Faculty Publications: October, 2014

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Title:
Femtosecond laser direct writing of monocrystalline hexagonal silver prisms
Authors:
Vora, Kevin; Kang, SeungYeon; Moebius, Michael; Mazur, Eric
Publication:
Applied Physics Letters, Volume 105, Issue 14, id.141114 (ApPhL Homepage)
Publication Date:
10/2014
Origin:
AIP
Abstract Copyright:
2014: AIP Publishing LLC
DOI:
10.1063/1.4897545
Bibliographic Code:
2014ApPhL.105n1114V

Abstract

Bottom-up growth methods and top-down patterning techniques are both used to fabricate metal nanostructures, each with a distinct advantage: One creates crystalline structures and the other offers precise positioning. Here, we present a technique that localizes the growth of metal crystals to the focal volume of a laser beam, combining advantages from both approaches. We report the fabrication of silver nanoprisms---hexagonal nanoscale silver crystals---through irradiation with focused femtosecond laser pulses. The growth of these nanoprisms is due to a nonlinear optical interaction between femtosecond laser pulses and a polyvinylpyrrolidone film doped with silver nitrate. The hexagonal nanoprisms have bases hundreds of nanometers in size and the crystal growth occurs over exposure times of less than 1 ms (8 orders of magnitude faster than traditional chemical techniques). Electron backscatter diffraction analysis shows that the hexagonal nanoprisms are monocrystalline. The fabrication method combines advantages from both wet chemistry and femtosecond laser direct-writing to grow silver crystals in targeted locations. The results presented in this letter offer an approach to directly positioning and growing silver crystals on a substrate, which can be used for plasmonic devices.

 

Title:
Efficient readout of a single spin state in diamond via spin-to-charge conversion
Authors:
Shields, B. J.; Unterreithmeier, Q. P.; de Leon, N. P.; Park, H.; Lukin, M. D.
Publication:
eprint arXiv:1410.0370
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
10 pages, 10 figures
Bibliographic Code:
2014arXiv1410.0370S

Abstract

Efficient readout of individual electronic spins associated with atom-like impurities in the solid state is essential for applications in quantum information processing and quantum metrology. We demonstrate a new method for efficient spin readout of nitrogen-vacancy (NV) centers in diamond. The method is based on conversion of the electronic spin state of the NV to a charge state distribution, followed by single-shot readout of the charge state. Conversion is achieved through a spin-dependent photoionization process in diamond at room temperature. Using NVs in nanofabricated diamond beams, we demonstrate that the resulting spin readout noise is within a factor of three of the spin projection noise level. Applications of this technique for nanoscale magnetic sensing are discussed.

 

Title:
All-optical initialization, readout, and coherent preparation of single silicon-vacancy spins in diamond
Authors:
Rogers, Lachlan J.; Jahnke, Kay D.; Metsch, Mathias H.; Sipahigil, Alp; Binder, Jan M.; Teraji, Tokuyuki; Sumiya, Hitoshi; Isoya, Junichi; Lukin, Mikhail D.; Hemmer, Philip; Jelezko, Fedor
Publication:
eprint arXiv:1410.1355
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Materials Science, Physics - Optics
Comment:
9 pages, 8 figures; Phys. Rev. Lett. 113, 197601 (2014); doi:10.1103/PhysRevLett.113.197601
Bibliographic Code:
2014arXiv1410.1355R

Abstract

The silicon-vacancy ($\mathrm{SiV}^-$) color center in diamond has attracted attention due to its unique optical properties. It exhibits spectral stability and indistinguishability that facilitate efficient generation of photons capable of demonstrating quantum interference. Here we show high fidelity optical initialization and readout of electronic spin in a single $\mathrm{SiV}^-$ center with a spin relaxation time of $T_1=2.4\pm0.2$ ms. Coherent population trapping (CPT) is used to demonstrate coherent preparation of dark superposition states with a spin coherence time of $T_2^\star=35\pm3$ ns. This is fundamentally limited by orbital relaxation, and an understanding of this process opens the way to extend coherences by engineering interactions with phonons. These results establish the $\mathrm{SiV}^-$ center as a solid-state spin-photon interface.

 

Title:
Bloch oscillations of bosonic lattice polarons
Authors:
Grusdt, Fabian; Shashi, Aditya; Abanin, Dmitry; Demler, Eugene
Publication:
eprint arXiv:1410.1513
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
25 pages, 12 figures
Bibliographic Code:
2014arXiv1410.1513G

Abstract

We consider a single impurity atom confined to an optical lattice and immersed in a homogeneous Bose-Einstein condensate (BEC). Interaction of the impurity with the phonon modes of the BEC leads to the formation of a stable quasiparticle, the polaron. We use a variational mean-field approach to study dispersion renormalization and derive equations describing non-equilibrium dynamics of polarons by projecting equations of motion into mean-field (MF) type wavefunctions. As a concrete example, we apply our method to study dynamics of impurity atoms in response to a suddenly applied force and explore the interplay of coherent Bloch oscillations and incoherent drift. We obtain a non-linear dependence of the drift velocity on the applied force, including a sub-Ohmic dependence for small forces for dimensionality d>1 of the BEC. For the case of heavy impurity atoms we derive a closed analytical expression for the drift velocity. Our results show considerable differences with the commonly used phenomenological Esaki-Tsu model.

 

Title:
Gauss-Manin connection in disguise: Calabi-Yau threefolds
Authors:
Alim, Murad; Movasati, Hossein; Scheidegger, Emanuel; Yau, Shing-Tung
Publication:
eprint arXiv:1410.1889
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
Mathematics - Algebraic Geometry, High Energy Physics - Theory, Mathematics - Number Theory, 14N35, 14J15, 32G20
Comment:
25 pages
Bibliographic Code:
2014arXiv1410.1889A

Abstract

We describe a Lie Algebra on the moduli space of Calabi-Yau threefolds enhanced with differential forms and its relation to the Bershadsky-Cecotti-Ooguri-Vafa holomorphic anomaly equation. In particular, we describe algebraic topological string partition functions $F_g^{alg}, g\geq 1$, which encode the polynomial structure of holomorphic and non-holomorphic topological string partition functions. Our approach is based on Grothendieck's algebraic de Rham cohomology and on the algebraic Gauss-Manin connection. In this way, we recover a result of Yamaguchi-Yau and Alim-L\"ange in an algebraic context. Our proofs use the fact that the special polynomial generators defined using the special geometry of deformation spaces of Calabi-Yau threefolds correspond to coordinates on such a moduli space. We discuss the mirror quintic as an example.

 

Title:
Renormalization group approach to the Fr\"ohlich polaron model: application to impurity-BEC problem
Authors:
Grusdt, F.; Shchadilova, Y. E.; Rubtsov, A. N.; Demler, E.
Publication:
eprint arXiv:1410.2203
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
13 pages, 7 figures
Bibliographic Code:
2014arXiv1410.2203G

Abstract

We develop a renormalization group approach for analyzing Fr\"ohlich polarons and apply it to a problem of impurity atoms immersed in a Bose-Einstein condensate of ultra cold atoms. Polaron energies obtained by our method are in excellent agreement with recent diagrammatic Monte Carlo calculations for a wide range of interaction strengths. We calculate the effective mass of polarons and find a smooth crossover from weak to strong coupling regimes. Possible experimental tests of our results in current experiments with ultra cold atoms are discussed.

 

Title:
Charge ordering in three-band models of the cuprates
Authors:
Thomson, Alexandra; Sachdev, Subir
Publication:
eprint arXiv:1410.3483
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons
Comment:
18+15 pages, 8 figures
Bibliographic Code:
2014arXiv1410.3483T

Abstract

We examine trends in the wavevectors and form-factors of charge density wave instabilities of three-band models of the underdoped cuprates. For instabilities from a high temperature state with a large Fermi surface, we extend a study by Bulut et al. (arXiv:1305.3301) to include a direct antiferromagnetic exchange coupling between the Cu sites. As in previous work, we invariably find that the primary instability has a diagonal wavevector $(\pm Q_0, \pm Q_0)$ and a $d$-form factor. The experimentally observed wavevectors along the principal axes $(\pm Q_0,0)$, $(0, \pm Q_0)$ have higher energy, and their form factor is found to be predominantly $d$. Next, we gap out the Fermi surface in the anti-nodal regions of the Brillouin zone by including static, long-range antiferromagnetic order at the wavevector $(\pi, \pi)$: this is a simple model of the pseudogap in which we assume the antiferromagnetic order averages to zero by `renormalized classical' thermal fluctuations in its orientation, valid when the antiferromagnetic correlation length is large. The charge density wave instabilities of this pseudogap state are found to have the optimal wavevector $(\pm Q_0,0)$, $(0, \pm Q_0)$, with the magnitude of the $d$-form factor decreasing with increasing magnetic order.

 

Title:
Updated Measurement of the Single Top Quark Production Cross Section and $V{tb}$ in the Missing Transverse Energy Plus Jets Topology in $p\bar{p}$ Collisions at $\sqrt{s} = 1.96$ TeV
Authors:
CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 396 coauthors
Publication:
eprint arXiv:1410.4909
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment
Comment:
submitted to Phys. Rev. Lett
Bibliographic Code:
2014arXiv1410.4909C

Abstract

An updated measurement of the single top quark production cross section is presented using the full data set collected by the Collider Detector at Fermilab (CDF) and corresponding to 9.5 fb${}^{-1}$ of integrated luminosity from proton-antiproton collisions at 1.96 TeV center-of-mass energy. The events selected contain an imbalance in the total transverse energy, jets identified as originating from $b$ quarks, and no identified leptons. The sum of the $s$- and $t$-channel single top quark cross sections is measured to be $3.53_{-1.16}^{+1.25}$ pb and a lower limit on $V_{tb}$ of 0.63 is obtained at the 95% credibility level. These measurements are combined with previously reported CDF results obtained from events with an imbalance in total transverse energy, jets identified as originating from $b$ quarks, and exactly one identified lepton. The combined cross section is measured to be $3.02_{-0.48}^{+0.49}$ pb and a lower limit on $V{tb}$ of 0.84 is obtained at the 95% credibility level.

 

Title:
Measurement of indirect CP-violating asymmetries in $D^0\to K^+K^-$ and $D^0\to \pi^+\pi^-$ decays at CDF
Authors:
CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;;... Franklin, M.;... Guimaraes da Costa, J.;... and 396 coauthors
Publication:
eprint arXiv:1410.5435
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment, High Energy Physics - Phenomenology
Comment:
7 pages, 3 figures, submitted to Phys. Rev. Lett
Bibliographic Code:
2014arXiv1410.5435C

Abstract

We report a measurement of the indirect CP-violating asymmetries ($A_{\Gamma}$) between effective lifetimes of anticharm and charm mesons reconstructed in $D^0\to K^+ K^-$ and $D^0\to \pi^+\pi^-$ decays. We use the full data set of proton-antiproton collisions collected by the Collider Detector at Fermilab experiment and corresponding to $9.7$~fb$^{-1}$ of integrated luminosity. The strong decay $D^{*+}\to D^0\pi^+$ is used to identify the meson at production as $D^0$ or $\overline{D}^0$. We statistically subtract $D^0$ and $\overline{D}^0$ mesons originating from $b$-hadron decays and measure the yield asymmetry between anticharm and charm decays as a function of decay time. We measure $A_\Gamma (K^+K^-) = (-0.19 \pm 0.15 (stat) \pm 0.04 (syst))\%$ and $A_\Gamma (\pi^+\pi^-)= (-0.01 \pm 0.18 (stat) \pm 0.03 (syst))\%$. The results are consistent with the hypothesis of CP symmetry and their combination yields $A_\Gamma = (-0.12 \pm 0.12)\%$.

 

Title:
Topological flat bands with Chern number C=2 by dipolar exchange interactions
Authors:
Peter, David; Yao, Norman Y.; Lang, Nicolai; Huber, Sebastian D.; Lukin, Mikhail D.; Büchler, Hans Peter
Publication:
eprint arXiv:1410.5667
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases
Comment:
7 pages, 5 figures
Bibliographic Code:
2014arXiv1410.5667P

Abstract

We demonstrate the realization of topological band structures by exploiting the intrinsic spin-orbit coupling of dipolar interactions in combination with broken time-reversal symmetry. The system is based on polar molecules trapped in a deep optical lattice, where the dynamics of rotational excitations follows a hopping Hamiltonian which is determined by the dipolar exchange interactions. We find topological bands with Chern number $C=2$ on the square lattice, while a very rich structure of different topological bands appears on the honeycomb lattice. We show that the system is robust against missing molecules. For certain parameters we obtain flat bands, providing a promising candidate for the realization of bosonic fractional Chern insulators.

 

Title:
Polaronic mass renormalization of impurities in BEC: correlated Gaussian wavefunction approach
Authors:
Shchadilova, Yulia E.; Grusdt, Fabian; Rubtsov, Alexey N.; Demler, Eugene
Publication:
eprint arXiv:1410.5691
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases
Comment:
6 pages, 4 figures + Supplementary Materials
Bibliographic Code:
2014arXiv1410.5691S

Abstract

We propose a class of variational Gaussian wavefunctions to describe Fr\"ohlich polarons at finite momenta. Our wavefunctions give polaron energies that are in excellent agreement with the existing Monte Carlo results for a broad range of interactions. We calculate the effective mass of polarons and find smooth crossover between weak and intermediate impurity-bosons coupling. Effective masses that we obtain are considerably larger than those predicted by the mean-field method. A novel prediction based on our variational wavefunctions is a special pattern of correlations between host atoms that can be measured in time-of-flight experiments. We discuss atomic mixtures in systems of ultracold atoms in which our results can be tested with current experimental technology.

 

Title:
Nanometre-scale probing of spin waves using single electron spins
Authors:
van der Sar, Toeno; Casola, Francesco; Walsworth, Ronald; Yacoby, Amir
Publication:
eprint arXiv:1410.6423
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Bibliographic Code:
2014arXiv1410.6423V

Abstract

Correlated-electron systems support a wealth of magnetic excitations, ranging from conventional spin waves to exotic fractional excitations in low-dimensional or geometrically-frustrated spin systems. Probing such excitations on nanometre length scales is essential for unravelling the underlying physics and developing new spintronic nanodevices. However, no established technique provides real-space, few-nanometre-scale probing of correlated-electron magnetic excitations under ambient conditions. Here we present a solution to this problem using magnetometry based on single nitrogen-vacancy (NV) centres in diamond. We focus on spin-wave excitations in a ferromagnetic microdisc, and demonstrate local, quantitative, and phase-sensitive detection of the spin-wave magnetic field at ~50 nm from the disc. We map the magnetic-field dependence of spin-wave excitations by detecting the associated local reduction in the disc's longitudinal magnetization. In addition, we characterize the spin-noise spectrum by NV-spin relaxometry, finding excellent agreement with a general analytical description of the stray fields produced by spin-spin correlations in a 2D magnetic system. These complementary measurement modalities pave the way towards imaging the local excitations of systems such as ferromagnets and antiferromagnets, skyrmions, atomically assembled quantum magnets, and spin ice.

 

Title:
Quasi Many-body Localization in Translation Invariant Systems
Authors:
Yao, N. Y.; Laumann, C. R.; Cirac, J. I.; Lukin, M. D.; Moore, J. E.
Publication:
eprint arXiv:1410.7407
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Statistical Mechanics, Condensed Matter - Strongly Correlated Electrons, Quantum Physics
Comment:
7 pages, 7 figures
Bibliographic Code:
2014arXiv1410.7407Y

Abstract

It is typically assumed that disorder is essential to realize Anderson localization. Recently, a number of proposals have suggested that an interacting, translation invariant system can also exhibit localization. We examine these claims in the context of a one-dimensional spin ladder. At intermediate time scales, we find slow growth of entanglement entropy consistent with the phenomenology of many-body localization. However, at longer times, all finite wavelength spin polarizations decay in a finite time, independent of system size. We identify a single length scale which parametrically controls both the eventual spin transport times and the divergence of the susceptibility to spin glass ordering. We dub this long pre-thermal dynamical behavior, intermediate between full localization and diffusion, quasi-many body localization.

 

Title:
Modeling Thermal Dust Emission with Two Components: Application to the Planck HFI Maps
Authors:
Meisner, Aaron; Finkbeiner, Douglas
Publication:
eprint arXiv:1410.7523
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
Astrophysics - Astrophysics of Galaxies
Comment:
accepted for publication in ApJ, for associated data release please visit http://faun.rc.fas.harvard.edu/ameisner/planckdust
Bibliographic Code:
2014arXiv1410.7523M

Abstract

We apply the Finkbeiner et al. (1999) two-component thermal dust emission model to the Planck HFI maps. This parametrization of the far-infrared dust spectrum as the sum of two modified blackbodies serves as an important alternative to the commonly adopted single modified blackbody (MBB) dust emission model. Analyzing the joint Planck/DIRBE dust spectrum, we show that two-component models provide a better fit to the 100-3000 GHz emission than do single-MBB models, though by a lesser margin than found by Finkbeiner et al. (1999) based on FIRAS and DIRBE. We also derive full-sky 6.1' resolution maps of dust optical depth and temperature by fitting the two-component model to Planck 217-857 GHz along with DIRBE/IRAS 100 micron data. Because our two-component model matches the dust spectrum near its peak, accounts for the spectrum's flattening at millimeter wavelengths, and specifies dust temperature at 6.1' FWHM, our model provides reliable, high-resolution thermal dust emission foreground predictions from 100 to 3000 GHz. We find that, in diffuse sky regions, our two-component 100-217 GHz predictions are on average accurate to within 2.2%, while extrapolating the Planck Collaboration (2013a) single-MBB model systematically underpredicts emission by 18.8% at 100 GHz, 12.6% at 143 GHz and 7.9% at 217 GHz. We calibrate our two-component optical depth to reddening, and compare with reddening estimates based on stellar spectra. We find the dominant systematic problems in our temperature/reddening maps to be zodiacal light on large angular scales and the cosmic infrared background anisotropy on small angular scales.

 

Title:
Study of quasielastic scattering using charged-current nu_mu-iron interactions in the MINOS Near Detector
Authors:
Adamson, P.; Anghel, I.; Aurisano, A.;... Feldman, G. J.;... and 107 coauthors
Publication:
eprint arXiv:1410.8613
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment
Comment:
20 pages, 13 figures, 3 Tables
Bibliographic Code:
2014arXiv1410.8613A

Abstract

Kinematic distributions from an inclusive sample of 1.41 x 10^6 charged-current nu_mu interactions on iron, obtained using the MINOS Near Detector exposed to a wide-band beam with peak flux at 3 GeV, are compared to a conventional treatment of neutrino scattering within a Fermi gas nucleus. Results are used to guide the selection of a subsample enriched in quasielastic nu_mu Fe interactions, containing an estimated 123,000 quasielastic events of incident energies 1 < E_nu < 8 GeV, with <E_nu> = 2.79 GeV. Four additional subsamples representing topological and kinematic sideband regions to quasielastic scattering are also selected for the purpose of evaluating backgrounds. Comparisons using subsample distributions in four-momentum transfer Q^2 show the Monte Carlo model to be inadequate at low Q^2. Its shortcomings are remedied via inclusion of a Q^2-dependent suppression function for baryon resonance production, developed from the data. A chi-square fit of the resulting Monte Carlo simulation to the shape of the Q^2 distribution for the quasielastic-enriched sample is carried out with the axial-vector mass M_A of the dipole axial-vector form factor of the neutron as a free parameter. The effective M_A which best describes the data is 1.23 +0.13/-0.09 (fit) +0.12/-0.15 (syst.) GeV.

 

Title:
Inverse Ising inference with correlated samples
Authors:
Obermayer, Benedikt; Levine, Erel
Publication:
eprint arXiv:1410.8703
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
Quantitative Biology - Populations and Evolution, Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Statistical Mechanics
Comment:
18 pages, 6 figures; accepted at New J Phys
Bibliographic Code:
2014arXiv1410.8703O

Abstract

Correlations between two variables of a high-dimensional system can be indicative of an underlying interaction, but can also result from indirect effects. Inverse Ising inference is a method to distinguish one from the other. Essentially, the parameters of the least constrained statistical model are learned from the observed correlations such that direct interactions can be separated from indirect correlations. Among many other applications, this approach has been helpful for protein structure prediction, because residues which interact in the 3D structure often show correlated substitutions in a multiple sequence alignment. In this context, samples used for inference are not independent but share an evolutionary history on a phylogenetic tree. Here, we discuss the effects of correlations between samples on global inference. Such correlations could arise due to phylogeny but also via other slow dynamical processes. We present a simple analytical model to address the resulting inference biases, and develop an exact method accounting for background correlations in alignment data by combining phylogenetic modeling with an adaptive cluster expansion algorithm. We find that popular reweighting schemes are only marginally effective at removing phylogenetic bias, suggest a rescaling strategy that yields better results, and provide evidence that our conclusions carry over to the frequently used mean-field approach to the inverse Ising problem.

 

Title:
The Polyacetylene Raman Spectrum, Decoded
Authors:
Heller, Eric J.; Yang, Yuan; Kocia, Lucas
Publication:
eprint arXiv:1410.8795
Publication Date:
10/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Other Condensed Matter
Comment:
Seven figures
Bibliographic Code:
2014arXiv1410.8795H

Abstract

More than 30 years ago, polyacetylene was very much in the limelight, an early example of a conducting polymer and source of many unusual spectroscopic features spawning disparate ideas as to their origin. Several versions of the polyacetylene spectrum story emerged, with contradictory conclusions. In this paper both ordinary and peculiar polyacetylene spectral features are explained in terms of standard (if disused) spectroscopic concepts, including the dependence of electronic transition moments on phonon coordinates, Born-Oppenheimer energy surface properties, and (much more familiarly) electron and phonon band structure. Raman sideband dispersion and line shapes are very well matched by theory in a fundamental way. Most importantly, clear ramifications emerge for the Raman spectroscopy of a wide range of extended systems, including graphene and beyond, suggesting changes to some common practice in condensed matter spectroscopy.

 

Title:
Uncovering the Mechanism of Trapping and Cell Orientation during Neisseria gonorrhoeae Twitching Motility
Authors:
Zaburdaev, Vasily; Biais, Nicolas; Schmiedeberg, Michael; Eriksson, Jens; Jonsson, Ann-Beth; Sheetz, Michael P.; Weitz, David A.
Publication:
Biophysical Journal, vol. 107, issue 7, pp. 1523-1531
Publication Date:
10/2014
Origin:
CROSSREF
DOI:
10.1016/j.bpj.2014.07.061
Bibliographic Code:
2014BpJ...107.1523Z

Abstract

Not Available

 

Title:
Imaging GFP-Based Reporters in Neurons with Multiwavelength Optogenetic Control
Authors:
Venkatachalam, Veena; Cohen, Adam E.
Publication:
Biophysical Journal, vol. 107, issue 7, pp. 1554-1563
Publication Date:
10/2014
Origin:
CROSSREF
DOI:
10.1016/j.bpj.2014.08.020
Bibliographic Code:
2014BpJ...107.1554V

Abstract

Not Available

 

Title:
Drops can bounce from perfectly hydrophilic surfaces
Authors:
Kolinski, J. M.; Mahadevan, L.; Rubinstein, S. M.
Publication:
Europhysics Letters, Volume 108, Issue 2, article id. 24001 (2014).
Publication Date:
10/2014
Origin:
IOP
DOI:
10.1209/0295-5075/108/24001
Bibliographic Code:
2014EL....10824001K

Abstract

Drops are well known to rebound from superhydrophobic surfaces and from liquid surfaces. Here, we show that drops can also rebound from a superhydrophilic solid surface such as an atomically smooth mica sheet. However, the coefficient of restitution CR associated with this process is significantly lower than that associated with rebound from superhydrophobic surfaces. A direct imaging method allows us to characterize the dynamics of the deformation of the drop in entering the vicinity of the surface. We find that drop bouncing occurs without the drop ever touching the solid and there is a nanometer-scale film of air that separates the liquid and solid, suggesting that shear in the air film is the dominant source of dissipation during rebound. Furthermore, we see that any discrete nanometer-height defects on an otherwise hydrophilic surface, such as treated glass, completely inhibits the bouncing of the drop, causing the liquid to wet the surface. Our study adds a new facet to the dynamics of droplet impact by emphasizing that the thin film of air can play a role not just in the context of splashing but also bouncing, while highlighting the role of rare surface defects in inhibiting this response.

 

Title:
Electron and photon energy calibration with the ATLAS detector using LHC Run 1 data
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;...Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2886 coauthors
Publication:
The European Physical Journal C, Volume 74, article id. #3071, 48 pp. (EPJC Homepage)
Publication Date:
10/2014
Origin:
SPRINGER
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1140/epjc/s10052-014-3071-4
Bibliographic Code:
2014EPJC...74.3071A

Abstract

This paper presents the electron and photon energy calibration achieved with the ATLAS detector using about 25 fb$^{-1}$ of LHC proton--proton collision data taken at centre-of-mass energies of $\sqrt{s}$ = 7 and 8 TeV. The reconstruction of electron and photon energies is optimised using multivariate algorithms. The response of the calorimeter layers is equalised in data and simulation, and the longitudinal profile of the electromagnetic showers is exploited to estimate the passive material in front of the calorimeter and reoptimise the detector simulation. After all corrections, the $Z$ resonance is used to set the absolute energy scale. For electrons from $Z$ decays, the achieved calibration is typically accurate to 0.05% in most of the detector acceptance, rising to 0.2% in regions with large amounts of passive material. The remaining inaccuracy is less than 0.2-1% for electrons with a transverse energy of 10 GeV, and is on average 0.3% for photons. The detector resolution is determined with a relative inaccuracy of less than 10% for electrons and photons up to 60 GeV transverse energy, rising to 40% for transverse energies above 500 GeV.

 

Title:
Measurement of the production cross-section using events with -tagged jets in collisions at and 8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2879 coauthors
Publication:
The European Physical Journal C, Volume 74, article id. #3109, 32 pp. (EPJC Homepage)
Publication Date:
10/2014
Origin:
SPRINGER
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1140/epjc/s10052-014-3109-7
Bibliographic Code:
2014EPJC...74.3109A

Abstract

Not Available

 

Title:
Naturalness, b --> sgamma, and SUSY heavy Higgses
Authors:
Katz, Andrey; Reece, Matthew; Sajjad, Aqil
Publication:
Journal of High Energy Physics, Volume 2014, article id. #102, 29 pp.
Publication Date:
10/2014
Origin:
SPRINGER
Keywords:
Supersymmetry Phenomenology
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP10(2014)102
Bibliographic Code:
2014JHEP...10..102K

Abstract

We explore naturalness constraints on the masses of the heavy Higgs bosons H 0 , H ±, and A 0 in supersymmetric theories. We show that, in any extension of MSSM which accommodates the 125 GeV Higgs at the tree level, one can derive an upper bound on the SUSY Higgs masses from naturalness considerations. As is well-known for the MSSM, these bounds become weak at large tan beta. However, we show that measurements of b --> sgamma together with naturalness arguments lead to an upper bound on tan beta, strengthening the naturalness case for heavy Higgs states near the TeV scale. The precise bound depends somewhat on the SUSY mediation scale: allowing a factor of 10 tuning in the stop sector, the measured rate of b --> sgamma implies tan beta ≲ 30 for running down from 10 TeV but tan beta ≲ 4 for mediation at or above 100 TeV, placing m A near the TeV scale for natural EWSB. Because the signatures of heavy Higgs bosons at colliders are less susceptible to being "hidden" than standard superpartner signatures, there is a strong motivation to make heavy Higgs searches a key part of the LHC's search for naturalness. In an appendix we comment on how the Goldstone boson equivalence theorem links the rates for H --> hh and H --> ZZ signatures.

 

Title:
New symmetries of massless QED
Authors:
He, Temple; Mitra, Prahar; Porfyriadis, Achilleas P.; Strominger, Andrew
Publication:
Journal of High Energy Physics, Volume 2014, article id. #112, 17 pp.
Publication Date:
10/2014
Origin:
SPRINGER
Keywords:
Spontaneous Symmetry Breaking, Scattering Amplitudes, Gauge Symmetry
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP10(2014)112
Bibliographic Code:
2014JHEP...10..112H

Abstract

An infinite number of physically nontrivial symmetries are found for abelian gauge theories with massless charged particles. They are generated by large U(1) gauge transformations that asymptotically approach an arbitrary function on the conformal sphere at future null infinity ([InlineMediaObject not available: see fulltext.]) but are independent of the retarded time. The value of ε at past null infinity ([InlineMediaObject not available: see fulltext.]) is determined from that on [InlineMediaObject not available: see fulltext.] by the condition that it take the same value at either end of any light ray crossing Minkowski space. The ε != constant symmetries are spontaneously broken in the usual vacuum. The associated Goldstone modes are zero-momentum photons and comprise a U(1) boson living on the conformal sphere. The Ward identity associated with this asymptotic symmetry is shown to be the abelian soft photon theorem.

 

Title:
Using the discrete dipole approximation and holographic microscopy to measure rotational dynamics of non-spherical colloidal particles
Authors:
Wang, Anna; Dimiduk, Thomas G.; Fung, Jerome; Razavi, Sepideh; Kretzschmar, Ilona; Chaudhary, Kundan; Manoharan, Vinothan N.
Publication:
Journal of Quantitative Spectroscopy and Radiative Transfer, Volume 146, p. 499-509. (JQSRT Homepage)
Publication Date:
10/2014
Origin:
ELSEVIER
Abstract Copyright:
(c) 2014 Elsevier Ltd
DOI:
10.1016/j.jqsrt.2013.12.019
Bibliographic Code:
2014JQSRT.146..499W

Abstract

We present a new, high-speed technique to track the three-dimensional translation and rotation of non-spherical colloidal particles. We capture digital holograms of micrometer-scale silica rods and sub-micrometer-scale Janus particles freely diffusing in water, and then fit numerical scattering models based on the discrete dipole approximation to the measured holograms. This inverse-scattering approach allows us to extract the position and orientation of the particles as a function of time, along with static parameters including the size, shape, and refractive index. The best-fit sizes and refractive indices of both particles agree well with expected values. The technique is able to track the center of mass of the rod to a precision of 35 nm and its orientation to a precision of 1.5°, comparable to or better than the precision of other 3D diffusion measurements on non-spherical particles. Furthermore, the measured translational and rotational diffusion coefficients for the silica rods agree with hydrodynamic predictions for a spherocylinder to within 0.3%. We also show that although the Janus particles have only weak optical asymmetry, the technique can track their 2D translation and azimuthal rotation over a depth of field of several micrometers, yielding independent measurements of the effective hydrodynamic radius that agree to within 0.2%. The internal and external consistency of these measurements validate the technique. Because the discrete dipole approximation can model scattering from arbitrarily shaped particles, our technique could be used in a range of applications, including particle tracking, microrheology, and fundamental studies of colloidal self-assembly or microbial motion.

 

Title:
Suppressing qubit dephasing using real-time Hamiltonian estimation
Authors:
Shulman, M. D.; Harvey, S. P.; Nichol, J. M.; Bartlett, S. D.; Doherty, A. C.; Umansky, V.; Yacoby, A.
Publication:
Nature Communications, Volume 5, id. 5156 (2014).
Publication Date:
10/2014
Origin:
NATURE
Abstract Copyright:
(c) 2014: Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.
DOI:
10.1038/ncomms6156
Bibliographic Code:
2014NatCo...5E5156S

Abstract

Unwanted interaction between a quantum system and its fluctuating environment leads to decoherence and is the primary obstacle to establishing a scalable quantum information processing architecture. Strategies such as environmental and materials engineering, quantum error correction and dynamical decoupling can mitigate decoherence, but generally increase experimental complexity. Here we improve coherence in a qubit using real-time Hamiltonian parameter estimation. Using a rapidly converging Bayesian approach, we precisely measure the splitting in a singlet-triplet spin qubit faster than the surrounding nuclear bath fluctuates. We continuously adjust qubit control parameters based on this information, thereby improving the inhomogenously broadened coherence time from tens of nanoseconds to >2 mus. Because the technique demonstrated here is compatible with arbitrary qubit operations, it is a natural complement to quantum error correction and can be used to improve the performance of a wide variety of qubits in both meteorological and quantum information processing applications.

 

Title:
Scaling macroscopic aquatic locomotion
Authors:
Gazzola, Mattia; Argentina, Médéric; Mahadevan, L.
Publication:
Nature Physics, Volume 10, Issue 10, pp. 758-761 (2014).
Publication Date:
10/2014
Origin:
NATURE
Abstract Copyright:
(c) 2014: Nature Publishing Group
DOI:
10.1038/nphys3078
Bibliographic Code:
2014NatPh..10..758G

Abstract

Inertial aquatic swimmers that use undulatory gaits range in length L from a few millimetres to 30 metres, across a wide array of biological taxa. Using elementary hydrodynamic arguments, we uncover a unifying mechanistic principle characterizing their locomotion by deriving a scaling relation that links swimming speed U to body kinematics (tail beat amplitude A and frequency omega) and fluid properties (kinematic viscosity nu). This principle can be simply couched as the power law Re ~ Swalpha, where Re = UL/nu >> 1 and Sw = omegaAL/nu, with alpha = 4/3 for laminar flows, and alpha = 1 for turbulent flows. Existing data from over 1,000 measurements on fish, amphibians, larvae, reptiles, mammals and birds, as well as direct numerical simulations are consistent with our scaling. We interpret our results as the consequence of the convergence of aquatic gaits to the performance limits imposed by hydrodynamics.

 

Title:
Perspectives on working at the physics-biology interface
Authors:
Berg, Howard; Blagoev, Krastan
Publication:
Physical Biology, Volume 11, Issue 5, article id. 050301 (2014).
Publication Date:
10/2014
Origin:
IOP
DOI:
10.1088/1478-3975/11/5/050301
Bibliographic Code:
2014PhBio..11e0301B

Abstract

Not Available

 

Title:
Fluid mechanical responses to nutrient depletion in fungi and biofilmsa)
Authors:
Brenner, Michael P.
Publication:
Physics of Fluids, Volume 26, Issue 10, id.101306 (PhFl Homepage)
Publication Date:
10/2014
Origin:
AIP
Abstract Copyright:
2014: AIP Publishing LLC
DOI:
10.1063/1.4896587
Bibliographic Code:
2014PhFl...26j1306B

Abstract

In both fungi and bacterial biofilms, when nutrients are depleted, the organisms cannot physically migrate to find a new source, but instead must develop adaptations that allow them to survive. This paper reviews our work attempting to discover design principles for these adaptations. We develop fluid mechanical models, and aim to understand whether these suggest organizing principles for the observed morphological diversity. Determining whether a proposed organizing principle explains extant biological designs is fraught with difficulty: simply because a design principle predicts characteristics similar to an organism's morphology could just as well be accidental as revealing. In each of the two sets of examples, we adopt different strategies to develop understanding in spite of this difficulty. Within the fungal phylum Ascomycota, we use the large observed diversity of different morphological solutions to the fundamental fluid mechanical problem to measure how far each solution is from a design optimum, thereby measuring how far the extant designs deviate from the hypothesized optimum. This allows comparing different design principles to each other. For biofilms, we use engineering principles to make qualitative predictions of what types of adaptations might exist given the physicochemical properties of the repertoire of proteins that bacteria can create, and then find evidence for these adaptations in experiments. While on the surface this paper addresses the particular adaptations used by the fungal phylum Ascomycota and bacterial biofilms, we also aim to motivate discussion of different approaches to using design principles, fluid mechanical or otherwise, to rationalize observed engineering solutions in biology.

 

Title:
Search for WZ resonances in the fully leptonic channel using pp collisions at &surd;{s}=8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;...Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2875 coauthors
Publication:
Physics Letters B, Volume 737, p. 223-243.
Publication Date:
10/2014
Origin:
ELSEVIER
Abstract Copyright:
(c) 2014 CERN for the benefit of the ATLAS Collaboration
DOI:
10.1016/j.physletb.2014.08.039
Bibliographic Code:
2014PhLB..737..223A

Abstract

A search for resonant WZ production in the lnul'l' (l,l'=e,mu) decay channel using 20.3 fb-1 of &surd;{s}=8 TeVpp collision data collected by the ATLAS experiment at LHC is presented. No significant deviation from the Standard Model prediction is observed and upper limits on the production cross sections of WZ resonances from an extended gauge model W' and from a simplified model of heavy vector triplets are derived. A corresponding observed (expected) lower mass limit of 1.52 (1.49) TeV is derived for the W' at the 95% confidence level.

 

Title:
Feedback of superconducting fluctuations on charge order in the underdoped cuprates
Authors:
Chowdhury, Debanjan; Sachdev, Subir
Publication:
Physical Review B, Volume 90, Issue 13, id.134516 (PhRvB Homepage)
Publication Date:
10/2014
Origin:
APS
PACS Keywords:
Non-Fermi-liquid ground states electron phase diagrams and phase transitions in model systems, Band and itinerant models
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevB.90.134516
Bibliographic Code:
2014PhRvB..90m4516C

Abstract

Metals interacting via short-range antiferromagnetic fluctuations are unstable to sign-changing superconductivity at low temperatures. For the cuprates, this leading instability leads to the well-known d -wave superconducting state. However, there is also a secondary instability to an incommensurate charge-density wave, with a predominantly d -wave form factor, arising from the same antiferromagnetic fluctuations. Recent experiments in the pseudogap regime of the hole-doped cuprates have found strong evidence for such a charge-density wave order and, in particular, the predicted d -wave form factor. However, the observed wave vector of the charge order differs from the leading instability in Hartree-Fock theory, and is that of a subleading instability. In this paper, we examine the feedback of superconducting fluctuations on these different charge-density wave states, and find that over at least a small temperature window, they prefer the experimentally observed wave vector.

 

Title:
Density wave instabilities in a correlated two-dimensional metal
Authors:
Allais, Andrea; Bauer, Johannes; Sachdev, Subir
Publication:
Physical Review B, Volume 90, Issue 15, id.155114 (PhRvB Homepage)
Publication Date:
10/2014
Origin:
APS
PACS Keywords:
Lattice fermion models, Strongly correlated electron systems, heavy fermions
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevB.90.155114
Bibliographic Code:
2014PhRvB..90o5114A

Abstract

Motivated by recent experimental evidence of charge order in the pseudogap phase of cuprates, we perform a variational analysis of spin-singlet density wave ordering in metals with antiferromagnetic interactions on the square lattice, using a wave function with double occupancy projected out. We examine ordering with and without time-reversal symmetry, with an arbitrary wave vector and a tunable form factor. Depending on parameters, we find d-form factor density wave ordering, with a wave vector either parallel to the lattice generators or diagonally oriented, or a ground state which carries a time-reversal breaking pattern of spontaneous currents.

 

Title:
Kramers pairs of Majorana fermions and parafermions in fractional topological insulators
Authors:
Klinovaja, Jelena; Yacoby, Amir; Loss, Daniel
Publication:
Physical Review B, Volume 90, Issue 15, id.155447 (PhRvB Homepage)
Publication Date:
10/2014
Origin:
APS
PACS Keywords:
Fermions in reduced dimensions, Proximity effects, Andreev effect, SN and SNS junctions, Fractional statistics systems
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevB.90.155447
Bibliographic Code:
2014PhRvB..90o5447K

Abstract

We propose a scheme based on topological insulators to generate Kramers pairs of Majorana fermions or parafermions in the complete absence of magnetic fields. Our setup consists of two topological insulators whose edge states are brought close to an s -wave superconductor. The resulting proximity effect leads to an interplay between a nonlocal crossed Andreev pairing, which is dominant in the strong electron-electron interaction regime, and usual superconducting pairing, which is dominant at large separation between the two topological insulator edges. As a result, there are zero-energy bound states localized at interfaces between spatial regions dominated by the two different types of pairing. Due to the preserved time-reversal symmetry, the bound states come in Kramers pairs. If the topological insulators carry fractional edge states, the zero-energy bound states are parafermions, otherwise, they are Majorana fermions.

 

Title:
dc resistivity at the onset of spin density wave order in two-dimensional metals
Authors:
Patel, Aavishkar A.; Sachdev, Subir
Publication:
Physical Review B, Volume 90, Issue 16, id.165146 (PhRvB Homepage)
Publication Date:
10/2014
Origin:
APS
PACS Keywords:
Non-Fermi-liquid ground states electron phase diagrams and phase transitions in model systems
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevB.90.165146
Bibliographic Code:
2014PhRvB..90p5146P

Abstract

The theory for the onset of spin density wave order in a metal in two dimensions flows to strong coupling, with strong interactions not only at the "hot spots," but on the entire Fermi surface. We advocate the computation of dc transport in a regime where there is rapid relaxation to local equilibrium around the Fermi surface by processes which conserve total momentum. The dc resistivity is then controlled by weaker perturbations which do not conserve momentum. We consider variations in the local position of the quantum-critical point, induced by long-wavelength disorder, and find a contribution to the resistivity which is linear in temperature (up to logarithmic corrections) at low temperature. Scattering of fermions between hot spots, by short-wavelength disorder, leads to a residual resistivity and a correction which is linear in temperature.

 

Title:
Measurement of long-range pseudorapidity correlations and azimuthal harmonics in &surd;sNN =5.02 TeV proton-lead collisions with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2885 coauthors
Publication:
Physical Review C, Volume 90, Issue 4, id.044906 (PhRvC Homepage)
Publication Date:
10/2014
Origin:
APS
PACS Keywords:
Particle and resonance production
Abstract Copyright:
2014: CERN
DOI:
10.1103/PhysRevC.90.044906
Bibliographic Code:
2014PhRvC..90d4906A

Abstract

Measurements of two-particle correlation functions and the first five azimuthal harmonics, v1 to v5, are presented, using 28 nb-1 of p +Pb collisions at a nucleon-nucleon center-of-mass energy of &surd;sNN =5.02 TeV measured with the ATLAS detector at the LHC. Significant long-range "ridgelike" correlations are observed for pairs with small relative azimuthal angle (|Deltavarphi |<pi/3) and back-to-back pairs (|Deltavarphi|>2pi/3) over the transverse momentum range 0.4<pT<12 GeV and in different intervals of event activity. The event activity is defined by either the number of reconstructed tracks or the total transverse energy on the Pb-fragmentation side. The azimuthal structure of such long-range correlations is Fourier decomposed to obtain the harmonics vn as a function of pT and event activity. The extracted vn values for n =2 to 5 decrease with n. The v2 and v3 values are found to be positive in the measured pT range. The v1 is also measured as a function of pT and is observed to change sign around pT≈1.5-2.0 GeV and then increase to about 0.1 for pT>4 GeV. The v2(pT), v3(pT), and v4(pT) are compared to the vn coefficients in Pb +Pb collisions at &surd;sNN =2.76 TeV with similar event multiplicities. Reasonable agreement is observed after accounting for the difference in the average pT of particles produced in the two collision systems.

 

Title:
Measurements of normalized differential cross sections for tt ¯ production in pp collisions at &surd;(s) =7 TeV using the ATLAS detector
Authors:
Aad, G.; Abajyan, T.; Abbott, B.;... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2868 coauthors
Publication:
Physical Review D, Volume 90, Issue 7, id.072004 (PhRvD Homepage)
Publication Date:
10/2014
Origin:
APS
PACS Keywords:
Hadron-induced high- and super-high-energy interactions, Experimental tests, Top quarks
Abstract Copyright:
2014: authors
DOI:
10.1103/PhysRevD.90.072004
Bibliographic Code:
2014PhRvD..90g2004A

Abstract

Measurements of normalized differential cross sections for top-quark pair production are presented as a function of the top-quark transverse momentum, and of the mass, transverse momentum, and rapidity of the tt ¯ system, in proton-proton collisions at a center-of-mass energy of &surd;s =7 TeV. The data set corresponds to an integrated luminosity of 4.6 fb-1, recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. Events are selected in the lepton +jets channel, requiring exactly one lepton and at least four jets with at least one of the jets tagged as originating from a b-quark. The measured spectra are corrected for detector efficiency and resolution effects and are compared to several Monte Carlo simulations and theory calculations. The results are in fair agreement with the predictions in a wide kinematic range. Nevertheless, data distributions are softer than predicted for higher values of the mass of the tt ¯ system and of the top-quark transverse momentum. The measurements can also discriminate among different sets of parton distribution functions.

 

Title:
Search for the lepton flavor violating decay Z -->e mu in p p collisions at &surd;{s }=8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2896 coauthors
Publication:
Physical Review D, Volume 90, Issue 7, id.072010 (PhRvD Homepage)
Publication Date:
10/2014
Origin:
APS
PACS Keywords:
Models beyond the standard model
Abstract Copyright:
2014: CERN
DOI:
10.1103/PhysRevD.90.072010
Bibliographic Code:
2014PhRvD..90g2010A

Abstract

The ATLAS detector at the Large Hadron Collider is used to search for the lepton flavor violating process Z -->e mu in p p collisions using 20.3 fb-1 of data collected at &surd;{s }=8 TeV . An enhancement in the e mu invariant mass spectrum is searched for at the Z -boson mass. The number of Z bosons produced in the data sample is estimated using events of similar topology, Z -->e e and mu mu , significantly reducing the systematic uncertainty in the measurement. There is no evidence of an enhancement at the Z -boson mass, resulting in an upper limit on the branching fraction, B (Z -->e mu )<7.5 ×1 0-7 at the 95% confidence level.

 

Title:
Local shear transformations in deformed and quiescent hard-sphere colloidal glasses
Authors:
Jensen, K. E.; Weitz, D. A.; Spaepen, F.
Publication:
Physical Review E, Volume 90, Issue 4, id.042305 (PhRvE Homepage)
Publication Date:
10/2014
Origin:
APS
PACS Keywords:
Colloids, Glasses, Deformation and plasticity
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevE.90.042305
Bibliographic Code:
2014PhRvE..90d2305J

Abstract

We perform a series of deformation experiments on a monodisperse, hard-sphere colloidal glass while simultaneously following the three-dimensional trajectories of roughly 50000 individual particles with a confocal microscope. In each experiment, we deform the glass in pure shear at a constant strain rate [(1-5)×10-5 s-1] to maximum macroscopic strains (5%-10%) and then reverse the deformation at the same rate to return to zero macroscopic strain. We also measure three-dimensional particle trajectories in an identically prepared quiescent glass in which the macroscopic strain is always zero. We find that shear transformation zones exist and are active in both sheared and quiescent colloidal glasses, revealed by a distinctive fourfold signature in spatial autocorrelations of the local shear strain. With increasing shear, the population of local shear transformations develops more quickly than in a quiescent glass and many of these transformations are irreversible. When the macroscopic strain is reversed, we observe partial elastic recovery, followed by plastic deformation of the opposite sign, required to compensate for the irreversibly transformed regions. The average diameter of the shear transformation zones in both strained and quiescent glasses is slightly more than two particle diameters.

 

Title:
Evidence for Electroweak Production of W±W±jj in pp Collisions at &surd;s =8 TeV with the ATLAS Detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2874 coauthors
Publication:
Physical Review Letters, Volume 113, Issue 14, id.141803 (PhRvL Homepage)
Publication Date:
10/2014
Origin:
APS
PACS Keywords:
W bosons, Extensions of electroweak gauge sector, Decays of W bosons, Inelastic scattering: two-particle final states
Abstract Copyright:
2014: CERN
DOI:
10.1103/PhysRevLett.113.141803
Bibliographic Code:
2014PhRvL.113n1803A

Abstract

This Letter presents the first study of W±W±jj, same-electric-charge diboson production in association with two jets, using 20.3 fb-1 of proton-proton collision data at &surd;s =8 TeV recorded by the ATLAS detector at the Large Hadron Collider. Events with two reconstructed same-charge leptons (e±e±, e±mu±, and mu±mu±) and two or more jets are analyzed. Production cross sections are measured in two fiducial regions, with different sensitivities to the electroweak and strong production mechanisms. First evidence for W±W±jj production and electroweak-only W±W±jj production is observed with a significance of 4.5 and 3.6 standard deviations, respectively. The measured production cross sections are in agreement with standard model predictions. Limits at 95% confidence level are set on anomalous quartic gauge couplings.

 

Title:
Interferometric Probes of Many-Body Localization
Authors:
Serbyn, M.; Knap, M.; Gopalakrishnan, S.; Papic, Z.; Yao, N. Y.; Laumann, C. R.; Abanin, D. A.; Lukin, M. D.; Demler, E. A.
Publication:
Physical Review Letters, Volume 113, Issue 14, id.147204 (PhRvL Homepage)
Publication Date:
10/2014
Origin:
APS
PACS Keywords:
Quantized spin models, Nonequilibrium and irreversible thermodynamics, Ultracold gases trapped gases, Localization effects
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.147204
Bibliographic Code:
2014PhRvL.113n7204S

Abstract

We propose a method for detecting many-body localization (MBL) in disordered spin systems. The method involves pulsed coherent spin manipulations that probe the dephasing of a given spin due to its entanglement with a set of distant spins. It allows one to distinguish the MBL phase from a noninteracting localized phase and a delocalized phase. In particular, we show that for a properly chosen pulse sequence the MBL phase exhibits a characteristic power-law decay reflecting its slow growth of entanglement. We find that this power-law decay is robust with respect to thermal and disorder averaging, provide numerical simulations supporting our results, and discuss possible experimental realizations in solid-state and cold-atom systems.

 

Title:
Far-from-Equilibrium Spin Transport in Heisenberg Quantum Magnets
Authors:
Hild, Sebastian; Fukuhara, Takeshi; Schauß, Peter; Zeiher, Johannes; Knap, Michael; Demler, Eugene; Bloch, Immanuel; Gross, Christian
Publication:
Physical Review Letters, Volume 113, Issue 14, id.147205 (PhRvL Homepage)
Publication Date:
10/2014
Origin:
APS
PACS Keywords:
Quantized spin models, Nonequilibrium and irreversible thermodynamics, Atoms in optical lattices, Spin chain models
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.147205
Bibliographic Code:
2014PhRvL.113n7205H

Abstract

We study experimentally the far-from-equilibrium dynamics in ferromagnetic Heisenberg quantum magnets realized with ultracold atoms in an optical lattice. After controlled imprinting of a spin spiral pattern with an adjustable wave vector, we measure the decay of the initial spin correlations through single-site resolved detection. On the experimentally accessible time scale of several exchange times, we find a profound dependence of the decay rate on the wave vector. In one-dimensional systems, we observe diffusionlike spin transport with a dimensionless diffusion coefficient of 0.22(1). We show how this behavior emerges from the microscopic properties of the closed quantum system. In contrast to the one-dimensional case, our transport measurements for two-dimensional Heisenberg systems indicate anomalous superdiffusion.

 

Title:
Search for Scalar Diphoton Resonances in the Mass Range 65-600 GeV with the ATLAS Detector in pp Collision Data at &surd;s =8 TeV
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2883 coauthors
Publication:
Physical Review Letters, Volume 113, Issue 17, id.171801 (PhRvL Homepage)
Publication Date:
10/2014
Origin:
APS
PACS Keywords:
Inclusive production with identified leptons photons or other nonhadronic particles, Photons
Abstract Copyright:
2014: authors
DOI:
10.1103/PhysRevLett.113.171801
Bibliographic Code:
2014PhRvL.113q1801A

Abstract

A search for scalar particles decaying via narrow resonances into two photons in the mass range 65-600 GeV is performed using 20.3 fb-1 of &surd;s =8 TeV pp collision data collected with the ATLAS detector at the Large Hadron Collider. The recently discovered Higgs boson is treated as a background. No significant evidence for an additional signal is observed. The results are presented as limits at the 95% confidence level on the production cross section of a scalar boson times branching ratio into two photons, in a fiducial volume where the reconstruction efficiency is approximately independent of the event topology. The upper limits set extend over a considerably wider mass range than previous searches.

 

Title:
Transport in Two-Dimensional Disordered Semimetals
Authors:
Knap, Michael; Sau, Jay D.; Halperin, Bertrand I.; Demler, Eugene
Publication:
Physical Review Letters, Volume 113, Issue 18, id.186801 (PhRvL Homepage)
Publication Date:
10/2014
Origin:
APS
PACS Keywords:
Electronic transport in nanoscale materials and structures, Thermal properties of amorphous solids and glasses: heat capacity thermal expansion etc., Theory of electronic transport, scattering mechanisms, Electron states and collective excitations in multilayers quantum wells mesoscopic and nanoscale systems
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.186801
Bibliographic Code:
2014PhRvL.113r6801K

Abstract

We theoretically study transport in two-dimensional semimetals. Typically, electron and hole puddles emerge in the transport layer of these systems due to smooth fluctuations in the potential. We calculate the electric response of the electron-hole liquid subject to zero and finite perpendicular magnetic fields using an effective medium approximation and a complementary mapping on resistor networks. In the presence of smooth disorder and in the limit of a weak electron-hole recombination rate, we find for small but finite overlap of the electron and hole bands an abrupt upturn in resistivity when lowering the temperature but no divergence at zero temperature. We discuss how this behavior is relevant for several experimental realizations and introduce a simple physical explanation for this effect.

 

Title:
Atom-like crystal defects: From quantum computers to biological sensors
Authors:
Childress, Lilian; Walsworth, Ronald; Lukin, Mikhail
Publication:
Physics Today, vol. 67, issue 10, pp. 38-43
Publication Date:
10/2014
Origin:
CROSSREF
DOI:
10.1063/PT.3.2549
Bibliographic Code:
2014PhT....67j..38C

Abstract

Not Available

 

Title:
Measurement of differential production cross-sections for a Z boson in association with b-jets in 7 TeV proton-proton collisions with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;.. Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2879 coauthors
Publication:
Journal of High Energy Physics, Volume 2014, article id. #141, 49 pp.
Publication Date:
10/2014
Origin:
SPRINGER
Keywords:
Electroweak interaction, Hadron-Hadron Scattering, QCD, Heavy quark production
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP10(2014)141
Bibliographic Code:
2014JHEP...10..141A

Abstract

Measurements of differential production cross-sections of a Z boson in association with b-jets in pp collisions at TeV are reported. The data analysed correspond to an integrated luminosity of 4.6 fb-1 recorded with the ATLAS detector at the Large Hadron Collider. Particle-level cross-sections are determined for events with a Z boson decaying into an electron or muon pair, and containing b-jets. For events with at least one b-jet, the cross-section is presented as a function of the Z boson transverse momentum and rapidity, together with the inclusive b-jet cross-section as a function of b-jet transverse momentum, rapidity and angular separations between the b-jet and the Z boson. For events with at least two b-jets, the cross-section is determined as a function of the invariant mass and angular separation of the two highest transverse momentum b-jets, and as a function of the Z boson transverse momentum and rapidity. Results are compared to leading-order and next-to-leading-order perturbative QCD calculations. [Figure not available: see fulltext.]

 

 


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