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)

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.

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

Generation of Bright Two-Color Continuous Variable Entanglement

We present the first measurement of squeezed-state entanglement between the twin beams produced in an Optical Parametric Oscillator (OPO) operating above threshold. Besides the usual squeezing in the intensity difference between the twin beams, we have measured squeezing in the sum of phase quadratures. Our scheme enables us to measure such phase anti-correlations between fields of different frequencies. In the present measurements, wavelengths differ by ~1 nm. Entanglement is demonstrated according to the Duan et al. criterion [Phys. Rev. Lett. 84, 2722 (2000)] $\Delta^2\hat{p}_- +\Delta^2\hat{q}_+=1.47(2)<2$. This experiment opens the way for new potential applications such as the transfer of quantum information between different parts of the electromagnetic spectrum.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let

An infrared view of AGN feedback in a type-2 quasar: the case of the Teacup galaxy

We present near-infrared integral field spectroscopy data obtained with VLT/SINFONI of "the Teacup galaxy". The nuclear K-band (1.95-2.45 micron) spectrum of this radio-quiet type-2 quasar reveals a blueshifted broad component of FWHM~1600-1800 km/s in the hydrogen recombination lines (Pa$\alpha$, Br$\delta$, and Br$\gamma$) and also in the coronal line [Si VI]$\lambda$1.963 micron. Thus the data confirm the presence of the nuclear ionized outflow previously detected in the optical and reveal its coronal counterpart. Both the ionized and coronal nuclear outflows are resolved, with seeing-deconvolved full widths at half maximum of 1.1$\pm$0.1 and 0.9$\pm$0.1 kpc along PA$\sim$72-74 deg. This orientation is almost coincident with the radio axis (PA=77 deg), suggesting that the radio jet could have triggered the nuclear outflow. In the case of the H$_2$ lines we do not require a broad component to reproduce the profiles, but the narrow lines are blueshifted by ~50 km/s on average from the galaxy systemic velocity. This could be an indication of the presence of a nuclear molecular outflow, although the bulk of the H$_2$ emission in the inner ~2 arcsec (~3 kpc) of the galaxy follows a rotation pattern. We find evidence for kinematically disrupted gas (FWHM>250 km/s) at up to 5.6 kpc from the AGN, which can be naturally explained by the action of the outflow. The narrow component of [Si VI] is redshifted with respect to the systemic velocity, unlike any other emission line in the K-band spectrum. This indicates that the region where the coronal lines are produced is not co-spatial with the narrow line region.Comment: 15 pages, 9 figures. Accepted for publication in MNRA

Jet-gas interactions in z~2.5 radio galaxies: evolution of the ultraviolet line and continuum emission with radio morphology

We present an investigation into the nature of the jet-gas interactions in a sample of 10 radio galaxies at 2.3<z<2.9 using deep spectroscopy of the UV line and continuum emission obtained at Keck II and the Very Large Telescope. Kinematically perturbed gas, which we have shown to be within the radio structure in previous publications, is always blueshifted with respect to the kinematically quiescent gas, is usually spatially extended, and is usually detected on both sides of the nucleus. In the three objects from this sample for which we are able to measure line ratios for both the perturbed and quiescent gases, we suggest that the former has a lower ionization state than the latter. We propose that the perturbed gas is part of a jet-induced outflow, with dust obscuring the outflowing gas that lies on the far side of the object. The spatial extent of the blueshifted perturbed gas, typically ~35 kpc, implies that the dust is spatially extended at least on similar spatial scales. We also find interesting interrelationships between UV line, UV continuum and radio continuum properties of this sample.Comment: Accepted for publication in MNRA

Generation of Kerr non-Gaussian motional states of trapped ions

Non-Gaussian states represent a powerful resource for quantum information protocols in the continuous variables regime. Cat states, in particular, have been produced in the motional degree of freedom of trapped ions by controlled displacements dependent on the ionic internal state. An alternative method harnesses the Kerr nonlinearity naturally existent in this kind of system. We present detailed calculations confirming its feasibility for typical experimental conditions. Additionally, this method permits the generation of complex non-Gaussian states with negative Wigner functions. Especially, superpositions of many coherent states are achieved at a fraction of the time necessary to produce the cat state.Comment: 6 pages, 5 figure