Faculty Publications: August, 2016

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

The following are Harvard Physics faculty members' publications, added to the ADS database last month. Please note that some publications which appeared in print last month may not be included in the database (and therefore may not appear on this list) until the following month.

Title:
Physical limits to biomechanical sensing
Authors:
Beroz, Farzan; Jawerth, Louise M.; Münster, Stefan; Weitz, David A.; Broedersz, Chase P.; Wingreen, Ned S.
Publication:
eprint arXiv:1608.01620
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter, Condensed Matter - Disordered Systems and Neural Networks, Physics - Biological Physics, Quantitative Biology - Cell Behavior, Quantitative Biology - Tissues and Organs
Comment:
30 pages, 14 figures
Bibliographic Code:
2016arXiv160801620B

Abstract

Cells actively probe and respond to the stiffness of their surroundings. Since mechanosensory cells in connective tissue are surrounded by a disordered network of biopolymers, their in vivo mechanical environment can be extremely heterogeneous. Here, we investigate how this heterogeneity impacts mechanosensing by modeling the cell as an idealized local stiffness sensor inside a disordered fiber network. For all types of networks we study, including experimentally-imaged collagen and fibrin architectures, we find that measurements applied at different points throughout a given network yield a strikingly broad range of local stiffnesses, spanning roughly two decades. We verify via simulations and scaling arguments that this broad range of local stiffnesses is a generic property of disordered fiber networks, and show that the range can be further increased by tuning specific network features, including the presence of long fibers and the proximity to elastic transitions. These features additionally allow for a highly tunable dependence of stiffness on probe length. Finally, we show that to obtain optimal, reliable estimates of global tissue stiffness, a cell must adjust its size, shape, and position to integrate multiple stiffness measurements over extended regions of space.

 

Title:
Imaging Electron Motion in Graphene
Authors:
Bhandari, Sagar; Westervelt, Robert M.
Publication:
eprint arXiv:1608.02226
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
11 pages, 8 figures, Review on Scanning Probe Microscope Imaging Technique
Bibliographic Code:
2016arXiv160802226B

Abstract

Research in semiconductor physics has advanced to the study of two-dimensional (2D) materials where the surface controls electronic transport. A scanning probe microscope (SPM) is an ideal tool to image electronic motion in these devices by using the SPM tip as a scanning gate. In prior work for a two dimensional electron gas (2DEG) in a GaAs/AlGaAs heterostructure, a number of phenomena were imaged, including electron flow from a quantum point contact, and tuning of a few electron quantum dot. This approach was also used to study InAs quantum dots grown in a InAs/InP nanowire heterostructure. New two-dimensional materials such as graphene show great promise for fundamental research and applications. We have extended or prior work to image the motion of electrons along cyclotron orbits in single atomic layer graphene passing from one point contact to a second point contact on the first magnetic focusing peak in graphene. The charged SPM tip defects electrons passing from one contact to the other, changing the conductance. A plot of the change in conductance vs. tip position presents an image of electron flow. A low temperature Scanning Capacitance Microscope (SCM) with a sensitive charge preamplifier located near the SPM tip achieves a charge noise level 0.13 e/Hz1/2 with high spatial resolution 100 nm, which promises to be useful to study electronic behavior in nanoscale devices.

 

Title:
Analysis of Scanned Probe Images for Magnetic Focusing in Graphene
Authors:
Bhandari, Sagar; Lee, Gil-Ho; Kim, Philip; Westervelt, Robert M.
Publication:
eprint arXiv:1608.02248
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
9 pages, 5 figures, Scanned Probe Imaging in Graphene
Bibliographic Code:
2016arXiv160802248B

Abstract

We use a cooled Scanning Probe Microscope (SPM) to electron motion in nanoscale devices. The charged tip of the SPM is raster scanned at a constant height above the surface as the conductance of the device is measured. The image charge scatters electrons away, changing the path of electrons through the sample.1-3 Using this technique, we have imaged cyclotron orbits3 for ballistic hBN-graphene-hBN devices that flow between two narrow contacts in the magnetic focusing regime. Here we present an analysis of our magnetic focusing imaging results based on the effects of the tip-created charge density dip on the motion of ballistic electrons. The density dip locally reduces the Fermi energy, creating a force that pushes electrons away from the tip. When the tip is above the cyclotron orbit, electrons are deflected away from the receiving contact, creating an image by reducing the transmission between contacts. The data and our analysis suggest that graphene edge is rather rough, and electrons scattering off the edge bounce in random directions. However, when the tip is close to the edge it can enhance transmission by bouncing electrons away from the edge, toward the receiving contact. Our results demonstrate that a cooled SPM is a promising tool to investigate the motion of electrons in ballistic graphene devices.

 

Title:
Imaging Electron Motion in a Few Layer MoS2 Device
Authors:
Bhandari, Sagar; Wang, Ke; Watanabe, Kenji; Taniguchi, Takashi; Kim, Philip; Westervelt, Robert M.
Publication:
eprint arXiv:1608.02250
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
5 pages, 3 figures, Scanned Probe Imagine in MoS2
Bibliographic Code:
2016arXiv160802250B

Abstract

Ultrathin sheets of MoS2 are a newly discovered 2D semiconductor that holds great promise for nanoelectronics. Understanding the pattern of current flow will be crucial for developing devices. In this talk, we present images of current flow in MoS2 obtained with a Scanned Probe Microscope (SPM) cooled to 4 K. We previously used this technique to image electron trajectories in GaAs/AlGaAs heterostructures and graphene. The charged SPM tip is held just above the sample surface, creating an image charge inside the device that scatters electrons. By measuring the change in resistance {\Delta}R while the tip is raster scanned above the sample, an image of electron flow is obtained. We present images of electron flow in an MoS2 device patterned into a hall bar geometry. A three-layer MoS2 sheet is encased by two hBN layers, top and bottom, and patterned into a hall-bar with multilayer graphene contacts. An SPM image shows the current flow pattern from the wide contact at the end of the device for a Hall density n = 1.3x10^12 cm^-2. The SPM tip tends to block flow, increasing the resistance R. The pattern of flow was also imaged for a narrow side contact on the sample. At density n = 5.4x10^11 cm^-2; the pattern seen in the SPM image is similar to the wide contact. The ability to image electron flow promises to be very useful for the development of ultrathin devices from new 2D materials.

 

Title:
Discrete time crystals: rigidity, criticality, and realizations
Authors:
Yao, Norman Y.; Potter, Andrew C.; Potirniche, Ionut-Dragos; Vishwanath, Ashvin
Publication:
eprint arXiv:1608.02589
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Quantum Gases, Condensed Matter - Statistical Mechanics, Condensed Matter - Strongly Correlated Electrons, Quantum Physics
Comment:
9 pages, 7 figures
Bibliographic Code:
2016arXiv160802589Y

Abstract

Despite being forbidden in equilibrium, spontaneous breaking of time translation symmetry can occur in periodically driven, Floquet systems with discrete time-translation symmetry. The period of the resulting discrete time crystal is quantized to an integer multiple of the drive period, arising from a combination of collective synchronization and many body localization. Here, we consider a simple model for a one dimensional discrete time crystal which explicitly reveals the rigidity of the emergent oscillations as the drive is varied. We numerically map out its phase diagram and compute the properties of the dynamical phase transition where the time crystal melts into a trivial Floquet insulator. Moreover, we demonstrate that the model can be realized with current experimental technologies and propose a blueprint based upon a one dimensional chain of trapped ions. Using experimental parameters (featuring long-range interactions), we identify the phase boundaries of the ion-time-crystal and propose a measurable signature of the symmetry breaking phase transition.

 

Title:
Magnetic noise spectroscopy as a probe of local electronic correlations in two-dimensional systems
Authors:
Agarwal, Kartiek; Schmidt, Richard; Halperin, Bertrand; Oganesyan, Vadim; Zaránd, Gergely; Lukin, Mikhail D.; Demler, Eugene
Publication:
eprint arXiv:1608.03278
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
27 pages, 11 figures
Bibliographic Code:
2016arXiv160803278A

Abstract

We develop the theoretical framework for calculating magnetic noise from conducting two-dimensional (2D) materials. We describe how local measurements of this noise can directly probe the wave-vector dependent transport properties of the material over a broad range of length scales, thus providing new insight into a range of correlated phenomena in 2D electronic systems. As an example, we demonstrate how transport in the hydrodynamic regime in an electronic system exhibits a unique signature in the magnetic noise profile that distinguishes it from diffusive and ballistic transport and how this can be used to measure the viscosity of the electronic fluid. We employ a Boltzmann approach in a two-time relaxation-time approximation to compute the conductivity of graphene and quantitatively illustrate these transport regimes and the experimental feasibility of observing them. Next, we discuss signatures of isolated impurities lodged inside the conducting 2D material. The noise near an impurity is found to be suppressed compared to the background by an amount that is directly proportional to the cross-section of electrons/holes scattering off of the impurity. We use these results to outline an experimental proposal to measure the temperature dependent level-shift and line-width of the resonance associated with an Anderson impurity.

 

Title:
Auxiliary fermion approach to the RIXS spectrum in a doped cuprate
Authors:
Shi, Yifei; James, Andrew; Demler, Eugene; Klich, Israel
Publication:
eprint arXiv:1608.03306
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Superconductivity
Bibliographic Code:
2016arXiv160803306S

Abstract

A phenomenological ansatz for the Green's function of doped cuprates, the Yang-Rice-Zhang (YRZ) Green's function, has been successful in describing the Fermi surface structure and magnetic properties of cuprates. We propose a method for using this Green's function as the underlying action in dynamical processes such as resonant inelastic X-ray scattering (RIXS), by introducing auxiliary fermions. This approach allows an exact calculation of the RIXS spectrum using a recent method that takes into account the effect of the core-hole, which is otherwise difficult. The core-hole pushes the RIXS peaks towards higher energy transfer, improving agreement with experiments.

 

Title:
Quantum Hall Drag of Exciton Superfluid in Graphene
Authors:
Liu, Xiaomeng; Watanabe, Kenji; Taniguchi, Takashi; Halperin, Bertrand I.; Kim, Philip
Publication:
eprint arXiv:1608.03726
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
12 pages, 3 figures and supplementary information
Bibliographic Code:
2016arXiv160803726L

Abstract

Excitons are pairs of electrons and holes bound together by the Coulomb interaction. At low temperatures, excitons can form a Bose-Einstein condensate (BEC), enabling macroscopic phase coherence and superfluidity. An electronic double layer (EDL), in which two parallel conducting layers are separated by an insulator, is an ideal platform to realize a stable exciton BEC. In an EDL under strong magnetic fields, electron-like and hole-like quasi-particles from partially filled Landau levels (LLs) bind into excitons and condense. However, in semiconducting double quantum wells, this magnetic-field-induced exciton BEC has been observed only in sub-Kelvin temperatures due to the relatively strong dielectric screening and large separation of the EDL. Here we report exciton condensation in bilayer graphene EDL separated by a few atomic layers of hexagonal boron nitride (hBN). Driving current in one graphene layer generates a quantized Hall voltage in the other layer, signifying coherent superfluid exciton transport. Owing to the strong Coulomb coupling across the atomically thin dielectric, we find that quantum Hall drag in graphene appears at a temperature an order of magnitude higher than previously observed in GaAs EDL. The wide-range tunability of densities and displacement fields enables exploration of a rich phase diagram of BEC across Landau levels with different filling factors and internal quantum degrees of freedom. The observed robust exciton superfluidity opens up opportunities to investigate various quantum phases of the exciton BEC and design novel electronic devices based on dissipationless transport.

 

Title:
Electron spin-flip correlations due to nuclear dynamics in driven GaAs double dots
Authors:
Pal, Arijeet; Nichol, John M.; Shulman, Michael D.; Harvey, Shannon P.; Umansky, Vladimir; Rashba, Emmanuel I.; Yacoby, Amir; Halperin, Bertrand I.
Publication:
eprint arXiv:1608.03955
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Disordered Systems and Neural Networks, Quantum Physics
Comment:
20 pages, 5 figures, 2 tables
Bibliographic Code:
2016arXiv160803955P

Abstract

We present experimental data and associated theory for correlations in a series of experiments involving repeated Landau-Zener sweeps through the crossing point of a singlet state and a spin aligned triplet state in a GaAs double quantum dot containing two conduction electrons, which are loaded in the singlet state before each sweep, and the final spin is recorded after each sweep. The experiments reported here measure correlations on time scales from 4 $\mu$s to 2 ms. When the magnetic field is aligned in a direction such that spin-orbit coupling cannot cause spin flips, the correlation spectrum has prominent peaks centered at zero frequency and at the differences of the Larmor frequencies of the nuclei, on top of a frequency-independent background. When the spin-orbit field is relevant, there are additional peaks, centered at the frequencies of the individual species. A theoretical model which neglects the effects of high-frequency charge noise correctly predicts the positions of the observed peaks, and gives a reasonably accurate prediction of the size of the frequency-independent background, but gives peak areas that are larger than the observed areas by a factor of two or more. The observed peak widths are roughly consistent with predictions based on nuclear dephasing times of the order of 60 $\mu$s. However, there is extra weight at the lowest observed frequencies, which suggests the existence of residual correlations on the scale of 2 ms. We speculate on the source of these discrepancies.

 

Title:
Non-Hookean statistical mechanics of clamped graphene ribbons
Authors:
Bowick, Mark J.; Kosmrlj, Andrej; Nelson, David R.; Sknepnek, Rastko
Publication:
eprint arXiv:1608.04197
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter, Condensed Matter - Statistical Mechanics
Bibliographic Code:
2016arXiv160804197B

Abstract

Thermally fluctuating sheets and ribbons provide an intriguing forum in which to investigate strong violations of Hooke's Law: large distance elastic parameters are in fact not constant, but instead depend on the macroscopic dimensions. Inspired by recent experiments on free-standing graphene cantilevers, we combine the statistical mechanics of thin elastic plates and large-scale numerical simulations to investigate the thermal renormalization of the bending rigidity of graphene ribbons clamped at one end. For ribbons of dimensions $W\times L$, $L\geq W$, the macroscopic bending rigidity $\kappa_R$ determined from cantilever deformations is independent of the width when $W<l_{th}$, where $l_{th}$ is a thermal length scale, as expected. When $W>l_{th}$, however, this thermally renormalized bending rigidity begins to systematically increase, in agreement with the scaling theory, although our data is not good enough to determine the expected power law dependence on $W$. When the ribbon length $L > l_p$, where $l_p$ is the $W$-dependent thermally renormalized ribbon persistence length, we observe a scaling collapse and the beginnings of large scale random walk behavior.

 

Title:
High-fidelity entangling gate for double-quantum-dot spin qubits
Authors:
Nichol, John M.; Orona, Lucas A.; Harvey, Shannon P.; Fallahi, Saeed; Gardner, Geoffrey C.; Manfra, Michael J.; Yacoby, Amir
Publication:
eprint arXiv:1608.04258
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Quantum Physics
Comment:
6+6 pages, 4 figures
Bibliographic Code:
2016arXiv160804258N

Abstract

Electron spins in semiconductors are promising qubits because their long coherence times enable nearly 10^9 coherent quantum gate operations. However, developing a scalable high-fidelity two-qubit gate remains challenging. Here, we demonstrate an entangling gate between two double-quantum-dot spin qubits in GaAs by using a magnetic field gradient between the two dots in each qubit to suppress decoherence due to charge noise. When the magnetic gradient dominates the voltage-controlled exchange interaction between electrons, qubit coherence times increase by an order of magnitude. Using randomized benchmarking and self-consistent quantum measurement, state, and process tomography, we measure single-qubit gate fidelities of approximately 99% and an entangling gate fidelity of 90%. In the future, operating double quantum dot spin qubits with large gradients in nuclear-spin-free materials, such as Si, should enable a two-qubit gate fidelity surpassing the threshold for fault-tolerant quantum information processing.

 

Title:
Expanded Comment on: Optical Properties of Fluid Hydrogen at the Transition to a Conducting State
Authors:
Silvera, Isaac F.; Husband, Rachel; Salamat, Ashkan; Zaghoo, Mohamed
Publication:
eprint arXiv:1608.04479
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Materials Science, Condensed Matter - Other Condensed Matter
Comment:
7 pages, 6 figures
Bibliographic Code:
2016arXiv160804479S

Abstract

We comment on a recent paper published by McWilliams et al claiming that high-pressure/high-temperature hydrogen is a semi-conductor or semi-metal, in conflict with all earlier measurements on this system which show that it is metallic. We point out problems and inconsistencies and propose an alternate interpretation such that their results can be compatible with the observation of metallic hydrogen.

 

Title:
Enantiomer-Specific State Transfer of Chiral Molecules
Authors:
Eibenberger, Sandra; Doyle, John; Patterson, David
Publication:
eprint arXiv:1608.04691
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Physics - Chemical Physics, Quantum Physics
Comment:
6 pages, 4 figures
Bibliographic Code:
2016arXiv160804691E

Abstract

State-selective enantiomeric excess is realized using microwave-driven coherent population transfer. The method selectively promotes either R- or S- molecules to a higher rotational state by phase-controlled microwave pulses that drive electric-dipole allowed rotational transitions. We demonstrate the method using a racemic mixture of 1,2-propanediol. This method of chiral enrichment can be applied to nearly any chiral molecule that can be vaporized and cooled to the point where rotationally resolved spectroscopy is possible, including molecules that rapidly racemize. The rapid chiral switching demonstrated here allows for new applications in high-precision spectroscopic searches for parity violation in chiral molecules.

 

Title:
Modeling and Analysis of the APOLLO Lunar Laser Ranging Data
Authors:
Reasenberg, R. D.; Chandler, J. F.; Colmenares, N. R.; Johnson, N. H.; Murphy, T. W.; Shapiro, I. I.
Publication:
eprint arXiv:1608.04758
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Astrophysics - Instrumentation and Methods for Astrophysics, General Relativity and Quantum Cosmology
Comment:
Presented at the Seventh Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, June 20-24, 2016
Bibliographic Code:
2016arXiv160804758R

Abstract

The Earth-Moon-Sun system has traditionally provided the best laboratory for testing the strong equivalence principle. For a decade, the Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) has been producing the world's best lunar laser ranging data. At present, a single observing session of about an hour yields a distance measurement with uncertainty of about 2~mm, an order of magnitude advance over the best pre-APOLLO lunar laser ranging data. However, these superb data have not yet yielded scientific results commensurate with their accuracy, number, and temporal distribution. There are two reasons for this. First, even in the relatively clean environment of the Earth-Moon system, a large number of effects modify the measured distance importantly and thus need to be included in the analysis model. The second reason is more complicated. The traditional problem with the analysis of solar-system metric data is that the physical model must be truncated to avoid extra parameters that would increase the condition number of the estimator. Even in a typical APOLLO analysis that does not include parameters of gravity physics, the condition number is very high: $8 \times 10^{10}$.

 

Title:
The Advanced LIGO Photon Calibrators
Authors:
Karki, S.; Tuyenbayev, D.; Kandhasamy, S.; Abbott, B. P.; Abbott, T. D.; Anders, E. H.; Berliner, J.; Betzwieser, J.; Daveloza, H. P.; Cahillane, C.; Canete, L.; Conley, C.; Gleason, J. R.; Goetz, E.; Kissel, J. S.; Izumi, K.; Mendell, G.; Quetschke, V.; Rodruck, M.; Sachdev, S.; Sadecki, T.; Schwinberg, P. B.; Sottile, A.; Wade, M.; Weinstein, A. J.; West, M.; Savage, R. L.
Publication:
eprint arXiv:1608.05055
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Astrophysics - Instrumentation and Methods for Astrophysics, Physics - Instrumentation and Detectors
Comment:
14 pages, 19 figures
Bibliographic Code:
2016arXiv160805055K

Abstract

The two interferometers of the Laser Interferometry Gravitaional-wave Observatory (LIGO) recently detected gravitational waves from the mergers of binary black hole systems. Accurate calibration of the output of these detectors was crucial for the observation of these events, and the extraction of parameters of the sources. The principal tools used to calibrate the responses of the second-generation (Advanced) LIGO detectors to gravitational waves are systems based on radiation pressure and referred to as Photon Calibrators. These systems, which were completely redesigned for Advanced LIGO, include several significant upgrades that enable them to meet the calibration requirements of second-generation gravitational wave detectors in the new era of gravitational-wave astronomy. We report on the design, implementation, and operation of these Advanced LIGO Photon Calibrators that are currently providing fiducial displacements on the order of $10^{-18}$ m/$\sqrt{\textrm{Hz}}$ with accuracy and precision of better than 1%.

 

Title:
Single-Photon Switching and Entanglement of Solid-State Qubits in an Integrated Nanophotonic System
Authors:
Sipahigil, Alp; Evans, Ruffin E.; Sukachev, Denis D.; Burek, Michael J.; Borregaard, Johannes; Bhaskar, Mihir K.; Nguyen, Christian T.; Pacheco, Jose L.; Atikian, Haig A.; Meuwly, Charles; Camacho, Ryan M.; Jelezko, Fedor; Bielejec, Edward; Park, Hongkun; Lončar, Marko; Lukin, Mikhail D.
Publication:
eprint arXiv:1608.05147
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Optics
Comment:
15 pages and 5 figures. Supplementary Material, 36 pages and 10 figures, available as an ancillary file
Bibliographic Code:
2016arXiv160805147S

Abstract

Efficient interfaces between photons and quantum emitters form the basis for quantum networks and enable nonlinear optical devices operating at the single-photon level. We demonstrate an integrated platform for scalable quantum nanophotonics based on silicon-vacancy (SiV) color centers coupled to nanoscale diamond devices. By placing SiV centers inside diamond photonic crystal cavities, we realize a quantum-optical switch controlled by a single color center. We control the switch using SiV metastable orbital states and verify optical switching at the single-photon level by using photon correlation measurements. We use Raman transitions to realize a single-photon source with a tunable frequency and bandwidth in a diamond waveguide. Finally, we create entanglement between two SiV centers by detecting indistinguishable Raman photons emitted into a single waveguide. Entanglement is verified using a novel superradiant feature observed in photon correlation measurements, paving the way for the realization of quantum networks.

 

Title:
Depolarization dynamics in a strongly interacting solid-state spin ensemble
Authors:
Choi, Soonwon; Choi, Joonhee; Kucsko, Georg; Maurer, Peter C.; Shields, Brendan J.; Sumiya, Hitoshi; Onoda, Shinobu; Isoya, Junichi; Demler, Eugene; Jelezko, Fedor; Yao, Norman Y.; Lukin, Mikhail D.
Publication:
eprint arXiv:1608.05471
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Statistical Mechanics, Condensed Matter - Strongly Correlated Electrons
Comment:
15 pages, 8 figures
Bibliographic Code:
2016arXiv160805471C

Abstract

We study the depolarization dynamics of a dense ensemble of dipolar interacting spins, associated with nitrogen-vacancy centers in diamond. We observe anomalously fast, density-dependent, and non-exponential spin relaxation. To explain these observations, we propose a microscopic model where an interplay of long-range interactions, disorder, and dissipation leads to predictions that are in quantitative agreement with both current and prior experimental results. Our results pave the way for controlled many-body experiments with long-lived and strongly interacting ensembles of solid-state spins.

 

Title:
On-chip all-dielectric fabrication-tolerant zero-index metamaterials
Authors:
Kita, Shota; Li, Yang; Muñoz, Philip; Reshef, Orad; Vulis, Daryl I.; Day, Robert W.; Mazur, Eric; Lončar, Marko
Publication:
eprint arXiv:1608.05488
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Physics - Optics
Comment:
5 pages, 6 figures
Bibliographic Code:
2016arXiv160805488K

Abstract

Zero-index metamaterials (ZIMs) offer unprecedented ways to manipulate the flow of light, and are of interest for wide range of applications including optical cloaking, super-coupling, and unconventional phase-matching properties in nonlinear optics. Impedance-matched ZIMs can be obtained through a photonic Dirac-cone (PDC) dispersion induced by an accidental degeneracy of two linear bands - typically an electric monopole mode and a transverse magnetic dipole mode - at the center of the Brillouin zone. Consequently, PDC can only be achieved for a particular combination of geometric parameters of the metamaterial, and hence is sensitive to fabrication imperfections. These fabrication imperfections may limit the usefulness in practical applications. In this work we overcome this obstacle and demonstrate robust all-dielectric (AD) ZIM that supports PDC dispersion over wide parameter space. Our structure, consisting of an array of Si pillars on silica substrate, is fabricated in silicon-oninsulator (SOI) platform and operates at telecom wavelengths.

 

Title:
Traversable Wormholes via a Double Trace Deformation
Authors:
Gao, Ping; Jafferis, Daniel Louis; Wall, Aron
Publication:
eprint arXiv:1608.05687
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
19 pages, 4 figures, 1 appendix
Bibliographic Code:
2016arXiv160805687G

Abstract

After turning on an interaction that couples the two boundaries of an eternal BTZ black hole, we find a quantum matter stress tensor with negative average null energy, whose gravitational backreaction renders the Einstein-Rosen bridge traversable. Such a traversable wormhole has an interesting interpretation in the context of ER=EPR, which we suggest might be related to quantum teleportation. However, it cannot be used to violate causality. We also discuss the implications for the energy and holographic entropy in the dual CFT description.

 

Title:
Measurement of single $\pi^0$ production by coherent neutral-current $\nu$ Fe interactions in the MINOS Near Detector
Authors:
Adamson, P.; Anghel, I.; Aurisano, A.;...Feldman, G. J.;... ; and 116 coauthors
Publication:
eprint arXiv:1608.05702
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment
Comment:
21 pages, 16 figures
Bibliographic Code:
2016arXiv160805702A

Abstract

Forward single $\pi^0$ production by coherent neutral-current interactions, $\nu \mathcal{A} \to \nu \mathcal{A} \pi^0$, is investigated using a 2.8$\times 10^{20}$ protons-on-target exposure of the MINOS Near Detector. For single-shower topologies, the event distribution in production angle exhibits a clear excess above the estimated background at very forward angles for visible energy in the range~1-8 GeV. Cross sections are obtained for the detector medium comprised of 80% iron and 20% carbon nuclei with $\langle \mathcal{A} \rangle = 48$, the highest-$\langle \mathcal{A} \rangle$ target used to date in the study of this coherent reaction. The total cross section for coherent neutral-current single-$\pi^0$ production initiated by the $\nu_\mu$ flux of the NuMI low-energy beam with mean (mode) $E_{\nu}$ of 4.9 GeV (3.0 GeV), is $77.6\pm5.0\,(\text{stat}) ^{+15.0}_{-16.8}\,(\text{syst})\times10^{-40}\,\text{cm}^2~\text{per nucleus}$. The results are in good agreement with predictions of the Berger-Sehgal model.

 

Title:
Quasi-local mass at the null infinity of the Vaidya spacetime
Authors:
Chen, Po-Ning; Wang, Mu-Tao; Yau, Shing-Tung
Publication:
eprint arXiv:1608.06165
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Mathematics - Differential Geometry, General Relativity and Quantum Cosmology
Comment:
15 pages
Bibliographic Code:
2016arXiv160806165C

Abstract

There are two important statements regarding the Trautman-Bondi mass [1,8,5] at null infinity: one is the positivity [7,6], and the other is the Bondi mass loss formula [1], which are both global in nature. The positivity of the quasi-local mass can potentially lead to a local description at null infinity. This is confirmed for the Vaidya spacetime in this note. We study the Wang-Yau quasi-local mass on surfaces of fixed size at the null infinity of the Vaidya spacetime. The optimal embedding equation is solved explicitly and the quasi-local mass is evaluated in terms of the mass aspect function of the Vaidya spacetime.

 

Title:
Modular Bootstrap Revisited
Authors:
Collier, Scott; Lin, Ying-Hsuan; Yin, Xi
Publication:
eprint arXiv:1608.06241
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Condensed Matter - Strongly Correlated Electrons
Comment:
32 pages, 20 figures
Bibliographic Code:
2016arXiv160806241C

Abstract

We constrain the spectrum of two-dimensional unitary, compact conformal field theories with central charge c > 1 using modular bootstrap. Upper bounds on the gap in the dimension of primary operators of any spin, as well as in the dimension of scalar primaries, are computed numerically as functions of the central charge using semi-definite programming. Our bounds refine those of Hellerman and Friedan-Keller, and are in some cases saturated by known CFTs. In particular, we show that unitary CFTs with c < 8 must admit relevant deformations, and that a nontrivial bound on the gap of scalar primaries exists for c < 25. We also study bounds on the dimension gap in the presence of twist gaps, bounds on the degeneracy of operators, and demonstrate how "extremal spectra" which maximize the degeneracy at the gap can be determined numerically.

 

Title:
Dicke phase transition without total spin conservation
Authors:
Dalla Torre, Emanuele G.; Shchadilova, Yulia; Wilner, Eli Y.; Lukin, Mikhail D.; Demler, Eugene
Publication:
eprint arXiv:1608.06293
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Quantum Gases, Condensed Matter - Strongly Correlated Electrons
Comment:
6 pages. Comments welcome
Bibliographic Code:
2016arXiv160806293D

Abstract

We develop a new fermionic path-integral formalism to analyze the phase diagram of open nonequilibrium systems. The formalism is applied to analyze an ensemble of two-level atoms interacting with a single-mode optical cavity, described by the Dicke model. While this model is often used as the paradigmatic example of a phase transition in driven-dissipative systems, earlier theoretical studies were limited to the special case when the total spin of the atomic ensemble is conserved. This assumption is not justified in most experimental realizations. Our new approach allows us to analyze the problem in a more general case, including the experimentally relevant case of dissipative processes that act on each atom individually and do not conserve the total spin. We obtain a general expression for the position of the transition, which contains as special cases the two previously known regimes: i) non-equilibrium systems with losses and conserved spin and ii) closed systems in thermal equilibrium and with the Gibbs ensemble averaging over the values of the total spin. We perform a detailed study of different types of baths and point out the possibility of a surprising non-monotonous dependence of the transition on the baths' parameters.

 

Title:
Constraints on Large Extra Dimensions from the MINOS Experiment
Authors:
Adamson, P.; Anghel, I.; Aurisano, A.;... Feldman, G. J.;... and 116 coauthors
Publication:
eprint arXiv:1608.06964
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment, High Energy Physics - Phenomenology
Comment:
- Added two references (12 and 14). - Corrected the year of reference 13
Bibliographic Code:
2016arXiv160806964A

Abstract

We report new constraints on the size of large extra dimensions from data collected by the MINOS experiment between 2005 and 2012. Our analysis employs a model in which sterile neutrinos arise as Kaluza-Klein states in large extra dimensions and thus modify the neutrino oscillation probabilities due to mixing between active and sterile neutrino states. Using Fermilab's NuMI beam exposure of $10.56 \times 10^{20}$ protons-on-target, we combine muon neutrino charged current and neutral current data sets from the Near and Far Detectors and observe no evidence for deviations from standard three-flavor neutrino oscillations. The ratios of reconstructed energy spectra in the two detectors constrain the size of large extra dimensions to be smaller than $0.45\,\mu\text{m}$ at 90% C.L. in the limit of a vanishing lightest active neutrino mass. Stronger limits are obtained for non-vanishing masses.

 

Title:
Population Genetics with Fluctuating Population Sizes
Authors:
Chotibut, Thiparat; Nelson, David R.
Publication:
eprint arXiv:1608.08166
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Quantitative Biology - Populations and Evolution, Condensed Matter - Statistical Mechanics, Physics - Biological Physics
Comment:
Submitted to Journal of Statistical Physics, Special Issue: Dedicated to the Memory of Leo Kadanoff. arXiv admin note: text overlap with arXiv:1412.6688
Bibliographic Code:
2016arXiv160808166C

Abstract

Standard neutral population genetics theory with a strictly fixed population size has important limitations. An alternative model that allows independently fluctuating population sizes and reproduces the standard neutral evolution is reviewed. We then study a situation such that the competing species are neutral at the equilibrium population size but population size fluctuations nevertheless favor fixation of one species over the other. In this case, a separation of timescales emerges naturally and allows adiabatic elimination of a fast population size variable to deduce the fluctuations-induced selection dynamics near the equilibrium population size. The results highlight the incompleteness of the standard population genetics with a strictly fixed population size.

 

Title:
Bloch oscillations in the absence of a lattice
Authors:
Meinert, Florian; Knap, Michael; Kirilov, Emil; Jag-Lauber, Katharina; Zvonarev, Mikhail B.; Demler, Eugene; Nägerl, Hanns-Christoph
Publication:
eprint arXiv:1608.08200
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases
Comment:
10 pages, 9 figures
Bibliographic Code:
2016arXiv160808200M

Abstract

We experimentally investigate the quantum motion of an impurity atom that is immersed in a strongly interacting one-dimensional Bose liquid and is subject to an external force. We find that the momentum distribution of the impurity exhibits characteristic Bragg reflections at the edge of an emergent Brillouin zone. While Bragg reflections are typically associated with lattice structures, in our strongly correlated quantum liquid they result from the interplay of short-range crystalline order and kinematic constraints on the many-body scattering processes in the one-dimensional system. As a consequence, the impurity exhibits periodic dynamics that we interpret as Bloch oscillations, which arise even though the quantum liquid is translationally invariant. Our observations are supported by large-scale numerical simulations.

 

Title:
Chiral Floquet Phases of Many-body Localized Bosons
Authors:
Po, Hoi Chun; Fidkowski, Lukasz; Morimoto, Takahiro; Potter, Andrew C.; Vishwanath, Ashvin
Publication:
eprint arXiv:1609.00006
Publication Date:
08/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Quantum Gases, Condensed Matter - Strongly Correlated Electrons, Quantum Physics
Comment:
(15+10) pages; (8+2) figures
Bibliographic Code:
2016arXiv160900006P

Abstract

We construct and classify chiral topological phases in driven (Floquet) systems of strongly interacting bosons, with finite-dimensional site Hilbert spaces, in two spatial dimensions. The construction proceeds by introducing exactly soluble models with chiral edges, which in the presence of many body localization in the bulk are argued to lead to stable chiral phases. These chiral phases do not require any symmetry, and in fact owe their existence to the absence of energy conservation in driven systems. Surprisingly, we show that they are classified by a quantized index, taking the form of the logarithm of a rational number, which can be related to the flow of quantum information. We explicitly compute this index for specific models, and show that the nontrivial topology leads to edge thermalization, which provides an interesting link between bulk topology and chaos at the edge. Some parallels with the free fermion Floquet topological phases are discussed, and possible experimental implementations are mentioned.

 

Title:
Visualizing Flagella while Tracking Bacteria
Authors:
Turner, Linda; Ping, Liam; Neubauer, Marianna; Berg, Howard C.
Publication:
Biophysical Journal, vol. 111, issue 3, pp. 630-639
Publication Date:
08/2016
Origin:
CROSSREF
DOI:
10.1016/j.bpj.2016.05.053
Bibliographic Code:
2016BpJ...111..630T

Abstract

Not Available

 

Title:
Search for single production of vector-like quarks decaying into Wb in pp collisions at √{s} = 8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2823 coauthors
Publication:
The European Physical Journal C, Volume 76, Issue 8, article id. #442, 26 pp. (EPJC Homepage)
Publication Date:
08/2016
Origin:
SPRINGER
Abstract Copyright:
(c) 2016: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-016-4281-8
Bibliographic Code:
2016EPJC...76..442A

Abstract

A search for singly produced vector-like Q quarks, where Q can be either a T quark with charge +2/3 or a Y quark with charge -4/3, is performed in proton-proton collisions recorded with the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 20.3 fb^{-1} and was produced with a centre-of-mass energy of √{s}=8 TeV. This analysis targets Q → Wb decays where the W boson decays leptonically. A veto on massive large-radius jets is used to reject the dominant tbar{t} background. The reconstructed Q-candidate mass, ranging from 0.4 to 1.2 TeV, is used in the search to discriminate signal from background processes. No significant deviation from the Standard Model expectation is observed, and limits are set on the Q → Wb cross-section times branching ratio. The results are also interpreted as limits on the QWb coupling and the mixing with the Standard Model sector for a singlet T quark or a Y quark from a doublet. T quarks with masses below 0.95 TeV are excluded at 95 % confidence level, assuming a unit coupling and a BR(T→ Wb) = 0.5, whereas the expected limit is 1.10 TeV.

 

Title:
Dynamical tunneling versus fast diffusion for a non-convex Hamiltonian
Authors:
Pittman, S. M.; Tannenbaum, E.; Heller, E. J.
Publication:
The Journal of Chemical Physics, Volume 145, Issue 5, id.054303 (JChPh Homepage)
Publication Date:
08/2016
Origin:
AIP
Abstract Copyright:
2016: Author(s)
DOI:
10.1063/1.4960134
Bibliographic Code:
2016JChPh.145e4303P

Abstract

This paper attempts to resolve the issue of the nature of the 0.01-0.1 cm-1 peak splittings observed in high-resolution IR spectra of polyatomic molecules. One hypothesis is that these splittings are caused by dynamical tunneling, a quantum-mechanical phenomenon whereby energy flows between two disconnected regions of phase-space across dynamical barriers. However, a competing classical mechanism for energy flow is Arnol'd diffusion, which connects different regions of phase-space by a resonance network known as the Arnol'd web. The speed of diffusion is bounded by the Nekhoroshev theorem, which guarantees stability on exponentially long time scales if the Hamiltonian is steep. Here we consider a non-convex Hamiltonian that contains the characteristics of a molecular Hamiltonian, but does not satisfy the Nekhoroshev theorem. The diffusion along the Arnol'd web is expected to be fast for a non-convex Hamiltonian. While fast diffusion is an unlikely competitor for longtime energy flow in molecules, we show how dynamical tunneling dominates compared to fast diffusion in the nearly integrable regime for a non-convex Hamiltonian, as well as present a new kind of dynamical tunneling.

 

Title:
Measurement of the inclusive isolated prompt photon cross section in pp collisions at √{s}=8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2856 coauthors
Publication:
Journal of High Energy Physics, Volume 2016, Issue 8, article id. #5, 42 pp.
Publication Date:
08/2016
Origin:
SPRINGER
Keywords:
Hadron-Hadron scattering (experiments), Photon production, proton-proton scattering
Abstract Copyright:
(c) 2016: The Author(s)
DOI:
10.1007/JHEP08(2016)005
Bibliographic Code:
2016JHEP...08..005A

Abstract

A measurement of the cross section for the inclusive production of isolated prompt photons in proton-proton collisions at a centre-of-mass energy of √{s}=8 TeV is presented. The measurement covers the pseudorapidity ranges | η γ | < 1 .37 and 1 .56 ≤ | η γ | < 2 .37 in the transverse energy range 25 < E T γ < 1500 GeV. The results are based on an integrated luminosity of 20.2 fb-1, recorded by the ATLAS detector at the LHC. Photon candidates are identified by combining information from the calorimeters and the inner tracker. The background is subtracted using a data-driven technique, based on the observed calorimeter shower-shape variables and the deposition of hadronic energy in a narrow cone around the photon candidate. The measured cross sections are compared with leading-order and next-to-leading order perturbative QCD calculations and are found to be in a good agreement over ten orders of magnitude. [Figure not available: see fulltext.]

 

Title:
Measurement of the double-differential high-mass Drell-Yan cross section in pp collisions at √{s}=8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2846 coauthors
Publication:
Journal of High Energy Physics, Volume 2016, Issue 8, article id. #9, 61 pp.
Publication Date:
08/2016
Origin:
SPRINGER
Keywords:
Hadron-Hadron scattering (experiments)
Abstract Copyright:
(c) 2016: The Author(s)
DOI:
10.1007/JHEP08(2016)009
Bibliographic Code:
2016JHEP...08..009A

Abstract

This paper presents a measurement of the double-differential cross section for the Drell-Yan Z/γ → ℓ+- and photon-induced γγ → ℓ+- processes where ℓ is an electron or muon. The measurement is performed for invariant masses of the lepton pairs, m ℓℓ, between 116 GeV and 1500 GeV using a sample of 20 .3 fb-1 of pp collisions data at centre-of-mass energy of √{s}=8 TeV collected by the ATLAS detector at the LHC in 2012. The data are presented double differentially in invariant mass and absolute dilepton rapidity as well as in invariant mass and absolute pseudorapidity separation of the lepton pair. The single-differential cross section as a function of mℓℓ is also reported. The electron and muon channel measurements are combined and a total experimental precision of better than 1% is achieved at low m ℓℓ. A comparison to next-to-next-to-leading order perturbative QCD predictions using several recent parton distribution functions and including next-to-leading order electroweak effects indicates the potential of the data to constrain parton distribution functions. In particular, a large impact of the data on the photon PDF is demonstrated. [Figure not available: see fulltext.]

 

Title:
Initial Performance of Bicep3: A Degree Angular Scale 95 GHz Band Polarimeter
Authors:
Wu, W. L. K.; Ade, P. A. R.; Ahmed, Z.; Alexander, K. D.; Amiri, M.; Barkats, D.; Benton, S. J.; Bischoff, C. A.; Bock, J. J.; Bowens-Rubin, R.; Buder, I.; Bullock, E.; Buza, V.; Connors, J. A.; Filippini, J. P.; Fliescher, S.; Grayson, J. A.; Halpern, M.; Harrison, S. A.; Hilton, G. C.; Hristov, V. V.; Hui, H.; Irwin, K. D.; Kang, J.; Karkare, K. S.; Karpel, E.; Kefeli, S.; Kernasovskiy, S. A.; Kovac, J. M.; Kuo, C. L.; Megerian, K. G.; Netterfield, C. B.; Nguyen, H. T.; O'Brient, R.; Ogburn, R. W.; Pryke, C.; Reintsema, C. D.; Richter, S.; Sorensen, C.; Staniszewski, Z. K.; Steinbach, B.; Sudiwala, R. V.; Teply, G. P.; Thompson, K. L.; Tolan, J. E.; Tucker, C. E.; Turner, A. D.; Vieregg, A. G.; Weber, A. C.; Wiebe, D. V.; Willmert, J.; Yoon, K. W.
Publication:
Journal of Low Temperature Physics, Volume 184, Issue 3-4, pp. 765-771 (JLTP Homepage)
Publication Date:
08/2016
Origin:
SPRINGER
Keywords:
Cosmic microwave background, Primordial gravitational waves, Inflation, Instrumentation: polarimetry, Telescopes
Abstract Copyright:
(c) 2016: The Author(s)
DOI:
10.1007/s10909-015-1403-x
Bibliographic Code:
2016JLTP..184..765W

Abstract

Bicep3 is a 550-mm aperture telescope with cold, on-axis, refractive optics designed to observe at the 95-GHz band from the South Pole. It is the newest member of the Bicep/ Keck family of inflationary probes specifically designed to measure the polarization of the cosmic microwave background (CMB) at degree angular scales. Bicep3 is designed to house 1280 dual-polarization pixels, which, when fully populated, totals to ˜ 9× the number of pixels in a single Keck 95-GHz receiver, thus further advancing the Bicep/ Keck program's 95 GHz mapping speed. Bicep3 was deployed during the austral summer of 2014-2015 with nine detector tiles, to be increased to its full capacity of 20 in the second season. After instrument characterization, measurements were taken, and CMB observation commenced in April 2015. Together with multi-frequency observation data from Planck, Bicep2, and the Keck Array, Bicep3 is projected to set upper limits on the tensor-to-scalar ratio to r lesssim 0.03 at 95 % C.L.

 

Title:
A Synoptic Map of Halo Substructures from the Pan-STARRS1 3π Survey
Authors:
Bernard, Edouard J.; Ferguson, Annette M. N.; Schlafly, Edward F.; Martin, Nicolas F.; Rix, Hans-Walter; Bell, Eric F.; Finkbeiner, Douglas P.; Goldman, Bertrand; Martínez-Delgado, David; Sesar, Branimir; Wyse, Rosemary F. G.; Burgett, William S.; Chambers, Kenneth C.; Draper, Peter W.; Hodapp, Klaus W.; Kaiser, Nicholas; Kudritzki, Rolf-Peter; Magnier, Eugene A.; Metcalfe, Nigel; Wainscoat, Richard J.; Waters, Christopher
Publication:
Monthly Notices of the Royal Astronomical Society, Advance Access (MNRAS Homepage)
Publication Date:
08/2016
Origin:
OUP
Astronomy Keywords:
Hertzsprung-Russell and colour-magnitude diagrams, surveys, Galaxy: halo, Galaxy: structure
Abstract Copyright:
2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
DOI:
10.1093/mnras/stw2134
Bibliographic Code:
2016MNRAS.tmp.1248B

Abstract

We present a panoramic map of the entire Milky Way halo north of δ ˜ -30° (˜ 30,000 deg2), constructed by applying the matched-filter technique to the Pan-STARRS1 3π Survey dataset. Using single-epoch photometry reaching to g ˜22, we are sensitive to stellar substructures with heliocentric distances between 3.5 and ˜35 kpc. We recover almost all previously-reported streams in this volume and demonstrate that several of these are significantly more extended than earlier datasets have indicated. In addition, we also report five new candidate stellar streams. One of these features appears significantly broader and more luminous than the others and is likely the remnant of a dwarf galaxy. The other four streams are consistent with a globular cluster origin, and three of these are rather short in projection (≲ 10°), suggesting that streams like Ophiuchus may not be that rare. Finally, a significant number of more marginal substructures are also revealed by our analysis; many of these features can also be discerned in matched-filter maps produced by other authors from SDSS data, and hence they are very likely to be genuine. However, the extant 3π data is currently too shallow to determine their properties or produce convincing CMDs. The global view of the Milky Way provided by Pan-STARRS1 provides further evidence for the important role of both globular cluster disruption and dwarf galaxy accretion in building the Milky Way's stellar halo.

 

Title:
Composite alginate gels for tunable cellular microenvironment mechanics
Authors:
Khavari, Adele; Nydén, Magnus; Weitz, David A.; Ehrlicher, Allen J.
Publication:
Nature Scientific Reports, Volume 6, id. 30854 (2016).
Publication Date:
08/2016
Origin:
NATURE
Abstract Copyright:
(c) 2016: The Author(s)
DOI:
10.1038/srep30854
Bibliographic Code:
2016NatSR...630854K

Abstract

The mechanics of the cellular microenvironment can be as critical as biochemistry in directing cell behavior. Many commonly utilized materials derived from extra-cellular-matrix create excellent scaffolds for cell growth, however, evaluating the relative mechanical and biochemical effects independently in 3D environments has been difficult in frequently used biopolymer matrices. Here we present 3D sodium alginate hydrogel microenvironments over a physiological range of stiffness (E = 1.85 to 5.29 kPa), with and without RGD binding sites or collagen fibers. We use confocal microscopy to measure the growth of multi-cellular aggregates (MCAs), of increasing metastatic potential in different elastic moduli of hydrogels, with and without binding factors. We find that the hydrogel stiffness regulates the growth and morphology of these cell clusters; MCAs grow larger and faster in the more rigid environments similar to cancerous breast tissue (E = 4–12 kPa) as compared to healthy tissue (E = 0.4–2 kpa). Adding binding factors from collagen and RGD peptides increases growth rates, and change maximum MCA sizes. These findings demonstrate the utility of these independently tunable mechanical/biochemistry gels, and that mechanical confinement in stiffer microenvironments may increase cell proliferation.

 

Title:
Search for resonances in the mass distribution of jet pairs with one or two jets identified as b-jets in proton-proton collisions at √{ s} = 13 TeV with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2848 coauthors
Publication:
Physics Letters B, Volume 759, p. 229-246.
Publication Date:
08/2016
Origin:
ELSEVIER
Abstract Copyright:
(c) 2016 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2016.05.064
Bibliographic Code:
2016PhLB..759..229A

Abstract

Searches for high-mass resonances in the dijet invariant mass spectrum with one or two jets identified as b-jets are performed using an integrated luminosity of 3.2 fb-1 of proton-proton collisions with a centre-of-mass energy of √{ s} = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. No evidence of anomalous phenomena is observed in the data, which are used to exclude, at 95% credibility level, excited b* quarks with masses from 1.1 TeV to 2.1 TeV and leptophobic Z‧ bosons with masses from 1.1 TeV to 1.5 TeV. Contributions of a Gaussian signal shape with effective cross sections ranging from approximately 0.4 to 0.001 pb are also excluded in the mass range 1.5-5.0 TeV.

 

Title:
Search for charged Higgs bosons produced in association with a top quark and decaying via H± → τν using pp collision data recorded at √{ s} = 13 TeV by the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2845 coauthors
Publication:
Physics Letters B, Volume 759, p. 555-574.
Publication Date:
08/2016
Origin:
ELSEVIER
Abstract Copyright:
(c) 2016 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2016.06.017
Bibliographic Code:
2016PhLB..759..555A

Abstract

Charged Higgs bosons produced in association with a single top quark and decaying via H± → τν are searched for with the ATLAS experiment at the LHC, using proton-proton collision data at √{ s} = 13 TeV corresponding to an integrated luminosity of 3.2 fb-1. The final state is characterised by the presence of a hadronic τ decay and missing transverse momentum, as well as a hadronically decaying top quark, resulting in the absence of high-transverse-momentum electrons and muons. The data are found to be consistent with the expected background from Standard Model processes. A statistical analysis leads to 95% confidence-level upper limits on the production cross section times branching fraction, σ (pp → [ b ] tH±) ×BR (H± → τν), between 1.9 pb and 15 fb, for charged Higgs boson masses ranging from 200 to 2000 GeV. The exclusion limits for this search surpass those obtained with the proton-proton collision data recorded at √{ s} = 8 TeV.

 

Title:
Measurement of W± and Z-boson production cross sections in pp collisions at √{ s} = 13 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; ... Franklin, M.;... Huth, J.;... Morii, M.;... and 2844 coauthors
Publication:
Physics Letters B, Volume 759, p. 601-621.
Publication Date:
08/2016
Origin:
ELSEVIER
Abstract Copyright:
(c) 2016 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2016.06.023
Bibliographic Code:
2016PhLB..759..601A

Abstract

Measurements of the W± →ℓ± ν and Z →ℓ+- production cross sections (where ℓ± =e±, μ±) in proton-proton collisions at √{ s} = 13 TeV are presented using data recorded by the ATLAS experiment at the Large Hadron Collider, corresponding to a total integrated luminosity of 81 pb-1. The total inclusive W±-boson production cross sections times the single-lepton-flavour branching ratios are σW+tot = 11.83 ± 0.02 (stat) ± 0.32 (sys) ± 0.25 (lumi) nb and σW-tot = 8.79 ± 0.02 (stat) ± 0.24 (sys) ± 0.18 (lumi) nb for W+ and W-, respectively. The total inclusive Z-boson production cross section times leptonic branching ratio, within the invariant mass window 66 <mℓℓ < 116 GeV, is σZtot = 1.981 ± 0.007 (stat) ± 0.038 (sys) ± 0.042 (lumi) nb. The W+, W-, and Z-boson production cross sections and cross-section ratios within a fiducial region defined by the detector acceptance are also measured. The cross-section ratios benefit from significant cancellation of experimental uncertainties, resulting in σW+fid / σW-fid = 1.295 ± 0.003 (stat) ± 0.010 (sys) and σW±fid / σZfid = 10.31 ± 0.04 (stat) ± 0.20 (sys). Theoretical predictions, based on calculations accurate to next-to-next-to-leading order for quantum chromodynamics and to next-to-leading order for electroweak processes and which employ different parton distribution function sets, are compared to these measurements.

 

Title:
Tailoring transport properties of phase-separated manganite films with ordered magnetic nanostructures
Authors:
Vlaminck, V.; Yánez, W.; Hoffman, J.; Hoffmann, A.; Niebieskikwiat, D.
Publication:
Physical Review B, Volume 94, Issue 6, id.064404 (PhRvB Homepage)
Publication Date:
08/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevB.94.064404
Bibliographic Code:
2016PhRvB..94f4404V

Abstract

The magnetotransport properties of thin manganite films (La0.7Ca0.3MnO3 ) coupled with arrays of permalloy (Py) nanodots deposited on the surface of the film are studied as a function of temperature, magnetic field, and the size of the dots. In the presence of the magnetic dots, a reduction of the electrical resistivity is observed, especially at the insulator-to-metal transition, as well as a shift of the transition peak towards higher temperatures. This indicates that, due to local interface exchange coupling, highly conductive ferromagnetic domains are nucleated in the manganite film underneath the Py nanodots. The use of a simplified resistor network model allows us to estimate the size of the metallic regions induced by exchange coupling. At low temperatures, these regions extend ˜70 nm beyond the edge of the nanodots, a length scale comparable to the correlation length of the ferromagnetic clusters in the phase-separated state of La0.7Ca0.3MnO3 .

 

Title:
Search for pair production of gluinos decaying via stop and sbottom in events with b -jets and large missing transverse momentum in p p collisions at √{s }=13 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2842 coauthors
Publication:
Physical Review D, Volume 94, Issue 3, id.032003 (PhRvD Homepage)
Publication Date:
08/2016
Origin:
APS
Abstract Copyright:
2016: CERN
DOI:
10.1103/PhysRevD.94.032003
Bibliographic Code:
2016PhRvD..94c2003A

Abstract

A search for supersymmetry involving the pair production of gluinos decaying via third-generation squarks to the lightest neutralino (χ˜10) is reported. It uses an LHC proton-proton data set at a center-of-mass energy √{s }=13 TeV with an integrated luminosity of 3.2 fb-1 collected with the ATLAS detector in 2015. The signal is searched for in events containing several energetic jets, of which at least three must be identified as b jets, large missing transverse momentum, and, potentially, isolated electrons or muons. Large-radius jets with a high mass are also used to identify highly boosted top quarks. No excess is found above the predicted background. For χ˜10 masses below approximately 700 GeV, gluino masses of less than 1.78 TeV and 1.76 TeV are excluded at the 95% C.L. in simplified models of the pair production of gluinos decaying via sbottom and stop, respectively. These results significantly extend the exclusion limits obtained with the √{s }=8 TeV data set.

 

Title:
Quantum Network of Atom Clocks: A Possible Implementation with Neutral Atoms
Authors:
Kómár, P.; Topcu, T.; Kessler, E. M.; Derevianko, A.; Vuletić, V.; Ye, J.; Lukin, M. D.
Publication:
Physical Review Letters, Volume 117, Issue 6, id.060506 (PhRvL Homepage)
Publication Date:
08/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevLett.117.060506
Bibliographic Code:
2016PhRvL.117f0506K

Abstract

We propose a protocol for creating a fully entangled Greenberger-Horne-Zeilinger-type state of neutral atoms in spatially separated optical atomic clocks. In our scheme, local operations make use of the strong dipole-dipole interaction between Rydberg excitations, which give rise to fast and reliable quantum operations involving all atoms in the ensemble. The necessary entanglement between distant ensembles is mediated by single-photon quantum channels and collectively enhanced light-matter couplings. These techniques can be used to create the recently proposed quantum clock network based on neutral atom optical clocks. We specifically analyze a possible realization of this scheme using neutral Yb ensembles.

 

Title:
Reprint of : Thermodynamic properties of a quantum Hall anti-dot interferometer
Authors:
Levy Schreier, Sarah; Stern, Ady; Rosenow, Bernd; Halperin, Bertrand I.
Publication:
Physica E: Low-dimensional Systems and Nanostructures, Volume 82, p. 145-150.
Publication Date:
08/2016
Origin:
ELSEVIER
Keywords:
Quantum Hall effect
Abstract Copyright:
(c) 2016 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physe.2016.02.024
Bibliographic Code:
2016PhyE...82..145L

Abstract

We study quantum Hall interferometers in which the interference loop encircles a quantum anti-dot. We base our study on thermodynamic considerations, which we believe reflect the essential aspects of interference transport phenomena. We find that similar to the more conventional Fabry-Perot quantum Hall interferometers, in which the interference loop forms a quantum dot, the anti-dot interferometer is affected by the electro-static Coulomb interaction between the edge modes defining the loop. We show that in the Aharonov-Bohm regime, in which effects of fractional statistics should be visible, is easier to access in interferometers based on anti-dots than in those based on dots. We discuss the relevance of our results to recent measurements on anti-dots interferometers.

 

Title:
Direct visualization of quasi-ordered oxygen chain structures on Au(110)-(1 × 2)
Authors:
Hiebel, F.; Montemore, M. M.; Kaxiras, E.; Friend, C. M.
Publication:
Surface Science, Volume 650, p. 5-10.
Publication Date:
08/2016
Origin:
ELSEVIER
Keywords:
Au(110), Scanning tunneling microscopy, Density functional calculations, Oxygen, Ordering
Abstract Copyright:
(c) 2016 Elsevier B.V.
DOI:
10.1016/j.susc.2015.09.018
Bibliographic Code:
2016SurSc.650....5H

Abstract

The Au(110) surface offers unique advantages for atomically-resolved model studies of catalytic oxidation processes on gold. We investigate the adsorption of oxygen on Au(110) using a combination of scanning tunneling microscopy (STM) and density functional theory (DFT) methods. We identify the typical (empty-states) STM contrast resulting from adsorbed oxygen as atomic-sized dark features of electronic origin. DFT-based image simulations confirm that chemisorbed oxygen is generally detected indirectly, from the binding-induced electronic structure modification of gold. STM images show that adsorption occurs without affecting the general structure of the pristine Au(110) missing-row reconstruction. The tendency to form one-dimensional structures is observed already at low coverage (< 0.05 ML), with oxygen adsorbing on alternate sides of the reconstruction ridges. Consistently, calculations yield preferred adsorption on the (111) facets of the reconstruction, on a 3-fold coordination site, with increased stability when adsorbed in chains. Gold atoms with two oxygen neighbors exhibit enhanced electronic hybridization with the O states. Finally, the species observed are reactive to CO oxidation at 200 K and desorption of CO2 leaves a clean and ordered gold surface.

 

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