Faculty Publications: April, 2014

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

 Title: Intra-unit-cell Nematic Density Wave: Unified Broken-Symmetry of the Cuprate Pseudogap State Authors: Fujita, K.; Hamidian, M. H.; Edkins, S. D.; Kim, Chung Koo; Kohsaka, Y.; Azuma, M.; Takano, M.; Takagi, H.; Eisaki, H.; Uchida, S.; Allais, A.; Lawler, M. J.; Kim, E.-A.; Sachdev, Subir; Séamus Davis, J. C. Publication: eprint arXiv:1404.0362 Publication Date: 04/2014 Origin: ARXIV Keywords: Condensed Matter - Superconductivity Bibliographic Code: 2014arXiv1404.0362F

Abstract

The identity of the fundamental broken symmetry (if any) in the cuprate pseudogap state is unresolved. In fact, two apparently distinct forms of electronic symmetry breaking, one of intra-unit-cell rotational symmetry (Q=0 nematic) and the other of lattice translational symmetry (Q$\neq$0 density wave), are reported extensively. However, indications of linkage between these two phenomena suggest the prospect of a unified fundamental description, with one intriguing possibility being an intra-unit-cell nematic density wave. Here we carry out site-specific measurements within each CuO$_2$ unit-cell, segregating the results into three separate electronic structure images containing only the Cu sites (Cu(r)) and only the x/y-axis O sites (O$_x$(r) and O$_y$(r)). Phase resolved Fourier analysis reveals directly that the incommensurate modulations in the O$_x$(r) and O$_y$(r) sublattice images consistently exhibit a relative phase of ${\pi}$. We confirm this discovery on two highly distinct cuprate compounds, ruling out tunnel matrix-element and materials specific systematics. These observations demonstrate by direct sublattice phase-resolved visualization that the cuprate density wave consists essentially of spatial modulations of the intra-unit-cell nematicity; this state can equally well be described as an intra-unit-cell density wave with a d-symmetry form factor.

 Title: Measurement of \boldmath $R = {\mathcal{B}\left(t \rightarrow Wb \right)/\mathcal{B}\left(t \rightarrow Wq \right)}$ in Top--Quark--Pair Decays using Dilepton Events and the Full CDF Run II Data Set Authors: CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 402 coauthors Publication: eprint arXiv:1404.3392 Publication Date: 04/2014 Origin: ARXIV Keywords: High Energy Physics - Experiment Comment: submitted to PRL Bibliographic Code: 2014arXiv1404.3392C

Abstract

We present a measurement of the ratio of the top-quark branching fractions $R=\mathcal{B}(t\rightarrow Wb)/\mathcal{B}(t\rightarrow$ $q$ represents quarks of flavors $b$, $s$, or $d$, in the final state, in events with two charged leptons, missing transverse energy and at least two jets. The measurement uses $\sqrt{s}$ = 1.96 TeV proton--antiproton collision data corresponding to an integrated luminosity of 8.7 fb$^{-1}$ and collected with the Collider Detector at Fermilab during Run II of the Tevatron. We measure $R=0.87 \pm 0.07$ (stat+syst), and extract the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element, $\left|V_{tb}\right| = 0.93 \pm 0.04$ (stat+syst) assuming three generations of quarks. Under these assumptions, a lower limit of $|V_{tb}|>0.85$ at 95% credibility level is set.

 Title: Measurement of the inclusive leptonic asymmetry in top-quark pairs that decay to two charged leptons at CDF Authors: CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 402 coauthors Publication: eprint arXiv:1404.3698 Publication Date: 04/2014 Origin: ARXIV Keywords: High Energy Physics - Experiment Bibliographic Code: 2014arXiv1404.3698C

Abstract

We measure the inclusive forward-backward asymmetry of the charged-lepton pseudorapidities from top-quark pairs produced in proton-antiproton collisions, and decaying to final states that contain two charged leptons (electrons or muons), using data collected with the Collider Detector at Fermilab. With an integrated luminosity of 9.1 $\rm{fb}^{-1}$, the leptonic forward-backward asymmetry, $A_{\text{FB}}^{\ell}$, is measured to be $0.072 \pm 0.060$ and the leptonic pair forward-backward asymmetry, $A_{\text{FB}}^{\ell\ell}$, is measured to be $0.076 \pm 0.082$, compared with the standard model predictions of $A_{\text{FB}}^{\ell} = 0.038 \pm 0.003$ and $A_{\text{FB}}^{\ell\ell} = 0.048 \pm 0.004$, respectively. Additionally, we combine the $A_{\text{FB}}^{\ell}$ result with a previous determination from a final state with a single lepton and hadronic jets and obtain $A_{\text{FB}}^{\ell} = 0.090^{+0.028}_{-0.026}$.

 Title: Superfluid spin transport through antiferromagnetic insulators Authors: Takei, So; Halperin, Bertrand I.; Yacoby, Amir; Tserkovnyak, Yaroslav Publication: eprint arXiv:1404.3987 Publication Date: 04/2014 Origin: ARXIV Keywords: Condensed Matter - Mesoscale and Nanoscale Physics Comment: 10 pages, 4 figures Bibliographic Code: 2014arXiv1404.3987T

Abstract

A theoretical proposal for realizing and detecting spin supercurrent in an isotropic antiferromagnetic insulator is reported. Superfluid spin transport is achieved by inserting the antiferromagnet between two metallic reservoirs and establishing a spin accumulation in one reservoir such that a spin bias is applied across the magnet. We consider a class of bipartite antiferromagnets with Neel ground states, and temperatures well below the ordering temperature, where spin transport is mediated essentially by the condensate. Landau-Lifshitz and magneto-circuit theories are used to directly relate spin current in different parts of the heterostructure to the spin-mixing conductances characterizing the antiferromagnet|metal interfaces and the antiferromagnet bulk damping parameters, quantities all obtainable from experiments. We study the efficiency of spin angular-momentum transfer at an antiferromagnet|metal interface by developing a microscopic scattering theory for the interface and extracting the spin-mixing conductance for a simple model. Within the model, a quantitative comparison between the spin-mixing conductances obtained for the antiferromagnet|metal and ferromagnet|metal interfaces is made.

 Title: Zeeman interaction in ThO $H^3\Delta_1$ for the electron EDM search Authors: Petrov, A. N.; Skripnikov, L. V.; Titov, A. V.; Hutzler, N. R.; Hess, P. W.; O'Leary, B. R.; Spaun, B.; DeMille, D.; Gabrielse, G.; Doyle, J. M. Publication: eprint arXiv:1404.4024 Publication Date: 04/2014 Origin: ARXIV Keywords: Physics - Atomic Physics Bibliographic Code: 2014arXiv1404.4024P

Abstract

The current limit on the electron's electric dipole moment, $|d_\mathrm{e}|<8.7\times 10^{-29} e {\cdotp} {\rm cm}$ (90% confidence), was set using the molecule thorium monoxide (ThO) in the $J=1$ rotational level of its $H ^3\Delta_1$ electronic state [Science $\bf 343$, 269 (2014)]. This state in ThO is very robust against systematic errors related to magnetic fields or geometric phases, due in part to its $\Omega$-doublet structure. These systematics can be further suppressed by operating the experiment under conditions where the $g$-factor difference between the $\Omega$-doublets is minimized. We consider the $g$-factors of the ThO $H^3\Delta_1$ state both experimentally and theoretically, including dependence on $\Omega$-doublets, rotational level, and external electric field. The calculated and measured values are in good agreement. We find that the $g$-factor difference between $\Omega$-doublets is smaller in $J=2$ than in $J=1$, and reaches zero at an experimentally accessible electric field. This means that the $H,J=2$ state should be even more robust against a number of systematic errors compared to $H,J=1$.

 Title: Evidence for a New Soft Graviton Theorem Authors: Cachazo, Freddy; Strominger, Andrew Publication: eprint arXiv:1404.4091 Publication Date: 04/2014 Origin: ARXIV Keywords: High Energy Physics - Theory Comment: 21 pages Bibliographic Code: 2014arXiv1404.4091C

Abstract

The single-soft-graviton limit of any quantum gravity scattering amplitude is given at leading order by the universal Weinberg pole formula. Gauge invariance of the formula follows from global energy-momentum conservation. In this paper evidence is given for a conjectured universal formula for the finite subleading term in the expansion about the soft limit, whose gauge invariance follows from global angular momentum conservation. The conjecture is non-trivially verified for all tree-level graviton scattering amplitudes using a BCFW recursion relation. One hopes to understand this infinity of new soft relations as a Ward identity for a new superrotation Virasoro symmetry of the quantum gravity S-matrix.

 Title: Measurement of Charged Pion Production Yields off the NuMI Target Authors: Paley, J. M.; Messier, M. D.; Raja, R.; Akgun, U.;... Feldman, G. J.;... and 51 coauthors Publication: eprint arXiv:1404.5882 Publication Date: 04/2014 Origin: ARXIV Keywords: High Energy Physics - Experiment, Nuclear Experiment Comment: 15 pages, 13 figures Bibliographic Code: 2014arXiv1404.5882P

Abstract

The fixed-target MIPP experiment, Fermilab E907, was designed to measure the production of hadrons from the collisions of hadrons of momenta ranging from 5 to 120 GeV/c on a variety of nuclei. These data will generally improve the simulation of particle detectors and predictions of particle beam fluxes at accelerators. The spectrometer momentum resolution is between 3 and 4%, and particle identification is performed for particles ranging between 0.3 and 80 GeV/c using $dE/dx$, time-of-flight and Cherenkov radiation measurements. MIPP collected $1.42 \times10^6$ events of 120 GeV Main Injector protons striking a target used in the NuMI facility at Fermilab. The data have been analyzed and we present here charged pion yields per proton-on-target determined in bins of longitudinal and transverse momentum between 0.5 and 80 GeV/c, with combined statistical and systematic relative uncertainties between 5 and 10%.

 Title: Feedback of superconducting fluctuations on charge order in the underdoped cuprates Authors: Chowdhury, Debanjan; Sachdev, Subir Publication: eprint arXiv:1404.6532 Publication Date: 04/2014 Origin: ARXIV Keywords: Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Superconductivity Comment: 17 pages, 9 figures Bibliographic Code: 2014arXiv1404.6532C

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 wavevector 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 charge-density wave states, and find that they prefer the experimentally observed wavevector.

 Title: Accelerating black holes, spin-3/2 fields and C-metric Authors: Lin, Hai; Saifullah, K.; Yau, Shing-Tung Publication: eprint arXiv:1404.7489 Publication Date: 04/2014 Origin: ARXIV Keywords: High Energy Physics - Theory, General Relativity and Quantum Cosmology Comment: 18 pages Bibliographic Code: 2014arXiv1404.7489L

Abstract

We consider spin-3/2 particles on the background of general accelerating black holes and C-metric. The Rarita-Schwinger equations of spin-3/2 particles are analyzed on these backgrounds. The emission and absorption probabilities of the spin-3/2 particles on these spacetimes are calculated. These backgrounds which we analyze contain both black hole horizon and acceleration horizon, and have general electric and magnetic charges, rotation, and acceleration parameter. The properties of the spin-3/2 field near the acceleration horizon are also computed.

 Title: Continuum dynamics of elastocapillary coalescence and arrest Authors: Wei, Z.; Mahadevan, L. Publication: Europhysics Letters, Volume 106, Issue 1, article id. 14002 (2014). Publication Date: 04/2014 Origin: IOP DOI: 10.1209/0295-5075/106/14002 Bibliographic Code: 2014EL....10614002W

Abstract

The surface-tension–driven coalescence of wet hair, nano-pillars and supported lamellae immersed in an evaporating liquid is eventually arrested elastically. To characterize this at a continuum level, we start from a discrete microscopic model of the process and derive a mesoscopic theory that couples the inhomogeneous dynamics of drying to the capillary forcing and elastic bending of the lamellae. Numerical simulations of the resulting partial differential equation capture the primary unstable mode seen in experiments, and the dynamic coalescence of the lamellae into dimers and quadrimers. Our theory also predicts the elastic arrest of the pattern or the separation of lamellar bundles into their constituents as a function of the amount of liquid left at the end of the process.

 Title: Measurement of the electroweak production of dijets in association with a Z-boson and distributions sensitive to vector boson fusion in proton-proton collisions at = 8 TeV using the ATLAS detector Authors: Aad, G.; Abajyan, T.; Abbott, B.;... da Costa, J. Barreiro Guimarães;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2878 coauthors Publication: Journal of High Energy Physics, Volume 2014, article id. #31 Publication Date: 04/2014 Origin: SPRINGER Keywords: Electroweak interaction, Jets, Hadron-Hadron Scattering Abstract Copyright: (c) 2014: The Author(s) DOI: 10.1007/JHEP04(2014)031 Bibliographic Code: 2014JHEP...04..031A

Abstract

Measurements of fiducial cross sections for the electroweak production of two jets in association with a Z-boson are presented. The measurements are performed using 20 .3 fb-1 of proton-proton collision data collected at a centre-of-mass energy of = 8 TeV by the ATLAS experiment at the Large Hadron Collider. The electroweak component is extracted by a fit to the dijet invariant mass distribution in a fiducial region chosen to enhance the electroweak contribution over the dominant background in which the jets are produced via the strong interaction. The electroweak cross sections measured in two fiducial regions are in good agreement with the Standard Model expectations and the background-only hypothesis is rejected with significance above the 5 σ level. The electroweak process includes the vector boson fusion production of a Z-boson and the data are used to place limits on anomalous triple gauge boson couplings. In addition, measurements of cross sections and differential distributions for inclusive Z-boson-plus-dijet production are performed in five fiducial regions, each with different sensitivity to the electroweak contribution. The results are corrected for detector effects and compared to predictions from the Sherpa and Powheg event generators. [Figure not available: see fulltext.]

 Title: Coherent Optical Transitions in Implanted Nitrogen Vacancy Centers Authors: Chu, Y.; de Leon, N. P.; Shields, B. J.; Hausmann, B.; Evans, R.; Togan, E.; Burek, M. J.; Markham, M.; Stacey, A.; Zibrov, A. S.; Yacoby, A.; Twitchen, D. J.; Loncar, M.; Park, H.; Maletinsky, P.; Lukin, M. D. Publication: Nano Letters, vol. 14, issue 4, pp. 1982-1986 Publication Date: 04/2014 Origin: CROSSREF DOI: 10.1021/nl404836p Bibliographic Code: 2014NanoL..14.1982C

Abstract

Not Available

 Title: Isotropic three-dimensional super-resolution imaging with a self-bending point spread function Authors: Jia, Shu; Vaughan, Joshua C.; Zhuang, Xiaowei Publication: Nature Photonics, Volume 8, Issue 4, pp. 302-306 (2014). Publication Date: 04/2014 Origin: NATURE Abstract Copyright: (c) 2014: Nature Publishing Group DOI: 10.1038/nphoton.2014.13 Bibliographic Code: 2014NaPho...8..302J

Abstract

Airy beams maintain their intensity profiles over a large propagation distance without substantial diffraction and exhibit lateral bending during propagation. This unique property has been exploited for the micromanipulation of particles, the generation of plasma channels and the guidance of plasmonic waves, but has not been explored for high-resolution optical microscopy. Here, we introduce a self-bending point spread function (SB-PSF) based on Airy beams for three-dimensional super-resolution fluorescence imaging. We designed a side-lobe-free SB-PSF and implemented a two-channel detection scheme to enable unambiguous three-dimensional localization of fluorescent molecules. The lack of diffraction and the propagation-dependent lateral bending make the SB-PSF well suited for precise three-dimensional localization of molecules over a large imaging depth. Using this method, we obtained super-resolution imaging with isotropic three-dimensional localization precision of 10-15 nm over a 3 µm imaging depth from ~2,000 photons per localization.

 Title: Subnanometre resolution in three-dimensional magnetic resonance imaging of individual dark spins Authors: Grinolds, M. S.; Warner, M.; de Greve, K.; Dovzhenko, Y.; Thiel, L.; Walsworth, R. L.; Hong, S.; Maletinsky, P.; Yacoby, A. Publication: Nature Nanotechnology, Volume 9, Issue 4, pp. 279-284 (2014). Publication Date: 04/2014 Origin: NATURE Abstract Copyright: (c) 2014: Nature Publishing Group DOI: 10.1038/nnano.2014.30 Bibliographic Code: 2014NatNa...9..279G

Abstract

Magnetic resonance imaging (MRI) has revolutionized biomedical science by providing non-invasive, three-dimensional biological imaging. However, spatial resolution in conventional MRI systems is limited to tens of micrometres, which is insufficient for imaging on molecular scales. Here, we demonstrate an MRI technique that provides subnanometre spatial resolution in three dimensions, with single electron-spin sensitivity. Our imaging method works under ambient conditions and can measure ubiquitous dark' spins, which constitute nearly all spin targets of interest. In this technique, the magnetic quantum-projection noise of dark spins is measured using a single nitrogen-vacancy (NV) magnetometer located near the surface of a diamond chip. The distribution of spins surrounding the NV magnetometer is imaged with a scanning magnetic-field gradient. To evaluate the performance of the NV-MRI technique, we image the three-dimensional landscape of electronic spins at the diamond surface and achieve an unprecedented combination of resolution (0.8 nm laterally and 1.5 nm vertically) and single-spin sensitivity. Our measurements uncover electronic spins on the diamond surface that can potentially be used as resources for improved magnetic imaging. This NV-MRI technique is immediately applicable to diverse systems including imaging spin chains, readout of spin-based quantum bits, and determining the location of spin labels in biological systems.

 Title: Topological excitations and the dynamic structure factor of spin liquids on the kagome lattice Authors: Punk, Matthias; Chowdhury, Debanjan; Sachdev, Subir Publication: Nature Physics, Volume 10, Issue 4, pp. 289-293 (2014). Publication Date: 04/2014 Origin: NATURE Abstract Copyright: (c) 2014: Nature Publishing Group DOI: 10.1038/nphys2887 Bibliographic Code: 2014NatPh..10..289P

Abstract

Recent neutron scattering experiments on the spin-1/2 kagome lattice antiferromagnet ZnCu3(OH)6Cl2 (Herbertsmithite) provide the first evidence of fractionalized excitations in a quantum spin liquid state in two spatial dimensions. In contrast to existing theoretical models of both gapped and gapless spin liquids, which give rise to sharp dispersing features in the dynamic structure factor, the measured dynamic structure factor reveals an excitation continuum that is remarkably flat as a function of frequency. Here we show that many experimentally observed features can be explained by the presence of topological vison excitations in a Z2 spin liquid. These visons form flat bands on the kagome lattice, and thus act as a momentum sink for spin-carrying excitations that are probed by neutron scattering. We compute the dynamic structure factor for two different Z2 spin liquids and find that our results for one of them are in qualitative agreement with the neutron scattering experiments above a very low energy cutoff, below which the structure factor is probably dominated by impurities.

 Title: Nanophotonic quantum phase switch with a single atom Authors: Tiecke, T. G.; Thompson, J. D.; de Leon, N. P.; Liu, L. R.; Vuletić, V.; Lukin, M. D. Publication: Nature, Volume 508, Issue 7495, pp. 241-244 (2014). (Nature Homepage) Publication Date: 04/2014 Origin: NATURE Abstract Copyright: (c) 2014: Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved. DOI: 10.1038/nature13188 Bibliographic Code: 2014Natur.508..241T

Abstract

By analogy to transistors in classical electronic circuits, quantum optical switches are important elements of quantum circuits and quantum networks. Operated at the fundamental limit where a single quantum of light or matter controls another field or material system, such a switch may enable applications such as long-distance quantum communication, distributed quantum information processing and metrology, and the exploration of novel quantum states of matter. Here, by strongly coupling a photon to a single atom trapped in the near field of a nanoscale photonic crystal cavity, we realize a system in which a single atom switches the phase of a photon and a single photon modifies the atom's phase. We experimentally demonstrate an atom-induced optical phase shift that is nonlinear at the two-photon level, a photon number router that separates individual photons and photon pairs into different output modes, and a single-photon switch in which a single gate' photon controls the propagation of a subsequent probe field. These techniques pave the way to integrated quantum nanophotonic networks involving multiple atomic nodes connected by guided light.

 Title: Quantum interference between independent reservoirs in open quantum systems Authors: Chan, Ching-Kit; Lin, Guin-Dar; Yelin, Susanne F.; Lukin, Mikhail D. Publication: Physical Review A, Volume 89, Issue 4, id.042117 (PhRvA Homepage) Publication Date: 04/2014 Origin: APS PACS Keywords: Decoherence, open systems, quantum statistical methods, Quantum description of interaction of light and matter, related experiments, Entanglement production and manipulation, Quantum fluctuations quantum noise and quantum jumps Abstract Copyright: 2014: American Physical Society DOI: 10.1103/PhysRevA.89.042117 Bibliographic Code: 2014PhRvA..89d2117C

Abstract

When a quantum system interacts with multiple reservoirs, the environmental effects are usually treated in an additive manner. We show that this assumption breaks down for non-Markovian environments that have finite memory times. Specifically, we demonstrate that quantum interferences between independent environments can qualitatively modify the dynamics of the physical system. We illustrate this effect with a two-level system coupled to two structured photonic reservoirs, discuss its origin using a nonequilibrium diagrammatic technique, and show an example when the application of this interference can result in an improved dark state preparation in a Λ system.

 Title: Measuring Z2 topological invariants in optical lattices using interferometry Authors: Grusdt, F.; Abanin, D.; Demler, E. Publication: Physical Review A, Volume 89, Issue 4, id.043621 (PhRvA Homepage) Publication Date: 04/2014 Origin: APS PACS Keywords: Ultracold gases trapped gases, Matter waves, Atom interferometry techniques, Phases: geometric, dynamic or topological Abstract Copyright: 2014: American Physical Society DOI: 10.1103/PhysRevA.89.043621 Bibliographic Code: 2014PhRvA..89d3621G

Abstract

We propose an interferometric method to measure Z2 topological invariants of time-reversal invariant topological insulators realized with optical lattices in two and three dimensions. We suggest two schemes which both rely on a combination of Bloch oscillations with Ramsey interferometry and can be implemented using standard tools of atomic physics. In contrast to topological Zak phase and Chern number, defined for individual one-dimensional and two-dimensional Bloch bands, the formulation of the Z2 invariant involves at least two Bloch bands related by time-reversal symmetry which one must keep track of in measurements. In one of our schemes this can be achieved by the measurement of Wilson loops, which are non-Abelian generalizations of Zak phases. The winding of their eigenvalues is related to the Z2 invariant. We thereby demonstrate that Wilson loops are not just theoretical concepts but can be measured experimentally. For the second scheme we introduce a generalization of time-reversal polarization which is continuous throughout the Brillouin zone. We show that its winding over half the Brillouin zone yields the Z2 invariant. To measure this winding, our protocol only requires Bloch oscillations within a single band, supplemented by coherent transitions to a second band which can be realized by lattice shaking.

 Title: Transmon-based simulator of nonlocal electron-phonon coupling: A platform for observing sharp small-polaron transitions Authors: Stojanović, Vladimir M.; Vanević, Mihajlo; Demler, Eugene; Tian, Lin Publication: Physical Review B, Volume 89, Issue 14, id.144508 (PhRvB Homepage) Publication Date: 04/2014 Origin: APS PACS Keywords: Josephson devices, Quantum algorithms protocols and simulations, Self-trapped or small polarons Abstract Copyright: 2014: American Physical Society DOI: 10.1103/PhysRevB.89.144508 Bibliographic Code: 2014PhRvB..89n4508S

Abstract

We propose an analog superconducting quantum simulator for a one-dimensional model featuring momentum-dependent (nonlocal) electron-phonon couplings of Su-Schrieffer-Heeger and "breathing-mode" types. Because its corresponding coupling vertex function depends on both the electron and phonon quasimomenta, this model does not belong to the realm of validity of the Gerlach-Löwen theorem that rules out any nonanalyticities in single-particle properties. The superconducting circuit behind the proposed simulator entails an array of transmon qubits and microwave resonators. By applying microwave driving fields to the qubits, a small-polaron Bloch state with an arbitrary quasimomentum can be prepared in this system within times several orders of magnitude shorter than the typical qubit decoherence times. We demonstrate that—by varying the externally tunable parameters—one can readily reach the critical coupling strength required for observing the sharp transition from a nondegenerate (single-particle) ground state corresponding to zero quasimomentum (Kgs=0) to a twofold-degenerate small-polaron ground state at nonzero quasimomenta Kgs and -Kgs. Through exact numerical diagonalization of our effective Hamiltonian, we show how this nonanalyticity is reflected in the relevant single-particle properties (ground-state energy, quasiparticle residue, average number of phonons). We also show that the proposed setup provides an ideal testbed for studying the nonequilibrium dynamics of small-polaron formation in the presence of strongly momentum-dependent electron-phonon interactions.

 Title: Transport near the Ising-nematic quantum critical point of metals in two dimensions Authors: Hartnoll, Sean A.; Mahajan, Raghu; Punk, Matthias; Sachdev, Subir Publication: Physical Review B, Volume 89, Issue 15, id.155130 (PhRvB Homepage) Publication Date: 04/2014 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.89.155130 Bibliographic Code: 2014PhRvB..89o5130H

Abstract

We consider two-dimensional metals near a Pomeranchuk instability which breaks 90∘ lattice rotation symmetry. Such metals realize strongly coupled non-Fermi liquids with critical fluctuations of an Ising-nematic order. At low temperatures, impurity scattering provides the dominant source of momentum relaxation and, hence, a nonzero electrical resistivity. We use the memory matrix method to compute the resistivity of this non-Fermi liquid to second order in the impurity potential, without assuming the existence of quasiparticles. Impurity scattering in the d-wave channel acts as a random "field" on the Ising-nematic order. We find contributions to the resistivity with a nearly linear temperature dependence, along with more singular terms; the most singular is the random-field contribution which diverges in the limit of zero temperature.

 Title: Combination of measurements of the top-quark pair production cross section from the Tevatron Collider Authors: Aaltonen, T.; Abazov, V. M.; Abbott, B.;... Franklin, M.;... Guimaraes da Costa, J.;... and 762 coauthors Publication: Physical Review D, Volume 89, Issue 7, id.072001 (PhRvD Homepage) Publication Date: 04/2014 Origin: APS PACS Keywords: Top quarks, Experimental tests, Inclusive production with identified leptons photons or other nonhadronic particles Abstract Copyright: 2014: American Physical Society DOI: 10.1103/PhysRevD.89.072001 Bibliographic Code: 2014PhRvD..89g2001A

Abstract

We combine six measurements of the inclusive top-quark pair (tt ¯) production cross section (σtt ¯) from data collected with the CDF and D0 detectors at the Fermilab Tevatron with proton-antiproton collisions at √s =1.96 TeV. The data correspond to integrated luminosities of up to 8.8 fb-1. We obtain a value of σtt ¯=7.60±0.41 pb for a top-quark mass of mt=172.5 GeV. The contributions to the uncertainty are 0.20 pb from statistical sources, 0.29 pb from systematic sources, and 0.21 pb from the uncertainty on the integrated luminosity. The result is in good agreement with the standard model expectation of 7.35-0.33+0.28 pb at next-to-next-to-leading order and next-to-next-to leading logarithms in perturbative QCD.

 Title: Indirect measurement of sin2θW (or MW) using μ+μ- pairs from γ*/Z bosons produced in pp ¯ collisions at a center-of-momentum energy of 1.96 TeV Authors: Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 403 coauthors Publication: Physical Review D, Volume 89, Issue 7, id.072005 (PhRvD Homepage) Publication Date: 04/2014 Origin: APS PACS Keywords: Electroweak radiative corrections, Inclusive production with identified leptons photons or other nonhadronic particles, Z bosons Abstract Copyright: 2014: American Physical Society DOI: 10.1103/PhysRevD.89.072005 Bibliographic Code: 2014PhRvD..89g2005A

Abstract

Drell-Yan lepton pairs are produced in the process pp ¯→μ+μ-+X through an intermediate γ*/Zboson. The forward-backward asymmetry in the polar-angle distribution of the μ- as a function of the invariant mass of the μ+μ- pair is used to obtain the effective leptonic determination sin2θefflept of the electroweak-mixing parameter sin2θW, from which the value of sin2θW is derived assuming the standard model. The measurement sample, recorded by the Collider Detector at Fermilab (CDF), corresponds to 9.2 fb-1 of integrated luminosity from pp ¯ collisions at a center-of-momentum energy of 1.96 TeV, and is the full CDF Run II data set. The value of sin2θefflept is found to be 0.2315±0.0010, where statistical and systematic uncertainties are combined in quadrature. When interpreted within the context of the standard model using the on-shell renormalization scheme, where sin2θW=1-MW2/MZ2, the measurement yields sin2θW=0.2233±0.0009, or equivalently a W-boson mass of 80.365±0.047 GeV/c2. The value of the W-boson mass is in agreement with previous determinations in electron-positron collisions and at the Tevatron collider.

 Title: Study of heavy-flavor quarks produced in association with top-quark pairs at √s =7 TeV using the ATLAS detector Authors: Aad, G.; Abajyan, T.; Abbott, B.;... Franklin, M.;... Guimaraes da Costa, J.;... Huth, J.;... Morii, M.;... and 2817 coauthors Publication: Physical Review D, Volume 89, Issue 7, id.072012 (PhRvD Homepage) Publication Date: 04/2014 Origin: APS PACS Keywords: Top quarks, Charmed quarks, Bottom quarks, Standard-model Higgs bosons Abstract Copyright: 2014: CERN DOI: 10.1103/PhysRevD.89.072012 Bibliographic Code: 2014PhRvD..89g2012A

Abstract

Using a sample of dilepton top-quark pair (tt¯) candidate events, a study is performed of the production of top-quark pairs together with heavy-flavor (HF) quarks, the sum of tt¯+b+X and tt¯+c+X, collectively referred to as tt¯ + HF. The data set used corresponds to an integrated luminosity of 4.7 fb-1 of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. The presence of additional HF (b or c) quarks in the tt¯ sample is inferred by looking for events with at least three b-tagged jets, where two are attributed to the b quarks from the tt¯ decays and the third to additional HF production. The dominant background to tt¯ + HF in this sample is tt¯+jet events in which a light-flavor jet is misidentified as a heavy-flavor jet. To determine the heavy- and light-flavor content of the additional b-tagged jets, a fit to the vertex mass distribution of b-tagged jets in the sample is performed. The result of the fit shows that 79 ± 14 (stat) ± 22 (syst) of the 105 selected extra b-tagged jets originate from HF quarks, 3 standard deviations away from the hypothesis of zero tt¯ + HF production. The result for extra HF production is quoted as a ratio (RHF) of the cross section for tt¯ + HF production to the cross section for tt¯ production with at least one additional jet. Both cross sections are measured in a fiducial kinematic region within the ATLAS acceptance. RHF is measured to be [6.2±1.1(stat)±1.8(syst)]% for jets with pT>25 GeV and |η|<2.5, in agreement with the expectations from Monte Carlo generators.

 Title: Mass and lifetime measurements of bottom and charm baryons in pp ¯ collisions at √s =1.96 TeV Authors: Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 403 coauthors Publication: Physical Review D, Volume 89, Issue 7, id.072014 (PhRvD Homepage) Publication Date: 04/2014 Origin: APS PACS Keywords: Hadronic decays, Baryon production, Bottom baryons Abstract Copyright: 2014: American Physical Society DOI: 10.1103/PhysRevD.89.072014 Bibliographic Code: 2014PhRvD..89g2014A

Abstract

We report on mass and lifetime measurements of several ground state charmed and bottom baryons, using a data sample corresponding to 9.6 fb-1 from pp ¯ collisions at √s =1.96 TeV and recorded with the Collider Detector at Fermilab. Baryon candidates are reconstructed from data collected with an online event selection designed for the collection of long-lifetime heavy-flavor decay products and a second event selection designed to collect J/ψ→μ+μ- candidates. First evidence for the process Ωb-→Ωc0π- is presented with a significance of 3.3σ. We measure the following baryon masses: M(Ξc0) =2470.85±0.24(stat)±0.55(syst) MeV/c2,M(Ξc+)=2468.00±0.18(stat)±0.51(syst) MeV/c2,M(Λb)=5620.15±0.31(stat)±0.47(syst) MeV/c2,M(Ξb0)=5788.7±4.3(stat)±1.4(syst) MeV/c2,andM(Ωb-)=6047.5±3.8(stat)±0.6(syst) MeV/c2. The isospin splitting of the Ξb-,0 states is found to be M(Ξb-)-M(Ξb0)=4.7±4.7(stat)±0.7(syst) MeV /c2. The isospin splitting of the Ξc0,+ states is found to be M(Ξc0)-M(Ξc+)=2.85±0.30(stat)±0.04(syst) MeV/c2. The following lifetime measurements are made: τ(Λb)=1.565±0.035(stat)±0.020(syst) ps,τ(Ξb-)=1.32±0.14(stat)±0.02(syst) ps,τ(Ωb-)=1.66-0.40+0.53(stat)±0.02(syst) ps

 Title: Lift-Off Instability During the Impact of a Drop on a Solid Surface Authors: Kolinski, John M.; Mahadevan, L.; Rubinstein, Shmuel M. Publication: Physical Review Letters, Volume 112, Issue 13, id.134501 (PhRvL Homepage) Publication Date: 04/2014 Origin: APS PACS Keywords: Drops and bubbles, Interfacial flows, Gas-liquid and vacuum-liquid interfaces Abstract Copyright: 2014: American Physical Society DOI: 10.1103/PhysRevLett.112.134501 Bibliographic Code: 2014PhRvL.112m4501K

Abstract

We directly measure the rapid spreading dynamics succeeding the impact of a droplet of fluid on a solid, dry surface. Upon impact, the air separating the liquid from the solid surface fails to drain and wetting is delayed as the liquid rapidly spreads outwards over a nanometer thin film of air. We show that the approach of the spreading liquid front toward the surface is unstable and the spreading front lifts off away from the surface. Lift-off ensues well before the liquid contacts the surface, in contrast with prevailing paradigm where lift-off of the liquid is contingent on solid-liquid contact and the formation of a viscous boundary layer. Here we investigate the dynamics of liquid spreading over a thin film of air and its lift-off away from the surface over a large range of fluid viscosities and find that the lift-off instability is dependent on viscosity and occurs at a time that scales with the viscosity to the power of one half.

 Title: Asymmetric Mutualism in Two- and Three-Dimensional Range Expansions Authors: Lavrentovich, Maxim O.; Nelson, David R. Publication: Physical Review Letters, Volume 112, Issue 13, id.138102 (PhRvL Homepage) Publication Date: 04/2014 Origin: APS PACS Keywords: Phase transitions, Lattice models, Noise in biological systems, Population dynamics and ecological pattern formation Abstract Copyright: 2014: American Physical Society DOI: 10.1103/PhysRevLett.112.138102 Bibliographic Code: 2014PhRvL.112m8102L

Abstract

Genetic drift at the frontiers of two-dimensional range expansions of microorganisms can frustrate local cooperation between different genetic variants, demixing the population into distinct sectors. In a biological context, mutualistic or antagonistic interactions will typically be asymmetric between variants. By taking into account both the asymmetry and the interaction strength, we show that the much weaker demixing in three dimensions allows for a mutualistic phase over a much wider range of asymmetric cooperative benefits, with mutualism prevailing for any positive, symmetric benefit. We also demonstrate that expansions with undulating fronts roughen dramatically at the boundaries of the mutualistic phase, with severe consequences for the population genetics along the transition lines.

 Title: Certifying Separability in Symmetric Mixed States of N Qubits, and Superradiance Authors: Wolfe, Elie; Yelin, S. F. Publication: Physical Review Letters, Volume 112, Issue 14, id.140402 (PhRvL Homepage) Publication Date: 04/2014 Origin: APS PACS Keywords: Entanglement and quantum nonlocality, Other multiphoton processes, Collective effects Abstract Copyright: 2014: American Physical Society DOI: 10.1103/PhysRevLett.112.140402 Bibliographic Code: 2014PhRvL.112n0402W

Abstract

Separability criteria are typically of the necessary, but not sufficient, variety, in that satisfying some separability criterion, such as positivity of eigenvalues under partial transpose, does not strictly imply separability. Certifying separability amounts to proving the existence of a decomposition of a target mixed state into some convex combination of separable states; determining the existence of such a decomposition is "hard." We show that it is effective to ask, instead, if the target mixed state "fits" some preconstructed separable form, in that one can generate a sufficient separability criterion relevant to all target states in some family by ensuring enough degrees of freedom in the preconstructed separable form. We demonstrate this technique by inducing a sufficient criterion for "diagonally symmetric" states of N qubits. A sufficient separability criterion opens the door to study precisely how entanglement is (not) formed; we use ours to prove that, counterintuitively, entanglement is not generated in idealized Dicke model superradiance despite its exemplification of many-body effects. We introduce a quantification of the extent to which a given preconstructed parametrization comprises the set of all separable states; for "diagonally symmetric" states our preconstruction is shown to be fully complete. This implies that our criterion is necessary in addition to sufficient, among other ramifications which we explore.

 Title: Quantum Error Correction for Metrology Authors: Kessler, E. M.; Lovchinsky, I.; Sushkov, A. O.; Lukin, M. D. Publication: Physical Review Letters, Volume 112, Issue 15, id.150802 (PhRvL Homepage) Publication Date: 04/2014 Origin: APS PACS Keywords: Metrology, Decoherence, open systems, quantum statistical methods, Quantum error correction and other methods for protection against decoherence, Nanocrystals and nanoparticles Abstract Copyright: 2014: American Physical Society DOI: 10.1103/PhysRevLett.112.150802 Bibliographic Code: 2014PhRvL.112o0802K

Abstract

We propose and analyze a new approach based on quantum error correction (QEC) to improve quantum metrology in the presence of noise. We identify the conditions under which QEC allows one to improve the signal-to-noise ratio in quantum-limited measurements, and we demonstrate that it enables, in certain situations, Heisenberg-limited sensitivity. We discuss specific applications to nanoscale sensing using nitrogen-vacancy centers in diamond in which QEC can significantly improve the measurement sensitivity and bandwidth under realistic experimental conditions.

 Title: Dark Matter as a Trigger for Periodic Comet Impacts Authors: Randall, Lisa; Reece, Matthew Publication: Physical Review Letters, Volume 112, Issue 16, id.161301 (PhRvL Homepage) Publication Date: 04/2014 Origin: APS PACS Keywords: Dark matter, Impact phenomena, Meteors meteorites and tektites Abstract Copyright: 2014: American Physical Society DOI: 10.1103/PhysRevLett.112.161301 Bibliographic Code: 2014PhRvL.112p1301R

Abstract

Although statistical evidence is not overwhelming, possible support for an approximately 35×106 yr periodicity in the crater record on Earth could indicate a nonrandom underlying enhancement of meteorite impacts at regular intervals. A proposed explanation in terms of tidal effects on Oort cloud comet perturbations as the Solar System passes through the galactic midplane is hampered by lack of an underlying cause for sufficiently enhanced gravitational effects over a sufficiently short time interval and by the time frame between such possible enhancements. We show that a smooth dark disk in the galactic midplane would address both these issues and create a periodic enhancement of the sort that has potentially been observed. Such a disk is motivated by a novel dark matter component with dissipative cooling that we considered in earlier work. We show how to evaluate the statistical evidence for periodicity by input of appropriate measured priors from the galactic model, justifying or ruling out periodic cratering with more confidence than by evaluating the data without an underlying model. We find that, marginalizing over astrophysical uncertainties, the likelihood ratio for such a model relative to one with a constant cratering rate is 3.0, which moderately favors the dark disk model. Our analysis furthermore yields a posterior distribution that, based on current crater data, singles out a dark matter disk surface density of approximately 10M⊙/pc2. The geological record thereby motivates a particular model of dark matter that will be probed in the near future.

 Title: Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in = 8 TeV pp collisions with the ATLAS detector Authors: Aad, G.; Abajyan, T.; Abbott, B.;... da Costa, J. Barreiro Guimarães;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2892 coauthors Publication: Journal of High Energy Physics, Volume 2014, article id. #169 Publication Date: 04/2014 Origin: SPRINGER Keywords: Hadron-Hadron Scattering Abstract Copyright: (c) 2014: The Author(s) DOI: 10.1007/JHEP04(2014)169 Bibliographic Code: 2014JHEP...04..169A

Abstract

A search for the direct production of charginos and neutralinos in final states with three leptons and missing transverse momentum is presented. The analysis is based on 20.3 fb-1 of = 8 TeV proton-proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with the Standard Model expectations and limits are set in R-parity-conserving phenomenological Minimal Supersymmetric Standard Models and in simplified supersymmetric models, significantly extending previous results. For simplified supersymmetric models of direct chargino and next-to-lightest neutralino production with decays to lightest neutralino via either all three generations of sleptons, staus only, gauge bosons, or Higgs bosons, and masses are excluded up to 700 GeV, 380 GeV, 345 GeV, or 148 GeV respectively, for a massless . [Figure not available: see fulltext.]

 Title: Measurement of the production cross section of prompt J/ψ mesons in association with a W± boson in pp collisions at = 7 TeV with the ATLAS detector Authors: Aad, G.; Abajyan, T.; Abbott, B.;... da Costa, J. Barreiro Guimarães;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2907 coauthors Publication: Journal of High Energy Physics, Volume 2014, article id. #172 Publication Date: 04/2014 Origin: SPRINGER Keywords: Hadron-Hadron Scattering Abstract Copyright: (c) 2014: The Author(s) DOI: 10.1007/JHEP04(2014)172 Bibliographic Code: 2014JHEP...04..172A

Abstract

The process pp → W ± J/ ψ provides a powerful probe of the production mechanism of charmonium in hadronic collisions, and is also sensitive to multiple parton interactions in the colliding protons. Using the 2011 ATLAS dataset of 4.5 fb-1 of = 7 TeV pp collisions at the LHC, the first observation is made of the production of W ± + prompt J/ ψ events in hadronic collisions, using W ± → μν μ and J/ ψ → μ + μ -. A yield of W ± + prompt J/ ψ events is observed, with a statistical significance of 5.1 σ. The production rate as a ratio to the inclusive W ± boson production rate is measured, and the double parton scattering contribution to the cross section is estimated. [Figure not available: see fulltext.]

 Title: Search for the decay B ¯0→Λc+p ¯pp ¯ Authors: Lees, J. P.; Poireau, V.; Tisserand, V.;...; Morii, M.;... and 338 coauthors Publication: Physical Review D, Volume 89, Issue 7, id.071102 (PhRvD Homepage) Publication Date: 04/2014 Origin: APS PACS Keywords: Decays of bottom mesons, Baryon production, Charmed baryons Abstract Copyright: 2014: American Physical Society DOI: 10.1103/PhysRevD.89.071102 Bibliographic Code: 2014PhRvD..89g1102L

Abstract

We report a search for the decay B ¯0→Λc+p ¯pp ¯. Using a data sample of 471×106 BB ¯ pairs collected with the BABAR detector at the PEP-II2 storage ring at SLAC, we find no events and set an upper limit on the branching fraction B(B ¯0→Λc+p ¯pp ¯)×B(Λ/c+→pK-π+)0.050<2.8×10-6 at 90% C.L., where we have normalized B(Λc+→pK-π+) to the world average value.