Sensitivity and Robustness of Quantum Spin-1/2 Rings to Parameter Uncertainty

Selective transfer of information between spin-1/2 particles arranged in a ring is achieved by optimizing the transfer fidelity over a readout time window via shaping, externally applied, static bias fields. Such static control fields have properties that clash with the expectations of classical control theory. Previous work has shown that there are cases in which the logarithmic differential sensitivity of the transfer fidelity to uncertainty in coupling strength or spillage of the bias field to adjacent spins is minimized by controllers that produce the best fidelity. Here we expand upon these examples and examine cases of both classical and non-classical behavior of logarithmic sensitivity to parameter uncertainty and robustness as measured by the p function for quantum systems. In particular we examine these properties in an 11-spin ring with a single uncertainty in coupling strength or a single bias spillage

GaBoDS: The Garching-Bonn Deep Survey -- II. Confirmation of EIS cluster candidates by weak gravitational lensing

We report the first confirmation of colour-selected galaxy cluster candidates by means of weak gravitational lensing. Significant lensing signals were identified in the course of the shear-selection programme of dark matter haloes in the Garching-Bonn Deep Survey, which currently covers 20 square degrees of deep, high-quality imaging data on the southern sky. The detection was made in a field that was previously covered by the ESO Imaging Survey (EIS) in 1997. A highly significant shear-selected mass-concentration perfectly coincides with the richest EIS cluster candidate at z~0.2, thus confirming its cluster nature. Several other shear patterns in the field can also be identified with cluster candidates, one of which could possibly be part of a filament at z~0.45.Comment: 4 pages, 4 figures, submitted to A&A Letter

GaBoDS: The Garching-Bonn Deep Survey - III. Lyman-Break Galaxies in the Chandra Deep Field South

We present first results of our search for high-redshift galaxies in deep CCD mosaic images. As a pilot study for a larger survey, very deep images of the Chandra Deep Field South (CDFS), taken withWFI@MPG/ESO2.2m, are used to select large samples of 1070 U-band and 565 B-band dropouts with the Lyman-break method. The data of these Lyman-break galaxies are made public as an electronic table. These objects are good candidates for galaxies at z~3 and z~4 which is supported by their photometric redshifts. The distributions of apparent magnitudes and the clustering properties of the two populations are analysed, and they show good agreement to earlier studies. We see no evolution in the comoving clustering scale length from z~3 to z~4. The techniques presented here will be applied to a much larger sample of U-dropouts from the whole survey in near future.Comment: 11 pages, 11 figures, replaced with version accepted by A&A. Minor changes and tabular appendix with LBG catalogues. Version with full resolution figures available at http://www.astro.uni-bonn.de/~hendrik/2544.pd

Coulombic Energy Transfer and Triple Ionization in Clusters

Using neon and its dimer as a specific example, it is shown that excited Auger decay channels that are electronically stable in the isolated monomer can relax in a cluster by electron emission. The decay mechanism, leading to the formation of a tricationic cluster, is based on an efficient energy-transfer process from the excited, dicationic monomer to a neighbor. The decay is ultrafast and expected to be relevant to numerous physical phenomena involving core holes in clusters and other forms of spatially extended atomic and molecular matter.Comment: 5 pages, 1 figure, to be published in PR

Review of biorthogonal coupled cluster representations for electronic excitation

Single reference coupled-cluster (CC) methods for electronic excitation are based on a biorthogonal representation (bCC) of the (shifted) Hamiltonian in terms of excited CC states, also referred to as correlated excited (CE) states, and an associated set of states biorthogonal to the CE states, the latter being essentially configuration interaction (CI) configurations. The bCC representation generates a non-hermitian secular matrix, the eigenvalues representing excitation energies, while the corresponding spectral intensities are to be derived from both the left and right eigenvectors. Using the perspective of the bCC representation, a systematic and comprehensive analysis of the excited-state CC methods is given, extending and generalizing previous such studies. Here, the essential topics are the truncation error characteristics and the separability properties, the latter being crucial for designing size-consistent approximation schemes. Based on the general order relations for the bCC secular matrix and the (left and right) eigenvector matrices, formulas for the perturbation-theoretical (PT) order of the truncation errors (TEO) are derived for energies, transition moments, and property matrix elements of arbitrary excitation classes and truncation levels. In the analysis of the separability properties of the transition moments, the decisive role of the so-called dual ground state is revealed. Due to the use of CE states the bCC approach can be compared to so-called intermediate state representation (ISR) methods based exclusively on suitably orthonormalized CE states. As the present analysis shows, the bCC approach has decisive advantages over the conventional CI treatment, but also distinctly weaker TEO and separability properties in comparison with a full (and hermitian) ISR method

Constraints on relaxation rates for N-level quantum systems

We study the constraints imposed on the population and phase relaxation rates by the physical requirement of completely positive evolution for open N-level systems. The Lindblad operators that govern the evolution of the system are expressed in terms of observable relaxation rates, explicit formulas for the decoherence rates due to population relaxation are derived, and it is shown that there are additional, non-trivial constraints on the pure dephasing rates for N>2. Explicit experimentally testable inequality constraints for the decoherence rates are derived for three and four-level systems, and the implications of the results are discussed for generic ladder-, Lambda- and V-systems, and transitions between degenerate energy levels.Comment: 10 pages, RevTeX, 4 figures (eps/pdf

A bacterial inflammation sensor regulates c-di-GMP signaling, adhesion, and biofilm formation

The reactive oxygen species produced during inflammation through the neutrophilic respiratory burst play profound roles in combating bacterial pathogens and regulating the microbiota. Among these, the neutrophilic oxidant bleach, hypochlorous acid (HOCl), is the most prevalent and strongest oxidizer and kills bacteria through non-specific oxidation of proteins, lipids, and DNA. Thus, HOCl can be viewed as a host-specific cue that conveys important information about what bacterial physiology and lifestyle programs may be required for successful colonization. Nevertheless, bacteria that colonize animals face a molecular challenge in how to achieve highly selective detection of HOCl due to its reactive and transient nature and chemical similarity to more benign and non-host-specific oxidants like hydrogen peroxide (H2O2). Here, we report that in response to increasing HOCl levels E. coli regulates biofilm production via activation of the diguanylate cyclase DgcZ. We show the molecular mechanism of this activation to be specific oxidation of a conserved cysteine that coordinates the zinc of its regulatory chemoreceptor zinc-binding (CZB) domain, forming a zinc-cysteine redox switch 685-fold more sensitive to oxidation by HOCl over H2O2. Dissection of the signal transduction mechanism through quantum mechanics, molecular dynamics, and biochemical analyses reveal how the cysteine redox state alters the delicate equilibrium of competition for Zn++ between the CZB domain and other zinc binders to relay the presence of HOCl through activating the associated GGDEF domain to catalyze c-di-GMP. We find biofilm formation and HOCl-sensing in vivo to be regulated by the conserved cysteine, and point mutants that mimic oxidized CZB states increase production of the biofilm matrix polymer poly-N-acetylglucosamine and total biofilm. We observe CZB-regulated diguanylate cyclases and chemoreceptors in phyla in which host-associated bacteria are prevalent and are possessed by pathogens that manipulate host inflammation as part of their colonization strategy. A phylogenetic survey of all known CZB sequences shows these domains to be conserved and widespread across diverse phyla, suggesting CZB origin predates the bacterial last universal common ancestor. The ability of bacteria to use CZB protein domains to perceive and thwart the host neutrophilic respiratory burst has implications for understanding the mechanisms of diseases of chronic inflammation and gut dysbiosis

Symmetric Informationally Complete Measurements of Arbitrary Rank

There has been much interest in so-called SIC-POVMs: rank 1 symmetric informationally complete positive operator valued measures. In this paper we discuss the larger class of POVMs which are symmetric and informationally complete but not necessarily rank 1. This class of POVMs is of some independent interest. In particular it includes a POVM which is closely related to the discrete Wigner function. However, it is interesting mainly because of the light it casts on the problem of constructing rank 1 symmetric informationally complete POVMs. In this connection we derive an extremal condition alternative to the one derived by Renes et al.Comment: Contribution to proceedings of International Conference on Quantum Optics, Minsk, 200

High-angular-resolution NIR view of the Orion Bar revealed by Keck/NIRC2

Context. Nearby photo-dissociation regions (PDRs), where the gas and dust are heated by the far-ultraviolet (FUV) irradiation emitted from stars, are ideal templates with which to study the main stellar feedback processes. Aims. With this study, we aim to probe the detailed structures at the interfaces between ionized, atomic, and molecular gas in the Orion Bar. This nearby prototypical strongly irradiated PDR are among the first targets of the James Webb Space Telescope (JWST) within the framework of the PDRs4All Early Release Science program. Methods. We employed the subarcsecond resolution accessible with Keck-II NIRC2 and its adaptive optics system to obtain images of the vibrationally excited line H2 1-0 S(1) at 2.12 μm that are more detailed and complete than ever before. H2 1-0 S(1) traces the dissociation front (DF), and the [FeII] and Brγ lines, at 1.64 and 2.16 μm, respectively, trace the ionization front (IF). The former is a powerful tracer of the FUV radiation field strength and gas density distribution at the PDR edge, while the last two trace the temperature and density distribution from the ionized gas to the PDR. We obtained narrow-band filter images in these key gas line diagnostics over ∼40″ at spatial scales of ∼0.1″ (∼0.0002 pc or ∼40 AU at 414 pc). Results. The Keck/Near Infrared Camera 2 (NIRC2) observations spatially resolve a plethora of irradiated substructures such as ridges, filaments, globules, and proplyds. This portends what JWST should accomplish and how it will complement the highest resolution Atacama Large Millimeter/submillimeter Array (ALMA) maps of the molecular cloud. We observe a remarkable spatial coincidence between the H2 1-0 S(1) vibrational and HCO+ J = 4-3 rotational emission previously obtained with ALMA. This likely indicates the intimate link between these two molecular species and highlights that in high-pressure PDRs, the H/H2 and C+/C/CO transitions zones come closer than in a typical layered structure of a constant density PDR. The H/H2 dissociation front appears as a highly structured region containing substructures with a typical thickness of a few ∼10-3 pc