Geometric Quantum Computation

We describe in detail a general strategy for implementing a conditional geometric phase between two spins. Combined with single-spin operations, this simple operation is a universal gate for quantum computation, in that any unitary transformation can be implemented with arbitrary precision using only single-spin operations and conditional phase shifts. Thus quantum geometrical phases can form the basis of any quantum computation. Moreover, as the induced conditional phase depends only on the geometry of the paths executed by the spins it is resilient to certain types of errors and offers the potential of a naturally fault-tolerant way of performing quantum computation.Comment: 15 pages, LaTeX, uses cite, eepic, epsfig, graphicx and amsfonts. Accepted by J. Mod. Op

Associations between observed temperament in preschoolers and parent psychopathology

Parent history of psychopathology is an established marker of children\u27s own risk for later disorder and can therefore be used as a means of validating other risks, such as child temperament. While associations between children\u27s temperament and parent psychopathology have been reported, few studies have used observational measures of child temperament or examined trait interactions, particularly between children\u27s affective and regulatory traits such as effortful control (EC). In this bottom-up family study of 968 three-year-olds and their parents, we examined interactions between preschoolers\u27 observed positive and negative affectivity (NA) and EC as predictors of a known marker of psychopathology risk: parent history of disorder. Children with lower positive affectivity had an increased probability of paternal depression history in the context of higher child NA. In addition, children with lower EC and higher NA had an increased probability of maternal anxiety. Findings shed new light on the main effects and interactions that account for associations between child temperament and parent history of disorder, one of the best-established markers of an individual\u27s own risk for future disorder, implicating reactive and regulatory traits that merit special consideration in future longitudinal work. Copyright © 2017 John Wiley & Sons, Ltd

Single or Double Degenerate Progenitors? Searching for Shock Emission in the SDSS-II Type Ia Supernovae

From the set of nearly 500 spectroscopically confirmed type~Ia supernovae and around 10,000 unconfirmed candidates from SDSS-II, we select a subset of 108 confirmed SNe Ia with well-observed early-time light curves to search for signatures from shock interaction of the supernova with a companion star. No evidence for shock emission is seen; however, the cadence and photometric noise could hide a weak shock signal. We simulate shocked light curves using SN Ia templates and a simple, Gaussian shock model to emulate the noise properties of the SDSS-II sample and estimate the detectability of the shock interaction signal as a function of shock amplitude, shock width, and shock fraction. We find no direct evidence for shock interaction in the rest-frame $B$-band, but place an upper limit on the shock amplitude at 9% of supernova peak flux ($M_B > -16.6$ mag). If the single degenerate channel dominates type~Ia progenitors, this result constrains the companion stars to be less than about 6 $M_{\odot}$ on the main sequence, and strongly disfavors red giant companions.Comment: 28 pages, 3 figure

Eddington-Limited Accretion in z~2 WISE-selected Hot, Dust-Obscured Galaxies

Hot, Dust-Obscured Galaxies, or "Hot DOGs", are a rare, dusty, hyperluminous galaxy population discovered by the WISE mission. Predominantly at redshifts 2-3, they include the most luminous known galaxies in the universe. Their high luminosities likely come from accretion onto highly obscured super massive black holes (SMBHs). We have conducted a pilot survey to measure the SMBH masses of five z~2 Hot DOGs via broad H_alpha emission lines, using Keck/MOSFIRE and Gemini/FLAMINGOS-2. We detect broad H_alpha emission in all five Hot DOGs. We find substantial corresponding SMBH masses for these Hot DOGs (~ 10^{9} M_sun), and their derived Eddington ratios are close to unity. These z~2 Hot DOGs are the most luminous AGNs at given BH masses, suggesting they are accreting at the maximum rates for their BHs. A similar property is found for known z~6 quasars. Our results are consistent with scenarios in which Hot DOGs represent a transitional, high-accretion phase between obscured and unobscured quasars. Hot DOGs may mark a special evolutionary stage before the red quasar and optical quasar phases, and they may be present at other cosmic epochs.Comment: 15 pages, 9 figures. Accepted by Ap

Theory of Spin Fluctuations in Striped Phases of Doped Antiferromagnetic Cuprates

We study the properties of generalized striped phases of doped cuprate planar quantum antiferromagnets. We invoke an effective, spatially anisotropic, non-linear sigma model in two space dimensions. Our theoretical predictions are in quantitative agreement with recent experiments in La_{2-x}Sr_xCuO_4 with $0 \leq x \leq 0.018$. We focus on (i) the magnetic correlation length, (ii) the staggered magnetization at $T=0$ and (iii) the N\'eel temperature, as functions of doping, using parameters determined previously and independently for this system. These results support the proposal that the low doping (antiferromagnetic) phase of the cuprates has a striped configuration.Comment: 4 pages, Revtex. To appear in the Proceedings of the International Conference "Stripes, Lattice Instabilities and High Tc Superconductivity", (Rome, Dec. 1996

The role of brain-derived neurotrophic factor genotype, parental depression, and relationship discord in predicting early-emerging negative emotionality

The brain-derived neurotrophic factor (BDNF) gene is a plausible candidate for early-emerging negative emotionality (NE), and evidence suggests that the effects of this gene may be especially salient in the context of familial risk for child maladjustment. We therefore examined whether the single-nucleotide polymorphism producing a valine-to-methionine substitution at codon 66 (val66met) of the BDNF gene was associated with childhood NE, in the context of parental depression and relationship discord. A sample of 413 three-year-old children was assessed for NE using standardized laboratory measures. The children\u27s parents completed clinical interviews as well as a measure of marital satisfaction. Children with at least one BDNF methionine (met) allele exhibited elevated NE when a parent had a history of depressive disorder or when relationship discord was reported by a parent. In contrast, this allele was associated with especially low NE when parental depression was absent and when the parental relationship was not discordant. Our findings suggest that the BDNF met allele confers increased child sensitivity to both positive and negative familial influences. © The Author(s) 2010