56,900 research outputs found
Spatial entanglement of twin quantum images
We show that spatial entanglement of two twin images obtained by parametric
down-conversion is complete, i.e. concerns both amplitude and phase. This is
realised through a homodyne detection of these images which allows for
measurement of the field quadrature components. EPR correlations are shown to
exist between symmetrical pixels of the two images. The best possible
correlation is obtained by adjusting the phase of the local oscillator field
(LO) in the area of maximal amplification. The results for quadrature
components hold unchanged even in absence of any input image i.e. for pure
parametric fluorescence. In this case they are not related to intensity and
phase fluctuations.Comment: 19 pages, 2 figure
Cross-spectral analysis of the X-ray variability of Mrk 421
Using the cross-spectral method, we confirm the existence of the X-ray hard
lags discovered with cross-correlation function technique during a large flare
of Mrk 421 observed with BeppoSAX . For the 0.1--2 versus 2--10keV light
curves, both methods suggest sub-hour hard lags. In the time domain, the degree
of hard lag, i.e., the amplitude of the 3.2--10 keV photons lagging the lower
energy ones, tends to increase with the decreasing energy. In the Fourier
frequency domain, by investigating the cross-spectra of the 0.1--2/2--10 keV
and the 2--3.2/3.2--10 keV pairs of light curves, the flare also shows hard
lags at the lowest frequencies. However, with the present data, it is
impossible to constrain the dependence of the lags on frequencies even though
the detailed simulations demonstrate that the hard lags at the lowest
frequencies probed by the flare are not an artifact of sparse sampling, Poisson
and red noise. As a possible interpretation, the implication of the hard lags
is discussed in the context of the interplay between the (diffusive)
acceleration and synchrotron cooling of relativistic electrons responsible for
the observed X-ray emission. The energy-dependent hard lags are in agreement
with the expectation of an energy-dependent acceleration timescale. The
inferred magnetic field (B ~ 0.11 Gauss) is consistent with the value inferred
from the Spectral Energy Distributions of the source. Future investigations
with higher quality data that whether or not the time lags are
energy-/frequency-dependent will provide a new constraint on the current models
of the TeV blazars.Comment: 11 pages, 6 figures, accepted by MNRA
A Cryogenic Underground Observatory for Rare Events: Cuore, an Update
CUORE is a proposed tightly packed array of 1000 TeO_{2} bolometers, each
being a cube 5 cm on a side with a mass of 750 gms. The array consists of 25
vertical towers, arranged in a square, of 5 towers by 5 towers, each containing
10 layers of 4 crystals. The design of the detector is optimized for ultralow-
background searches for neutrinoless double beta decay of ^{130}Te (33.8%
abundance), cold dark matter, solar axions, and rare nuclear decays. A
preliminary experiment involving 20 crystals of various sizes (MIBETA) has been
completed, and a single CUORE tower is being constructed as a smaller scale
experiment called CUORICINO. The expected performance and sensitivity, based on
Monte Carlo simulations and extrapolations of present results, are reported.Comment: in press: Nucl. Phys. of Russian Academy of Sc
Fractal fluctuations in quantum integrable scattering
We theoretically and numerically demonstrate that completely integrable
scattering processes may exhibit fractal transmission fluctuations, due to
typical spectral properties of integrable systems.
Similar properties also occur with scattering processes in the presence of
strong dynamical localization, thus explaining recent numerical observations of
fractality in the latter class of systems.Comment: revtex, 4 pages, 3 eps figure
Nonequilibrium wetting of finite samples
As a canonical model for wetting far from thermal equilibrium we study a
Kardar-Parisi-Zhang interface growing on top of a hard-core substrate.
Depending on the average growth velocity the model exhibits a non-equilibrium
wetting transition which is characterized by an additional surface critical
exponent theta. Simulating the single-step model in one spatial dimension we
provide accurate numerical estimates for theta and investigate the distribution
of contact points between the substrate and the interface as a function of
time. Moreover, we study the influence of finite-size effects, in particular
the time needed until a finite substrate is completely covered by the wetting
layer for the first time.Comment: 17 pages, 8 figures, revisio
Intensity correlations, entanglement properties and ghost imaging in multimode thermal-seeded parametric downconversion: Theory
We address parametric-downconversion seeded by multimode pseudo-thermal
fields. We show that this process may be used to generate multimode pairwise
correlated states with entanglement properties that can be tuned by controlling
the seed intensities. Multimode pseudo-thermal fields seeded
parametric-downconversion represents a novel source of correlated states, which
allows one to explore the classical-quantum transition in pairwise correlations
and to realize ghost imaging and ghost diffraction in regimes not yet explored
by experiments.Comment: 9 pages, 3 figure
The ratchet effect and the transporting islands in the chaotic sea
We study directed transport in a classical deterministic dissipative system.
We consider the generic case of mixed phase space and show that large ratchet
currents can be generated thanks to the presence, in the Hamiltonian limit, of
transporting stability islands embedded in the chaotic sea. Due to the
simultaneous presence of chaos and dissipation the stationary value of the
current is independent of initial conditions, except for initial states with
very small measure.Comment: 5 pages, 6 figure
Semiclassical model for a memory dephasing channel
We study a dephasing channel with memory, described by a Hamiltonian model in
which the system-environment interaction is described by a stochastic process.
We propose a useful way to describe the channel uses correlations. Moreover, we
give a general expression for the coherences decay factors as a function of the
number of channel uses and of the stochastic process power spectrum. We also
study the impact of memory on the three qubit code, showing that correlations
among channel uses affect very little the code performance.Comment: 8pages, 3 figures, proceedings of CEWQO 2008 Conferenc
Unified Dark Matter scalar field models with fast transition
We investigate the general properties of Unified Dark Matter (UDM) scalar
field models with Lagrangians with a non-canonical kinetic term, looking
specifically for models that can produce a fast transition between an early
Einstein-de Sitter CDM-like era and a later Dark Energy like phase, similarly
to the barotropic fluid UDM models in JCAP1001(2010)014. However, while the
background evolution can be very similar in the two cases, the perturbations
are naturally adiabatic in fluid models, while in the scalar field case they
are necessarily non-adiabatic. The new approach to building UDM Lagrangians
proposed here allows to escape the common problem of the fine-tuning of the
parameters which plague many UDM models. We analyse the properties of
perturbations in our model, focusing on the the evolution of the effective
speed of sound and that of the Jeans length. With this insight, we can set
theoretical constraints on the parameters of the model, predicting sufficient
conditions for the model to be viable. An interesting feature of our models is
that what can be interpreted as w_{DE} can be <-1 without violating the null
energy conditions.Comment: Slightly revised version accepted for publication in JCAP, with a few
added references; 27 pages, 13 figure
The Asymptotic Dynamics of de Sitter Gravity in three Dimensions
We show that the asymptotic dynamics of three-dimensional gravity with
positive cosmological constant is described by Euclidean Liouville theory. This
provides an explicit example of a correspondence between de Sitter gravity and
conformal field theories. In the case at hand, this correspondence is
established by formulating Einstein gravity with positive cosmological constant
in three dimensions as an SL(2,C) Chern-Simons theory. The de Sitter boundary
conditions on the connection are divided into two parts. The first part reduces
the CS action to a nonchiral SL(2,C) WZNW model, whereas the second provides
the constraints for a further reduction to Liouville theory, which lives on the
past boundary of dS_3.Comment: 12 pages, LaTeX, no figures, v2: Minor changes, references adde
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