1,696 research outputs found
Security of entanglement-based QKD with realistic parametric down-conversion sources
The paper analyzes security aspects of practical entanglement-based quantum
key distribution (QKD), namely, BBM92 or entanglement-based BB84 protocol.
Similar to prepare-and-measure QKD protocols, practical implementations of the
entanglement-based QKD have to rely upon non-ideal photon sources. A typical
solution for entanglement generation is the spontaneous parametric
down-conversion. However, this process creates not only single photon pairs,
but also quantum states with more than two photons, which potentially may lead
to security deterioration. We show that this effect does not impair the
security of entanglement-based QKD systems. We also review the available
security proofs and show that properties of the entanglement source have
nothing to do with security degradation.Comment: 6 page
Minimalist design of a robust real-time quantum random number generator
We present a simple and robust construction of a real-time quantum random
number generator (QRNG). Our minimalist approach ensures stable operation of
the device as well as its simple and straightforward hardware implementation as
a stand-alone module. As a source of randomness the device uses measurements of
time intervals between clicks of a single-photon detector. The obtained raw
sequence is then filtered and processed by a deterministic randomness
extractor, which is realized as a look-up table. This enables high speed
on-the-fly processing without the need of extensive computations. The overall
performance of the device is around 1 random bit per detector click, resulting
in 1.2 Mbit/s generation rate in our implementation
Generic scaling relation in the scalar model
The results of analysis of the one--loop spectrum of anomalous dimensions of
composite operators in the scalar model are presented. We give the
rigorous constructive proof of the hypothesis on the hierarchical structure of
the spectrum of anomalous dimensions -- the naive sum of any two anomalous
dimensions generates a limit point in the spectrum. Arguments in favor of the
nonperturbative character of this result and the possible ways of a
generalization to other field theories are briefly discussed.Comment: 15 pages, Latex, 50 K
Once More About the Possibility of Determining the Local Electron Concentration by the Dispersion Method with the Help of AES and on New Ionization Maxima in the Ionosphere
Reliability of ionospheric density measurements by satellites using dispersion metho
Ocean eddy dynamics in a coupled ocean-atmosphere model
Author Posting. © American Meteorological Society, 2007. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 37 (2007): 1103-1121, doi:10.1175/jpo3041.1.The role of mesoscale oceanic eddies is analyzed in a quasigeostrophic coupled ocean–atmosphere model operating at a large Reynolds number. The model dynamics are characterized by decadal variability that involves nonlinear adjustment of the ocean to coherent north–south shifts of the atmosphere. The oceanic eddy effects are diagnosed by the dynamical decomposition method adapted for nonstationary external forcing. The main effects of the eddies are an enhancement of the oceanic eastward jet separating the subpolar and subtropical gyres and a weakening of the gyres. The flow-enhancing effect is due to nonlinear rectification driven by fluctuations of the eddy forcing. This is a nonlocal process involving generation of the eddies by the flow instabilities in the western boundary current and the upstream part of the eastward jet. The eddies are advected by the mean current to the east, where they backscatter into the rectified enhancement of the eastward jet. The gyre-weakening effect, which is due to the time-mean buoyancy component of the eddy forcing, is a result of the baroclinic instability of the westward return currents. The diagnosed eddy forcing is parameterized in a non-eddy-resolving ocean model, as a nonstationary random process, in which the corresponding parameters are derived from the control coupled simulation. The key parameter of the random process—its variance—is related to the large-scale flow baroclinicity index. It is shown that the coupled model with the non-eddy-resolving ocean component and the parameterized eddies correctly simulates climatology and low-frequency variability of the control eddy-resolving coupled solution.Funding for this work came from NSF Grants
OCE 02-221066 and OCE 03-44094. Additional funding
for PB was provided by the U.K. Royal Society Fellowship
and by WHOI Grants 27100056 and 52990035
Energy level statistics of a critical random matrix ensemble
We study level statistics of a critical random matrix ensemble of a power-law
banded complex Hermitean matrices. We compute numerically the level
compressibility via the level number variance and compare it with the
analytical formula for the exactly solvable model of Moshe, Neuberger and
Shapiro.Comment: 8 pages, 3 figure
A mechanistic model of mid-latitude decadal climate variability
Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Physica D: Nonlinear Phenomena 237 (2008): 584-599, doi:10.1016/j.physd.2007.09.025.A simple heuristic model of coupled decadal ocean–atmosphere modes in middle
latitudes is developed. Previous studies have treated atmospheric intrinsic variability
as a linear stochastic process modified by a deterministic coupling to the ocean.
The present paper takes an alternative view: based on observational, as well as
process modeling results, it represents this variability in terms of irregular transitions
between two anomalously persistent, high-latitude and low-latitude jet-stream
states. Atmospheric behavior is thus governed by an equation analogous to that describing
the trajectory of a particle in a double-well potential, subject to stochastic
forcing. Oceanic adjustment to a positional shift in the atmospheric jet involves
persistent circulation anomalies maintained by the action of baroclinic eddies; this
process is parameterized in the model as a delayed oceanic response. The associated
sea-surface temperature anomalies provide heat fluxes that affect atmospheric
circulation by modifying the shape of the double-well potential. If the latter coupling
is strong enough, the model’s spectrum exhibits a peak at a periodicity related
to the ocean’s eddy-driven adjustment time. A nearly analytical approximation of
the coupled model is used to study the sensitivity of this behavior to key model
parameters.This research
was supported by National Science Foundation grant OCE-02-221066 (all coauthors)
and the Department of Energy grant DE-FG-03-01ER63260 (MG
and SK)
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