634 research outputs found
Impulsive Spin-Motion Entanglement for Fast Quantum Computation and Sensing
We perform entanglement of spin and motional degrees of freedom of a single,
ground-state trapped ion through the application of a ps laser pulse. The
duration of the interaction is significantly shorter than both the motional
timescale ( s) and spin precession timescale (
ns), demonstrating that neither sets a fundamental speed limit on this
operation for quantum information processing. Entanglement is demonstrated
through the collapse and revival of spin coherence as the spin components of
the wavefunction separate and recombine in phase space. We infer the fidelity
of these single qubit operations to be .Comment: 5 pages, 4 figure
Modeling the transmission and thermal emission in a pupil image behind the Keck II adaptive optics system
The design and performance of astronomical instruments depend critically on the total system throughput as well as the background emission from the sky and instrumental sources. In designing a pupil stop for background- limited imaging, one seeks to balance throughput and background rejection to optimize measurement signal-to-noise ratios. Many sources affect transmission and emission in infrared imaging behind the Keck Observatory’s adaptive optics systems, such as telescope segments, segment gaps, secondary support structure, and AO bench optics. Here we describe an experiment, using the pupil-viewing mode of NIRC2, to image the pupil plane as a function of wavelength. We are developing an empirical model of throughput and background emission as a function of position in the pupil plane. This model will be used in part to inform the optimal design of cold pupils in future instruments, such as the new imaging camera for OSIRIS
The Relational Bottleneck as an Inductive Bias for Efficient Abstraction
A central challenge for cognitive science is to explain how abstract concepts
are acquired from limited experience. This effort has often been framed in
terms of a dichotomy between empiricist and nativist approaches, most recently
embodied by debates concerning deep neural networks and symbolic cognitive
models. Here, we highlight a recently emerging line of work that suggests a
novel reconciliation of these approaches, by exploiting an inductive bias that
we term the relational bottleneck. We review a family of models that employ
this approach to induce abstractions in a data-efficient manner, emphasizing
their potential as candidate models for the acquisition of abstract concepts in
the human mind and brain
Modeling instrumental field-dependent aberrations in the NIRC2 instrument on the Keck II telescope
We present a model of field-dependent aberrations arising in the NIRC2 instrument on the W. M. Keck II telescope. We use high signal-to-noise phase diversity data employing a source in the Nasmyth focal plane to construct a model of the optical path difference as a function of field position and wavelength. With a differential wavefront error of up to 190 nm, this effect is one of the main sources of astrometric and photometric measurement uncertainties. Our tests of temporal stability show sufficient reliability for our measurements over a 20-month period at the field extrema. Additionally, while chromaticity exists, applying a correction for field-dependent aberrations provides overall improvement compared to the existing aberrations present across the field of view
Clergy work-related satisfactions in parochial ministry: the influence of personality and churchmanship
The aim of this study was to test several hypotheses that clergy work-related satisfaction could be better explained by a multidimensional rather than a unidimensional model. A sample of 1071 male stipendiary parochial clergy in the Church of England completed the Clergy Role Inventory, together with the short-form Revised Eysenck Personality Questionnaire. Factor analysis of the Clergy Role Inventory identified five separate clergy roles: Religious Instruction, Administration, Statutory Duties (conducting marriages and funerals), Pastoral Care, and Role Extension (including extra-parochial activities). Respondents also provided an indication of their predispositions on the catholic-evangelical and liberal-conservative dimensions. The significant associations of the satisfactions derived from each of the roles with the demographic, personality, and churchmanship variables were numerous, varied, and, with few exceptions, small in magnitude. Separate hierarchical regressions for each of the five roles indicated that the proportion of total variance explained by churchmanship was, in general, at least as great as that explained by personality, and was greater for three roles: Religious Instruction, Statutory Duties, and Role Extension. It was concluded that clergy satisfactions derived from different roles are not uniform and that churchmanship is at least as important as personality in accounting for clergy work satisfaction
String-Inspired Higher-Curvature Terms and the Randall-Sundrum Scenario
We consider the O(a') string effective action, with Gauss-Bonnet
curvature-squared and fourth-order dilaton-derivative terms, which is derived
by a matching procedure with string amplitudes in five space-time dimensions.
We show that a non-factorizable metric of the Randall-Sundrum (RS) type, with
four-dimensional conformal factor Exp(-2 k|z|), can be a solution of the
pertinent equations of motion. The parameter k is found proportional to the
string coupling g_s and thus the solution appears to be non-perturbative. It is
crucial that the Gauss-Bonnet combination has the right (positive in our
conventions) sign, relative to the Einstein term, which is the case
necessitated by compatibility with string (tree) amplitude computations. We
study the general solution for the dilaton and metric functions, and thus
construct the appropriate phase-space diagram in the solution space. In the
case of an anti-de-Sitter bulk, we demonstrate that there exists a continuous
interpolation between (part of) the RS solution at z=infinity and an
(integrable) naked singularity at z=0. This implies the dynamical formation of
domain walls (separated by an infinite distance), thus restricting the physical
bulk space time to the positive z axis. Some brief comments on the possibility
of fine-tuning the four-dimensional cosmological constant to zero are also
presented.Comment: 28 pages Latex, three eps figures incorporated, minor change
String Theory and Inflation
String theory abounds with light scalar fields (the dilaton and various
moduli) which create a host of observational problems, and notably some serious
cosmological difficulties similar to the ones associated with the Polonyi field
in the earliest versions of spontaneously broken supergravity. We show that all
these problems are naturally avoided if a recently introduced mechanism for
fixing the vacuum expectation values of the dilaton and/or moduli is at work.
We study both the classical evolution and the quantum fluctuations of such
scalar fields during a primordial inflationary era and find that the results
are naturally compatible with observational facts. In this model, dilatons or
moduli within a very wide range of masses (which includes the SUSY-breaking
favored 1 TeV value and extends up to the Planck scale) qualify to define a
novel type of essentially stable ultra-weakly interacting massive particles
able to provide enough mass density to close the universeComment: 25 page
A population of dust-enshrouded objects orbiting the Galactic black hole
The central 0.1 parsecs of the Milky Way host a supermassive black hole
identified with the position of the radio and infrared source Sagittarius A*, a
cluster of young, massive stars (the S stars) and various gaseous features.
Recently, two unusual objects have been found to be closely orbiting
Sagittarius A*: the so-called G sources, G1 and G2. These objects are
unresolved (having a size of the order of 100 astronomical units, except at
periapse, where the tidal interaction with the black hole stretches them along
the orbit) and they show both thermal dust emission and line emission from
ionized gas. G1 and G2 have generated attention because they appear to be
tidally interacting with the supermassive Galactic black hole, possibly
enhancing its accretion activity. No broad consensus has yet been reached
concerning their nature: the G objects show the characteristics of gas and dust
clouds but display the dynamical properties of stellar-mass objects. Here we
report observations of four additional G objects, all lying within 0.04 parsecs
of the black hole and forming a class that is probably unique to this
environment. The widely varying orbits derived for the six G objects
demonstrate that they were commonly but separately formed
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