8,962 research outputs found
Experimental observation of three-color optical quantum correlations
Quantum correlations between bright pump, signal, and idler beams produced by
an optical parametric oscillator, all with different frequencies, are
experimentally demonstrated. We show that the degree of entanglement between
signal and idler fields is improved by using information of pump fluctuations.
This is the first observation of three-color optical quantum correlations.Comment: 3 pages, 3 figure
Multitarget tracking via restless bandit marginal productivity indices and Kalman Filter in discrete time
This paper designs, evaluates, and tests a tractable priority-index policy for scheduling target updates in a discrete-time multitarget tracking model, which aims to be close to optimal relative to a discounted or average performance objective accounting for tracking-error variance and measurement costs. The policy is to be used by a sensor system composed of M phased-array radars coordinated to track the positions of N targets moving according to independent scalar Gauss-Markov linear dynamics, which therefore allows for the use of the Kalman Filter for track estimation. The paper exploits the natural problem formulation as a multiarmed restless bandit problem (MARBP) with real-state projects subject to deterministic dynamics by deploying Whittle's (1988) index policy for the MARBP. The challenging issues of indexability (existence of the index) and index evaluation are resolved by applying a method recently introduced by the first author for the analysis of real-state restless bandits. Computational results are reported demonstrating the tractability of index evaluation, the substantial performance gains that the Whittle's marginal productivity (MP) index policy achieves against myopic policies advocated in previous work and the resulting index policies suboptimality gaps. Further, a preliminary small scale computational study shows that the (MP) index policy exhibits a nearly optimal behavior as the number of distinct objective targets grows with the number of radars per target constant.Multitarget tracking, Sensor management, Phased array radar, Radar scheduling, Scaled track-error variance (STEV), Kalman Filter, Index policy, Marginal productivity (MP) index, Real-state multiarmed restless bandit problems (MARBP)
The quest for three-color entanglement: experimental investigation of new multipartite quantum correlations
We experimentally investigate quadrature correlations between pump, signal,
and idler fields in an above-threshold optical parametric oscillator. We
observe new quantum correlations among the pump and signal or idler beams, as
well as among the pump and a combined quadrature of signal and idler beams. A
further investigation of unforeseen classical noise observed in this system is
presented, which hinders the observation of the recently predicted tripartite
entanglement. In spite of this noise, current results approach the limit
required to demonstrate three-color entanglement.Comment: 10 pages, 5 figures, submitted to Opt. Expres
Direct Production of Tripartite Pump-Signal-Idler Entanglement in the Above-Threshold Optical Parametric Oscillator
We calculate the quantum correlations existing among the three output fields
(pump, signal, and idler) of a triply resonant non-degenerate Optical
Parametric Oscillator operating above threshold. By applying the standard
criteria [P. van Loock and A. Furusawa, Phys. Rev. A 67, 052315 (2003)], we
show that strong tripartite continuous-variable entanglement is present in this
well-known and simple system. Furthermore, since the entanglement is generated
directly from a nonlinear process, the three entangled fields can have very
different frequencies, opening the way for multicolored quantum information
networks.Comment: 4 pages, 3 figure
Low-Ionization Emission Regions in Quasars: Gas Properties Probed with Broad O I and Ca II Lines
We have compiled the emission-line fluxes of O I 8446, O I 11287, and the
near-IR Ca II triplet (8579) observed in 11 quasars. These lines are considered
to emerge from the same gas as do the Fe II lines in the low-ionized portion of
the broad emission line region (BELR). The compiled quasars are distributed
over wide ranges of redshift (0.06 < z < 1.08) and of luminosity (-29.8 < M_B <
-22.1), thus representing a useful sample to investigate the line-emitting gas
properties in various quasar environments. The measured line strengths and
velocities, as functions of the quasar properties, are analyzed using
photoionization model calculations. We found that the flux ratio between Ca II
and O I 8446 is hardly dependent on the redshift or luminosity, indicating
similar gas density in the emission region from quasar to quasar. On the other
hand, a scatter of the O I 11287/8446 ratios appears to imply the diversity of
the ionization parameter. These facts invoke a picture of the line-emitting
gases in quasars that have similar densities and are located at regions exposed
to various ionizing radiation fluxes. The observed O I line widths are found to
be remarkably similar over more than 3 orders of magnitude in luminosity, which
indicates a kinematically determined location of the emission region and is in
clear contrast to the well-studied case of H I lines. We also argue about the
dust presence in the emission region since the region is suggested to be
located near the dust sublimation point at the outer edge of the BELR.Comment: Accepted for publication in ApJ; minor rewordings mad
Geometric phases under the presence of a composite environment
We compute the geometric phase for a spin-1/2 particle under the presence of
a composite environment, composed of an external bath (modeled by an infinite
set of harmonic oscillators) and another spin-1/2 particle. We consider both
cases: an initial entanglement between the spin-1/2 particles and an initial
product state in order to see if the initial entanglement has an enhancement
effect on the geometric phase of one of the spins. We follow the nonunitary
evolution of the reduced density matrix and evaluate the geometric phase for a
single two-level system. We also show that the initial entanglement enhances
the sturdiness of the geometric phase under the presence of an external
composite environment.Comment: 10 pages, 12 figures. Version to appear in Phys. Rev.
Integral Field Spectroscopy of two radio galaxies at z~2.3
In this article we study the morphology, kinematics and ionization properties
of the giant ionized gas nebulae surrounding two high redshift radio galaxies,
4C40.36 (z=2.27) and 4C48.48 (z=2.34).}{Integral Field Spectroscopy
observations were taken using the PPAK bundle of the PMAS spectrograph, mounted
on the 3.5m on the Calar Alto Observatory, in order to cover a field-of-view of
64" X 72" centered in each radio galaxy. The observations spanned over 5
nights, using two different spectral resolutions (with FWHM~4 AA and ~8 AA
respectively), covering the optical wavelength range from ~3700 AA to ~7100 AA,
which corresponds to the rest-frame ultraviolet range from ~1100 AA to ~2000 AA
>. Various emission lines are detected within this wavelength range, including
Lyalpha (1216 AA), NV (1240 AA), CIV (1549 AA), HeII (1640 AA), OIII] (1663 AA)
and CIII] (1909\AA). The dataset was used to derive the spatial distribution of
the flux intensity of each of these lines and the gas kinematics. The
properties of the emission lines in the nuclear regions were studied in
detail.In agreement with previous studies, we find that both objects are
embedded in a large ionized gas nebula, where Ly alpha emission is extended
across ~100 kpc or more. The CIV and HeII emission lines are also spatially
extended. The nebulae are generally aligned with the radio axis, although we
detect emission far from it. In 4C+48.48, there is a band of low Ly-alpha/CIV
running perpendicular to the radio axis, at the location of the active nucleus.
This feature might be the observational signature of an edge-on disk of neutral
gas. The kinematics of both nebulae are inconsistent with stable rotation,
although they are not inconsistent with infall or outflow.Comment: 14 pages, 5 figures, accepted for publishing in Astronomy &
Astrophysic
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