the quantum communication
protocol recently presented by Bostrom and Felbinger [Phys. Rev. Lett. 89,
187902 (2002)] is not secure as far as quantum channel losses are taken into
account
Comment on "Quantum dense key distribution"
In this Comment we question the security of recently proposed by Degiovanni
et al. [Phys. Rev. A 69 (2004) 032310] scheme of quantum dense key
distribution
Discrete Time Quantum Walk Approach to State Transfer
We show that a quantum state transfer, previously studied as a continuous
time process in networks of interacting spins, can be achieved within the model
of discrete time quantum walks with position dependent coin. We argue that due
to additional degrees of freedom, discrete time quantum walks allow to observe
effects which cannot be observed in the corresponding continuous time case.
First, we study a discrete time version of the engineered coupling protocol due
to Christandl et. al. [Phys. Rev. Lett. 92, 187902 (2004)] and then discuss the
general idea of conversion between continuous time quantum walks and discrete
time quantum walks.Comment: 9 pages, 6 figures, comments welcom
Image restoration using HOS and the Radon transform
The authors propose the use of higher-order statistics (HOS) to study the problem of image restoration. They consider images degraded by linear or zero phase blurring point spread functions (PSF) and additive Gaussian noise. The complexity associated with the combination of two-dimensional signal processing and higher-order statistics is reduced by means of the Radon transform. The projection at each angle is an one-dimensional signal that can be processed by any existing 1-D higher-order statistics-based method. They apply two methods that have proven to attain good one-dimensional signal reconstruction, especially in the presence of noise. After the ideal projections have been estimated, the inverse Radon transform gives the restored image. Simulation results are provided.Peer ReviewedPostprint (published version
Laboratory studies, analysis, and interpretation of the spectra of hydrocarbons present in planetary atmospheres including cyanoacetylene, acetylene, propane, and ethane
Combining broadband Fourier transform spectrometers (FTS) from the McMath facility at NSO and from NRC in Ottawa and narrow band TDL data from the laboratories with computational physics techniques has produced a broad range of results for the study of planetary atmospheres. Motivation for the effort flows from the Voyager/IRIS observations and the needs of Voyager analysis for laboratory results. In addition, anticipation of the Cassini mission adds incentive to pursue studies of observed and potentially observable constituents of planetary atmospheres. Current studies include cyanoacetylene, acetylene, propane, and ethane. Particular attention is devoted to cyanoacetylen (H3CN) which is observed in the atmosphere of Titan. The results of a high resolution infrared laboratory study of the line positions of the 663, 449, and 22.5/cm fundamental bands are presented. Line position, reproducible to better than 5 MHz for the first two bands, are available for infrared astrophysical searches. Intensity and broadening studies are in progress. Acetylene is a nearly ubiquitous atmospheric constituent of the outer planets and Titan due to the nature of methane photochemistry. Results of ambient temperature absolute intensity measurements are presented for the fundamental and two two-quantum hotband in the 730/cm region. Low temperature hotband intensity and linewidth measurements are planned
Towards symmetric scheme for superdense coding between multiparties
Recently Liu, Long, Tong and Li [Phys. Rev. A 65, 022304 (2002)] have
proposed a scheme for superdense coding between multiparties. This scheme seems
to be highly asymmetric in the sense that only one sender effectively exploits
entanglement. We show that this scheme can be modified in order to allow more
senders to benefit of the entanglement enhanced information transmission.Comment: 6 page
Exclusive meson pair production in proton-proton collisions
We present a study of the exclusive production of meson pairs in the
four-body , reactions at high
energies which constitute an irreducible background to resonance states (e.g.
, , , , ). We consider
central diffractive contribution mediated by Pomeron and Reggeon exchanges and
new diffractive mechanism of emission of pions/kaons from the proton lines. We
include absorption effects due to proton-proton interaction and pion/kaon
rescattering. Predictions for the total cross section and differential
distributions in pion/kaon rapidity and transverse momentum as well as
two-pion/kaon invariant mass are presented for the RHIC, Tevatron and LHC
colliders. Finally we consider a measurement of exclusive production of a
scalar meson via ,
decay.Comment: 4 pp., 4 figures, talk presented by PL at MESON2012 - 12th
International Workshop on Meson Production, Properties and Interaction,
Krakow, Poland, 31 May - 5 June 201
Dynamics and nonequilibrium states in the Hamiltonian mean-field model: A closer look
We critically revisit the evidence for the existence of quasistationary
states in the globally coupled XY (or Hamiltonian mean-field) model. A
slow-relaxation regime at long times is clearly revealed by numerical
realizations of the model, but no traces of quasistationarity are found during
the earlier stages of the evolution. We point out the nonergodic properties of
this system in the short-time range, which makes a standard statistical
description unsuitable. New aspects of the evolution during the nonergodic
regime, and of the energy distribution function in the final approach to
equilibrium, are disclosed
Inhomogeneous Quasi-stationary States in a Mean-field Model with Repulsive Cosine Interactions
The system of N particles moving on a circle and interacting via a global
repulsive cosine interaction is well known to display spatially inhomogeneous
structures of extraordinary stability starting from certain low energy initial
conditions. The object of this paper is to show in a detailed manner how these
structures arise and to explain their stability. By a convenient canonical
transformation we rewrite the Hamiltonian in such a way that fast and slow
variables are singled out and the canonical coordinates of a collective mode
are naturally introduced. If, initially, enough energy is put in this mode, its
decay can be extremely slow. However, both analytical arguments and numerical
simulations suggest that these structures eventually decay to the spatially
uniform equilibrium state, although this can happen on impressively long time
scales. Finally, we heuristically introduce a one-particle time dependent
Hamiltonian that well reproduces most of the observed phenomenology.Comment: to be published in J. Phys.
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