Faculty Publications: May, 2017

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Title:
The Rest Mass of an Asymptotically Anti-de Sitter Spacetime
Authors:
Chen, Po-Ning; Hung, Pei-Ken; Wang, Mu-Tao; Yau, Shing-Tung
Publication:
Annales Henri Poincaré, vol. 18, issue 5, pp. 1493-1518
Publication Date:
05/2017
Origin:
CROSSREF
DOI:
10.1007/s00023-017-0555-4
Bibliographic Code:
2017AIHPA..18.1493C

Abstract

Not Available

 

Title:
Soft Factorization in QED from 2D Kac-Moody Symmetry
Authors:
Nande, Anjalika; Pate, Monica; Strominger, Andrew
Publication:
eprint arXiv:1705.00608
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
20 pages
Bibliographic Code:
2017arXiv170500608N

Abstract

The soft factorization theorem for 4D abelian gauge theory states that the $\mathcal{S}$-matrix factorizes into soft and hard parts, with the universal soft part containing all soft and collinear poles. Similarly, correlation functions on the sphere in a 2D CFT with a $U(1)$ Kac-Moody current algebra factorize into current algebra and non-current algebra factors, with the current algebra factor fully determined by its pole structure. In this paper, we show that these 4D and 2D factorizations are mathematically the same phenomena. The soft `tHooft-Wilson lines and soft photons are realized as a complexified 2D current algebra on the celestial sphere at null infinity. The current algebra level is determined by the cusp anomalous dimension. The associated complex $U(1)$ boson lives on a torus whose modular parameter is $\tau =\frac {2\pi i }{e^2}+\frac{\theta}{ 2 \pi}$. The correlators of this 2D current algebra fully reproduce the known soft part of the 4D $\mathcal{S}$-matrix, as well as a conjectured generalization involving magnetic charges.

 

Title:
Weyl and Dirac Semimetals in Three Dimensional Solids
Authors:
Armitage, N. P.; Mele, E. J.; Vishwanath, Ashvin
Publication:
eprint arXiv:1705.01111
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons
Comment:
61 pages, 37 figures; Comprehensive review on Weyl and Dirac Semimetals submitted to Reviews of Modern Physics on December 23rd, 2016; Feedback, comments, and criticism welcome
Bibliographic Code:
2017arXiv170501111A

Abstract

Weyl and Dirac semimetals are three dimensional phases of matter with gapless electronic excitations that are protected by topology and symmetry. As three dimensional analogs of graphene, they have generated much recent interest. Deep connections exist with particle physics models of relativistic chiral fermions, and -- despite their gaplessness -- to solid-state topological and Chern insulators. Their characteristic electronic properties lead to protected surface states and novel responses to applied electric and magnetic fields. Here we review the theoretical foundations of these phases, their proposed realizations in solid state systems, recent experiments on candidate materials, as well as their relation to other states of matter.

 

Title:
Active elastohydrodynamics of vesicles in narrow, blind constrictions
Authors:
Fai, Thomas G.; Kusters, Remy; Harting, Jens; Rycroft, Chris H.; Mahadevan, L.
Publication:
eprint arXiv:1705.01765
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter
Bibliographic Code:
2017arXiv170501765F

Abstract

Fluid-resistance limited transport of vesicles through narrow constrictions is a recurring theme in many biological and engineering applications. Inspired by the motor-driven movement of soft membrane-bound vesicles into closed neuronal dendritic spines, here we study this problem using a combination of passive three-dimensional simulations and a simplified semi-analytical theory for active transport of vesicles that are forced through such constrictions by molecular motors. We show that the motion of these objects is characterized by two dimensionless quantities related to the geometry and the strength of forcing relative to the vesicle elasticity. We use numerical simulations to characterize the transit time for a vesicle forced by fluid pressure through a constriction in a channel, and find that relative to an open channel, transport into a blind end leads to the formation of an effective lubrication layer that strongly impedes motion. When the fluid pressure forcing is complemented by forces due to molecular motors that are responsible for vesicle trafficking into dendritic spines, we find that the competition between motor forcing and fluid drag results in multistable dynamics reminiscent of the real system. Our study highlights the role of non-local hydrodynamic effects in determining the kinetics of vesicular transport in constricted geometries.

 

Title:
BICEP2 / Keck Array IX: New Bounds on Anisotropies of CMB Polarization Rotation and Implications for Axion-Like Particles and Primordial Magnetic Fields
Authors:
Array, Keck; BICEP2 Collaborations; Ade, P. A. R.; Ahmed, Z.; Aikin, R. W.;... Dvorkin, C.;... Kovac, J. M.;... and 60 coauthors
Publication:
eprint arXiv:1705.02523
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Astrophysics - Cosmology and Nongalactic Astrophysics, High Energy Physics - Experiment, High Energy Physics - Phenomenology
Comment:
6 pages, 2 figures
Bibliographic Code:
2017arXiv170502523A

Abstract

We present the strongest constraints to date on anisotropies of CMB polarization rotation derived from $150$ GHz data taken by the BICEP2 & Keck Array CMB experiments up to and including the 2014 observing season (BK14). The definition of polarization angle in BK14 maps has gone through self-calibration in which the overall angle is adjusted to minimize the observed $TB$ and $EB$ power spectra. After this procedure, the $QU$ maps lose sensitivity to a uniform polarization rotation but are still sensitive to anisotropies of polarization rotation. This analysis places constraints on the anisotropies of polarization rotation, which could be generated by CMB photons interacting with axion-like pseudoscalar fields or Faraday rotation induced by primordial magnetic fields. The sensitivity of BK14 maps ($\sim 3\mu$K-arcmin) makes it possible to reconstruct anisotropies of polarization rotation angle and measure their angular power spectrum much more precisely than previous attempts. Our data are found to be consistent with no polarization rotation anisotropies, improving the upper bound on the amplitude of the rotation angle spectrum by roughly an order of magnitude compared to the previous best constraints. Our results lead to an order of magnitude better constraint on the coupling constant of the Chern-Simons electromagnetic term $f_a \geq 1.7\times 10^2\times (H_I/2\pi)$ ($2\sigma$) than the constraint derived from uniform rotation, where $H_I$ is the inflationary Hubble scale. The upper bound on the amplitude of the primordial magnetic fields is 30nG ($2\sigma$) from the polarization rotation anisotropies.

 

Title:
Topology-optimized Dual-Polarization Dirac Cones
Authors:
Lin, Zin; Christakis, Lysander; Li, Yang; Mazur, Eric; Rodriguez, Alejandro W.; Lončar, Marko
Publication:
eprint arXiv:1705.03574
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Physics - Optics
Bibliographic Code:
2017arXiv170503574L

Abstract

We apply a large-scale computational technique, known as topology optimization, to the inverse design of photonic Dirac cones. In particular, we report on a variety of photonic crystal geometries, realizable in simple isotropic dielectric materials, which exhibit dual-polarization and dual-wavelength Dirac cones. We demonstrate the flexibility of this technique by designing photonic crystals of different symmetry types, such as ones with four-fold and six-fold rotational symmetry, which possess Dirac cones at different points within the Brillouin zone. The demonstrated and related optimization techniques could open new avenues to band-structure engineering and manipulating the propagation of light in periodic media, with possible applications in exotic optical phenomena such as effective zero-index media and topological photonics.

 

Title:
Infrared Divergences in QED, Revisited
Authors:
Kapec, Daniel; Perry, Malcolm; Raclariu, Ana-Maria; Strominger, Andrew
Publication:
eprint arXiv:1705.04311
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, High Energy Physics - Phenomenology
Comment:
21 pages, 3 figures
Bibliographic Code:
2017arXiv170504311K

Abstract

Recently it has been shown that the vacuum state in QED is infinitely degenerate. Moreover a transition among the degenerate vacua is induced in any nontrivial scattering process and determined from the associated soft factor. Conventional computations of scattering amplitudes in QED do not account for this vacuum degeneracy and therefore always give zero. This vanishing of all conventional QED amplitudes is usually attributed to infrared divergences. Here we show that if these vacuum transitions are properly accounted for, the resulting amplitudes are nonzero and infrared finite. Our construction of finite amplitudes is mathematically equivalent to, and amounts to a physical reinterpretation of, the 1970 construction of Faddeev and Kulish.

 

Title:
Universal geometric constraints during epithelial jamming
Authors:
Atia, Lior; Bi, Dapeng; Sharma, Yasha; Mitchel, Jennifer A.; Gweon, Bomi; Koehler, Stephan; DeCamp, Stephen J.; Lan, Bo; Hirsch, Rebecca; Pegoraro, Adrian F.; Lee, Kyu Ha; Starr, Jacqueline; Weitz, David A.; Martin, Adam C.; Park, Jin-Ah; Butler, James P.; Fredberg, Jeffrey J.
Publication:
eprint arXiv:1705.04660
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Physics - Biological Physics, Quantitative Biology - Cell Behavior
Comment:
First three authors had equal contribution | Video links are given in the Supplementary Videos section (pages 31-32)
Bibliographic Code:
2017arXiv170504660A

Abstract

As an injury heals, an embryo develops, or a carcinoma spreads, epithelial cells systematically change their shape. In each of these processes cell shape is studied extensively, whereas variation of shape from cell-to-cell is dismissed most often as biological noise. But where do cell shape and variation of cell shape come from? Here we report that cell shape and shape variation are mutually constrained through a relationship that is purely geometrical. That relationship is shown to govern maturation of the pseudostratified bronchial epithelial layer cultured from both non-asthmatic and asthmatic donors as well as formation of the ventral furrow in the epithelial monolayer of the Drosophila embryo in vivo. Across these and other vastly different epithelial systems, cell shape variation collapses to a family of distributions that is common to all and potentially universal. That distribution, in turn, is accounted for quantitatively by a mechanistic theory of cell-cell interaction showing that cell shape becomes progressively less elongated and less variable as the layer becomes progressively more jammed. These findings thus uncover a connection between jamming and geometry that is generic -spanning jammed living and inert systems alike- and demonstrate that proximity of the cell layer to the jammed state is the principal determinant of the most primitive features of epithelial cell shape and shape variation.

 

Title:
Last Electroweak WIMP Standing: Pseudo-Dirac Higgsino Status and Compact Stars as Future Probes
Authors:
Krall, Rebecca; Reece, Matthew
Publication:
eprint arXiv:1705.04843
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology
Bibliographic Code:
2017arXiv170504843K

Abstract

Electroweak WIMPs are under intense scrutiny from direct detection, indirect detection, and collider experiments. Nonetheless the pure (pseudo-Dirac) higgsino, one of the simplest such WIMPs, remains elusive. We present an up-to-date assessment of current experimental constraints on neutralino dark matter. The strongest bound on pure higgsino dark matter currently may arise from AMS-02 measurements of antiprotons, though the interpretation of these results has sizable uncertainty. We discuss whether future astrophysical observations could offer novel ways to test higgsino dark matter, especially in the challenging regime with order MeV mass splitting between the two neutral higgsinos. We find that heating of white dwarfs by annihilation of higgsinos captured via inelastic scattering could be one useful probe, although it will require challenging observations of distant dwarf galaxies or a convincing case to be made for substantial dark matter content in Omega Centauri, a globular cluster that may be a remnant of a disrupted dwarf galaxy. White dwarfs and neutron stars give a target for astronomical observations that could eventually help to close the last, most difficult corner of parameter space for dark matter with weak interactions.

 

Title:
Acoustic Traps and Lattices for Electrons in Semiconductors
Authors:
Schuetz, Martin J. A.; Knörzer, Johannes; Giedke, Geza; Vandersypen, Lieven M. K.; Lukin, Mikhail D.; Cirac, J. Ignacio
Publication:
eprint arXiv:1705.04860
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
Manuscript: 10.5 pages, 5 figures, 1 table. Appendices: 8 pages, 1 table
Bibliographic Code:
2017arXiv170504860S

Abstract

We propose and analyze a solid-state platform based on surface acoustic waves (SAWs) for trapping, cooling and controlling (charged) particles, as well as the simulation of quantum many-body systems. We develop a general theoretical framework demonstrating the emergence of effective time-independent acoustic trapping potentials for particles in two- or one-dimensional structures. As our main example we discuss in detail the generation and applications of a stationary, but movable acoustic pseudo-lattice (AL) with lattice parameters that are reconfigurable in situ. We identify the relevant figures of merit, discuss potential experimental platforms for a faithful implementation of such an acoustic lattice, and provide estimates for typical system parameters. With a projected lattice spacing on the scale of 100nm, this approach allows for relatively large energy scales in the realization of fermionic Hubbard models, with the ultimate prospect of entering the low temperature, strong interaction regime. Experimental imperfections as well as read-out schemes are discussed.

 

Title:
ADE String Chains and Mirror Symmetry
Authors:
Haghighat, Babak; Yan, Wenbin; Yau, Shing-Tung
Publication:
eprint arXiv:1705.05199
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Mathematics - Algebraic Geometry
Comment:
28 pages, 8 figures
Bibliographic Code:
2017arXiv170505199H

Abstract

6d superconforaml field theories (SCFTs) are the SCFTs in the highest possible dimension. They can be geometrically engineered in F-theory by compactifying on non-compact elliptic Calabi-Yau manifolds. In this paper we focus on the class of SCFTs whose base geometry is determined by $-2$ curves intersecting according to ADE Dynkin diagrams and derive the corresponding mirror Calabi-Yau manifold. The mirror geometry is uniquely determined in terms of the mirror curve which has also an interpretation in terms of the Seiberg-Witten curve of the four-dimensional theory arising from torus compactification. Adding the affine node of the ADE quiver to the base geometry, we connect to recent results on SYZ mirror symmetry for the $A$ case and provide a physical interpretation in terms of little string theory. Our results, however, go beyond this case as our construction naturally covers the $D$ and $E$ cases as well.

 

Title:
Dyonic Lieb-Shultz-Mattis Theorem and Symmetry Protected Topological Phases in Decorated Dimer Models
Authors:
Yang, Xu; Jiang, Shenghan; Vishwanath, Ashvin; Ran, Ying
Publication:
eprint arXiv:1705.05421
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons
Comment:
25 pages, 16 figures
Bibliographic Code:
2017arXiv170505421Y

Abstract

We consider 2+1D lattice models of interacting bosons or spins, with both magnetic flux and fractional spin in the unit cell. We propose and prove a modified Lieb-Shultz Mattis (LSM) theorem in this setting, which applies even when the spin in the enlarged magnetic unit cell is integral. There are two nontrivial outcomes for gapped ground states that preserve all symmetries. In the first case, one necessarily obtains a symmetry protected topological (SPT) phase with protected edge states. This allows us to readily construct models of SPT states by decorating dimer models of Mott insulators to yield SPT phases, which should be useful in their physical realization. In the second case, exotic bulk excitations, i.e. topological order, is necessarily present. While both scenarios require fractional spin in the lattice unit cell, the second requires that the symmetries protecting the fractional spin is related to that involved in the magnetic translations. Our discussion encompasses the general notion of fractional spin (projective symmetry representations) and magnetic flux (magnetic translations tied to a symmetry generator). The resulting SPTs display a dyonic character in that they associate charge with symmetry flux, allowing the flux in the unit cell to screen the projective representation on the sites. We provide an explicit formula that encapsulates this physics, which identifies a specific set of allowed SPT phases.

 

Title:
Towards Classification of 5d SCFTs: Single Gauge Node
Authors:
Jefferson, Patrick; Kim, Hee-Cheol; Vafa, Cumrun; Zafrir, Gabi
Publication:
eprint arXiv:1705.05836
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
52 pages + appendix, 11 tables, 12 figures
Bibliographic Code:
2017arXiv170505836J

Abstract

We propose a number of apparently equivalent criteria necessary for the consistency of a 5d SCFT in its Coulomb phase and use these criteria to classify 5d SCFTs arising from a gauge theory with simple gauge group. These criteria include the convergence of the 5-sphere partition function; the positivity of particle masses and monopole string tensions; and the positive definiteness of the metric in some region in the Coulomb branch. We find that for large rank classical groups simple classes of SCFTs emerge where the bounds on the matter content and the Chern-Simons level grow linearly with rank. For classical groups of rank less than or equal to 8, our classification leads to additional cases which do not fit in the large rank analysis. We also classify the allowed matter content for all exceptional groups.

 

Title:
Genus Two Modular Bootstrap
Authors:
Cho, Minjae; Collier, Scott; Yin, Xi
Publication:
eprint arXiv:1705.05865
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
23 pages, 6 figures. v2: updated references, typos corrected
Bibliographic Code:
2017arXiv170505865C

Abstract

We study the Virasoro conformal block decomposition of the genus two partition function of a two-dimensional CFT by expanding around a Z3-invariant Riemann surface that is a three-fold cover of the Riemann sphere branched at four points, and explore constraints from genus two modular invariance and unitarity. In particular, we find 'critical surfaces' that constrain the structure constants of a CFT beyond what is accessible via the crossing equation on the sphere.

 

Title:
Graphene Terahertz Absorption
Authors:
Yang, Yuan; Kolesov, Grigory; Kocia, Lucas; Heller, Eric J.
Publication:
eprint arXiv:1705.06267
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Bibliographic Code:
2017arXiv170506267Y

Abstract

The unique terahertz properties of graphene has been identified for novel optoelectronic applications. In a graphene sample with bias voltage added, there is an enhanced absorption in the far infrared region and a diminished absorption in the infrared region. The strength of enhancement(diminishment) increases with the gate voltage, and the enhancement compensates the diminishment. We find that it is the coherence length of electrons in graphene that allows pure electronic transitions between states differing by small momentums and makes intraband transition possible, is responsible for the far infrared enhancement. Phonon assisted processes are not necessary and would not in any case contribute to a sum rule. This naturally leads to results obeying the general sum-rule in optical absorptions. Our prediction of the strength of enhancement(diminishment) in terms of the bias agrees with experiments. This is the first direct calculation we are aware of, since the prior phonon assisted model for indirect transition should not obey a sum rule.

 

Title:
$\mathbb{Z}_2$ topological order near the N\'eel state of the square lattice antiferromagnet
Authors:
Chatterjee, Shubhayu; Sachdev, Subir; Scheurer, Mathias
Publication:
eprint arXiv:1705.06289
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory
Comment:
4+2 pages, 4 figures
Bibliographic Code:
2017arXiv170506289C

Abstract

We classify quantum states proximate to the semiclassical N\'eel state of the spin $S=1/2$ square lattice antiferromagnet with two-spin near-neighbor and four-spin ring exchange interactions. Motivated by a number of recent experiments on the cuprates and the iridates, we examine states with $\mathbb{Z}_2$ topological order, an order which is not present in the semiclassical limit. Some of the states break one or more of reflection, time-reversal, and lattice rotation symmetries, and can account for the observations. We discuss implications for the pseudogap phase.

 

Title:
Reducing the Top Quark Mass Uncertainty with Jet Grooming
Authors:
Andreassen, Anders; Schwartz, Matthew D.
Publication:
eprint arXiv:1705.07135
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology
Comment:
21 pages, 7 figures
Bibliographic Code:
2017arXiv170507135A

Abstract

The measurement of the top quark mass has large systematic uncertainties coming from the Monte Carlo simulations that are used to match theory and experiment. We explore how much that uncertainty can be reduced by using jet grooming procedures. We estimate the inherent ambiguity in what is meant by Monte Carlo mass to be around 530 MeV without any corrections. This uncertainty can be reduced by 60% to 200 MeV by calibrating to the W mass and a further 33% to 140 MeV by applying soft-drop jet grooming (or by 20% more to 170 MeV with trimming). At e+e- colliders, the associated uncertainty is around 110 MeV, reducing to 50 MeV after calibrating to the W mass. By analyzing the tuning parameters, we conclude that the importance of jet grooming after calibrating to the W mass is to reduce sensitivity to the underlying event.

 

Title:
The c=1 String Theory S-Matrix Revisited
Authors:
Balthazar, Bruno; Rodriguez, Victor A.; Yin, Xi
Publication:
eprint arXiv:1705.07151
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
31 pages, 7 figures; references added, typos corrected
Bibliographic Code:
2017arXiv170507151B

Abstract

We revisit the perturbative S-matrix of c=1 string theory from the worldsheet perspective. We clarify the origin of the leg pole factors, the non-analyticity of the string amplitudes, and the validity as well as limitations of earlier computations based on resonance momenta. We compute the tree level 4-point amplitude and the genus one 2-point reflection amplitude by numerically integrating Virasoro conformal blocks with DOZZ structure constants on the sphere and on the torus, with sufficiently generic complex Liouville momenta, and find agreement with known answers from the c=1 matrix model.

 

Title:
Astro-comb calibrator using a turn-key laser frequency comb
Authors:
Ravi, Aakash; Phillips, David F.; Beck, Matthias; Martin, Leopoldo L.; Cecconi, Massimo; Ghedina, Adriano; Molinari, Emilio; Bartels, Albrecht; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald L.
Publication:
eprint arXiv:1705.07192
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Astrophysics - Instrumentation and Methods for Astrophysics, Physics - Optics, Quantum Physics
Comment:
7 pages, 7 figures, submitted to Optics Express (astrophotonics feature issue)
Bibliographic Code:
2017arXiv170507192R

Abstract

Using a turn-key Ti:sapphire femtosecond laser frequency comb and an off-the-shelf supercontinuum device, we report the generation of a 16 GHz frequency comb spanning an 80 nm band about a center wavelength of 570 nm. The light from this turn-key astro-comb is used to calibrate the HARPS-N astrophysical spectrograph for precision radial velocity measurements. The comb-calibrated spectrograph achieves a stability of $\sim$ 1 cm/s within half an hour of averaging time. We also use the turn-key astro-comb to perform calibration of solar spectra obtained with a compact telescope, and to study intrapixel sensitivity variations on the CCD of the spectrograph.

 

Title:
Atomically thin mirrors made of monolayer semiconductors
Authors:
Scuri, Giovanni; Zhou, You; High, Alexander A.; Wild, Dominik S.; Shu, Chi; De Greve, Kristiaan; Jauregui, Luis A.; Taniguchi, Takashi; Watanabe, Kenji; Kim, Philip; Lukin, Mikhail D.; Park, Hongkun
Publication:
eprint arXiv:1705.07245
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science, Physics - Applied Physics, Physics - Optics
Comment:
4 figures
Bibliographic Code:
2017arXiv170507245S

Abstract

Transition metal dichalcogenide monolayers are promising candidates for exploring new electronic and optical phenomena and for realizing atomically thin optoelectronic devices. They host tightly bound electron-hole pairs (excitons) that can be efficiently excited by resonant light fields. Here, we demonstrate that a single monolayer of molybdenum diselenide (MoSe2) can dramatically modify light transmission near the excitonic resonance, acting as an electrically switchable mirror that reflects up to 85% of incident light at cryogenic temperatures. This high reflectance is a direct consequence of the excellent coherence properties of excitons in this atomically thin semiconductor, encapsulated by hexagonal boron nitride. Furthermore, we show that the MoSe2 monolayer exhibits power- and wavelength-dependent nonlinearities that stem from exciton-based lattice heating in the case of continuous-wave excitation and exciton-exciton interactions when fast, pulsed laser excitation is used. These observations open up new possibilities for studying quantum nonlinear optical phenomena and topological photonics, and for miniaturizing optical devices.

 

Title:
Thermal crumpling of perforated two-dimensional sheets
Authors:
Yllanes, D.; Bhabesh, S.; Nelson, D. R.; Bowick, M. J.
Publication:
eprint arXiv:1705.07379
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter, Condensed Matter - Materials Science, Condensed Matter - Statistical Mechanics
Comment:
9 pages, 11 figures
Bibliographic Code:
2017arXiv170507379Y

Abstract

Thermalized elastic membranes without distant self-avoidance are believed to undergo a crumpling transition when the microscopic bending stiffness is comparable to $kT$. Most potential physical realizations of such membranes have a bending stiffness well in excess of experimentally achievable temperatures and are therefore unlikely ever to access the crumpling regime. We propose a mechanism to tune the onset of the crumpling transition by altering the geometry and topology of the sheet itself. We have carried out extensive molecular dynamics simulations of perforated sheets with a dense periodic array of holes and observed that the critical temperature is controlled by the total fraction of removed area, independent of the precise arrangement and size of the individual holes. The critical exponents for the perforated membrane are compatible with those of the standard crumpling transition.

 

Title:
Thermal diffusivity and chaos in metals without quasiparticles
Authors:
Blake, Mike; Davison, Richard A.; Sachdev, Subir
Publication:
eprint arXiv:1705.07896
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Condensed Matter - Strongly Correlated Electrons
Comment:
27 pages
Bibliographic Code:
2017arXiv170507896B

Abstract

We study the thermal diffusivity $D_T$ in models of metals without quasiparticle excitations (`strange metals'). The many-body quantum chaos and transport properties of such metals can be efficiently described by a holographic representation in a gravitational theory in an emergent curved spacetime with an additional spatial dimension. We find that at generic infra-red fixed points $D_T$ is always related to parameters characterizing many-body quantum chaos: the butterfly velocity $v_B$, and Lyapunov time $\tau_L$ through $D_T \sim v_B^2 \tau_L$. The relationship holds independently of the charge density, periodic potential strength or magnetic field at the fixed point. The generality of this result follows from the observation that the thermal conductivity of strange metals depends only on the metric near the horizon of a black hole in the emergent spacetime, and is otherwise insensitive to the profile of any matter fields.

 

itle:
High Resolution Magnetic Resonance Spectroscopy Using Solid-State Spins
Authors:
Bucher, Dominik B.; Glenn, David R.; Lee, Junghyun; Lukin, Mikhail D.; Park, Hongkun; Walsworth, Ronald L.
Publication:
eprint arXiv:1705.08887
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Quantum Physics
Bibliographic Code:
2017arXiv170508887B

Abstract

We demonstrate a synchronized readout (SR) technique for spectrally selective detection of oscillating magnetic fields with sub-millihertz resolution, using coherent manipulation of solid state spins. The SR technique is implemented in a sensitive magnetometer (~50 picotesla/Hz^(1/2)) based on nitrogen vacancy (NV) centers in diamond, and used to detect nuclear magnetic resonance (NMR) signals from liquid-state samples. We obtain NMR spectral resolution ~3 Hz, which is nearly two orders of magnitude narrower than previously demonstrated with NV based techniques, using a sample volume of ~1 picoliter. This is the first application of NV-detected NMR to sense Boltzmann-polarized nuclear spin magnetization, and the first to observe chemical shifts and J-couplings.

 

Title:
Wandering in the Lyman-alpha Forest: A Study of Dark Matter-Dark Radiation Interactions
Authors:
Krall, Rebecca; Cyr-Racine, Francis-Yan; Dvorkin, Cora
Publication:
eprint arXiv:1705.08894
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Astrophysics - Cosmology and Nongalactic Astrophysics, High Energy Physics - Phenomenology
Comment:
11 pages + references, 3 figures, 3 tables, v2: added references
Bibliographic Code:
2017arXiv170508894K

Abstract

The amplitude of large-scale matter fluctuations inferred from the observed Sunyaev-Zeldovich (SZ) cluster mass function and from weak gravitational lensing studies, when taken at face value, is in tension with measurements of the cosmic microwave background (CMB) and baryon acoustic oscillation (BAO). In this work, we revisit whether this possible discrepancy can be attributed to new interactions in the dark matter sector. Focusing on a cosmological model where dark matter interacts with a dark radiation species until the epoch of matter-radiation equality, we find that measurements of the Lyman-alpha flux power spectrum from the Sloan Digital Sky Survey provides no support to the hypothesis that new dark matter interactions can resolve the possible tension between CMB and large-scale structure (LSS). Indeed, while the addition of dark matter-dark radiation interactions leads to an improvement of $2\Delta\ln\mathcal{L}=12$ with respect to the standard $\Lambda$ cold dark matter ($\Lambda$CDM) model when only CMB, BAO, and LSS data are considered, the inclusion of Lyman-alpha data reduces the improvement of the fit to $2\Delta\ln\mathcal{L}=6$ relative to $\Lambda$CDM. We thus conclude that the statistical evidence for new dark matter interactions (largely driven by the Planck SZ dataset) is marginal at best, and likely caused by systematics in the data. We also perform a Fisher forecast analysis for the reach of a future dataset composed of a CMB-S4 experiment combined with the Large Synoptic Survey Telescope galaxy survey. We find that the constraint on the effective number of fluid-like dark radiation species, $\Delta N_{\rm fluid}$, will be improved by an order of magnitude compared to current bounds.

 

Title:
Fourier optical processing enables new capabilities in diamond magnetic imaging
Authors:
Backlund, Mikael P.; Kehayias, Pauli; Walsworth, Ronald L.
Publication:
eprint arXiv:1705.09241
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Physics - Optics, Physics - Applied Physics, Physics - Chemical Physics
Comment:
40 pages, 11 figures
Bibliographic Code:
2017arXiv170509241B

Abstract

Diamond-based magnetic field sensors have attracted great interest in recent years. In particular, wide-field magnetic imaging using nitrogen-vacancy (NV) centers in diamond has been previously demonstrated in condensed matter, biological, and paleomagnetic applications. Vector magnetic imaging with NV ensembles typically requires an applied field (>10 G) to separate the contributions from four crystallographic orientations, hindering studies of magnetic samples that require measurement in low or independently specified bias fields. Here we decompose the NV ensemble magnetic resonance spectrum without such a bias field by modulating the collected light at the microscope's Fourier plane. In addition to enabling vector magnetic imaging at arbitrarily low fields, our method can be used to extend the dynamic range at a given bias field. As demonstrated here, optically-detected diamond magnetometry stands to benefit from Fourier optical approaches, which have already found widespread utility in other branches of photonics.

 

Title:
Symmetric Fermion Mass Generation as Deconfined Quantum Criticality
Authors:
You, Yi-Zhuang; He, Yin-Chen; Xu, Cenke; Vishwanath, Ashvin
Publication:
eprint arXiv:1705.09313
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons
Comment:
12 papers, 4 figures, 3 appendices
Bibliographic Code:
2017arXiv170509313Y

Abstract

Massless 2+1D Dirac fermions arise in a variety of systems from graphene to the surfaces of topological insulators, where generating a mass is typically associated with breaking a symmetry. However, with strong interactions, a symmetric gapped phase can arise for multiples of eight Dirac fermions. A continuous quantum phase transition from the massless Dirac phase to this massive phase, which we term Symmetric Mass Generation (SMG), is necessarily beyond the Landau paradigm and is hard to describe even at the conceptual level. Nevertheless, such transition has been consistently observed in several numerical studies recently. Here, we propose a theory for the SMG transition which is reminiscent of deconfined criticality and involves emergent non-Abelian gauge fields coupled both to Dirac fermions and to critical Higgs bosons. We motivate the theory using an explicit parton construction and discuss predictions for numerics. Additionally, we show that the fermion Green's function is expected to undergo a zero to pole transition across the critical point.

 

Title:
Directional Detection of Dark Matter using Spectroscopy of Crystal Defects
Authors:
Rajendran, Surjeet; Zobrist, Nicholas; Sushkov, Alexander O.; Walsworth, Ronald; Lukin, Mikhail
Publication:
eprint arXiv:1705.09760
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology, Quantum Physics
Comment:
9 pages, 3 figures
Bibliographic Code:
2017arXiv170509760R

Abstract

We propose a method to identify the direction of an incident Weakly Interacting Massive Particle (WIMP) via induced nuclear recoil. Our method is based on spectroscopic interrogation of quantum defects in macroscopic solid-state crystals . When a WIMP scatters in a crystal, the induced nuclear recoil creates a tell-tale damage cluster, localized to within about 50 nm, with an orientation to the damage trail that correlates well with the direction of the recoil and hence the incoming WIMP. This damage cluster induces strain in the crystal, shifting the energy levels of nearby quantum defects. These level shifts can be measured optically (or through paramagnetic resonance) making it possible to detect the strain environment around the defect in a solid sample. As a specific example, we consider nitrogen vacancy centers in diamond, for which high defect densities and nanoscale localization of individual defects have been demonstrated. To localize the millimeter-scale region of a nuclear recoil within the crystal due to a potential dark matter event, we can use conventional WIMP detection techniques such as the collection of ionization/scintillation. Once an event is identified, the quantum defects in the vicinity of the event can be interrogated to map the strain environment, thus determining the direction of the recoil. In principle, this approach should be able to identify the recoil direction with an efficiency greater than 70% at a false positive rate less than 5% for 10 keV recoil energies. If successful, this method would allow for directional detection of WIMP-induced nuclear recoils at solid state densities, enabling probes of WIMP parameter space below the solar neutrino floor. This technique could also potentially be applied to identify the direction of particles such as neutrons whose low scattering cross-section requires detectors with a large target mass.

 

Title:
Radio Frequency Magneto-Optical Trapping of CaF with High Density
Authors:
Anderegg, Loic; Augenbraun, Benjamin; Chae, Eunmi; Hemmerling, Boerge; Hutzler, Nicholas R.; Ravi, Aakash; Collopy, Alejandra; Ye, Jun; Ketterle, Wolfgang; Doyle, John
Publication:
eprint arXiv:1705.10288
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Physics - Atomic Physics
Comment:
5 Pages, 4 Figures
Bibliographic Code:
2017arXiv170510288A

Abstract

We demonstrate significantly improved magneto-optical trapping of molecules using a very slow cryogenic beam source and RF modulated and DC magnetic fields. The RF MOT confines $1.1(3) \times 10^5$ CaF molecules at a density of $4(1) \times 10^6$ cm$^{-3}$, which is an order of magnitude greater than previous molecular MOTs. Near Doppler-limited temperatures of $340(20)$ $\mu$K are attained. The achieved density enables future work to directly load optical tweezers and create optical arrays for quantum simulation.

 

Title:
PCAT: Probabilistic Cataloger
Authors:
Daylan, Tansu; Portillo, K. N. Stephen; Finkbeiner, Douglas P.
Publication:
Astrophysics Source Code Library, record ascl:1705.004
Publication Date:
05/2017
Origin:
ASCL
Keywords:
Software
Bibliographic Code:
2017ascl.soft05004D

Abstract

PCAT (Probabilistic Cataloger) samples from the posterior distribution of a metamodel, i.e., union of models with different dimensionality, to compare the models. This is achieved via transdimensional proposals such as births, deaths, splits and merges in addition to the within-model proposals. This method avoids noisy estimates of the Bayesian evidence that may not reliably distinguish models when sampling from the posterior probability distribution of each model.

The code has been applied in two different subfields of astronomy: high energy photometry, where transdimensional elements are gamma-ray point sources; and strong lensing, where light-deflecting dark matter subhalos take the role of transdimensional elements.

 

Title:
Measurements of top-quark pair differential cross-sections in the eμ channel in pp collisions at √{s} = 13 TeV using the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;...; and 2849 coauthors
Publication:
The European Physical Journal C, Volume 77, Issue 5, article id. #292, 30 pp. (EPJC Homepage)
Publication Date:
05/2017
Origin:
SPRINGER
Abstract Copyright:
(c) 2017: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-017-4821-x
Bibliographic Code:
2017EPJC...77..292A

Abstract

This article presents measurements of t\bar{t} differential cross-sections in a fiducial phase-space region, using an integrated luminosity of 3.2 fb^{-1} of proton-proton data at a centre-of-mass energy of √{s} = 13 TeV recorded by the ATLAS experiment at the LHC in 2015. Differential cross-sections are measured as a function of the transverse momentum and absolute rapidity of the top quark, and of the transverse momentum, absolute rapidity and invariant mass of the t\bar{t} system. The t\bar{t} events are selected by requiring one electron and one muon of opposite electric charge, and at least two jets, one of which must be tagged as containing a b-hadron. The measured differential cross-sections are compared to predictions of next-to-leading order generators matched to parton showers and the measurements are found to be consistent with all models within the experimental uncertainties with the exception of the Powheg-Box + Herwig++ predictions, which differ significantly from the data in both the transverse momentum of the top quark and the mass of the t\bar{t} system.

 

Title:
Performance of the ATLAS trigger system in 2015
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;...; and 2852 coauthors
Publication:
The European Physical Journal C, Volume 77, Issue 5, article id. #317, 53 pp. (EPJC Homepage)
Publication Date:
05/2017
Origin:
SPRINGER
Abstract Copyright:
(c) 2017: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-017-4852-3
Bibliographic Code:
2017EPJC...77..317A

Abstract

During 2015 the ATLAS experiment recorded 3.8 {fb}^{-1} of proton-proton collision data at a centre-of-mass energy of 13 {TeV}. The ATLAS trigger system is a crucial component of the experiment, responsible for selecting events of interest at a recording rate of approximately 1 kHz from up to 40 MHz of collisions. This paper presents a short overview of the changes to the trigger and data acquisition systems during the first long shutdown of the LHC and shows the performance of the trigger system and its components based on the 2015 proton-proton collision data.

 

Title:
Reconstruction of primary vertices at the ATLAS experiment in Run 1 proton-proton collisions at the LHC
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;...; and 2848 coauthors
Publication:
The European Physical Journal C, Volume 77, Issue 5, article id. #332, 35 pp. (EPJC Homepage)
Publication Date:
05/2017
Origin:
SPRINGER
Abstract Copyright:
(c) 2017: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-017-4887-5
Bibliographic Code:
2017EPJC...77..332A

Abstract

This paper presents the method and performance of primary vertex reconstruction in proton-proton collision data recorded by the ATLAS experiment during Run 1 of the LHC. The studies presented focus on data taken during 2012 at a centre-of-mass energy of √{s} = 8 TeV. The performance has been measured as a function of the number of interactions per bunch crossing over a wide range, from one to seventy. The measurement of the position and size of the luminous region and its use as a constraint to improve the primary vertex resolution are discussed. A longitudinal vertex position resolution of about 30μm is achieved for events with high multiplicity of reconstructed tracks. The transverse position resolution is better than 20μm and is dominated by the precision on the size of the luminous region. An analytical model is proposed to describe the primary vertex reconstruction efficiency as a function of the number of interactions per bunch crossing and of the longitudinal size of the luminous region. Agreement between the data and the predictions of this model is better than 3% up to seventy interactions per bunch crossing.

 

Title:
Make dark matter charged again
Authors:
Agrawal, Prateek; Cyr-Racine, Francis-Yan; Randall, Lisa; Scholtz, Jakub
Publication:
Journal of Cosmology and Astroparticle Physics, Issue 05, article id. 022 (2017). (JCAP Homepage)
Publication Date:
05/2017
Origin:
IOP
DOI:
10.1088/1475-7516/2017/05/022
Bibliographic Code:
2017JCAP...05..022A

Abstract

We revisit constraints on dark matter that is charged under a U(1) gauge group in the dark sector, decoupled from Standard Model forces. We find that the strongest constraints in the literature are subject to a number of mitigating factors. For instance, the naive dark matter thermalization timescale in halos is corrected by saturation effects that slow down isotropization for modest ellipticities. The weakened bounds uncover interesting parameter space, making models with weak-scale charged dark matter viable, even with electromagnetic strength interaction. This also leads to the intriguing possibility that dark matter self-interactions within small dwarf galaxies are extremely large, a relatively unexplored regime in current simulations. Such strong interactions suppress heat transfer over scales larger than the dark matter mean free path, inducing a dynamical cutoff length scale above which the system appears to have only feeble interactions. These effects must be taken into account to assess the viability of darkly-charged dark matter. Future analyses and measurements should probe a promising region of parameter space for this model.

 

Title:
Superrotation charge and supertranslation hair on black holes
Authors:
Hawking, Stephen W.; Perry, Malcolm J.; Strominger, Andrew
Publication:
Journal of High Energy Physics, Volume 2017, Issue 5, article id. #161, 33 pp.
Publication Date:
05/2017
Origin:
SPRINGER
Keywords:
Black Holes, Gauge Symmetry, Nonperturbative Effects
Abstract Copyright:
(c) 2017: The Author(s)
DOI:
10.1007/JHEP05(2017)161
Bibliographic Code:
2017JHEP...05..161H

Abstract

It is shown that black hole spacetimes in classical Einstein gravity are characterized by, in addition to their ADM mass M, momentum \overrightarrow{P} , angular momentum \overrightarrow{J} and boost charge \overrightarrow{K} , an infinite head of supertranslation hair. The distinct black holes are distinguished by classical superrotation charges measured at infinity. Solutions with super-translation hair are diffeomorphic to the Schwarzschild spacetime, but the diffeomorphisms are part of the BMS subgroup and act nontrivially on the physical phase space. It is shown that a black hole can be supertranslated by throwing in an asymmetric shock wave. A leading-order Bondi-gauge expression is derived for the linearized horizon supertranslation charge and shown to generate, via the Dirac bracket, supertranslations on the linearized phase space of gravitational excitations of the horizon. The considerations of this paper are largely classical augmented by comments on their implications for the quantum theory.

 

Title:
Performance of the ATLAS Transition Radiation Tracker in Run 1 of the LHC: tracker properties
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;...; and 2832 coauthors
Publication:
Journal of Instrumentation, Volume 12, Issue 05, pp. P05002 (2017).
Publication Date:
05/2017
Origin:
IOP
DOI:
10.1088/1748-0221/12/05/P05002
Bibliographic Code:
2017JInst..12P5002A

Abstract

The tracking performance parameters of the ATLAS Transition Radiation Tracker (TRT) as part of the ATLAS inner detector are described in this paper for different data-taking conditions in proton-proton, proton-lead and lead-lead collisions at the Large Hadron Collider (LHC). The performance is studied using data collected during the first period of LHC operation (Run 1) and is compared with Monte Carlo simulations. The performance of the TRT, operating with two different gas mixtures (xenon-based and argon-based) and its dependence on the TRT occupancy is presented. These studies show that the tracking performance of the TRT is similar for the two gas mixtures and that a significant contribution to the particle momentum resolution is made by the TRT up to high particle densities.

 

Title:
Population Genetics with Fluctuating Population Sizes
Authors:
Chotibut, Thiparat; Nelson, David R.
Publication:
Journal of Statistical Physics, Volume 167, Issue 3-4, pp. 777-791
Publication Date:
05/2017
Origin:
SPRINGER
Keywords:
Population genetics, Fluctuating population sizes, Dynamical system, Stochastic process
Abstract Copyright:
(c) 2017: Springer Science+Business Media New York
DOI:
10.1007/s10955-017-1741-y
Bibliographic Code:
2017JSP...167..777C

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 fluctuation-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:
Cores in Dwarf Galaxies from Fermi Repulsion
Authors:
Randall, Lisa; Scholtz, Jakub; Unwin, James
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 467, Issue 2, p.1515-1525 (MNRAS Homepage)
Publication Date:
05/2017
Origin:
OUP
Astronomy Keywords:
Cosmology: theory, dark matter, elementary particles, galaxies: dwarf, cosmology: theory
Abstract Copyright:
2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
DOI:
10.1093/mnras/stx161
Bibliographic Code:
2017MNRAS.467.1515R

Abstract

We show that Fermi repulsion can lead to cored density profiles in dwarf galaxies for sub-keV fermionic dark matter. We treat the dark matter as a quasi-degenerate self-gravitating Fermi gas and calculate its density profile assuming hydrostatic equilibrium. We find that suitable dwarf galaxy cores of size ≳130 pc can be achieved for fermion dark matter with mass in the range of 70-400 eV. While in conventional dark matter scenarios such sub-keV thermal dark matter would be excluded by free streaming bounds, the constraints are ameliorated in models with dark matter at a lower temperature than conventional thermal scenarios, such as the Flooded Dark Matter model that we have previously considered. Modifying the arguments of Tremaine and Gunn, we derive a conservative lower bound on the mass of fermionic dark matter of 70 eV and a stronger lower bound from Lymanα clouds of about 470 eV, leading to slightly smaller cores than have been observed. We comment on this result and how the tension is relaxed in dark matter scenarios with non-thermal momentum distributions.

 

Title:
Scalable focused ion beam creation of nearly lifetime-limited single quantum emitters in diamond nanostructures
Authors:
Schröder, Tim; Trusheim, Matthew E.; Walsh, Michael; Li, Luozhou; Zheng, Jiabao; Schukraft, Marco; Sipahigil, Alp; Evans, Ruffin E.; Sukachev, Denis D.; Nguyen, Christian T.; Pacheco, Jose L.; Camacho, Ryan M.; Bielejec, Edward S.; Lukin, Mikhail D.; Englund, Dirk
Publication:
Nature Communications, Volume 8, id. 15376 (2017).
Publication Date:
05/2017
Origin:
NATURE
Abstract Copyright:
(c) 2017: The Author(s)
DOI:
10.1038/ncomms15376
Bibliographic Code:
2017NatCo...815376S

Abstract

The controlled creation of defect centre--nanocavity systems is one of the outstanding challenges for efficiently interfacing spin quantum memories with photons for photon-based entanglement operations in a quantum network. Here we demonstrate direct, maskless creation of atom-like single silicon vacancy (SiV) centres in diamond nanostructures via focused ion beam implantation with ~32 nm lateral precision and <50 nm positioning accuracy relative to a nanocavity. We determine the Si+ ion to SiV centre conversion yield to be ~2.5% and observe a 10-fold conversion yield increase by additional electron irradiation. Low-temperature spectroscopy reveals inhomogeneously broadened ensemble emission linewidths of ~51 GHz and close to lifetime-limited single-emitter transition linewidths down to 126+/-13 MHz corresponding to ~1.4 times the natural linewidth. This method for the targeted generation of nearly transform-limited quantum emitters should facilitate the development of scalable solid-state quantum information processors.

 

Title:
CMOS nanoelectrode array for all-electrical intracellular electrophysiological imaging
Authors:
Abbott, Jeffrey; Ye, Tianyang; Qin, Ling; Jorgolli, Marsela; Gertner, Rona S.; Ham, Donhee; Park, Hongkun
Publication:
Nature Nanotechnology, Volume 12, Issue 5, pp. 460-466 (2017).
Publication Date:
05/2017
Origin:
NATURE
Abstract Copyright:
(c) 2017: Nature Publishing Group
DOI:
10.1038/nnano.2017.3
Bibliographic Code:
2017NatNa..12..460A

Abstract

Developing a new tool capable of high-precision electrophysiological recording of a large network of electrogenic cells has long been an outstanding challenge in neurobiology and cardiology. Here, we combine nanoscale intracellular electrodes with complementary metal-oxide-semiconductor (CMOS) integrated circuits to realize a high-fidelity all-electrical electrophysiological imager for parallel intracellular recording at the network level. Our CMOS nanoelectrode array has 1,024 recording/stimulation 'pixels' equipped with vertical nanoelectrodes, and can simultaneously record intracellular membrane potentials from hundreds of connected in vitro neonatal rat ventricular cardiomyocytes. We demonstrate that this network-level intracellular recording capability can be used to examine the effect of pharmaceuticals on the delicate dynamics of a cardiomyocyte network, thus opening up new opportunities in tissue-based pharmacological screening for cardiac and neuronal diseases as well as fundamental studies of electrogenic cells and their networks.

 

Title:
A cold-atom Fermi–Hubbard antiferromagnet
Authors:
Mazurenko, Anton; Chiu, Christie S.; Ji, Geoffrey; Parsons, Maxwell F.; Kanász-Nagy, Márton; Schmidt, Richard; Grusdt, Fabian; Demler, Eugene; Greif, Daniel; Greiner, Markus
Publication:
Nature, Volume 545, Issue 7655, pp. 462-466 (2017). (Nature Homepage)
Publication Date:
05/2017
Origin:
NATURE
Abstract Copyright:
(c) 2017: Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
DOI:
10.1038/nature22362
Bibliographic Code:
2017Natur.545..462M

Abstract

Exotic phenomena in systems with strongly correlated electrons emerge from the interplay between spin and motional degrees of freedom. For example, doping an antiferromagnet is expected to give rise to pseudogap states and high-temperature superconductors. Quantum simulation using ultracold fermions in optical lattices could help to answer open questions about the doped Hubbard Hamiltonian, and has recently been advanced by quantum gas microscopy. Here we report the realization of an antiferromagnet in a repulsively interacting Fermi gas on a two-dimensional square lattice of about 80 sites at a temperature of 0.25 times the tunnelling energy. The antiferromagnetic long-range order manifests through the divergence of the correlation length, which reaches the size of the system, the development of a peak in the spin structure factor and a staggered magnetization that is close to the ground-state value. We hole-dope the system away from half-filling, towards a regime in which complex many-body states are expected, and find that strong magnetic correlations persist at the antiferromagnetic ordering vector up to dopings of about 15 per cent. In this regime, numerical simulations are challenging and so experiments provide a valuable benchmark. Our results demonstrate that microscopy of cold atoms in optical lattices can help us to understand the low-temperature Fermi–Hubbard model.

 

Title:
High-ET isolated-photon plus jets production in pp collisions at √{ s} = 8 TeV with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;...; and 2846 coauthors
Publication:
Nuclear Physics, Section B, Volume 918, p. 257-316.
Publication Date:
05/2017
Origin:
ELSEVIER
Abstract Copyright:
(c) 2017 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.nuclphysb.2017.03.006
Bibliographic Code:
2017NuPhB.918..257A

Abstract

The dynamics of isolated-photon plus one-, two- and three-jet production in pp collisions at a centre-of-mass energy of 8 TeV are studied with the ATLAS detector at the LHC using a data set with an integrated luminosity of 20.2 fb-1. Measurements of isolated-photon plus jets cross sections are presented as functions of the photon and jet transverse momenta. The cross sections as functions of the azimuthal angle between the photon and the jets, the azimuthal angle between the jets, the photon-jet invariant mass and the scattering angle in the photon-jet centre-of-mass system are presented. The pattern of QCD radiation around the photon and the leading jet is investigated by measuring jet production in an annular region centred on each object; enhancements are observed around the leading jet with respect to the photon in the directions towards the beams. The experimental measurements are compared to several different theoretical calculations, and overall a good description of the data is found.

 

Title:
Superresolution optical magnetic imaging and spectroscopy using individual electronic spins in diamond
Authors:
Jaskula, Jean-Christophe; Bauch, Erik; Arroyo-Camejo, Silvia; Lukin, Mikhail D.; Hell, Stefan W.; Trifonov, Alexei S.; Walsworth, Ronald L.
Publication:
Optics Express, vol. 25, issue 10, p. 11048
Publication Date:
05/2017
Origin:
CROSSREF
DOI:
10.1364/OE.25.011048
Bibliographic Code:
2017OExpr..2511048J

Abstract

Nitrogen vacancy (NV) color centers in diamond are a leading modality for both superresolution optical imaging and nanoscale magnetic field sensing. In this work, we solve the remaining key challenge of performing optical magnetic imaging and spectroscopy selectively on multiple NV centers that are located within a diffraction-limited field-of-view. We use spin-RESOLFT microscopy to enable precision nanoscale mapping of magnetic field patterns with resolution down to ~20 nm, while employing a low power optical depletion beam. Moreover, we use a shallow NV to demonstrate the detection of proton nuclear magnetic resonance (NMR) signals exterior to the diamond, with 50 nm lateral imaging resolution and without degrading the proton NMR linewidth.

 

Title:
Monolithic CMOS-compatible zero-index metamaterials
Authors:
Vulis, Daryl I.; Li, Yang; Reshef, Orad; Camayd-Muñoz, Philip; Yin, Mei; Kita, Shota; Lončar, Marko; Mazur, Eric
Publication:
Optics Express, vol. 25, issue 11, p. 12381
Publication Date:
05/2017
Origin:
CROSSREF
DOI:
10.1364/OE.25.012381
Bibliographic Code:
2017OExpr..2512381V

Abstract

Zero-index materials exhibit exotic optical properties that can be utilized for integrated-optics applications. However, practical implementation requires compatibility with complementary metallic-oxide-semiconductor (CMOS) technologies. We demonstrate a CMOS-compatible zero-index metamaterial consisting of a square array of air holes in a 220-nm-thick silicon-on-insulator (SOI) wafer. This design is achieved through a Dirac-cone dispersion. The metamaterial is entirely composed of silicon and offers compatibility through low-aspect-ratio structures that can be simply fabricated in a standard device layer. This platform enables mass adoption and exploration of zero-index-based photonic devices at low cost and high fidelity.

 

Title:
Full counting statistics of time-of-flight images
Authors:
Lovas, Izabella; Dóra, Balázs; Demler, Eugene; Zaránd, Gergely
Affiliation:
AA(Budapest University of Technology and Economics, 1111 Budapest, Hungary), AB(Budapest University of Technology and Economics, 1111 Budapest, Hungary), AC(Harvard University, Cambridge, Massachusetts 02138, USA), AD(Budapest University of Technology and Economics, 1111 Budapest, Hungary)
Publication:
Physical Review A, Volume 95, Issue 5, id.053621 (PhRvA Homepage)
Publication Date:
05/2017
Origin:
APS
Abstract Copyright:
2017: American Physical Society
DOI:
10.1103/PhysRevA.95.053621
Bibliographic Code:
2017PhRvA..95e3621L

Abstract

Inspired by recent advances in cold atomic systems and nonequilibrium physics, we introduce a characterization scheme, the time-of-flight full counting statistics. We benchmark this method on an interacting one-dimensional Bose gas and show that there the time-of-flight image displays several universal regimes. Finite momentum fluctuations are observed at larger distances, where a crossover from exponential to Gamma distribution occurs upon decreasing momentum resolution. Zero-momentum particles, on the other hand, obey a Gumbel distribution in the weakly interacting limit, characterizing the quantum fluctuations of the former quasicondensate. Time-of-flight full counting statistics is demonstrated to capture (pre-)thermalization processes after a quantum quench and can be useful for characterizing exotic quantum states such as many-body localized systems or models of holography.


Title:
Floquet topological phases protected by time glide symmetry
Authors:
Morimoto, Takahiro; Po, Hoi Chun; Vishwanath, Ashvin
Affiliation:
AA(University of California, Berkeley, California 94720, USA), AB(University of California, Berkeley, California 94720, USA; Harvard University, Cambridge, Massachusetts 02138, USA), AC(University of California, Berkeley, California 94720, USA; Harvard University, Cambridge, Massachusetts 02138, USA)
Publication:
Physical Review B, Volume 95, Issue 19, id.195155 (PhRvB Homepage)
Publication Date:
05/2017
Origin:
APS
Abstract Copyright:
2017: American Physical Society
DOI:
10.1103/PhysRevB.95.195155
Bibliographic Code:
2017PhRvB..95s5155M

Abstract

We study Floquet topological phases in periodically driven systems that are protected by "time glide symmetry", a combination of reflection and half time period translation. Time glide symmetry is an analog of glide symmetry with partial time translation replacing the partial space translation and, hence, is an intrinsically dynamical symmetry which may be engineered in periodically driven systems by exploiting the controllability of driving. We present lattice models of time glide symmetric Floquet topological insulators in two and three dimensions. The topological numbers characterizing those Floquet topological phases are derived from the half-period time-evolution operator along with time glide operator. Moreover, we classify Floquet topological phases protected by time glide symmetry in general dimensions using a Clifford algebra approach. The obtained classification table is similar to that for topological crystalline insulators protected by static reflection symmetry, but shows nontrivial entries in different combination of symmetries, which clarifies that time glide symmetric Floquet topological phases are a distinct set of topological phases from topological crystalline insulators. We also classify Floquet topological phases with "time screw symmetry", defined as a twofold spatial rotation accompanied by half-period time translation.


Title:
Quantum heat waves in a one-dimensional condensate
Authors:
Agarwal, Kartiek; Dalla Torre, Emanuele G.; Schmiedmayer, Jörg; Demler, Eugene
Publication:
Physical Review B, Volume 95, Issue 19, id.195157 (PhRvB Homepage)
Publication Date:
05/2017
Origin:
APS
Abstract Copyright:
2017: American Physical Society
DOI:
10.1103/PhysRevB.95.195157
Bibliographic Code:
2017PhRvB..95s5157A

Abstract

We study the dynamics of phase relaxation between a pair of one-dimensional condensates created by a bi-directional, supersonic `unzipping' of a finite single condensate. We find that the system fractures into different extensive chunks of space-time, within which correlations appear thermal but correspond to different effective temperatures. Coherences between different eigen-modes are crucial for understanding the development of such thermal correlations; at no point in time can our system be described by a generalized Gibbs' ensemble despite nearly always appearing locally thermal. We rationalize a picture of propagating fronts of hot and cold sound waves, populated at effective, relativistically red- and blue-shifted temperatures to intuitively explain our findings. The disparity between these hot and cold temperatures vanishes for the case of instantaneous splitting but diverges in the limit where the splitting velocity approaches the speed of sound; in this limit, a sonic boom occurs wherein the system is excited only along an infinitely narrow, and infinitely hot beam. We expect our findings to apply generally to the study of superluminal perturbations in systems with emergent Lorentz symmetry.


Title:
Spectrum of conformal gauge theories on a torus
Authors:
Thomson, Alex; Sachdev, Subir
Publication:
Physical Review B, Volume 95, Issue 20, id.205128 (PhRvB Homepage)
Publication Date:
05/2017
Origin:
APS
Abstract Copyright:
2017: American Physical Society
DOI:
10.1103/PhysRevB.95.205128
Bibliographic Code:
2017PhRvB..95t5128T

Abstract

Many model quantum spin systems have been proposed to realize critical points or phases described by 2+1 dimensional conformal gauge theories. On a torus of size L and modular parameter τ , the energy levels of such gauge theories equal (1 /L ) times universal functions of τ. We compute the universal spectrum of QED3, a U(1) gauge theory with Nf two-component massless Dirac fermions, in the large-Nf limit. We also allow for a Chern-Simons term at level k , and show how the topological k -fold ground state degeneracy in the absence of fermions transforms into the universal spectrum in the presence of fermions; these computations are performed at fixed Nf/k in the large-Nf limit.

Title:
Insulators and metals with topological order and discrete symmetry breaking
Authors:
Chatterjee, Shubhayu; Sachdev, Subir
Publication:
Physical Review B, Volume 95, Issue 20, id.205133 (PhRvB Homepage)
Publication Date:
05/2017
Origin:
APS
Abstract Copyright:
2017: American Physical Society
DOI:
10.1103/PhysRevB.95.205133
Bibliographic Code:
2017PhRvB..95t5133C

Abstract

Numerous experiments have reported discrete symmetry breaking in the high-temperature pseudogap phase of the hole-doped cuprates, including breaking of one or more of lattice rotation, inversion, and time-reversal symmetries. In the absence of translational symmetry breaking or topological order, these conventional order parameters cannot explain the gap in the charged fermion excitation spectrum in the antinodal region. Zhao et al. [L. Zhao, D. H. Torchinsky, H. Chu, V. Ivanov, R. Lifshitz, R. Flint, T. Qi, G. Cao, and D. Hsieh, Nat. Phys. 12, 32 (2016), 10.1038/nphys3517] and Jeong et al. [J. Jeong, Y. Sidis, A. Louat, V. Brouet, and P. Bourges, Nat. Commun. 8, 15119 (2017), 10.1038/ncomms15119] have also reported inversion and time-reversal symmetry breaking in insulating Sr2IrO4 similar to that in the metallic cuprates, but coexisting with Néel order. We extend an earlier theory of topological order in insulators and metals, in which the topological order combines naturally with the breaking of these conventional discrete symmetries. We find translationally invariant states with topological order coexisting with both Ising-nematic order and spontaneous charge currents. The link between the discrete broken symmetries and the topological-order-induced pseudogap explains why the broken symmetries do not survive in the confining phases without a pseudogap at large doping. Our theory also connects to the O(3) nonlinear sigma model and CP1 descriptions of quantum fluctuations of the Néel order. In this framework, the optimal doping criticality of the cuprates is primarily associated with the loss of topological order.

 

Title:
Duality and bosonization of (2 +1 ) -dimensional Majorana fermions
Authors:
Metlitski, Max A.; Vishwanath, Ashvin; Xu, Cenke
Publication:
Physical Review B, Volume 95, Issue 20, id.205137 (PhRvB Homepage)
Publication Date:
05/2017
Origin:
APS
Abstract Copyright:
2017: American Physical Society
DOI:
10.1103/PhysRevB.95.205137
Bibliographic Code:
2017PhRvB..95t5137M

Abstract

We construct a dual-bosonized description of a massless Majorana fermion in (2+1)d . In contrast to Dirac fermions, for which a bosonized description can be constructed using a flux attachment procedure, neutral Majorana fermions call for a different approach.We argue that the dual theory is an SO (N)1 Chern-Simons gauge theory with a critical SO (N ) vector bosonic matter field (N ≥3 ). The monopole of the SO (N ) gauge field is identified with the Majorana fermion. We provide evidence for the duality by establishing the correspondence of adjacent gapped phases and by a parton construction. We also propose a generalization of the duality to Nf flavors of Majorana fermions, and discuss possible resolutions of a caveat associated with an emergent global Z2 symmetry. Finally, we conjecture a dual description of an N =1 supersymmetric fixed point in (2+1)d , which is realized by tuning a single flavor of Majorana fermions to an interacting (Gross-Neveu) critical point.

 


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