Deterministic Dicke state preparation with continuous measurement and control

We characterize the long-time projective behavior of the stochastic master equation describing a continuous, collective spin measurement of an atomic ensemble both analytically and numerically. By adding state based feedback, we show that it is possible to prepare highly entangled Dicke states deterministically.Comment: Additional information is available at http://minty.caltech.edu/Ensemble

Current Challenges in Autonomous Vehicle Development

The field of autonomous vehicles is a rapidly growing one, with significant interest from both government and industry sectors. Autonomous vehicles represent the intersection of artificial intelligence (AI) and robotics, combining decision-making with real-time control. Autonomous vehicles are desired for use in search and rescue, urban reconnaissance, mine detonation, supply convoys, and more. The general adage is to use robots for anything dull, dirty, dangerous or dumb. While a great deal of research has been done on autonomous systems, there are only a handful of fielded examples incorporating machine autonomy beyond the level of teleoperation, especially in outdoor/complex environments. In an attempt to assess and understand the current state of the art in autonomous vehicle development, a few areas where unsolved problems remain became clear. This paper outlines those areas and provides suggestions for the focus of science and technology research. The first step in evaluating the current state of autonomous vehicle development was to develop a definition of autonomy. A number of autonomy level classification systems were reviewed. The resulting working definitions and classification schemes used by the authors are summarized in the opening sections of the paper. The remainder of the report discusses current approaches and challenges in decision-making and real-time control for autonomous vehicles. Suggested research focus areas for near-, mid-, and long-term development are also presented

Getting More from Less in Defined Benefit Plans: Three Levers for a Low-Return World

As global interest rates hover near historic lows, defined benefit pension plan sponsors must grapple with the prospect of lower investment returns. This paper examines three levers that can enhance portfolio outcomes in a low-return world. The levers include: increased contributions; reduced investment costs; and increased portfolio risk. We use portfolio simulations based on a stochastic asset class forecasting model to evaluate each lever according to two criteria—its magnitude of impact and the certainty that this impact will be realized. Our analysis indicates that increased contributions have the greatest and most certain impact. Reduced costs have a more modest, but equally certain impact. Increased risk can deliver a significant impact, but with the least certainty

Tribute to Donald A. Winslow

This article is comprised of a series of tributes to Donald A. Winslow, who was a law professor at the University of Kentucky College of Law

A Compact Early-type Galaxy at z = 0.6 Under a Magnifying Lens: Evidence For Inside-out Growth

We use Keck laser guide star adaptive optics imaging and exploit the magnifying effects of strong gravitational lensing (the effective resolution is FWHM ~ 200 pc) to investigate the sub-kpc scale of an intermediate-redshift (z = 0.63) massive early-type galaxy being lensed by a foreground early-type galaxy; we dub this class of strong gravitational lens systems EELs, e.g., early-type/early-type lenses. We find that the background source is massive (M* = 10^{10.9} M_sun) and compact (r_e = 1.1 kpc), and a two-component fit is required to model accurately the surface brightness distribution, including an extended low-surface-brightness component. This extended component may arise from the evolution of higher-redshift `red nuggets' or may already be in place at z ~ 2 but is unobservable due to cosmological surface brightness dimming.Comment: 5 pages, 4 figures; accepted to MNRA

Bellman equations for optimal feedback control of qubit states

Using results from quantum filtering theory and methods from classical control theory, we derive an optimal control strategy for an open two-level system (a qubit in interaction with the electromagnetic field) controlled by a laser. The aim is to optimally choose the laser's amplitude and phase in order to drive the system into a desired state. The Bellman equations are obtained for the case of diffusive and counting measurements for vacuum field states. A full exact solution of the optimal control problem is given for a system with simpler, linear, dynamics. These linear dynamics can be obtained physically by considering a two-level atom in a strongly driven, heavily damped, optical cavity.Comment: 10 pages, no figures, replaced the simpler model in section

Detection of non-thermal X-ray emission in the lobes and jets of Cygnus A

This article has been published in Monthly Notices of the Royal Astronomical Society © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. 21 pages, 8 figuresWe present a spectral analysis of the lobes and X-ray jets of Cygnus A, using more than 2 Ms of $\textit{Chandra}$ observations. The X-ray jets are misaligned with the radio jets and significantly wider. We detect non-thermal emission components in both lobes and jets. For the eastern lobe and jet, we find 1 keV flux densities of $71_{-10}^{+10}$ nJy and $24_{-4}^{+4}$ nJy, and photon indices of $1.72_{-0.03}^{+0.03}$ and $1.64_{-0.04}^{+0.04}$ respectively. For the western lobe and jet, we find flux densities of $50_{-13}^{+12}$ nJy and $13_{-5}^{+5}$ nJy, and photon indices of $1.97_{-0.10}^{+0.23}$ and $1.86_{-0.12}^{+0.18}$ respectively. Using these results, we modeled the electron energy distributions of the lobes as broken power laws with age breaks. We find that a significant population of non-radiating particles is required to account for the total pressure of the eastern lobe. In the western lobe, no such population is required and the low energy cutoff to the electron distribution there needs to be raised to obtain pressures consistent with observations. This discrepancy is a consequence of the differing X-ray photon indices, which may indicate that the turnover in the inverse-Compton spectrum of the western lobe is at lower energies than in the eastern lobe. We modeled the emission from both jets as inverse-Compton emission. There is a narrow region of parameter space for which the X-ray jet can be a relic of an earlier active phase, although lack of knowledge about the jet's electron distribution and particle content makes the modelling uncertain.Peer reviewedFinal Published versio

Characterizing the entanglement of symmetric many-particle spin-1/2 systems

Analyzing the properties of entanglement in many-particle spin-1/2 systems is generally difficult because the system's Hilbert space grows exponentially with the number of constituent particles, $N$. Fortunately, it is still possible to investigate many-particle entanglement when the state of the system possesses sufficient symmetry. In this paper, we present a practical method for efficiently computing various bipartite entanglement measures for states in the symmetric subspace and perform these calculations for $N\sim 10^3$. By considering all possible bipartite splits, we construct a picture of the multiscale entanglement in large symmetric systems. In particular, we characterize dynamically generated spin-squeezed states by comparing them to known reference states (e.g., GHZ and Dicke states) and new families of states with near-maximal bipartite entropy. We quantify the trade-off between the degree of entanglement and its robustness to particle loss, emphasizing that substantial entanglement need not be fragile.Comment: Updated version reflects changes made in January 200

Chandra detection of the intracluster medium around 3C294 at z=1.786

We present a Chandra observation of the powerful radio galaxy 3C294 showing clear evidence for a surrounding intracluster medium. At a redshift of 1.786 this is the most distant cluster of galaxies yet detected in X-rays. The radio core is detected as a point source, which has a spectrum consistent with a heavily-absorbed power law implying an intrinsic 2-10 keV luminosity of ~10^45 erg/s. A small excess of emission is associated with the southern radio hotspots. The soft, diffuse emission from the intracluster medium is centred on the radio source. It has an hour-glass shape in the N-S direction, extending to radii of at least 100 kpc, well beyond the radio source. The X-ray spectrum of this extended component is fit by a thermal model with temperature ~5 keV, or by gas cooling from above 7 keV at rates of ~400-700 Msolar/yr. The rest-frame 0.3-10 keV luminosity of the cluster is ~4.5x10^44 erg/s. The existence of such a cluster is consistent with a low density universe.Comment: 5 pages, 6 figures, accepted by MNRA