Faculty Publications: September, 2015

Query Results from the Smithsonian/NASA Astrophysics Data System (ADS)

 Title: A Three-dimensional Map of Milky Way Dust Authors: Green, Gregory M.; Schlafly, Edward F.; Finkbeiner, Douglas P.; Rix, Hans-Walter; Martin, Nicolas; Burgett, William; Draper, Peter W.; Flewelling, Heather; Hodapp, Klaus; Kaiser, Nicholas; Kudritzki, Rolf Peter; Magnier, Eugene; Metcalfe, Nigel; Price, Paul; Tonry, John; Wainscoat, Richard Publication: The Astrophysical Journal, Volume 810, Issue 1, article id. 25, 23 pp. (2015). (ApJ Homepage) Publication Date: 09/2015 Origin: IOP Astronomy Keywords: dust, extinction, Galaxy: structure, methods: statistical DOI: 10.1088/0004-637X/810/1/25 Bibliographic Code: 2015ApJ...810...25G

Abstract

We present a three-dimensional map of interstellar dust reddening, covering three-quarters of the sky out to a distance of several kiloparsecs, based on Pan-STARRS 1 (PS1) and 2MASS photometry. The map reveals a wealth of detailed structure, from filaments to large cloud complexes. The map has a hybrid angular resolution, with most of the map at an angular resolution of 3\buildrel{ \prime}\over{.} 4–13\buildrel{ \prime}\over{.} 7, and a maximum distance resolution of ∼ 25%. The three-dimensional distribution of dust is determined in a fully probabilistic framework, yielding the uncertainty in the reddening distribution along each line of sight, as well as stellar distances, reddenings, and classifications for 800 million stars detected by PS1. We demonstrate the consistency of our reddening estimates with those of two-dimensional emission-based maps of dust reddening. In particular, we find agreement with the Planck {τ }353{GHz}-based reddening map to within 0.05 {mag} in E(B-V) to a depth of 0.5 {mag}, and explore systematics at reddenings less than E(B-V)≈ 0.08 {mag}. We validate our per-star reddening estimates by comparison with reddening estimates for stars with both Sloan Digital Sky Survey photometry and Sloan Extension for Galactic Understanding and Exploration spectral classifications, finding per-star agreement to within 0.1 {mag} out to a stellar E(B-V) of 1 mag. We compare our map to two existing three-dimensional dust maps, by Marshall et al. and Lallement et al., demonstrating our finer angular resolution, and better distance resolution compared to the former within ∼ 3 {kpc}. The map can be queried or downloaded at http://argonaut.skymaps.info. We expect the three-dimensional reddening map presented here to find a wide range of uses, among them correcting for reddening and extinction for objects embedded in the plane of the Galaxy, studies of Galactic structure, calibration of future emission-based dust maps, and determining distances to objects of known reddening.

 Title: F-Theory, Spinning Black Holes and Multi-string Branches Authors: Haghighat, Babak; Murthy, Sameer; Vafa, Cumrun; Vandoren, Stefan Publication: eprint arXiv:1509.00455 Publication Date: 09/2015 Origin: ARXIV Keywords: High Energy Physics - Theory Comment: 58 pages, 7 figures. v2: references added, typos corrected Bibliographic Code: 2015arXiv150900455H

Abstract

We study 5d supersymmetric black holes which descend from strings of generic $\mathcal{N}=(1,0)$ supergravity in 6d. These strings have an F-theory realization in 6d as D3 branes wrapping smooth genus $g$ curves in the base of elliptic 3-folds. They enjoy $(0,4)$ worldsheet supersymmetry with an extra $SU(2)_L$ current algebra at level $g$ realized on the left-movers. When the smooth curves degenerate they lead to multi-string branches and we find that the microscopic worldsheet theory flows in the IR to disconnected 2d CFTs having different central charges. The single string sector is the one with maximal central charge, which when wrapped on a circle, leads to a 5d spinning BPS black hole whose horizon volume agrees with the leading entropy prediction from the Cardy formula. However, we find new phenomena where this branch meets other branches of the CFT. These include multi-string configurations which have no bound states in 6 dimensions but are bound through KK momenta when wrapping a circle, as well as loci where the curves degenerate to spheres where they lead to arbitrarily large violation of the cosmic censorship bound $M^3>J^2$ by an exponentially large number of states.

 Title: Magnetic Corrections to the Soft Photon Theorem Authors: Strominger, Andrew Publication: eprint arXiv:1509.00543 Publication Date: 09/2015 Origin: ARXIV Keywords: High Energy Physics - Theory, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology, Mathematical Physics Comment: 12 pages Bibliographic Code: 2015arXiv150900543S

Abstract

The soft photon theorem, in its standard form, requires corrections when the asymptotic particle states carry magnetic charges. These corrections are deduced using electromagnetic duality and the resulting soft formula conjectured to be exact for all abelian gauge theories. Recent work has shown that the standard soft theorem implies an infinity of conserved electric charges. The associated symmetries are identified as large' electric gauge transformations. Here the magnetic corrections to the soft theorem are shown to imply a second infinity of conserved magnetic charges. The associated symmetries are identified as large' magnetic gauge transformations. The large magnetic symmetries are naturally subsumed in a complexification of the electric ones.

 Title: Measuring entanglement entropy through the interference of quantum many-body twins Authors: Islam, Rajibul; Ma, Ruichao; Preiss, Philipp M.; Tai, M. Eric; Lukin, Alexander; Rispoli, Matthew; Greiner, Markus Publication: eprint arXiv:1509.01160 Publication Date: 09/2015 Origin: ARXIV Keywords: Condensed Matter - Quantum Gases, Physics - Atomic Physics, Quantum Physics Comment: 14 pages, 12 figures (6 in the main text, 6 in supplementary material) Bibliographic Code: 2015arXiv150901160I

Abstract

Entanglement is one of the most intriguing features of quantum mechanics. It describes non-local correlations between quantum objects, and is at the heart of quantum information sciences. Entanglement is rapidly gaining prominence in diverse fields ranging from condensed matter to quantum gravity. Despite this generality, measuring entanglement remains challenging. This is especially true in systems of interacting delocalized particles, for which a direct experimental measurement of spatial entanglement has been elusive. Here, we measure entanglement in such a system of itinerant particles using quantum interference of many-body twins. Leveraging our single-site resolved control of ultra-cold bosonic atoms in optical lattices, we prepare and interfere two identical copies of a many-body state. This enables us to directly measure quantum purity, Renyi entanglement entropy, and mutual information. These experiments pave the way for using entanglement to characterize quantum phases and dynamics of strongly-correlated many-body systems.

 Title: Gravitational wave memory in de Sitter spacetime Authors: Bieri, Lydia; Garfinkle, David; Yau, Shing-Tung Publication: eprint arXiv:1509.01296 Publication Date: 09/2015 Origin: ARXIV Keywords: General Relativity and Quantum Cosmology Bibliographic Code: 2015arXiv150901296B

Abstract

We examine gravitational wave memory in the case where sources and detector are in an expanding cosmology. For simplicity, we treat the case where the cosmology is de Sitter spacetime, and discuss the possibility of generalizing our results to the case of a more realistic cosmology. We find results very similar to those of gravitational wave memory in an asymptotically flat spacetime, but with the magnitude of the effect multiplied by a redshift factor.

 Title: Experimental reconstruction of Wilson lines in Bloch bands Authors: Li, Tracy; Duca, Lucia; Reitter, Martin; Grusdt, Fabian; Demler, Eugene; Endres, Manuel; Schleier-Smith, Monika; Bloch, Immanuel; Schneider, Ulrich Publication: eprint arXiv:1509.02185 Publication Date: 09/2015 Origin: ARXIV Keywords: Condensed Matter - Quantum Gases, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Other Condensed Matter, Quantum Physics Comment: 5+8 pages Bibliographic Code: 2015arXiv150902185L

Abstract

Topology and geometry are essential to our understanding of modern physics, underlying many foundational concepts from a variety of fields. In condensed matter systems, the electronic properties of a solid are determined not only by the scalar dispersion of the bands, but also by the geometry of the band eigenstates. While this information is encoded in the Berry connection and the corresponding Berry phase in the specific case of a single band, the geometry of general multi-band systems is described by the matrix-valued Wilczek-Zee connection and the corresponding Wilson lines. Whereas Berry phases have been directly observed in Bloch bands, Wilson lines have solely been employed as a theoretical construct. Here, we report on the realization of strong-force dynamics in Bloch bands that are described by Wilson lines. The resulting evolution of band populations is purely geometric in origin and can directly reveal both the geometric structure and dispersion of the bands. Our techniques enable a full determination of band eigenstates, Berry curvature, and topological invariants, including Chern and $Z_2$ numbers.

 Title: Probing Scalar Coupling Differences via Long-Lived Singlet States Authors: DeVience, Stephen J.; Walsworth, Ronald L.; Rosen, Matthew S. Publication: eprint arXiv:1509.02240 Publication Date: 09/2015 Origin: ARXIV Keywords: Quantum Physics, Physics - Chemical Physics Bibliographic Code: 2015arXiv150902240D

Abstract

We probe small scalar coupling differences via the coherent interactions between two nuclear spin singlet states in organic molecules. We show that the spin-lock induced crossing (SLIC) technique enables the coherent transfer of singlet order between one spin pair and another. The transfer is mediated by the difference in cis and trans vicinal J couplings among the spins. By measuring the transfer rate, we calculate a J coupling difference of $8 \pm 2$ mHz in phenylalanine-glycine-glycine and $2.57 \pm 0.04$ Hz in glutamate. We also characterize a coherence between two singlet states in glutamate, which may enable the creation of a long-lived quantum memory.

 Title: Controlled Finite Momentum Pairing and Spatially Varying Order Parameter in Proximitized HgTe Quantum Wells Authors: Hart, Sean; Ren, Hechen; Kosowsky, Michael; Ben-Shach, Gilad; Leubner, Philipp; Brüne, Christoph; Buhmann, Hartmut; Molenkamp, Laurens W.; Halperin, Bertrand I.; Yacoby, Amir Publication: eprint arXiv:1509.02940 Publication Date: 09/2015 Origin: ARXIV Keywords: Condensed Matter - Mesoscale and Nanoscale Physics Bibliographic Code: 2015arXiv150902940H

Abstract

Conventional $s$-wave superconductivity is understood to arise from singlet pairing of electrons with opposite Fermi momenta, forming Cooper pairs whose net momentum is zero [1]. Several recent studies have focused on structures where such conventional $s$-wave superconductors are coupled to systems with an unusual configuration of electronic spin and momentum at the Fermi surface. Under these conditions, the nature of the paired state can be modified and the system may even undergo a topological phase transition [2, 3]. Here we present measurements and theoretical calculations of several HgTe quantum wells coupled to either aluminum or niobium superconductors and subject to a magnetic field in the plane of the quantum well. By studying the oscillatory response of Josephson interference to the magnitude of the in-plane magnetic field, we find that the induced pairing within the quantum well is spatially varying. Cooper pairs acquire a tunable momentum that grows with magnetic field strength, directly reflecting the response of the spin-dependent Fermi surfaces to the in-plane magnetic field. In addition, in the regime of high electron density, nodes in the induced superconductivity evolve with the electron density in agreement with our model based on the Hamiltonian of Bernevig, Hughes, and Zhang [4]. This agreement allows us to quantitatively extract the value of $\tilde{g}/v_{F}$, where $\tilde{g}$ is the effective g-factor and $v_{F}$ is the Fermi velocity. However, at low density our measurements do not agree with our model in detail. Our new understanding of the interplay between spin physics and superconductivity introduces a way to spatially engineer the order parameter, as well as a general framework within which to investigate electronic spin texture at the Fermi surface of materials.

 Title: Fractionalized Fermi liquid on the surface of a topological Kondo insulator Authors: Thomson, Alex; Sachdev, Subir Publication: eprint arXiv:1509.03314 Publication Date: 09/2015 Origin: ARXIV Keywords: Condensed Matter - Strongly Correlated Electrons Comment: 18 pages, 4 figures Bibliographic Code: 2015arXiv150903314T

Abstract

We argue that topological Kondo insulators can also have 'intrinsic' topological order associated with fractionalized excitations on their surfaces. The hydridization between the local moments and conduction electrons can weaken near the surface, and this enables the local moments to form spin liquids. This co-exists with the conduction electron surface states, realizing a surface fractionalized Fermi liquid. We present mean-field solutions of a Kondo-Heisenberg model which display such surfaces.

 Title: Continuum-Mediated Dark Matter-Baryon Scattering Authors: Katz, Andrey; Reece, Matthew; Sajjad, Aqil Publication: eprint arXiv:1509.03628 Publication Date: 09/2015 Origin: ARXIV Keywords: High Energy Physics - Phenomenology Bibliographic Code: 2015arXiv150903628K

Abstract

Many models of dark matter scattering with baryons may be treated either as a simple contact interaction or as the exchange of a light mediator particle. We study an alternative, in which a continuum of light mediator states may be exchanged. This could arise, for instance, from coupling to a sector which is approximately conformal at the relevant momentum transfer scale. In the non-relativistic effective theory of dark matter-baryon scattering, which is useful for parametrizing direct detection signals, the effect of such continuum mediators is to multiply the amplitude by a function of the momentum transfer q, which in the simplest case is just a power law. We develop the basic framework and study two examples: the case where the mediator is a scalar operator coupling to the Higgs portal (which turns out to be highly constrained) and the case of an antisymmetric tensor operator ${\cal O}_{\mu \nu}$ that mixes with the hypercharge field strength and couples to dark matter tensor currents, which has an interesting viable parameter space. We describe the effect of such mediators on the cross sections and recoil energy spectra that could be observed in direct detection.

 Title: Observation of the Dirac fluid and the breakdown of the Wiedemann-Franz law in graphene Authors: Crossno, Jesse; Shi, Jing K.; Wang, Ke; Liu, Xiaomeng; Harzheim, Achim; Lucas, Andrew; Sachdev, Subir; Kim, Philip; Taniguchi, Takashi; Watanabe, Kenji; Ohki, Thomas A.; Chung Fong, Kin Publication: eprint arXiv:1509.04713 Publication Date: 09/2015 Origin: ARXIV Keywords: Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons Comment: 5+5 pages, 3+7 figures Bibliographic Code: 2015arXiv150904713C

Abstract

Interactions between particles in quantum many-body systems can lead to collective behavior described by hydrodynamics. One such system is the electron-hole plasma in graphene near the charge neutrality point which can form a strongly coupled Dirac fluid. This charge neutral plasma of quasi-relativistic fermions is expected to exhibit a substantial enhancement of the thermal conductivity, due to decoupling of charge and heat currents within hydrodynamics. Employing high sensitivity Johnson noise thermometry, we report the breakdown of the Wiedemann-Franz law in graphene, with a thermal conductivity an order of magnitude larger than the value predicted by Fermi liquid theory. This result is a signature of the Dirac fluid, and constitutes direct evidence of collective motion in a quantum electronic fluid.

 Title: Sharpening the Weak Gravity Conjecture with Dimensional Reduction Authors: Heidenreich, Ben; Reece, Matthew; Rudelius, Tom Publication: eprint arXiv:1509.06374 Publication Date: 09/2015 Origin: ARXIV Keywords: High Energy Physics - Theory Bibliographic Code: 2015arXiv150906374H

Abstract

We investigate the behavior of the Weak Gravity Conjecture (WGC) under toroidal compactification and RG flows, finding evidence that WGC bounds for single photons become weaker in the infrared. By contrast, we find that a photon satisfying the WGC will not necessarily satisfy it after toroidal compactification when black holes charged under the Kaluza-Klein photons are considered. Doing so either requires an infinite number of states of different charges to satisfy the WGC in the original theory or a restriction on allowed compactification radii. These subtleties suggest that if the Weak Gravity Conjecture is true, we must seek a stronger form of the conjecture that is robust under compactification. We propose a "Lattice Weak Gravity Conjecture" that meets this requirement: a superextremal particle should exist for every charge in the charge lattice. The perturbative heterotic string satisfies this conjecture. We also use compactification to explore the extent to which the WGC applies to axions. We argue that gravitational instanton solutions in theories of axions coupled to dilaton-like fields are analogous to extremal black holes, motivating a WGC for axions. This is further supported by a match between the instanton action and that of wrapped black branes in a higher-dimensional UV completion.

 Title: On Galactic density modeling in the presence of dust extinction Authors: Bovy, Jo; Rix, Hans-Walter; Green, Gregory M.; Schlafly, Edward F.; Finkbeiner, Douglas P. Publication: eprint arXiv:1509.06751 Publication Date: 09/2015 Origin: ARXIV Keywords: Astrophysics - Astrophysics of Galaxies Comment: ApJ, submitted; code available at https://github.com/jobovy/mwdust and at https://github.com/jobovy/apogee-maps Bibliographic Code: 2015arXiv150906751B

Abstract

Inferences about the spatial density or phase-space structure of stellar populations in the Milky Way require a precise determination of the effective survey volume. The volume observed by surveys such as Gaia or near-infrared spectroscopic surveys, which have good coverage of the Galactic mid-plane region, is highly complex because of the abundant small-scale structure in the three-dimensional interstellar dust extinction. We introduce a novel framework for analyzing the importance of small-scale structure in the extinction. This formalism demonstrates that the spatially-complex effect of extinction on the selection function of a pencil-beam or contiguous sky survey is equivalent to a low-pass filtering of the extinction-affected selection function with the smooth density field. We find that the angular resolution of current 3D extinction maps is sufficient for analyzing Gaia sub-samples of millions of stars. However, the current distance resolution is inadequate and needs to be improved by an order of magnitude, especially in the inner Galaxy. We also present a practical and efficient method for properly taking the effect of extinction into account in analyses of Galactic structure through an effective survey selection function. We illustrate its use with the selection function of red-clump stars in APOGEE using and comparing a variety of current 3D extinction maps.

 Title: Nanoscale Imaging of Orbital Texture in Single-Layer FeSe/SrTiO$_3$ Authors: Huang, Dennis; Webb, Tatiana A.; Fang, Shiang; Song, Can-Li; Chang, Cui-Zu; Moodera, Jagadeesh S.; Kaxiras, Efthimios; Hoffman, Jennifer E. Publication: eprint arXiv:1509.07110 Publication Date: 09/2015 Origin: ARXIV Keywords: Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons Comment: 9 pages, 9 figures Bibliographic Code: 2015arXiv150907110H

Abstract

We use scanning tunneling microscopy (STM) and quasiparticle interference (QPI) imaging to investigate the low-energy orbital texture of single-layer FeSe/SrTiO$_3$. We develop a $T$-matrix model of multi-orbital QPI to disentangle scattering intensities from Fe $3d_{xz}$ and $3d_{yz}$ bands, enabling the use of STM as a nanoscale detection tool of orbital nematicity. By sampling multiple spatial regions of a single-layer FeSe/SrTiO$_3$ film, we quantitatively exclude static $xz/yz$ orbital ordering with domain size larger than $\delta r^2$ = 20 nm $\times$ 20 nm, $xz/yz$ Fermi wave vector difference larger than $\delta k$ = 0.014 $\pi$, and energy splitting larger than $\delta E$ = 3.5 meV. The lack of detectable ordering pinned around defects places qualitative constraints on models of fluctuating nematicity.

 Title: Invariant Solutions to the Strominger System on Complex Lie Groups and Their Quotients Authors: Fei, Teng; Yau, Shing-Tung Publication: Communications in Mathematical Physics, Volume 338, Issue 3, pp.1183-1195 Publication Date: 09/2015 Origin: SPRINGER Abstract Copyright: (c) 2015: Springer-Verlag Berlin Heidelberg DOI: 10.1007/s00220-015-2374-0 Bibliographic Code: 2015CMaPh.338.1183F

Abstract

Using canonical 1-parameter family of Hermitian connections on the tangent bundle, we provide invariant solutions to the Strominger system on certain complex Lie groups and their quotients. Both flat and non-flat cases are discussed in detail. This paper answers a question proposed by Andreas and Garcia-Fernandez in Comm Math Phys 332(3):1381-1383, 2014.

 Title: Colloids at interfaces: Pinned down Authors: Manoharan, Vinothan N. Affiliation: AA(Vinothan N. Manoharan is at the Harvard John A. Paulson School of Engineering and Applied Sciences and in the Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA; vnm@seas.harvard.edu) Publication: Nature Materials, Volume 14, Issue 9, pp. 869-870 (2015). Publication Date: 09/2015 Origin: NATURE Abstract Copyright: (c) 2015: Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved. DOI: 10.1038/nmat4400 Bibliographic Code: 2015NatMa..14..869M

Abstract

A colloidal particle straddling an air/water interface experiences an unexpectedly large viscous drag.

 Title: Optimal control of plates using incompatible strains Authors: Jones, G. W.; Mahadevan, L. Publication: Nonlinearity, Volume 28, Issue 9, article id. 3153 (2015). Publication Date: 09/2015 Origin: IOP DOI: 10.1088/0951-7715/28/9/3153 Bibliographic Code: 2015Nonli..28.3153J

Abstract

A flat plate will bend into a curved shell if it experiences an inhomogeneous growth field or if constrained appropriately at a boundary. While the forward problem associated with this process is well studied, the inverse problem of designing the boundary conditions or growth fields to achieve a particular shape is much less understood. We use ideas from variational optimization theory to formulate a well posed version of this inverse problem to determine the optimal growth field or boundary condition that will give rise to an arbitrary target shape, optimizing for both closeness to the target shape and for smoothness of the growth field. We solve the resulting system of PDE numerically using finite element methods with examples for both the fully non-symmetric case as well as for simplified one-dimensional and axisymmetric geometries. We also show that the system can also be solved semi-analytically by positing an ansatz for the deformation and growth fields in a circular disk with given thickness profile, leading to paraboloidal, cylindrical and saddle-shaped target shapes, and show how a soft mode can arise from a non-axisymmetric deformation of a structure with axisymmetric material properties.

 Title: Centrality and rapidity dependence of inclusive jet production in √{sNN} = 5.02 TeV proton-lead collisions with the ATLAS detector Authors: Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2885 coauthors Publication: Physics Letters B, Volume 748, p. 392-413. Publication Date: 09/2015 Origin: ELSEVIER Abstract Copyright: (c) 2015 CERN for the benefit of the ATLAS Collaboration DOI: 10.1016/j.physletb.2015.07.023 Bibliographic Code: 2015PhLB..748..392A

Abstract

Measurements of the centrality and rapidity dependence of inclusive jet production in √{sNN} = 5.02 TeV proton-lead (p + Pb) collisions and the jet cross-section in √{ s} = 2.76 TeV proton-proton collisions are presented. These quantities are measured in datasets corresponding to an integrated luminosity of 27.8 nb-1 and 4.0 pb-1, respectively, recorded with the ATLAS detector at the Large Hadron Collider in 2013. The p + Pb collision centrality was characterised using the total transverse energy measured in the pseudorapidity interval - 4.9 < η < - 3.2 in the direction of the lead beam. Results are presented for the double-differential per-collision yields as a function of jet rapidity and transverse momentum (pT) for minimum-bias and centrality-selected p + Pb collisions, and are compared to the jet rate from the geometric expectation. The total jet yield in minimum-bias events is slightly enhanced above the expectation in a pT-dependent manner but is consistent with the expectation within uncertainties. The ratios of jet spectra from different centrality selections show a strong modification of jet production at all pT at forward rapidities and for large pT at mid-rapidity, which manifests as a suppression of the jet yield in central events and an enhancement in peripheral events. These effects imply that the factorisation between hard and soft processes is violated at an unexpected level in proton-nucleus collisions. Furthermore, the modifications at forward rapidities are found to be a function of the total jet energy only, implying that the violations may have a simple dependence on the hard parton-parton kinematics.

 Title: Low-frequency conductivity in many-body localized systems Authors: Gopalakrishnan, Sarang; Müller, Markus; Khemani, Vedika; Knap, Michael; Demler, Eugene; Huse, David A. Publication: Physical Review B, Volume 92, Issue 10, id.104202 (PhRvB Homepage) Publication Date: 09/2015 Origin: APS PACS Keywords: Localization effects, Metal-insulator transitions and other electronic transitions, Quantum transport Abstract Copyright: 2015: American Physical Society DOI: 10.1103/PhysRevB.92.104202 Bibliographic Code: 2015PhRvB..92j4202G

Abstract

We argue that the ac conductivity σ (ω ) in the many-body localized phase is a power law of frequency ω at low frequency: specifically, σ (ω ) ˜ωα with the exponent α approaching 1 at the phase transition to the thermal phase, and asymptoting to 2 deep in the localized phase. We identify two separate mechanisms giving rise to this power law: deep in the localized phase, the conductivity is dominated by rare resonant pairs of configurations; close to the transition, the dominant contributions are rare regions that are locally critical or in the thermal phase. We present numerical evidence supporting these claims, and discuss how these power laws can also be seen through polarization-decay measurements in ultracold atomic systems.

 Title: Exact CNOT gates with a single nonlocal rotation for quantum-dot qubits Authors: Pal, Arijeet; Rashba, Emmanuel I.; Halperin, Bertrand I. Publication: Physical Review B, Volume 92, Issue 12, id.125409 (PhRvB Homepage) Publication Date: 09/2015 Origin: APS PACS Keywords: Quantum dots, Quantum computation Abstract Copyright: 2015: American Physical Society DOI: 10.1103/PhysRevB.92.125409 Bibliographic Code: 2015PhRvB..92l5409P

Abstract

We investigate capacitively-coupled exchange-only two-qubit quantum gates based on quantum dots. For exchange-only coded qubits electron spin S and its projection Sz are exact quantum numbers. Capacitive coupling between qubits, as distinct from interqubit exchange, preserves these quantum numbers. We prove, both analytically and numerically, that conservation of the spins of individual qubits has a dramatic effect on the performance of two-qubit gates. By varying the level splittings of individual qubits, Ja and Jb, and the interqubit coupling time, t , we can find an infinite number of triples (Ja,Jb,t ) for which the two-qubit entanglement, in combination with appropriate single-qubit rotations, can produce an exact cnot gate. This statement is true for practically arbitrary magnitude and form of capacitive interqubit coupling. Our findings promise a large decrease in the number of nonlocal (two-qubit) operations in quantum circuits.

 Title: Measurement of the correlation between flow harmonics of different order in lead-lead collisions at √{sNN}=2.76 TeV with the ATLAS detector Authors: Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2821 coauthors Publication: Physical Review C, Volume 92, Issue 3, id.034903 (PhRvC Homepage) Publication Date: 09/2015 Origin: APS PACS Keywords: Particle and resonance production Abstract Copyright: 2015: CERN DOI: 10.1103/PhysRevC.92.034903 Bibliographic Code: 2015PhRvC..92c4903A

Abstract

Correlations between the elliptic or triangular flow coefficients vm (m =2 or 3) and other flow harmonics vn (n =2 to 5) are measured using √{sNN}=2.76 TeV Pb +Pb collision data collected in 2010 by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of 7 μ b-1. The vm-vn correlations are measured in midrapidity as a function of centrality, and, for events within the same centrality interval, as a function of event ellipticity or triangularity defined in a forward rapidity region. For events within the same centrality interval, v3 is found to be anticorrelated with v2 and this anticorrelation is consistent with similar anticorrelations between the corresponding eccentricities, ɛ2 and ɛ3. However, it is observed that v4 increases strongly with v2, and v5 increases strongly with both v2 and v3. The trend and strength of the vm-vn correlations for n = 4 and 5 are found to disagree with ɛmn correlations predicted by initial-geometry models. Instead, these correlations are found to be consistent with the combined effects of a linear contribution to vn and a nonlinear term that is a function of v22 or of v2v3, as predicted by hydrodynamic models. A simple two-component fit is used to separate these two contributions. The extracted linear and nonlinear contributions to v4 and v5 are found to be consistent with previously measured event-plane correlations.

 Title: Measurement of differential J /ψ production cross sections and forward-backward ratios in p + Pb collisions with the ATLAS detector Authors: Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2805 coauthors Publication: Physical Review C, Volume 92, Issue 3, id.034904 (PhRvC Homepage) Publication Date: 09/2015 Origin: APS PACS Keywords: Photon lepton and heavy quark production in relativistic heavy ion collisions Abstract Copyright: 2015: CERN DOI: 10.1103/PhysRevC.92.034904 Bibliographic Code: 2015PhRvC..92c4904A

Abstract

Measurements of differential cross sections for J /ψ production in p+Pb collisions at √{sN N}=5.02 TeV at the CERN Large Hadron Collider with the ATLAS detector are presented. The data set used corresponds to an integrated luminosity of 28.1 nb-1. The J/ψ mesons are reconstructed in the dimuon decay channel over the transverse momentum range 8 <pT<30 GeV and over the center-of-mass rapidity range -2.87 <y*<1.94. Prompt J/ψ are separated from J /ψ resulting from b -hadron decays through an analysis of the distance between the J /ψ decay vertex and the event primary vertex. The differential cross section for production of nonprompt J /ψ is compared to a FONLL calculation that does not include nuclear effects. Forward-backward production ratios are presented and compared to theoretical predictions. These results complement previously published results by covering a region of higher transverse momentum and more central rapidity. They thus constrain the kinematic dependence of nuclear modifications of charmonium and b -quark production in p +Pb collisions.

 Title: Search for Higgs bosons decaying to a a in the μ μ τ τ final state in p p collisions at √{s }=8 TeV with the ATLAS experiment Authors: Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2821 coauthors Publication: Physical Review D, Volume 92, Issue 5, id.052002 (PhRvD Homepage) Publication Date: 09/2015 Origin: APS Abstract Copyright: 2015: CERN DOI: 10.1103/PhysRevD.92.052002 Bibliographic Code: 2015PhRvD..92e2002A

Abstract

A search for the decay to a pair of new particles of either the 125 GeV Higgs boson (h ) or a second charge parity (C P )-even Higgs boson (H) is presented. The data set corresponds to an integrated luminosity of 20.3 fb-1 of p p collisions at √{s }=8 TeV recorded by the ATLAS experiment at the LHC in 2012. The search was done in the context of the next-to-minimal supersymmetric standard model, in which the new particles are the lightest neutral pseudoscalar Higgs bosons (a). One of the two a bosons is required to decay to two muons while the other is required to decay to two τ leptons. No significant excess is observed above the expected backgrounds in the dimuon invariant mass range from 3.7 to 50 GeV. Upper limits are placed on the production of h →a a relative to the standard model g g →h production, assuming no coupling of the a boson to quarks. The most stringent limit is placed at 3.5% for ma=3.75 GeV . Upper limits are also placed on the production cross section of H →a a from 2.33 to 0.72 pb, for fixed ma=5 GeV with mH ranging from 100 to 500 GeV.

 Title: Precision measurement of the speed of propagation of neutrinos using the MINOS detectors Authors: Adamson, P.; Anghel, I.; Ashby, N.;... Feldman, G. J.;... and 121 coauthors Publication: Physical Review D, Volume 92, Issue 5, id.052005 (PhRvD Homepage) Publication Date: 09/2015 Origin: APS PACS Keywords: Ordinary neutrinos (nuW bosons, Velocity acceleration and rotation Abstract Copyright: (c) 2015: American Physical Society DOI: 10.1103/PhysRevD.92.052005 Bibliographic Code: 2015PhRvD..92e2005A

Abstract

We report a two-detector measurement of the propagation speed of neutrinos over a baseline of 734 km. The measurement was made with the NuMI beam at Fermilab between the near and far MINOS detectors. The fractional difference between the neutrino speed and the speed of light is determined to be (v /c -1 )=(1.0 ±1.1 )×10-6 , consistent with relativistic neutrinos.

 Title: Coulomb Bound States of Strongly Interacting Photons Authors: Maghrebi, M. F.; Gullans, M. J.; Bienias, P.; Choi, S.; Martin, I.; Firstenberg, O.; Lukin, M. D.; Büchler, H. P.; Gorshkov, A. V. Publication: Physical Review Letters, Volume 115, Issue 12, id.123601 (PhRvL Homepage) Publication Date: 09/2015 Origin: APS PACS Keywords: Quantum optical phenomena in absorbing dispersive and conducting media, Rydberg states, Interatomic potentials and forces, Effects of atomic coherence on propagation absorption and amplification of light, electromagnetically induced transparency and absorption Abstract Copyright: (c) 2015: American Physical Society DOI: 10.1103/PhysRevLett.115.123601 Bibliographic Code: 2015PhRvL.115l3601M

Abstract

We show that two photons coupled to Rydberg states via electromagnetically induced transparency can interact via an effective Coulomb potential. This interaction gives rise to a continuum of two-body bound states. Within the continuum, metastable bound states are distinguished in analogy with quasibound states tunneling through a potential barrier. We find multiple branches of metastable bound states whose energy spectrum is governed by the Coulomb potential, thus obtaining a photonic analogue of the hydrogen atom. Under certain conditions, the wave function resembles that of a diatomic molecule in which the two polaritons are separated by a finite "bond length." These states propagate with a negative group velocity in the medium, allowing for a simple preparation and detection scheme, before they slowly decay to pairs of bound Rydberg atoms.

 Title: Search for Dark Matter in Events with Missing Transverse Momentum and a Higgs Boson Decaying to Two Photons in p p Collisions at √{s }=8 TeV with the ATLAS Detector Authors: Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2821 coauthors Publication: Physical Review Letters, Volume 115, Issue 13, id.131801 (PhRvL Homepage) Publication Date: 09/2015 Origin: APS PACS Keywords: Limits on production of particles, Inclusive production with identified leptons photons or other nonhadronic particles, Standard-model Higgs bosons, Dark matter Abstract Copyright: 2015: CERN DOI: 10.1103/PhysRevLett.115.131801 Bibliographic Code: 2015PhRvL.115m1801A

Abstract

Results of a search for new phenomena in events with large missing transverse momentum and a Higgs boson decaying to two photons are reported. Data from proton-proton collisions at a center-of-mass energy of 8 TeV and corresponding to an integrated luminosity of 20.3 fb-1 have been collected with the ATLAS detector at the LHC. The observed data are well described by the expected standard model backgrounds. Upper limits on the cross section of events with large missing transverse momentum and a Higgs boson candidate are also placed. Exclusion limits are presented for models of physics beyond the standard model featuring dark-matter candidates.

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