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  • Springer Nature  (10)
  • American Physical Society (APS)  (6)
  • American Association for the Advancement of Science  (5)
  • Oxford University Press  (4)
  • 2010-2014  (20)
  • 1995-1999  (5)
  • 1
    Publication Date: 2012-05-12
    Description: Author(s): Wayne M. Witzel, Rajib Rahman, and Malcolm S. Carroll We theoretically study the nuclear spin induced decoherence of a quantum dot in Si that is confined at a SiGe interface. We calculate decoherence time dependence on 73 Ge in the barrier layer to evaluate the importance of Ge as well as Si enrichment for long decoherence times. We use atomistic tight-... [Phys. Rev. B 85, 205312] Published Fri May 11, 2012
    Keywords: Semiconductors II: surfaces, interfaces, microstructures, and related topics
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
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  • 2
    Publication Date: 2012-05-19
    Description: Author(s): Matthew D. Grace, Jason M. Dominy, Wayne M. Witzel, and Malcolm S. Carroll Constructing high-fidelity control fields that are robust to control, system, and/or surrounding environment uncertainties is a crucial objective for quantum information processing. Using the two-state Landau-Zener model for illustrative simulations of a controlled qubit, we generate optimal control... [Phys. Rev. A 85, 052313] Published Fri May 18, 2012
    Keywords: Quantum information
    Print ISSN: 1050-2947
    Electronic ISSN: 1094-1622
    Topics: Physics
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  • 3
    Publication Date: 2012-01-06
    Description: Author(s): Matthew R. Sears and Wayne M. Saslow [Phys. Rev. B 85, 014404] Published Thu Jan 05, 2012
    Keywords: Magnetism
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
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  • 4
    Publication Date: 2012-01-31
    Description: Author(s): Matthew R. Sears and Wayne M. Saslow Recent spin-Seebeck experiments on thin ferromagnetic films apply a temperature difference Δ T x along the length x and measure a (transverse) voltage difference Δ V y along the width y . The connection between these involves: (1) thermal equilibration between sample and substrate, (2) spin currents alon... [Phys. Rev. B 85, 035446] Published Mon Jan 30, 2012
    Keywords: Surface physics, nanoscale physics, low-dimensional systems
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
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  • 5
    Publication Date: 2014-09-26
    Description: Author(s): Wayne M. Witzel, Kevin Young, and Sankar Das Sarma We present a cluster expansion method for approximating quantum spin-bath dynamics in terms of a classical Gaussian stochastic process. The cluster expansion produces the two-point correlation function of the approximate classical bath, permitting rapid evaluation of noise-mitigating quantum control... [Phys. Rev. B 90, 115431] Published Thu Sep 25, 2014
    Keywords: Surface physics, nanoscale physics, low-dimensional systems
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
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  • 6
    Publication Date: 2014-12-02
    Description: Author(s): Tomohiro Taniguchi and Wayne M. Saslow Based on spin-dependent transport theory and thermodynamics, we develop a generalized theory of the Joule heating in the presence of a spin current. Along with the conventional Joule heating consisting of an electric current and electrochemical potential, it is found that the spin current and spin a... [Phys. Rev. B 90, 214407] Published Mon Dec 01, 2014
    Keywords: Magnetism
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
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  • 7
    Publication Date: 2014-04-14
    Description: The mechanistic basis of regulatory variation and the prevailing evolutionary forces shaping that variation are known to differ between sexes and between chromosomes. Regulatory variation of gene expression can be due to functional changes within a gene itself ( cis ) or in other genes elsewhere in the genome ( trans ). The evolutionary properties of cis mutations are expected to differ from mutations affecting gene expression in trans . We analyze allele-specific expression across a set of X substitution lines in intact adult Drosophila simulans to evaluate whether regulatory variation differs for cis and trans , for males and females, and for X-linked and autosomal genes. Regulatory variation is common (56% of genes), and patterns of variation within D. simulans are consistent with previous observations in Drosophila that there is more cis than trans variation within species (47% vs. 25%, respectively). The relationship between sex-bias and sex-limited variation is remarkably consistent across sexes. However, there are differences between cis and trans effects: cis variants show evidence of purifying selection in the sex toward which expression is biased, while trans variants do not. For female-biased genes, the X is depleted for trans variation in a manner consistent with a female-dominated selection regime on the X. Surprisingly, there is no evidence for depletion of trans variation for male-biased genes on X. This is evidence for regulatory feminization of the X, trans -acting factors controlling male-biased genes are more likely to be found on the autosomes than those controlling female-biased genes.
    Electronic ISSN: 1759-6653
    Topics: Biology
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  • 8
    Publication Date: 2013-01-24
    Description: Nature Materials 12, 103 (2013). doi:10.1038/nmat3499 Authors: Gavin W. Morley, Petra Lueders, M. Hamed Mohammady, Setrak J. Balian, Gabriel Aeppli, Christopher W. M. Kay, Wayne M. Witzel, Gunnar Jeschke & Tania S. Monteiro Pulsed magnetic resonance allows the quantum state of electronic and nuclear spins to be controlled on the timescale of nanoseconds and microseconds respectively. The time required to flip dilute spins is orders of magnitude shorter than their coherence times, leading to several schemes for quantum information processing with spin qubits. Instead, we investigate ‘hybrid nuclear–electronic’ qubits consisting of near 50:50 superpositions of the electronic and nuclear spin states. Using bismuth-doped silicon, we demonstrate quantum control over these states in 32 ns, which is orders of magnitude faster than previous experiments using pure nuclear states. The coherence times of up to 4 ms are five orders of magnitude longer than the manipulation times, and are limited only by naturally occurring 29Si nuclear spin impurities. We find a quantitative agreement between our experiments and an analytical theory for the resonance positions, as well as their relative intensities and Rabi oscillation frequencies. These results bring spins in a solid material a step closer to research on ion-trap qubits.
    Print ISSN: 1476-1122
    Electronic ISSN: 1476-4660
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 9
    Publication Date: 2013-01-06
    Description: We explore the evolutionary origins of dosage compensation (DC) in sex chromosomes in the context of metabolic control theory. We consider first the cost of gene loss (hemizygosity) per se in reducing flux, and examine two relationships between flux and fitness (linear and Gaussian) to calculate a fitness cost of hemizygosity. Recognizing that new sex chromosomes are derived from autosomes, we also calculate the cost of unmasking deleterious mutations segregating on the nascent sex chromosomes as loci become hemizygous. The importance of deleterious mutations to the fitness cost of hemizygosity depends on their frequency, and on the relative costs of halving gene dose for wild-type alleles. We then consider the evolution of DC in response to gene loss, and include a cost of overexpression (i.e., DC such that expression exceeds the wild-type homozygote). Even with costs to excess flux, hypomorphic mutations can cause the optimal level of DC to be higher than 2-fold when the absolute cost of hemizygosity is small. Finally, we propose a three-step model of DC evolution: 1) once recombination ceases and the Y begins to deteriorate, genes from longer metabolic pathways should be lost first, as halving these genes does not drastically reduce flux or, thereby, fitness; 2) both the cost of hemizygosity and the presence of hypomorphic mutations will drive an increase in expression, that is, DC; 3) existing DC will now permit loss of genes in short pathways.
    Electronic ISSN: 1759-6653
    Topics: Biology
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  • 10
    Publication Date: 2013-03-05
    Description: Recently, magnons, which are quasiparticles describing the collective motion of spins, were found to undergo Bose-Einstein condensation (BEC) at room temperature in films of Yttrium Iron Garnet (YIG). Unlike other quasiparticle BEC systems, this system has a spectrum with two degenerate minima, which makes it possible for the system to have two condensates in momentum space. Recent Brillouin Light Scattering studies for a microwave-pumped YIG film of thickness d = 5 μm and field H = 1 kOe find a low-contrast interference pattern at the characteristic wavevector Q of the magnon energy minimum. In this report, we show that this modulation pattern can be quantitatively explained as due to unequal but coherent Bose-Einstein condensation of magnons into the two energy minima. Our theory predicts a transition from a high-contrast symmetric state to a low-contrast non-symmetric state on varying the d and H, and a new type of collective oscillation. Scientific Reports 3 doi: 10.1038/srep01372
    Electronic ISSN: 2045-2322
    Topics: Natural Sciences in General
    Published by Springer Nature
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