Coherent Error Suppression in Multi-Qubit Entangling Gates

We demonstrate a simple pulse shaping technique designed to improve the fidelity of spin-dependent force operations commonly used to implement entangling gates in trapped-ion systems. This extension of the M{\o}lmer-S{\o}rensen gate can theoretically suppress the effects of certain frequency and timing errors to any desired order and is demonstrated through Walsh modulation of a two-qubit entangling gate on trapped atomic ions. The technique is applicable to any system of qubits coupled through collective harmonic oscillator modes

Vortex Lock-In Deep in the Bose Glass

We use a Bi gaussmeter of micron dimensions to explore the magnetic field dependence of the magnetization relaxation rate and the critical current down to millikelvin temperatures in untwinned single crystals of YBa_2Cu_3O_(7-δ) with columnar defects. The response separates into three regimes as a function of the ratio of vortex density to columnar defect density B/B_φ: enhancements in both critical current and quantum creep in the dilute limit, vanishing magnetization relaxation at the matching density (the proposed "Mott insulator'' phase line), and the emergence of temperature-dependent vortex motion for B≫B_φ

Local probe of vortex pinning energies in the Bose glass

Columnar defects provide strong pinning centers for vortices in high-T_c superconductors, increasing global critical currents. Using a magnetometer array of micron dimensions, we characterize the local held profiles in untwinned single crystals of YBa_2Cu_3O_(7-δ) with equivalent columnar defect densities B_φ. We find that the critical current is large only where the internal magnetic field BB _ φ, the critical current is sharply reduced. We model both local and global critical current measurements by generalizing the Bean picture to the case of irradiated high-T_c superconductors

“We thought you were undercover, here to inspect us” – Some of the challenges of ethnographic fieldwork in schools

This paper provides an insight into the challenges associated with conducting ethnographic fieldwork in a primary school and a secondary school in South Wales. Drawing on personal reflections and experiences, it provides an account of the lessons learnt. Themes include gaining access, role selection, establishing trust, developing relationships and role conflict. More specifically, the differences associated with conducting research in a primary and secondary school are identified, whilst highlighting the fragile nature of pupil-centred research

Analyses of Sweet Receptor Gene (Tas1r2) and Preference for Sweet Stimuli in Species of Carnivora

The extent to which taste receptor specificity correlates with, or even predicts, diet choice is not known. We recently reported that the insensitivity to sweeteners shown by species of Felidae can be explained by their lacking of a functional Tas1r2 gene. To broaden our understanding of the relationship between the structure of the sweet receptors and preference for sugars and artificial sweeteners, we measured responses to 12 sweeteners in 6 species of Carnivora and sequenced the coding regions of Tas1r2 in these same or closely related species. The lion showed no preference for any of the 12 sweet compounds tested, and it possesses the pseudogenized Tas1r2. All other species preferred some of the natural sugars, and their Tas1r2 sequences, having complete open reading frames, predict functional sweet receptors. In addition to preferring natural sugars, the lesser panda also preferred 3 (neotame, sucralose, and aspartame) of the 6 artificial sweeteners. Heretofore, it had been reported that among vertebrates, only Old World simians could taste aspartame. The observation that the lesser panda highly preferred aspartame could be an example of evolutionary convergence in the identification of sweet stimul

A Preliminary Study Investigating Maternal Neurocognitive Mechanisms Underlying a Child-Supportive Parenting Intervention

Although interventions that promote child-supportive parenting for children have been shown to positively impact caregiving behaviors as well as child behavioral and neurobiological functioning, less is known about which aspects of maternal brain functioning are affected by such interventions. In the present study, we conducted a preliminary evaluation of the impact of the Filming Interactions to Nurture Development (FIND) video coaching program on mothers with at least one child age four or younger. We employed a waitlist control design with pre-post data. Compared to mothers in the control condition (n = 16), mothers who received FIND (n = 16) showed changes in neural measures of inhibitory control and behavioral measures of parenting self-evaluation during a series of functional neuroimaging tasks. Specifically, we found a group by time interaction in clusters in the left inferior frontal gyrus (IFG) and insula for the Correct Stop > Correct Go contrast of the stop signal task (SST), where FIND increased brain activity associated with inhibitory control compared to mothers in the control condition; and FIND increased mothers’ endorsement of child-supportive parenting traits in the parenting self-evaluation task (PSET). Exploratory moderators, study limitations, and the implications of these findings for strength-based parenting programs are discussed

Reducing sequencing complexity in dynamical quantum error suppression by Walsh modulation

We study dynamical error suppression from the perspective of reducing sequencing complexity, in order to facilitate efficient semi-autonomous quantum-coherent systems. With this aim, we focus on digital sequences where all interpulse time periods are integer multiples of a minimum clock period and compatibility with simple digital classical control circuitry is intrinsic, using so-called em Walsh functions as a general mathematical framework. The Walsh functions are an orthonormal set of basis functions which may be associated directly with the control propagator for a digital modulation scheme, and dynamical decoupling (DD) sequences can be derived from the locations of digital transitions therein. We characterize the suite of the resulting Walsh dynamical decoupling (WDD) sequences, and identify the number of periodic square-wave (Rademacher) functions required to generate a Walsh function as the key determinant of the error-suppressing features of the relevant WDD sequence. WDD forms a unifying theoretical framework as it includes a large variety of well-known and novel DD sequences, providing significant flexibility and performance benefits relative to basic quasi-periodic design. We also show how Walsh modulation may be employed for the protection of certain nontrivial logic gates, providing an implementation of a dynamically corrected gate. Based on these insights we identify Walsh modulation as a digital-efficient approach for physical-layer error suppression.Comment: 15 pages, 3 figure

The Discovery of the Most Metal-Rich White Dwarf: Composition of a Tidally Disrupted Extrasolar Dwarf Planet

Cool white dwarf stars are usually found to have an outer atmosphere that is practically pure in hydrogen or helium. However, a small fraction have traces of heavy elements that must originate from the accretion of extrinsic material, most probably circumstellar matter. Upon examining thousands of Sloan Digital Sky Survey spectra, we discovered that the helium-atmosphere white dwarf SDSS J073842.56+183509.6 shows the most severe metal pollution ever seen in the outermost layers of such stars. We present here a quantitative analysis of this exciting star by combining high S/N follow-up spectroscopic and photometric observations with model atmospheres and evolutionary models. We determine the global structural properties of our target star, as well as the abundances of the most significant pollutants in its atmosphere, i.e., H, O, Na, Mg, Si, Ca, and Fe. The relative abundances of these elements imply that the source of the accreted material has a composition similar to that of Bulk Earth. We also report the signature of a circumstellar disk revealed through a large infrared excess in JHK photometry. Combined with our inferred estimate of the mass of the accreted material, this strongly suggests that we are witnessing the remains of a tidally disrupted extrasolar body that was as large as Ceres.Comment: 7 pages in emulateapj, 5 figures, accepted for publication in Ap

An asteroseismic test of diffusion theory in white dwarfs

The helium-atmosphere (DB) white dwarfs are commonly thought to be the descendants of the hotter PG1159 stars, which initially have uniform He/C/O atmospheres. In this evolutionary scenario, diffusion builds a pure He surface layer which gradually thickens as the star cools. In the temperature range of the pulsating DB white dwarfs (T_eff ~ 25,000 K) this transformation is still taking place, allowing asteroseismic tests of the theory. We have obtained dual-site observations of the pulsating DB star CBS114, to complement existing observations of the slightly cooler star GD358. We recover the 7 independent pulsation modes that were previously known, and we discover 4 new ones to provide additional constraints on the models. We perform objective global fitting of our updated double-layered envelope models to both sets of observations, leading to determinations of the envelope masses and pure He surface layers that qualitatively agree with the expectations of diffusion theory. These results provide new asteroseismic evidence supporting one of the central assumptions of spectral evolution theory, linking the DB white dwarfs to PG1159 stars.Comment: 7 pages, 3 figures, 3 tables, accepted for publication in A&