Faculty Publications: January, 2014

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Title:
The Dust to 5 kpc from Pan-STARRS1
Authors:
Schlafly, Eddie; Green, G.; Finkbeiner, D. P.; Rix, H.
Publication:
American Astronomical Society, AAS Meeting #223, #116.04
Publication Date:
01/2014
Origin:
AAS
Abstract Copyright:
(c) 2014: American Astronomical Society
Bibliographic Code:
2014AAS...22311604S

Abstract

We present a map of the dust reddening to 5 kpc derived from Pan-STARRS1 stellar photometry. The wide coverage and high-quality photometry of the PanSTARRS-1 mission enables the map to cover almost the entire sky north of declination -30 degrees. We use PanSTARRS-1 photometry for more than 500 million stars to determine the map. Our technique is designed to study the dust in the plane, where many other techniques are stymied by the presence of multiple dust clouds at different distances along each line of sight. The map agrees closely with the Schlegel, Finkbeiner, and Davis (1998; SFD) far-infrared dust map outside the Galactic plane, and the largest differences between the two maps stem from known limitations of SFD. The use of optical data from Pan-STARRS1 yields reddening uncertainty as low as 20 mmag E(B-V) in 7 arcminute pixels.

Title:
The Heart of Factorization
Authors:
Schwartz, Matthew D.
Publication:
International Journal of Modern Physics: Conference Series, vol. 25, p. 1460014
Publication Date:
01/2014
Origin:
CROSSREF
DOI:
10.1142/S2010194514600143
Bibliographic Code:
2014IJMPS..2560014S

Abstract

Not Available

 

Title:
Dynamics of a nanodroplet under a transmission electron microscope
Authors:
Leong, Fong Yew; Mirsaidov, Utkur M.; Matsudaira, Paul; Mahadevan, L.
Publication:
Physics of Fluids, Volume 26, Issue 1, id.012003 (PhFl Homepage)
Publication Date:
01/2014
Origin:
AIP
Abstract Copyright:
2014: Author(s)
DOI:
10.1063/1.4862801
Bibliographic Code:
2014PhFl...26a2003L

Abstract

We investigate the cyclical stick-slip motion of water nanodroplets on a hydrophilic substrate viewed with and stimulated by a transmission electron microscope. Using a continuum long wave theory, we show how the electrostatic stress imposed by non-uniform charge distribution causes a pinned convex drop to deform into a toroidal shape, with the shape characterized by the competition between the electrostatic stress and the surface tension of the drop, as well as the charge density distribution which follows a Poisson equation. A horizontal gradient in the charge density creates a lateral driving force, which when sufficiently large, overcomes the pinning induced by surface heterogeneities in the substrate disjoining pressure, causing the drop to slide on the substrate via a cyclical stick-slip motion. Our model predicts step-like dynamics in drop displacement and surface area jumps, qualitatively consistent with experimental observations.

 

Title:
A 3D Dust Reddening Map from Pan-STARRS1
Authors:
Green, Gregory; Schlafly, E.; Finkbeiner, D. P.
Publication:
American Astronomical Society, AAS Meeting #223, #116.05
Publication Date:
01/2014
Origin:
AAS
Abstract Copyright:
(c) 2014: American Astronomical Society
Bibliographic Code:
2014AAS...22311605G

Abstract

We present a 3D map of dust reddening in the Milky Way, derived from PS1 photometry of ~600 million stars. We first determine the full probability density of distance, reddening and stellar type for each well observed star in the survey. In each line of sight, we then model dust reddening as a function of distance, inferring a set of dust profiles which are consistent with the stellar distances and reddenings, as described in detail in Green et al. (2013). Our map is thus probabilistic: it reports the range of possible reddenings at each distance along each direction. Our map agrees well with the Schlegel, Finkbeiner and Davis (1998) map of cumulative dust extinction, and additionally reveals a wealth of 3D dust structure. Our map extends to a heliocentric distance of several kiloparsecs, depending on the dust column in each direction, and probes dust columns up to E(B-V) ~ 4. We expect our 3D dust map to be of use in correcting obsevations of Galactic objects, constraining Galactic structure and kinematics, and in determining distances to objects of known reddening.

 

Title:
A Pan-STARRS1-based recalibration of the Sloan Digital Sky Survey photometry
Authors:
Finkbeiner, Douglas P.; Schlafly, E.; Green, G.
Publication:
American Astronomical Society, AAS Meeting #223, #116.14
Publication Date:
01/2014
Origin:
AAS
Abstract Copyright:
(c) 2014: American Astronomical Society
Bibliographic Code:
2014AAS...22311614F

Abstract

We present a recalibration of the SDSS DR9 photometry with new flat fields and zero points derived from Pan-STARRS. Using PSF photometry of 60 million stars with 16 < r < 20, we obtain SDSS flat-field and amplifier gain corrections stable to 3 millimagnitudes (mmag) in g,r,i,z bands and 15 mmag in u band. We also identify transient non-photometric periods in SDSS ("contrails") based on photometric deviations co-temporal in SDSS bands. The recalibrated SDSS and PS1 photometry agree with systematics at the 7 mmag level.

 

Title:
Towards a Full-sky, High-resolution Dust Extinction Map with WISE and Planck
Authors:
Meisner, Aaron M.; Finkbeiner, D. P.
Publication:
American Astronomical Society, AAS Meeting #223, #138.04
Publication Date:
01/2014
Origin:
AAS
Abstract Copyright:
(c) 2014: American Astronomical Society
Bibliographic Code:
2014AAS...22313804M

Abstract

We have recently completed a custom processing of the entire WISE 12 micron All-sky imaging data set. The result is a full-sky map of diffuse, mid-infrared Galactic dust emission with angular resolution of 15 arcseconds, and with contaminating artifacts such as compact sources removed. At the same time, the 2013 Planck HFI maps represent a complementary data set in the far-infrared, with zero-point relatively immune to zodiacal contamination and angular resolution superior to previous full-sky data sets at similar frequencies. Taken together, these WISE and Planck data products present an opportunity to improve upon the SFD (1998) dust extinction map, by virtue of enhanced angular resolution and potentially better-controlled systematics on large scales. We describe our continuing efforts to construct and test high-resolution dust extinction and temperature maps based on our custom WISE processing and Planck HFI data.

 

Title:
Distances and Reddenings for a Billion Stars: Constructing a 3D Reddening Map
Authors:
Green, Gregory; Schlafly, E.; Finkbeiner, D. P.
Publication:
American Astronomical Society, AAS Meeting #223, #351.10
Publication Date:
01/2014
Origin:
AAS
Abstract Copyright:
(c) 2014: American Astronomical Society
Bibliographic Code:
2014AAS...22335110G

Abstract

We present a method for constructing a 3D map of Galactic dust reddening, using broadband stellar photometry. We first determine the full probability density of stellar type, distance and dust extinction for observed stars along a line of sight. We then infer the extinction along the line of sight by combining information from the individual stars. For individual stars, our reddening estimates are unbiased, with a scatter of ~0.15 magnitudes in E(B-V), based on comparisons with the SEGUE catalog (Green et al. 2013). Based on comparisons with mock catalogs, we expect to recover stellar distances to within 30% to 50%, depending on stellar type. We have applied this technique to ~650 million stars observed by Pan-STARRS 1 to construct a 3D extinction map out to a distance of several kiloparsecs, probing dust columns of up to ~4 magnitudes in E(B-V). At large distances, our map is in good agreement with the 2D dust map of Schlegel, Finkbeiner and Davis (1998). At intermediate distances, our map reveals large-scale dust structure.

 

Title:
A Catalog of Distances to Molecular Clouds from Pan-STARRS1
Authors:
Schlafly, Eddie; Green, G.; Finkbeiner, D. P.; Rix, H.
Affiliation:
AA(MPIA, Germany), AB(Harvard), AC(Harvard), AD(MPIA, Germany)
Publication:
American Astronomical Society, AAS Meeting #223, #351.11
Publication Date:
01/2014
Origin:
AAS
Abstract Copyright:
(c) 2014: American Astronomical Society
Bibliographic Code:
2014AAS...22335111S

Abstract

We present a catalog of distances to molecular clouds, derived from PanSTARRS-1 photometry. We simultaneously infer the full probability distribution function of reddening and distance of the stars towards these clouds using the technique of Green et al. (2013) (see neighboring poster). We fit the resulting measurements using a simple dust screen model to infer the distance to each cloud. The result is a large, homogeneous catalog of distances to molecular clouds. For clouds with heliocentric distances greater than about 200 pc, typical statistical uncertainties in the distances are 5%, with systematic uncertainty stemming from the quality of our stellar models of about 10%. We have applied this analysis to many of the most well-studied clouds in the δ > -30° sky, including Orion, California, Taurus, Perseus, and Cepheus. We have also studied the entire catalog of Magnani, Blitz, and Mundy (1985; MBM), though for about half of those clouds we can provide only upper limits on the distances. We compare our distances with distances from the literature, when available, and find good agreement.

 

Title:
Measuring the CMB Dipole at 11 GHz—for cheap!
Authors:
Markowitz, Aaron; Harrison, S.; Karkare, K.; Kimbert, R.; Kovac, J. M.
Publication:
American Astronomical Society, AAS Meeting #223, #439.07
Publication Date:
01/2014
Origin:
AAS
Abstract Copyright:
(c) 2014: American Astronomical Society
Bibliographic Code:
2014AAS...22343907M

Abstract

We report the design of a telescope capable of making mK-sensitivity maps of the microwave sky, with potential to map large-scale structure of the CMB and galaxy, within the budget of a classroom or amateur astronomer. This project modifies a telescope designed by Harvard’s advanced undergraduate astrophysics lab course, with the goal of improving sensitivity enough to detect the CMB dipole. The telescope’s design allows replication of the experiment within the resources of most similar undergraduate laboratory research courses. We use a low-noise block (LNB) receiver and a bandpass filter to amplify radiation near 10.7 GHz and remove RFI, and we rotate the telescope at constant angular velocity and elevation to provide coverage of the entire visible sky over 24 hours. Before modifications, the telescope accurately measured the isotropic CMB temperature, but interference and 1/f noise limited detection of isotropies in the microwave signal. With current modifications, the telescope can collect data continuously for over 24 hours, and produce maps used to constrain galactic and CMB signals.

 

Title:
A Full-sky, High-resolution Atlas of Galactic 12 μm Dust Emission with WISE
Authors:
Meisner, Aaron M.; Finkbeiner, Douglas P.
Publication:
The Astrophysical Journal, Volume 781, Issue 1, article id. 5, 15 pp. (2014). (ApJ Homepage)
Publication Date:
01/2014
Origin:
IOP
Astronomy Keywords:
dust, extinction, infrared: ISM, ISM: structure
DOI:
10.1088/0004-637X/781/1/5
Bibliographic Code:
2014ApJ...781....5M

Abstract

We describe our custom processing of the entire Wide-field Infrared Survey Explorer (WISE) 12 μm imaging data set, and present a high-resolution, full-sky map of diffuse Galactic dust emission that is free of compact sources and other contaminating artifacts. The principal distinctions between our resulting co-added images and the WISE Atlas stacks are our removal of compact sources, including their associated electronic and optical artifacts, and our preservation of spatial modes larger than 1.°5. We provide access to the resulting full-sky map via a set of 430 12.°5 × 12.°5 mosaics. These stacks have been smoothed to 15'' resolution and are accompanied by corresponding coverage maps, artifact images, and bit-masks for point sources, resolved compact sources, and other defects. When combined appropriately with other mid-infrared and far-infrared data sets, we expect our WISE 12 μm co-adds to form the basis for a full-sky dust extinction map with angular resolution several times better than Schlegel et al.

 

Title:
Variational Polaron Method for Bose-Bose Mixtures
Authors:
Benjamin, David; Demler, Eugene
Publication:
eprint arXiv:1401.0311
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Condensed Matter - Statistical Mechanics
Comment:
5 pages, 2 figures
Bibliographic Code:
2014arXiv1401.0311B

Abstract

We study degenerate mixtures of "heavy" bosons and "light" superfluid bosons using a variational polaron transformation. We consider the Mott insulator-superfluid transition of the heavy species and find that at $T=0$ interaction favors the superfluid phase of the heavy species. Our analytic results agree well with numerically exact quantum Monte Carlo simulations in two dimensions. We then show that in three dimensions the variational polaron transformation can be combined with a Gutzwiller approximation to give good results.

 

Title:
General Framework for Discrete Surface Ricci Flow
Authors:
Zhang, Min; Guo, Ren; Zeng, Wei; Luo, Feng; Yau, Shing-Tung; Gu, Xianfeng
Publication:
eprint arXiv:1401.0401
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Mathematics - Geometric Topology, Mathematics - Metric Geometry
Comment:
25 pages, 14 figures
Bibliographic Code:
2014arXiv1401.0401Z

Abstract

Ricci flow deforms the Riemannian metric proportionally to the curvature, such that the curvature evolves according to a heat diffusion process and eventually becomes constant everywhere. Ricci flow has demonstrated its great potential by solving various problems in many fields, which can be hardly handled by alternative methods so far. This work introduces the unified theoretic framework for discrete Surface Ricci Flow, including all common schemes: Thurston's Circle Packing, Tangential Circle Packing, Inversive Distance Circle Packing and Discrete Yamabe. Furthermore, this work also introduces a novel scheme, virtual radius circle packing, under the unified framework. This work gives explicit geometric interpretation to the discrete Ricci energy for all the schemes, and Hessian of the discrete Ricci energy for schemes with Euclidean back ground geometry. The unified frame work deepen our understanding to the the discrete surface Ricci flow theory, and inspired us to discover the new schemes, improved the flexibility and robustness of the algorithms, greatly simplified the implementation and improved the debugging efficiency. Experimental results shows the unified surface Ricci flow algorithms can handle general surfaces with different topologies, and is robust to meshes with different qualities, and effective for solving real problems.

 

Title:
On the validity of the definition of angular momentum in general relativity
Authors:
Chen, Po-Ning; Huang, Lan-Hsuan; Wang, Mu-Tao; Yau, Shing-Tung
Publication:
eprint arXiv:1401.0597
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Mathematics - Differential Geometry, General Relativity and Quantum Cosmology
Bibliographic Code:
2014arXiv1401.0597C

Abstract

We exam the validity of the definition of the ADM angular momentum without the parity assumption. Explicit examples of asymptotically flat hypersurfaces in the Minkowski spacetime with zero ADM energy-momentum vector and finite non-zero angular momentum vector are presented. We also discuss the Beig-\'O Murchadha-Regge-Teitelboim center of mass and study analogous examples in the Schwarzschild spacetime.

 

Title:
Radio frequency spectroscopy of polarons in ultracold Bose gases
Authors:
Shashi, Aditya; Grusdt, Fabian; Abanin, Dmitry A.; Demler, Eugene
Publication:
eprint arXiv:1401.0952
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
18 pages, including 7 figures and 2 Appendices
Bibliographic Code:
2014arXiv1401.0952S

Abstract

Recent experimental advances enabled the realization of mobile impurities immersed in a Bose-Einstein condensate (BEC) of ultracold atoms. Here we consider impurities with two or more internal hyperfine states, and study their radio-frequency (RF) absorption spectra, which correspond to transitions between two different hyperfine states. We calculate RF spectra for the case when one of the hyperfine states involved interacts with the BEC, while the other state is non-interacting, by performing a non-perturbative resummation of the probabilities of exciting different numbers of phonon modes. In the presence of interactions the impurity gets dressed by Bogoliubov excitations of the BEC, and forms a polaron. The RF signal contains a delta-function peak centered at the energy of the polaron measured relative to the bare impurity transition frequency with a weight equal to the amount of bare impurity character in the polaron state. The RF spectrum also has a broad incoherent part arising from the background excitations of the BEC, with a characteristic power-law tail that appears as a consequence of the universal physics of contact interactions. We discuss both the direct RF measurement, in which the impurity is initially in an interacting state, and the inverse RF measurement, in which the impurity is initially in a non-interacting state. In the latter case, in order to calculate the RF spectrum, we solve the problem of polaron formation: a mobile impurity dynamically gets dressed by Bogoliubov phonons. Our solution based on a time-dependent variational ansatz of coherent states of Bogoliubov phonons, becomes exact when the impurity is localized. Moreover we show that such an ansatz compares well with a semiclassical estimate of the propagation amplitude of a mobile impurity in the BEC. Our technique can be extended to cases when both initial and final impurity states interact with the BEC.

 

Title:
Comparison of Analytical and Numerical Resolution Functions in Sputter Depth Profiling
Authors:
Hofmann, S.; Liu, Y.; Wang, J. Y.; Kovac, J.
Publication:
eprint arXiv:1401.1014
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Materials Science
Comment:
35 pages, 22 figures
Bibliographic Code:
2014arXiv1401.1014H

Abstract

Quantification of sputter depth profiles is frequently done by fitting the convolution integral over concentration and depth resolution function. For a thin delta layer, there exist analytical solutions. The analytical depth resolution functions of two popular approaches, that of the MRI model and that of Dowsett and coworkers are compared. It is concluded that the analytical depth resolution function of the MRI model gives the correct location of a buried delta layer with respect to the measured profile, and a clear description of the information depth in AES, XPS and SIMS. Both analytical solutions can be extended to larger layer thickness. But they are less flexible with respect to physical parameters which are not constant with concentration or sputtered depth, such as detection sensitivity, atomic mixing, roughness or preferential sputtering. For these cases, numerical solutions have to be used.

 

Title:
Measuring Distances and Reddenings for a Billion Stars: Towards A 3D Dust Map from Pan-STARRS 1
Authors:
Green, Gregory Maurice; Schlafly, Edward F.; Finkbeiner, Douglas P.; Jurić, Mario; Rix, Hans Walter; Burgett, Will; Chambers, Kenneth C.; Draper, Peter W.; Flewelling, Heather; Kudritzki, Rolf Peter; Magnier, Eugene; Martin, Nicolas; Metcalfe, Nigel; Tonry, John; Wainscoat, Richard; Waters, Christopher
Publication:
eprint arXiv:1401.1508
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Astrophysics - Galaxy Astrophysics
Comment:
18 pages, 12 figures
Bibliographic Code:
2014arXiv1401.1508G

Abstract

We present a method to infer reddenings and distances to stars, based only on their broad-band photometry, and show how this method can be used to produce a three-dimensional dust map of the Galaxy. Our method samples from the full probability density function of distance, reddening and stellar type for individual stars, as well as the full uncertainty in reddening as a function of distance in the 3D dust map. We incorporate prior knowledge of the distribution of stars in the Galaxy and the detection limits of the survey. For stars in the Pan-STARRS 1 (PS1) 3 pi survey, we demonstrate that our reddening estimates are unbiased, and accurate to ~0.13 mag in E(B-V) for the typical star. Based on comparisons with mock catalogs, we expect distances for main-sequence stars to be constrained to within ~20% - 60%, although this range can vary, depending on the reddening of the star, the precise stellar type and its position on the sky. A further paper will present a 3D map of dust over the three quarters of the sky surveyed by PS1. Both the individual stellar inferences and the 3D dust map will enable a wealth of Galactic science in the plane. The method we present is not limited to the passbands of the PS1 survey, but may be extended to incorporate photometry from other surveys, such as 2MASS, SDSS (where available), and in the future, LSST and Gaia.

 

Title:
Quantum hexatic order in two-dimensional dipolar and charged fluids
Authors:
Bruun, Georg M.; Nelson, David R.
Publication:
eprint arXiv:1401.2237
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Condensed Matter - Statistical Mechanics
Comment:
10 pages, 7 figures
Bibliographic Code:
2014arXiv1401.2237B

Abstract

Recent advances in cold atom experimentation suggest that studies of quantum two-dimensional melting of dipolar molecules, with dipoles aligned perpendicular to ordering plane, may be on the horizon. An intriguing aspect of this problem is that two-dimensional \emph{classical} aligned dipoles (already studied in great detail in soft matter experiments on magnetic colloids) are known to melt via a two-stage process, with an intermediate hexatic phase separating the usual crystal and isotropic fluid phases. We estimate here the effect of quantum fluctuations on this hexatic phase, for both dipolar systems and charged Wigner crystals. Our approximate phase diagrams rely on a pair of Lindemann criteria, suitably adapted to deal with effects of thermal fluctuations in two dimensions. As part of our analysis, we determine the phonon spectra of quantum particles on a triangular lattice interacting with repulsive $1/r^3$ and $1/r$ potentials. A large softening of the transverse and longitudinal phonon frequencies, due to both lattice effects and quantum fluctuations, plays a significant role in our analysis. The hexatic phase is predicted to survive down to very low temperatures.

 

Title:
Sub-nanometer 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:
eprint arXiv:1401.2674
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Quantum Physics
Comment:
7 pages, 4 figures
Bibliographic Code:
2014arXiv1401.2674G

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 microns, which is insufficient for imaging on molecular and atomic scales. Here we demonstrate an MRI technique that provides sub-nanometer 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 and cannot otherwise be individually detected. 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 spatial 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 dark electronic spins at and just below 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 previously unidentified electronic spins on the diamond surface, which can potentially be used as resources for improved magnetic imaging of samples proximal to the NV-diamond sensor. This three-dimensional NV-MRI technique is immediately applicable to diverse systems including imaging spin chains, readout of individual spin-based quantum bits, and determining the precise location of spin labels in biological systems.

 

Title:
Gravity Waves from Kerr/CFT
Authors:
Porfyriadis, Achilleas P.; Strominger, Andrew
Publication:
eprint arXiv:1401.3746
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, General Relativity and Quantum Cosmology
Comment:
23 pages
Bibliographic Code:
2014arXiv1401.3746P

Abstract

Dynamics at large redshift near the horizon of an extreme Kerr black hole are governed by an infinite-dimensional conformal symmetry. This symmetry may be exploited to analytically, rather than numerically, compute a variety of potentially observable processes. In this paper we compute and study the conformal transformation properties of the gravitational radiation emitted by an orbiting mass in the large-redshift near-horizon region.

 

Title:
Measurement of Collective Dynamical Mass of Dirac Fermions in Graphene
Authors:
Yoon, Hosang; Forsythe, Carlos; Wang, Lei; Tombros, Nikolaos; Watanabe, Kenji; Taniguchi, Takashi; Hone, James; Kim, Philip; Ham, Donhee
Publication:
eprint arXiv:1401.4240
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Bibliographic Code:
2014arXiv1401.4240Y

Abstract

Individual electrons in graphene behave as massless quasiparticles. In surprising twist, it is inferred from plasmonic investigations that collectively excited graphene electrons must exhibit non-zero mass and its inertial acceleration is essential for graphene plasmonics. Despite such importance, this collective mass has defied direct unequivocal measurement. It may be directly measured by accelerating it with a time-varying voltage and quantifying the phase delay of the resulting current; this voltage-current phase relation would manifest as kinetic inductance, representing the collective inertia's reluctance to accelerate. However, at optical (infrared) frequencies phase measurement of current is generally difficult and at microwave frequencies the inertial phase delay has been buried under electron scattering. Here we directly, precisely measure the kinetic inductance, thus, collective mass, by combining innovative device engineering that reduces electron scattering and delicate microwave phase measurements. Particularly, encapsulation of graphene between hexagonal-boron-nitride layers, one-dimensional edge contacts, and a proximate top gate configured as microwave ground together enable resolving the inertial phase delay from the electron scattering. Beside the fundamental importance, the kinetic inductance demonstrated here to be orders-of-magnitude larger than magnetic inductance can dramatically miniaturize radio-frequency integrated circuits. Moreover, its bias-dependency heralds a solid-state voltage-controlled inductor to complement the prevalent voltage-controlled capacitor.

 

Title:
Transmon-based simulator of nonlocal electron-phonon coupling: a platform for observing sharp small-polaron transitions
Authors:
Stojanovic, Vladimir M.; Vanevic, Mihajlo; Demler, Eugene; Tian, Lin
Publication:
eprint arXiv:1401.4783
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Quantum Physics
Comment:
13 pages, 6 figures
Bibliographic Code:
2014arXiv1401.4783S

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 vertex function depends on both the electron- and phonon quasimomenta, this model does not belong to the realm of validity of the Gerlach-L\"{o}wen 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 in this system -- by varying the circuit 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 ($K_{\textrm{gs}}=0$) to a twofold-degenerate small-polaron ground state at nonzero quasimomenta $K_{\textrm{gs}}$ and $-K_{\textrm{gs}}$. 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). The proposed setup provides an ideal testbed for studying quantum dynamics of polaron formation in systems with strongly momentum-dependent electron-phonon interactions.

 

Title:
State-specific detection of trapped HfF$^+$ by photodissociation
Authors:
Ni, Kang-Kuen; Loh, Huanqian; Grau, Matt; Cossel, Kevin C.; Ye, Jun; Cornell, Eric A.
Publication:
eprint arXiv:1401.5423
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Physics - Atomic Physics, Physics - Chemical Physics
Comment:
4 pages, 5 figures
Bibliographic Code:
2014arXiv1401.5423N

Abstract

We use (1+1$'$) resonance-enhanced multiphoton photodissociation (REMPD) to detect the population in individual rovibronic states of trapped HfF$^+$ with a single-shot absolute efficiency of 18%, which is over 200 times better than that obtained with fluorescence detection. The first photon excites a specific rotational level to an intermediate vibronic band at 35,000-36,500 cm$^{-1}$, and the second photon, at 37,594 cm$^{-1}$ (266 nm), dissociates HfF$^+$ into Hf$^+$ and F. Mass-resolved time-of-flight ion detection then yields the number of state-selectively dissociated ions. Using this method, we observe rotational-state heating of trapped HfF$^+$ ions from collisions with neutral Ar atoms. Furthermore, we measure the lifetime of the $^3\Delta_1$ $v=0,\, J=1$ state to be 2.1(2) s. This state will be used for a search for a permanent electric dipole moment of the electron.

 

Title:
Theory of confinement-induced interlayer molecular resonances
Authors:
Kanász-Nagy, Márton; Demler, Eugene A.; Zaránd, Gergely
Publication:
eprint arXiv:1401.5798
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Physics - Atomic Physics, Quantum Physics
Comment:
8 pages, 5 figures
Bibliographic Code:
2014arXiv1401.5798K

Abstract

We study theoretically the interaction between two species of bosons confined parabolically in one transverse direction but with a finite separation between the centers of the confining potentials. We demonstrate the existence of new types of confinement-induced Feshbach resonances that can be tuned by changing separation between the layers. They are much sharper than usual two-dimensional confinement-induced resonances, and can be observed in the shaking spectrum of the two-dimensional layers, as shown by detailed many-body calculations for a thermal Bose gas.

 

Title:
Quantum Fluctuations of the Transverse Field Ising Chain
Authors:
Kinross, A. W.; Fu, M.; Munsie, T. J.; Dabkowska, H. A.; Luke, G. M.; Sachdev, S.; Imai, T.
Publication:
eprint arXiv:1401.6917
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Statistical Mechanics, Condensed Matter - Superconductivity
Comment:
8 pages and 9 figures, including Supplementary Information
Bibliographic Code:
2014arXiv1401.6917K

Abstract

We report 93Nb NMR measurements on the transverse field Ising chain system CoNb$_{2}$O$_{6}$. From the measurements of the nuclear spin-lattice relaxation rate 1/T_1, we identify the 1D quantum critical point as h~5.3 Tesla, map the evolution of the quantum fluctuations, and establish the experimental T-h phase diagram for the ferromagnetic Ising chain. Based on comparison with the quantum critical scaling theory, we demonstrate that the quantum criticality persists in temperature to as high as T ~ 0.4J, where J is the intra-chain exchange interaction between Co spins.

 

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:
eprint arXiv:1401.7012
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory
Comment:
31 pages, 7 figures
Bibliographic Code:
2014arXiv1401.7012H

Abstract

We consider two-dimensional metals near a Pomeranchuk instability which breaks 90$^\circ$ 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 non-zero 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:
BMS supertranslations and Weinberg's soft graviton theorem
Authors:
He, Temple; Lysov, Vyacheslav; Mitra, Prahar; Strominger, Andrew
Publication:
eprint arXiv:1401.7026
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, General Relativity and Quantum Cosmology
Comment:
14 pages
Bibliographic Code:
2014arXiv1401.7026H

Abstract

Recently it was conjectured that a certain infinite-dimensional "diagonal" subgroup of BMS supertranslations acting on past and future null infinity (${\mathscr I}^-$ and ${\mathscr I}^+$) is an exact symmetry of the quantum gravity ${\cal S}$-matrix, and an associated Ward identity was derived. In this paper we show that this supertranslation Ward identity is precisely equivalent to Weinberg's soft graviton theorem. Along the way we construct the canonical generators of supertranslations at ${\mathscr I}^\pm$, including the relevant soft graviton contributions. Boundary conditions at the past and future of ${\mathscr I}^\pm$ and a correspondingly modified Dirac bracket are required. The soft gravitons enter as boundary modes and are manifestly the Goldstone bosons of spontaneously broken supertranslation invariance.

 

Title:
Towards an Effective Field Theory on the Light-Shell
Authors:
Georgi, Howard; Kestin, Greg; Sajjad, Aqil
Publication:
eprint arXiv:1401.7667
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology, High Energy Physics - Theory
Bibliographic Code:
2014arXiv1401.7667G

Abstract

We discuss our work toward the construction of a light-shell effective theory (LSET), an effective field theory for describing the matter emerging from high-energy collisions and the accompanying radiation. We work in the highly simplified venue of 0-flavor scalar quantum electrodynamics, with a gauge invariant product of scalar fields at the origin of space-time as the source of high-energy charged particles. Working in this simple gauge theory allows us to focus on the essential features of LSET. We describe how the effective theory is constructed and argue that it can reproduce the full theory tree-level amplitude. We study the 1-loop radiative corrections in the LSET and suggest how the leading double-logs in the full theory at 1-loop order can be reproduced by a purely angular integral in the LSET.

 

Title:
A New Look at Higgs Constraints on Stops
Authors:
Fan, JiJi; Reece, Matthew
Publication:
eprint arXiv:1401.7671
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology
Bibliographic Code:
2014arXiv1401.7671F

Abstract

We present a simple new way to visualize the constraints of Higgs coupling measurements on light stops in natural SUSY scenarios beyond the MSSM, which works directly in the plane of stop mass eigenvalues (with no need to make assumptions about mixing angles). For given stop mass eigenvalues, the smallest value of $X_t$ that can bring the correction to the $h \to gg$ and $h\to \gamma\gamma$ couplings into agreement with data is computed. Requiring that this $X_t$ is consistent--i.e. that the chosen mass eigenvalues can be the outcome of diagonalizing a matrix with a given off-diagonal term--rules out the possibility that both stops have a mass below $\approx$ 400 GeV. Requiring that $X_t$ is not fine-tuned for agreement with the data shows that neither stop can be lighter than $\approx$ 100 GeV. These constraints are interesting because, unlike direct searches, they apply no matter how stops decay, and suggest a minimum electroweak fine-tuning of between a factor of 5 and 10. We show that a multi-parameter fit can slightly weaken this conclusion by allowing a large Higgs coupling to $b$-quarks, but only if a second Higgs boson is within reach of experiment. Certain models, like $R$-symmetric models with Dirac gauginos, are much more strongly constrained because they predict negligible $X_t$. We illustrate how the constraints will evolve given precise measurements at future colliders (HL-LHC, ILC, and TLEP), and comment on the more difficult case of Folded Supersymmetry.

 

Title:
Quantum quenches and competing orders: I. Time-dependent Hartree-Fock+BCS theory
Authors:
Fu, Wenbo; Hung, Ling-Yan; Sachdev, Subir
Publication:
eprint arXiv:1401.7674
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons
Comment:
14+4 pages, 16 figures
Bibliographic Code:
2014arXiv1401.7674F

Abstract

We study the non-equlibrium dynamics of an electronic model of competing bond density wave order and $d$-wave superconductivity. In a time-dependent Hartree-Fock+BCS approximation, the dynamics reduces to the equations of motion of operators realizing the generators of SU(4) at each pair of momenta, $(\boldsymbol{k}, -\boldsymbol{k})$, in the Brillouin zone. We compare the results of numerical studies of our model with recent picosecond optical experiments.

 

Title:
Scale-invariant hyperscaling-violating holographic theories and the resistivity of strange metals with random-field disorder
Authors:
Lucas, Andrew; Sachdev, Subir; Schalm, Koenraad
Publication:
eprint arXiv:1401.7993
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Condensed Matter - Strongly Correlated Electrons
Comment:
19 pages. v2: minor changes, more references
Bibliographic Code:
2014arXiv1401.7993L

Abstract

We compute the direct current resistivity of a scale-invariant, $d$-dimensional strange metal with dynamic critical exponent $z$ and hyperscaling-violating exponent $\theta$, weakly perturbed by a scalar operator coupled to random-field disorder that locally breaks a $\mathbb{Z}_2$ symmetry. Independent calculations via Einstein-Maxwell-Dilaton holography and memory matrix methods lead to the same results. We show that random field disorder has a strong effect on resistivity: charge carriers in the infrared are easily depleted, as the relaxation time for momentum is surprisingly small. In the course of our holographic calculation we use a non-trivial dilaton coupling to the disordered scalar, allowing us to study a strongly-coupled scale invariant theory with $\theta \ne 0$. Using holography, we are also able to determine the disorder strength at which perturbation theory breaks down. Curiously, for locally critical theories this breakdown occurs when the resistivity is proportional to the entropy density, up to a possible logarithmic correction.

 

Title:
Expansion and rupture of charged microcapsules
Authors:
Datta, Sujit S.; Abbaspourrad, Alireza; Weitz, David A.
Publication:
eprint arXiv:1401.8270
Publication Date:
01/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science, Physics - Fluid Dynamics
Comment:
Supplementary information available online at journal webpage; Materials Horizons 1, 92-95 (2014); doi:10.1039/C3MH00099K
Bibliographic Code:
2014arXiv1401.8270D

Abstract

We study the deformations of pH-responsive spherical microcapsules -- micrometer-scale liquid drops surrounded by thin, solid shells -- under the influence of electrostatic forces. When exposed to a large concentration of NaOH, the microcapsules become highly charged, and expand isotropically. We find that the extent of this expansion can be understood by coupling electrostatics with shell theory; moreover, the expansion dynamics is well described by Darcy's law for fluid flow through the microcapsule shell. Unexpectedly, however, below a threshold NaOH concentration, the microcapsules begin to disintegrate, and eventually rupture; they then expand non-uniformly, ultimately forming large, jellyfish-like structures. Our results highlight the fascinating range of behaviors exhibited by pH-responsive microcapsules, driven by the interplay between electrostatic and mechanical forces.

 

Title:
Osmotic-pressure-controlled concentration of colloidal particles in thin-shelled capsules
Authors:
Kim, Shin-Hyun; Park, Jin-Gyu; Choi, Tae Min; Manoharan, Vinothan N.; Weitz, David A.
Publication:
Nature Communications, Volume 5, id. 3068 (2014).
Publication Date:
01/2014
Origin:
NATURE
Abstract Copyright:
(c) 2014: Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.
DOI:
10.1038/ncomms4068
Bibliographic Code:
2014NatCo...5E3068K

Abstract

Colloidal crystals are promising structures for photonic applications requiring dynamic control over optical properties. However, for ease of processing and reconfigurability, the crystals should be encapsulated to form ‘ink’ capsules rather than confined in a thin film. Here we demonstrate a class of encapsulated colloidal photonic structures whose optical properties can be controlled through osmotic pressure. The ordering and separation of the particles within the microfluidically created capsules can be tuned by changing the colloidal concentration through osmotic pressure-induced control of the size of the individual capsules, modulating photonic stop band. The rubber capsules exhibit a reversible change in the diffracted colour, depending on osmotic pressure, a property we call osmochromaticity. The high encapsulation efficiency and capsule uniformity of this microfluidic approach, combined with the highly reconfigurable shapes and the broad control over photonic properties, make this class of structures particularly suitable for photonic applications such as electronic inks and reflective displays.

 

Title:
Nutrient depletion in Bacillus subtilis biofilms triggers matrix production
Authors:
Zhang, Wenbo; Seminara, Agnese; Suaris, Melanie; Brenner, Michael P.; Weitz, David A.; Angelini, Thomas E.
Publication:
New Journal of Physics, Volume 16, Issue 1, article id. 015028 (2014).
Publication Date:
01/2014
Origin:
IOP
DOI:
10.1088/1367-2630/16/1/015028
Bibliographic Code:
2014NJPh...16a5028Z

Abstract

Many types of bacteria form colonies that grow into physically robust and strongly adhesive aggregates known as biofilms. A distinguishing characteristic of bacterial biofilms is an extracellular polymeric substance (EPS) matrix that encases the cells and provides physical integrity to the colony. The EPS matrix consists of a large amount of polysaccharide, as well as protein filaments, DNA and degraded cellular materials. The genetic pathways that control the transformation of a colony into a biofilm have been widely studied, and yield a spatiotemporal heterogeneity in EPS production. Spatial gradients in metabolites parallel this heterogeneity in EPS, but nutrient concentration as an underlying physiological initiator of EPS production has not been explored. Here, we study the role of nutrient depletion in EPS production in Bacillus subtilis biofilms. By monitoring simultaneously biofilm size and matrix production, we find that EPS production increases at a critical colony thickness that depends on the initial amount of carbon sources in the medium. Through studies of individual cells in liquid culture we find that EPS production can be triggered at the single-cell level by reducing nutrient concentration. To connect the single-cell assays with conditions in the biofilm, we calculate carbon concentration with a model for the reaction and diffusion of nutrients in the biofilm. This model predicts the relationship between the initial concentration of carbon and the thickness of the colony at the point of internal nutrient deprivation.

 

Title:
Measurement of the mass difference between top and anti-top quarks in pp collisions at s=7 TeV using the ATLAS detector
Authors:
Aad, G.; Abajyan, T.; Abbott, B.;... Barreiro Guimarães da Costa, J.; ... Franklin, M.; ... Huth, J. ;... Morii, M.; ...; and 2928 coauthors
Publication:
Physics Letters B, Volume 728, p. 363-379.
Publication Date:
01/2014
Origin:
ELSEVIER
Abstract Copyright:
The Authors
DOI:
10.1016/j.physletb.2013.12.010
Bibliographic Code:
2014PhLB..728..363A

Abstract

A measurement of the mass difference between top and anti-top quarks is presented. In a 4.7 fb data sample of proton–proton collisions at s=7 TeV recorded with the ATLAS detector at the LHC, events consistent with tt¯ production and decay into a single charged lepton final state are reconstructed. For each event, the mass difference between the top and anti-top quark candidate is calculated. A two b-tag requirement is used in order to reduce the background contribution. A maximum likelihood fit to these per-event mass differences yields Δm≡mt‑m=0.67±0.61(stat)±0.41(syst) GeV, consistent with CPT invariance.

 

Title:
Search for new phenomena in photon + jet events collected in proton–proton collisions at s=8 TeV with the ATLAS detector
Authors:
Aad, G.; Abajyan, T.; Abbott, B.;... ... Barreiro Guimarães da Costa, J.; ... Franklin, M.; ... Huth, J. ;... Morii, M.; ...; and 2917 coauthors
Publication:
Physics Letters B, Volume 728, p. 562-578.
Publication Date:
01/2014
Origin:
ELSEVIER
Abstract Copyright:
The Authors
DOI:
10.1016/j.physletb.2013.12.029
Bibliographic Code:
2014PhLB..728..562A

Abstract

This Letter describes a model-independent search for the production of new resonances in photon + jet (γ+jet) events using 20 fb-1 of proton–proton LHC data recorded with the ATLAS detector at a centre-of-mass energy of s=8 TeV. The γ+jet mass distribution is compared to a background model fit from data; no significant deviation from the background-only hypothesis is found. Limits are set at 95% credibility level on generic Gaussian-shaped signals and two benchmark phenomena beyond the Standard Model: non-thermal quantum black holes and excited quarks. Non-thermal quantum black holes are excluded below masses of 4.6 TeV and excited quarks are excluded below masses of 3.5 TeV.

 

Title:
Application of Laser Frequency Combs and Nitrogen Vacancy Diamond Magnetometers to Searches for New Physics
Authors:
Phillips, D. F.; Walsworth, R. L.
Publication:
CPT and Lorentz Symmetry - Proceedings of the Sixth Meeting. Edited by KOSTELECKY ALAN. Published by World Scientific Publishing Co. Pte. Ltd., 2014. ISBN #9789814566438, pp. 249-251
Publication Date:
01/2014
Origin:
WSPC
DOI:
10.1142/9789814566438_0063
Bibliographic Code:
2014cls..conf..249P

Abstract

Searches for new physics often benefit from improved technologies. Here we discuss possible applications of two emerging technologies to searches for physics beyond the Standard Model. First, laser frequency combs enable broad spectral coverage and coherent conversion between optical and RF signals. We are investigating tests of the nonminimal Standard-Model Extension using frequency combs coupled to broadband optical cavities. Second, nitrogen vacancy centers in diamond enable precision nanoscale magnetometry with applications from imaging to quantum science. We are investigating their use in searches for short-range spin-spin couplings.

 

Title:
A spatio-temporal coupling method to reduce the time-to-solution of cardiovascular simulations
Authors:
Randles, A.; Kaxiras, E.
Publication:
2014 IEEE International Parallel & Distributed Processing Symposium (IPDPS). Phoenix, AZ, USA, 20140519
Publication Date:
01/2014
Publisher:
IEEE
Database:
Inspec
Inspec Headings:
cardiovascular system; haemodynamics; lattice Boltzmann methods; spatiotemporal phenomena
DOI:
10.1109/IPDPS.2014.68

Abstract

We present a new parallel-in-time method designed to reduce the overall time-to-solution of a patient-specific cardiovascular flow simulation. Using a modified Para real algorithm, our approach extends strong scalability beyond spatial parallelism with fully controllable accuracy and no decrease in stability. We discuss the coupling of spatial and temporal domain decompositions used in our implementation, and showcase the use of the method on a study of blood flow through the aorta. We observe an additional 40% reduction in overall wall clock time with no significant loss of accuracy, in agreement with a predictive performance model.


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