16,904 research outputs found
Effects of squeezing on quantum nonlocality of superpositions of coherent states
We analyze effects of squeezing upon superpositions of coherent states (SCSs)
and entangled coherent states (ECSs) for Bell-inequality tests. We find that
external squeezing can always increase the degrees of Bell violations, if the
squeezing direction is properly chosen, for the case of photon parity
measurements. On the other hand, when photon on/off measurements are used, the
squeezing operation can enhance the degree of Bell violations only for moderate
values of amplitudes and squeezing. We point out that a significant improvement
is required over currently available squeezed SCSs in order to directly
demonstrate a Bell-inequality violation in a real experiment.Comment: 7 pages, 4 figures, accepted for publication in Phys. Rev.
Faithful test of non-local realism with entangled coherent states
We investigate the violation of Leggett's inequality for non-local realism
using entangled coherent states and various types of local measurements. We
prove mathematically the relation between the violation of the
Clauser-Horne-Shimony-Holt form of Bell's inequality and Leggett's one when
tested by the same resources. For Leggett inequalities, we generalize the
non-local realistic bound to systems in Hilbert spaces larger than
bidimensional ones and introduce an optimization technique that allows to
achieve larger degrees of violation by adjusting the local measurement
settings. Our work describes the steps that should be performed to produce a
self-consistent generalization of Leggett's original arguments to
continuous-variable states.Comment: 8 pages, 6 figures, to be published in Phys. Rev.
Simultaneous dual-frequency radio observations of S5 0716+714: A search for intraday variability with the Korean VLBI Network
This study aims to search for the existence of intraday variability (IDV) of
BL Lac object S5 0716+714 at high radio frequencies for which the interstellar
scintillation effect is not significant. Using the 21-meter radio telescope of
the Korean VLBI Network (KVN), we present results of multi-epoch simultaneous
dual-frequency radio observations. Single-dish observations of S5 0716+714 were
simultaneously conducted at 21.7 GHz (K-band) and 42.4 GHz (Q-band), with a
high cadence of 30-60 minute intervals.We observed four epochs between December
2009 and June 2010. Over the whole set of observation epochs, S5 0716+714
showed significant inter-month variations in flux density at both the K- and
Q-bands, with modulation indices of approximately 19% for the K-band and
approximately 36% for the Q-band. In all epochs, no clear intraday variability
was detected at either frequency. The source shows monotonic flux density
increase in epochs 1 and 3 and monotonic flux density decrease in epochs 2 and
4. In the flux density increasing phases, the flux densities at the Q-band
increase more rapidly. In the decreasing phase, no significant flux density
difference is seen at the two frequencies. The situation could be different
close to flux density peaks that we did not witness in our observations. We
find an inverted spectrum with mean spectral indices of -0.57+-0.13 in epoch 1
and -0.15+-0.11 in epoch 3. On the other hand, we find relatively steep indices
of +0.24+-0.14 and +0.17+-0.18 in epochs 2 and 4, respectively. We conclude
that the frequency dependence of the variability and the change of the spectral
index are caused by source-intrinsic effects rather than by any extrinsic
scintillation effect.Comment: 6 pages and 4 figures and 4 table
High-dimensional Bell test for a continuous variable state in phase space and its robustness to detection inefficiency
We propose a scheme for testing high-dimensional Bell inequalities in phase
space. High-dimensional Bell inequalities can be recast into the forms of a
phase-space version using quasiprobability functions with the complex-valued
order parameter. We investigate their violations for two-mode squeezed states
while increasing the dimension of measurement outcomes, and finally show the
robustness of high-dimensional tests to detection inefficiency.Comment: 8 pages, 2 figures; title and abstract changed, published versio
Ballistic spin field-effect transistors: Multichannel effects
We study a ballistic spin field-effect transistor (SFET) with special
attention to the issue of multi-channel effects. The conductance modulation of
the SFET as a function of the Rashba spin-orbit coupling strength is
numerically examined for the number of channels ranging from a few to close to
100. Even with the ideal spin injector and collector, the conductance
modulation ratio, defined as the ratio between the maximum and minimum
conductances, decays rapidly and approaches one with the increase of the
channel number. It turns out that the decay is considerably faster when the
Rashba spin-orbit coupling is larger. Effects of the electronic coherence are
also examined in the multi-channel regime and it is found that the coherent
Fabry-Perot-like interference in the multi-channel regime gives rise to a
nested peak structure. For a nonideal spin injector/collector structure, which
consists of a conventional metallic ferromagnet-thin insulator-2DEG
heterostructure, the Rashba-coupling-induced conductance modulation is strongly
affected by large resonance peaks that arise from the electron confinement
effect of the insulators. Finally scattering effects are briefly addressed and
it is found that in the weakly diffusive regime, the positions of the resonance
peaks fluctuate, making the conductance modulation signal sample-dependent.Comment: 18 pages, 15 figure
Topology of Luminous Red Galaxies from the Sloan Digital Sky Survey
We present measurements of the genus topology of luminous red galaxies (LRGs)
from the Sloan Digital Sky Survey (SDSS) Data Release 7 catalog, with
unprecedented statistical significance. To estimate the uncertainties in the
measured genus, we construct 81 mock SDSS LRG surveys along the past light cone
from the Horizon Run 3, one of the largest N-body simulations to date that
evolved 7210^3 particles in a 10815 Mpc/h size box. After carefully modeling
and removing all known systematic effects due to finite pixel size, survey
boundary, radial and angular selection functions, shot noise and galaxy
biasing, we find the observed genus amplitude to reach 272 at 22 Mpc/h
smoothing scale with an uncertainty of 4.2%; the estimated error fully
incorporates cosmic variance. This is the most accurate constraint of the genus
amplitude to date, which significantly improves on our previous results. In
particular, the shape of the genus curve agrees very well with the mean
topology of the SDSS LRG mock surveys in the LCDM universe. However, comparison
with simulations also shows small deviations of the observed genus curve from
the theoretical expectation for Gaussian initial conditions. While these
discrepancies are mainly driven by known systematic effects such as those of
shot noise and redshift-space distortions, they do contain important
cosmological information on the physical effects connected with galaxy
formation, gravitational evolution and primordial non-Gaussianity. We address
here the key role played by systematics on the genus curve, and show how to
accurately correct for their effects to recover the topology of the underlying
matter. In a forthcoming paper, we provide an interpretation of those
deviations in the context of the local model of non-Gaussianity.Comment: 23 pages, 18 figures. APJ Supplement Series 201
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