Faculty Publications: March, 2017

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Title:
Collaborative exams: Cheating? Or learning?
Authors:
Jang, Hyewon; Lasry, Nathaniel; Miller, Kelly; Mazur, Eric
Publication:
American Journal of Physics, Volume 85, Issue 3, p.223-227
Publication Date:
03/2017
Origin:
AIP
Abstract Copyright:
2017: American Association of Physics Teachers
DOI:
10.1119/1.4974744
Bibliographic Code:
2017AmJPh..85..223J

Abstract

Virtually all human activity involves collaboration, and yet, collaboration during an examination is typically considered cheating. Collaborative assessments have not been widely adopted because of the perceived lack of individual accountability and the notion that collaboration during assessments simply causes propagation of correct answers. Hence, collaboration could help weaker students without providing much benefit to stronger students. In this paper, we examine student performance in open-ended, two-stage collaborative assessments comprised of an individually accountable round followed by an automatically scored, collaborative round. We show that collaboration entails more than just propagation of correct answers. We find greater rates of correct answers after collaboration for all students, including the strongest members of a team. We also find that half of teams that begin without a correct answer to propagate still obtain the correct answer in the collaborative round. Our findings, combined with the convenience of automatic feedback and grading of open-ended questions, provide a strong argument for adopting collaborative assessments as an integral part of education.

 

Title:
Mapping the Extinction Curve in 3D: Structure on Kiloparsec Scales
Authors:
Schlafly, E. F.; Peek, J. E. G.; Finkbeiner, D. P.; Green, G. M.
Publication:
The Astrophysical Journal, Volume 838, Issue 1, article id. 36, 11 pp. (2017). (ApJ Homepage)
Publication Date:
03/2017
Origin:
IOP
Astronomy Keywords:
dust, extinction, ISM: clouds, ISM: structure
DOI:
10.3847/1538-4357/aa619d
Bibliographic Code:
2017ApJ...838...36S

Abstract

Near-infrared spectroscopy from APOGEE and wide-field optical photometry from Pan-STARRS1 have recently made precise measurements of the shape of the extinction curve possible for tens of thousands of stars, parameterized by R(V). These measurements revealed structures in R(V) with large angular scales, which are challenging to explain in existing dust paradigms. In this work, we combine three-dimensional maps of dust column density with R(V) measurements to constrain the three-dimensional distribution of R(V) in the Milky Way. We find that the variations in R(V) are correlated on kiloparsec scales. In particular, most of the dust within one kiloparsec in the outer Galaxy, including many local molecular clouds (Orion, Taurus, Perseus, California, and Cepheus), has a significantly lower R(V) than more distant dust in the Milky Way. These results provide new input to models of dust evolution and processing, and complicate the application of locally derived extinction curves to more distant regions of the Milky Way and to other galaxies.

 

Title:
Realizing and Adiabatically Preparing Bosonic Integer and Fractional Quantum Hall states in Optical Lattices
Authors:
He, Yin-Chen; Grusdt, Fabian; Kaufman, Adam; Greiner, Markus; Vishwanath, Ashvin
Publication:
eprint arXiv:1703.00430
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Quantum Gases
Comment:
refs added, typo corrected
Bibliographic Code:
2017arXiv170300430H

Abstract

We study the ground states of 2D lattice bosons in an artificial gauge field. Using state of the art DMRG simulations we obtain the zero temperature phase diagram for hardcore bosons at densities $n_b$ with flux $n_\phi$ per unit cell, which determines a filling $\nu=n_b/n_\phi$. We find several robust quantum Hall phases, including (i) a bosonic integer quantum Hall phase (BIQH) at $\nu=2$, that realizes an interacting symmetry protected topological phase in 2D (ii) bosonic fractional quantum Hall phases including robust states at $\nu=2/3$ and a Laughlin state at $\nu=1/2$. The observed states correspond to the bosonic Jain sequence ($\nu=p/(p+1)$) pointing towards an underlying composite fermion picture. In addition to identifying Hamiltonians whose ground states realize these phases, we discuss their preparation beginning from independent chains, and ramping up interchain couplings. Using time dependent DMRG simulations, these are shown to reliably produce states close to the ground state for experimentally relevant system sizes. Besides the wave-function overlap, we utilize a simple physical signature of these phases, the non-monotonic behavior of a two-point correlation, a direct consequence of edge states in a finite system, to numerically assess the effectiveness of the preparation scheme. Our proposal only utilizes existing experimental capabilities.

 

Title:
Measurement of the inclusive-isolated prompt-photon cross section in $p\bar{p}$ collisions using the full CDF data set
Authors:
CDF Collaboration; Aaltonen, T.; Albrow, M. G.; Amerio, S.;... Franklin, M.;... and 394 coauthors
Publication:
eprint arXiv:1703.00599
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment
Comment:
submitted to Phys. Rev. D - RC
Bibliographic Code:
2017arXiv170300599C

Abstract

A measurement of the inclusive production cross section of isolated prompt photons in proton-antiproton collisions at center-of-mass energy $\sqrt{s}$=1.96TeV is presented. The results are obtained using the full Run II data sample collected with the Collider Detector at the Fermilab Tevatron, which corresponds to an integrated luminosity of 9.5fb$^{-1}$. The cross section is measured as a function of photon transverse energy, $E_T^{\gamma}$, in the range 30$ < E_T^{\gamma} <$500GeV and in the pseudorapidity region $|\eta^{\gamma}|<$1.0. The results are compared with predictions from parton-shower Monte Carlo models at leading order in quantum chromodynamics (QCD) and from next-to-leading order perturbative QCD calculations. The latter show good agreement with the measured cross section.

 

Title:
Complete Theory of Symmetry-based Indicators of Band Topology
Authors:
Po, Hoi Chun; Vishwanath, Ashvin; Watanabe, Haruki
Publication:
eprint arXiv:1703.00911
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science
Comment:
(7+epsilon)+13 pages; 2 figures, (1+10) tables
Bibliographic Code:
2017arXiv170300911P

Abstract

The interplay between symmetry and topology leads to a rich variety of electronic topological phases, protecting states such as topological insulators and Dirac semimetals. Here we focus on a different aspect of this interplay, where symmetry unambiguously indicates the presence of a topological band structure. Our study is comprehensive, encompassing all 230 space groups, and is built on two key advances. First, we find an efficient way to represent band structures in terms of elementary basis states, which are readily computed for each space group. Next, we isolate topological band structures by removing the set that represent simple atomic insulators, corresponding to localized Wannier orbitals. Special cases of our theory include the Fu-Kane parity criterion for inversion symmetric $\mathbb{Z}_2$ topological insulators, and the previously described filling-enforced quantum band insulators. We describe applications arising from new results.

 

Title:
Thermal Transport Signatures of Broken-Symmetry Phases in Graphene
Authors:
Pientka, Falko; Waissman, Jonah; Kim, Philip; Halperin, Bertrand I.
Publication:
eprint arXiv:1703.01235
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
5 pages, 3 figures, plus supplementary material
Bibliographic Code:
2017arXiv170301235P

Abstract

In the half-filled zero-energy Landau level of bilayer graphene, competing phases with spontaneously broken symmetries and an intriguing quantum critical behavior have been predicted. Here we investigate signatures of these broken-symmetry phases in thermal transport measurements. To this end we calculate the spectrum of spin and valley waves in the $\nu=0$ quantum Hall state of bilayer graphene. The presence of Goldstone modes enables heat transport even at low temperatures, which can serve as compelling evidence for spontaneous symmetry breaking. By varying external electric and magnetic fields it is possible to determine the nature of the symmetry breaking and temperature-dependent measurements may yield additional information about gapped modes.

 

Title:
Improved Point Source Detection in Crowded Fields using Probabilistic Cataloging
Authors:
Portillo, Stephen K. N.; Lee, Benjamin C. G.; Daylan, Tansu; Finkbeiner, Douglas P.
Publication:
eprint arXiv:1703.01303
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Astrophysics - Instrumentation and Methods for Astrophysics
Comment:
18 pages, 17 figures, submitted to the Astrophysical Journal
Bibliographic Code:
2017arXiv170301303P

Abstract

Cataloging is challenging in crowded fields because sources are extremely covariant with their neighbors and blending makes even the number of sources ambiguous. We present the first optical probabilistic catalog, cataloging a crowded (~0.1 sources per pixel brighter than 22nd magnitude in F606W) Sloan Digital Sky Survey r band image from M2. Probabilistic cataloging returns an ensemble of catalogs inferred from the image and thus can capture source-source covariance and deblending ambiguities. By comparing to a traditional catalog of the same image and a Hubble Space Telescope catalog of the same region, we show that our catalog ensemble better recovers sources from the image. It goes more than a magnitude deeper than the traditional catalog while having a lower false discovery rate brighter than 20th magnitude. We also present an algorithm for reducing this catalog ensemble to a condensed catalog that is similar to a traditional catalog, except it explicitly marginalizes over source-source covariances and nuisance parameters. We show that this condensed catalog has a similar completeness and false discovery rate to the catalog ensemble. Future telescopes will be more sensitive, and thus more of their images will be crowded. Probabilistic cataloging performs better than existing software in crowded fields and so should be considered when creating photometric pipelines in the Large Synoptic Space Telescope era.

 

Title:
Bulk reconstruction and the Hartle-Hawking wavefunction
Authors:
Jafferis, Daniel Louis
Publication:
eprint arXiv:1703.01519
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, General Relativity and Quantum Cosmology
Comment:
24 pages, 2 color figures
Bibliographic Code:
2017arXiv170301519J

Abstract

In this work, a relation is found between state dependence of bulk observables in the gauge/gravity correspondence and nonperturbative diffeomorphism invariance. Certain bulk constraints, such as the black hole information paradox, appear to obstruct the existence of a linear map from bulk operators to exact CFT operators that is valid over the entire expected range of validity of the bulk effective theory. By formulating the bulk gravitational physics in the Hartle-Hawking framework to address these nonperturbative IR questions, I will demonstrate, in the context of eternal AdS-Schwarzschild, that the problematic operators fail to satisfy the Hamiltonian constraints nonperturbatively. In this way, the map between bulk effective theory Hartle-Hawking wavefunctions and exact CFT states can be linear on the full Hilbert space.

 

Title:
Visible quantum plasmons in highly-doped few-layer graphene
Authors:
Shirodkar, Sharmila N.; Mattheakis, Marios; Cazeaux, Paul; Narang, Prineha; Soljačić, Marin; Kaxiras, Efthimios
Publication:
eprint arXiv:1703.01558
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Comment:
12 pages, 3 figures in main text, 2 pages, 2 figures in supplementary text
Bibliographic Code:
2017arXiv170301558S

Abstract

Doped graphene can support plasmon modes, but the limited range of doping achieved by gating prevents their frequency from reaching the visible to infrared range. Here we show, through the use of first-principles calculations, that the high levels of doping achieved by lithium intercalation in bilayer and trilayer graphene shift the plasmon frequencies into the visible range. To obtain physically meaningful results, we introduce a correction of the effect of plasmon interaction across the vacuum in a periodic cell by employing transparent boundary conditions in the direction perpendicular to the layers, a significant improvement over the Exact Coulomb cutoff technique employed in earlier works. We describe the features of these quantum plasmons, including the dispersion relation, losses and field localization. Our findings point to a strategy for fine-tuning the plasmon frequencies in graphene and other two dimensional materials.

 

Title:
Floquet topological phases protected by time glide symmetry
Authors:
Morimoto, Takahiro; Po, Hoi Chun; Vishwanath, Ashvin
Publication:
eprint arXiv:1703.02553
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
17 pages, 5 figures
Bibliographic Code:
2017arXiv170302553M

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 two-fold spatial rotation accompanied by half-period time translation.

 

Title:
Response to critiques on Observation of the Wigner-Huntington transition to metallic hydrogen
Authors:
Silvera, Isaac; Dias, Ranga
Publication:
eprint arXiv:1703.03064
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Materials Science, Condensed Matter - Other Condensed Matter, Condensed Matter - Quantum Gases
Comment:
12 pages, 9 figures
Bibliographic Code:
2017arXiv170303064S

Abstract

We reported the first observation of metallic hydrogen (MH) in the low temperature limit at a pressure of ~495 GPa in an article published in Science (1). This transition was first predicted by Wigner and Huntington (WE) over 80 years ago (2) at a pressure of ~25 GPa. In recent decades it became clear that the required pressure for metallization was far greater, in the 400-500 GPa range. Until now the observation of the WE transition in diamond anvil cells (DACs) has been prevented by one problem: the diamonds break before a sufficiently high pressure has been achieved. This has driven the high-pressure community to improve DACs and experimental methods to understand and overcome the conditions that limited the performance of diamonds and the pressure. In our experiment, with increasing pressure, we observed a clear transition from a transparent sample of solid molecular hydrogen to an opaque black sample to a shiny reflective sample of MH, as determined by reflectance measurements. There is no doubt that MH was produced at the highest pressures. Yet there have been criticisms concerning the pressure that was achieved, the possibility that the 50 nm alumina layer, deposited on diamonds to inhibit diffusion of hydrogen, might be transformed to a metal and be responsible for the reflectance, and analysis of the reflectance. Here we respond to the criticisms posted on the condensed matter arXiv by Loubeyre, Occelli, and Dumas (LOD)- arXiv:1702.07192, Eremets and Drozdov (ED)- arXiv:1702.05125, and Goncharov and Struzhkin (GS)- arXiv:1702.04246.

 

Title:
Constraints on oscillation parameters from $\nu_e$ appearance and $\nu_\mu$ disappearance in NOvA
Authors:
Adamson, P.; Aliaga, L.; Ambrose, D.;... Feldman, G. J.;... and 176 coauthors
Publication:
eprint arXiv:1703.03328
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment
Comment:
6 pages, 4 figures
Bibliographic Code:
2017arXiv170303328A

Abstract

Results are reported from an improved measurement of $\nu_\mu \rightarrow \nu_e$ transitions by the NOvA experiment. Using an exposure equivalent to $6.05\times10^{20}$ protons-on-target 33 $\nu_e$ candidates were observed with a background of $8.2\pm0.8$ (syst.). Combined with the latest NOvA $\nu_\mu$ disappearance data and external constraints from reactor experiments on $\sin^22\theta_{13}$, the hypothesis of inverted mass hierarchy with $\theta_{23}$ in the lower octant is disfavored at greater than $93\%$ C.L. for all values of $\delta_{CP}$.

 

Title:
Dynamically induced many-body localization
Authors:
Choi, Soonwon; Abanin, Dmitry A.; Lukin, Mikhail D.
Publication:
eprint arXiv:1703.03809
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Quantum Gases, Condensed Matter - Strongly Correlated Electrons, Quantum Physics
Comment:
5 pages, 3 figures
Bibliographic Code:
2017arXiv170303809C

Abstract

We show that a quantum phase transition from ergodic to many-body localized (MBL) phases can be induced via periodic pulsed manipulation of spin systems. Such a transition is enabled by the interplay between weak disorder and slow heating rates. Specifically, we demonstrate that the Hamiltonian of a weakly disordered ergodic spin system can be effectively engineered, by using sufficiently fast coherent controls, to yield a stable MBL phase, which in turn completely suppresses the energy absorption from external control field. Our results imply that a broad class of existing many-body systems can be used to probe non-equilibrium phases of matter for a long time, limited only by coupling to external environment.

 

Title:
Critical time crystals in dipolar systems
Authors:
Ho, Wen Wei; Choi, Soonwon; Lukin, Mikhail D.; Abanin, Dmitry A.
Publication:
eprint arXiv:1703.04593
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons, Quantum Physics
Comment:
5 + 4 pages, 3 figures, updated references and corrected some typos
Bibliographic Code:
2017arXiv170304593H

Abstract

We analyze quantum dynamics of periodically driven, disordered systems in the presence of long-range interactions. Focusing on stability of discrete time crystalline (DTC) order in such systems, we use a perturbative procedure to evaluate its lifetime. For 3D systems with dipolar interactions, we show that the corresponding decay is parametrically slow, implying that robust, long-lived DTC order can be obtained. We further predict a sharp crossover from the stable DTC regime into a regime where DTC order is lost, reminiscent of a phase transition. These results are in good agreement with the recent experiments utilizing a dense, dipolar spin ensemble in diamond [Nature 543, 221-225 (2017)]. They demonstrate the existence of a novel, critical DTC regime that is stabilized not by many-body localization but rather by slow, critical dynamics. Our analysis shows that DTC response can be used as a sensitive probe of non-equilibrium quantum matter.

 

Title:
Topological Quantum Optics in Two-Dimensional Atomic Arrays
Authors:
Perczel, Janos; Borregaard, Johannes; Chang, Darrick; Pichler, Hannes; Yelin, Susanne F.; Zoller, Peter; Lukin, Mikhail D.
Publication:
eprint arXiv:1703.04849
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Quantum Physics, Physics - Atomic Physics, Physics - Optics
Comment:
9 pages, 8 figures
Bibliographic Code:
2017arXiv170304849P

Abstract

We demonstrate that two-dimensional atomic arrays with subwavelength spacing can be used to create topologically protected quantum optical systems where the photon propagation is robust against large imperfections while losses associated with free space emission are strongly suppressed. Breaking time-reversal symmetry with a magnetic field results in gapped photonic bands with non-trivial Chern numbers. Such a system displays topologically protected bound states and unidirectional emission by individual atoms into long-lived edge states. Possible experimental realizations and applications are discussed.

 

Title:
Lectures on the Infrared Structure of Gravity and Gauge Theory
Authors:
Strominger, Andrew
Publication:
eprint arXiv:1703.05448
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology, Mathematical Physics
Comment:
154 pages, 21 figures
Bibliographic Code:
2017arXiv170305448S

Abstract

This is a redacted transcript of a course given by the author at Harvard in spring semester 2016. It contains a pedagogical overview of recent developments connecting the subjects of soft theorems, the memory effect and asymptotic symmetries in four-dimensional QED, nonabelian gauge theory and gravity with applications to black holes. The lectures may be viewed online at https://goo.gl/3DJdOr. Please send typos or corrections to strominger@physics.harvard.edu.

 

Title:
Manipulating polarized light with a planar slab of Black Phosphorus
Authors:
Valagiannopoulos, Constantinos A.; Mattheakis, Marios; Shirodkar, Sharmila N.; Kaxiras, Efthimios
Publication:
eprint arXiv:1703.06383
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Physics - Optics
Bibliographic Code:
2017arXiv170306383V

Abstract

Wave polarization contains valuable information for electromagnetic signal processing and the ability to manipulate it can be extremely useful in photonic devices. In this work, we propose designs comprised of one of the emerging and interesting two-dimensional media: Black Phosphorus. Due to substantial in-plane anisotropy, a single slab of Black Phosphorus can be very efficient for manipulating the polarization state of electromagnetic waves. We investigate Black Phosphorus slabs that filter the fields along one direction, or achieve large magnetic-free Faraday rotation, or convert linear polarization to circular. These slabs can be employed as components in numerous mid-IR integrated devices.

 

Title:
Quantum butterfly effect in weakly interacting diffusive metals
Authors:
Patel, Aavishkar A.; Chowdhury, Debanjan; Sachdev, Subir; Swingle, Brian
Publication:
eprint arXiv:1703.07353
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Disordered Systems and Neural Networks, High Energy Physics - Theory, Quantum Physics
Comment:
18 pages, 7 figures
Bibliographic Code:
2017arXiv170307353P

Abstract

We study scrambling, an avatar of chaos, in a weakly interacting metal in the presence of random potential disorder. It is well known that charge and heat spread via diffusion in such an interacting disordered metal. In contrast, we show within perturbation theory that chaos spreads in a ballistic fashion. The squared anticommutator of the electron field operators inherits a light-cone like growth, arising from an interplay of a growth (Lyapunov) exponent that scales as the inelastic electron scattering rate and a diffusive piece due to the presence of disorder. In two spatial dimensions, the Lyapunov exponent is universally related at weak coupling to the sheet resistivity. We are able to define an effective temperature-dependent butterfly velocity, a speed limit for the propagation of quantum information, that is much slower than microscopic velocities such as the Fermi velocity and that is qualitatively similar to that of a quantum critical system with a dynamical critical exponent $z > 1$.

 

Title:
Interacting invariants for Floquet phases of fermions in two dimensions
Authors:
Fidkowski, Lukasz; Po, Hoi Chun; Potter, Andrew C.; Vishwanath, Ashvin
Publication:
eprint arXiv:1703.07360
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons
Comment:
20 pages
Bibliographic Code:
2017arXiv170307360F

Abstract

We construct a many-body quantized invariant that sharply distinguishes among two dimensional non-equilibrium driven phases of interacting fermions. This is an interacting generalization of a band-structure Floquet quasi-energy winding number, and describes chiral pumping of quantum information along the edge. In particular, our invariant sharply distinguishes between a trivial and anomalous Floquet Anderson insulator in the interacting, many-body localized setting. It also applies more generally to models where only fermion parity is conserved, where it differentiates between trivial models and ones that pump Kitaev Majorana chains to the boundary, such as ones recently introduced in the context of emergent fermions arising from eigenstate $\Z_2$ topological order. We evaluate our invariant for the edge of such a system with eigenstate $\Z_2$ topological order, and show that it is necessarily nonzero when the Floquet unitary exchanges electric and magnetic excitations, proving a connection between bulk anyonic symmetry and edge chirality.

 

Title:
Termite mounds harness diurnal temperature oscillations for ventilation
Authors:
King, Hunter; Ocko, Samuel A.; Mahadevan, L.
Publication:
eprint arXiv:1703.08067
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Physics - Biological Physics, Physics - Fluid Dynamics, Quantitative Biology - Quantitative Methods
Comment:
18 Pages, 20 Figures; Proceedings of the National Academy of Sciences 112.37 (2015): 11589-11593
Bibliographic Code:
2017arXiv170308067K

Abstract

Many species of millimetric fungus-harvesting termites collectively build uninhabited, massive mound structures enclosing a network of broad tunnels which protrude from the ground meters above their subterranean nests. It is widely accepted that the purpose of these mounds is to give the colony a controlled micro-climate in which to raise fungus and brood by managing heat, humidity, and respiratory gas exchange. While different hypotheses such as steady and fluctuating external wind and internal metabolic heating have been proposed for ventilating the mound, the absence of direct in-situ measurement of internal air flows has precluded a definitive mechanism for this critical physiological function. By measuring diurnal variations in flow through the surface conduits of the mounds of the species Odontotermes obesus, we show that a simple combination of geometry, heterogeneous thermal mass and porosity allows the mounds to use diurnal ambient temperature oscillations for ventilation. In particular, the thin outer flute-like conduits heat up rapidly during the day relative to the deeper chimneys, pushing air up the flutes and down the chimney in a closed convection cell, with the converse situation at night. These cyclic flows in the mound flush out $\text{CO}_2$ from the nest and ventilate the colony, in a novel example of deriving useful work from thermal oscillations.

 

Title:
Collinear factorization violation and effective field theory
Authors:
Schwartz, Matthew D.; Yan, Kai; Zhu, Hua Xing
Publication:
eprint arXiv:1703.08572
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology
Comment:
55 Pages, 5 figures
Bibliographic Code:
2017arXiv170308572S

Abstract

The factorization of amplitudes into hard, soft and collinear parts is known to be violated in situations where incoming particles are collinear to outgoing ones. This result was first derived by studying limits where non-collinear particles become collinear. We show that through an effective field theory framework with Glauber operators, these factorization-violating effects can be reproduced from an amplitude that is factorized before the splitting occurs. We confirm results at one-loop, through single Glauber exchange, and at two-loops, through double Glauber exchange. To approach the calculation, we begin by reviewing the importance of Glauber scaling for factorization. We show that for any situation where initial state and final state particles are not collinear, the Glauber contribution is entirely contained in the soft contribution. The contributions coming from Glauber operators are necessarily non-analytic functions of external momentum, with the non-analyticity arising from the rapidity regulator. The non-analyticity is critical so that Glauber operators can both preserve factorization when it holds and produce factorization-violating effects when they are present.

 

Title:
Sub-cellular mRNA localization modulates the regulation of gene expression by small RNAs in bacteria
Authors:
Teimouri, Hamid; Korkmazhan, Elgin; Stavans, Joel; Levine, Erel
Publication:
eprint arXiv:1703.08574
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Physics - Biological Physics
Bibliographic Code:
2017arXiv170308574T

Abstract

Small non-coding RNAs can exert significant regulatory activity on gene expression in bacteria. In recent years, substantial progress has been made in understanding bacterial gene expression by sRNAs. However, recent findings that demonstrate that families of mRNAs show non-trivial sub-cellular distributions raise the question of how localization may affect the regulatory activity of sRNAs. Here we address this question within a simple mathematical model. We show that the non-uniform spatial distributions of mRNA can alter the threshold-linear response that characterizes sRNAs that act stoichiometrically, and modulate the hierarchy among targets co-regulated by the same sRNA. We also identify conditions where the sub-cellular organization of cofactors in the sRNA pathway can induce spatial heterogeneity on sRNA targets. Our results suggest that under certain conditions, interpretation and modeling of natural and synthetic gene regulatory circuits need to take into account the spatial organization of the transcripts of participating genes.

 

Title:
Periodic Orbit Scar in Propagation of Wavepacket
Authors:
Tomiya, Mitsuyoshi; Sakamoto, Shoichi; Heller, Eric J.
Publication:
eprint arXiv:1703.08613
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Quantum Physics, Nonlinear Sciences - Chaotic Dynamics, 81Q50, G.1.7, J.2
Comment:
24 pages,11 figures
Bibliographic Code:
2017arXiv170308613T

Abstract

This study analyzed the scar-like localization in the time-average of a timeevolving wavepacket on the desymmetrized stadium billiard. When a wavepacket is launched along the orbits, it emerges on classical unstable periodic orbits as a scar in the stationary states. This localization along the periodic orbit is clarified through the semiclassical approximation. It essentially originates from the same mechanism of a scar in stationary states: the piling up of the contribution from the classical actions of multiply repeated passes on a primitive periodic orbit. To create this enhancement, several states are required in the energy range, which is determined by the initial wavepacket.

 

Title:
Quantum correlations at infinite temperature: the dynamical Nagaoka effect
Authors:
Kanasz-Nagy, Marton; Lovas, Izabella; Grusdt, Fabian; Greif, Daniel; Greiner, Markus; Demler, Eugene A.
Publication:
eprint arXiv:1703.09231
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Physics - Computational Physics, Quantum Physics
Comment:
10 pages, 5 figures; Supplementary Material (4 pages, 5 figures)
Bibliographic Code:
2017arXiv170309231K

Abstract

Do quantum correlations play a role in high temperature dynamics of many-body systems? A common expectation is that thermal fluctuations lead to fast decoherence and make dynamics classical. In this paper, we provide a striking example of a single particle created in a featureless, infinite temperature spin bath which not only exhibits non-classical dynamics but also induces strong long-lived correlations between the surrounding spins. We study the non-equilibrium dynamics of a hole created in a fermionic or bosonic Mott insulator in the atomic limit, which corresponds to a degenerate spin system. In the absence of interactions, the spin correlations arise purely from quantum interference, and the correlations are both antiferromagnetic and ferromagnetic, in striking contrast to the equilibrium Nagaoka effect. These results are relevant for several condensed matter spin systems, and should be observable using state of the art bosonic or fermionic quantum gas microscopes.

 

Title:
Monolayer FeSe on SrTiO$_3$
Authors:
Huang, Dennis; Hoffman, Jennifer E.
Publication:
eprint arXiv:1703.09306
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons
Comment:
27 pages, 14 figures; Annu. Rev. Condens. Matter Phys. 8 (2017); doi:10.1146/annurev-conmatphys-031016-025242
Bibliographic Code:
2017arXiv170309306H

Abstract

Epitaxial engineering of solid-state heterointerfaces is a leading avenue to realizing enhanced or novel electronic states of matter. As a recent example, bulk FeSe is an unconventional superconductor with a modest transition temperature ($T_c$) of 9 K. When a single atomic layer of FeSe is grown on SrTiO$_3$, however, its $T_c$ can skyrocket by an order of magnitude to 65 K or 109 K. Since this discovery in 2012, efforts to reproduce, understand, and extend these findings continue to draw both excitement and scrutiny. In this review, we first present a critical survey of experimental measurements performed using a wide range of techniques. We then turn to the open question of microscopic mechanisms of superconductivity. We examine contrasting indications for both phononic (conventional) and magnetic/orbital (unconventional) means of electron pairing, and speculations about whether they could work cooperatively to boost $T_c$ in a monolayer of FeSe.

 

Title:
Graphene-based Josephson junction single photon detector
Authors:
Walsh, Evan D.; Efetov, Dmitri K.; Lee, Gil-Ho; Heuck, Mikkel; Crossno, Jesse; Ohki, Thomas A.; Kim, Philip; Englund, Dirk; Chung Fong, Kin
Publication:
eprint arXiv:1703.09736
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science, Condensed Matter - Superconductivity
Comment:
11 pages, 6 figures, and 1 table in the main text
Bibliographic Code:
2017arXiv170309736W

Abstract

We show that it is possible for graphene-based Josephson junctions (gJjs) to detect single photons in a wide electromagnetic spectrum from visible to radio frequencies. Our approach takes advantage of the exceptionally low electronic heat capacity of monolayer graphene and its constricted thermal conductance to its phonon degrees of freedom. Such a system could provide high sensitivity photon detection required for research areas including quantum information processing and radio-astronomy. As an example, we present our device concepts for gJj single photon detectors in both the microwave and infrared regimes. The dark count rate and intrinsic quantum efficiency are computed based on parameters from a measured gJj, demonstrating feasibility within existing technologies.

 

Title:
Recursive Representations of Arbitrary Virasoro Conformal Blocks
Authors:
Cho, Minjae; Collier, Scott; Yin, Xi
Publication:
eprint arXiv:1703.09805
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
38 pages, 8 figures, v2: comments on references added, reference added, typos corrected
Bibliographic Code:
2017arXiv170309805C

Abstract

We derive recursive representations in the internal weights of N-point Virasoro conformal blocks in the sphere linear channel and the torus necklace channel, and recursive representations in the central charge of arbitrary Virasoro conformal blocks on the sphere, the torus, and higher genus Riemann surfaces in the plumbing frame.

 

Title:
Dynamical engineering of interactions in qudit ensembles
Authors:
Choi, Soonwon; Yao, Norman Y.; Lukin, Mikhail D.
Publication:
eprint arXiv:1703.09808
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
6+7 pages, 2+2 figures
Bibliographic Code:
2017arXiv170309808C

Abstract

We propose and analyze a method to engineer effective interactions in an ensemble of d-level systems (qudits) driven by global control fields. In particular, we present (i) a necessary and sufficient condition under which a given interaction can be turned off (decoupled), (ii) the existence of a universal sequence that decouples any (cancellable) interaction, and (iii) an efficient algorithm to engineer a target Hamiltonian from an initial Hamiltonian (if possible). As examples, we provide a 6-pulse sequence that decouples effective spin-1 dipolar interactions and demonstrate that a spin- 1 Ising chain can be engineered to study transitions among three distinct symmetry protected topological phases.

 

Title:
Wrinkling instability of an inhomogeneously stretched viscous sheet
Authors:
Srinivasan, Siddarth; Wei, Zhiyan; Mahadevan, L.
Publication:
eprint arXiv:1703.10313
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Physics - Fluid Dynamics, Condensed Matter - Soft Condensed Matter
Comment:
26 pages, 7 figures
Bibliographic Code:
2017arXiv170310313S

Abstract

Motivated by the redrawing of hot glass into thin sheets, we investigate the shape and stability of a thin viscous sheet that is inhomogeneously stretched in an imposed non-uniform temperature field. We first determine the associated base flow by solving the long-timescale stretching flow of a flat sheet as a function of two dimensionless parameters: the normalized stretching velocity $\alpha$, and a dimensionless width of the heating zone $\beta$. This allows us to determine the conditions for the onset of an out-of-plane wrinkling instability stated in terms of an eigenvalue problem for a linear partial differential equation governing the displacement of the midsurface of the sheet. We show the sheet can become unstable in two regions that are upstream and downstream of the heating zone where the minimum in-plane stress is negative. This yields the shape and growth rates of the most unstable buckling mode in both regions for various values of the stretching velocity and heating zone width. A transition from stationary to oscillatory unstable modes is found in the upstream region with increasing $\beta$ while the downstream region is always stationary. We show that the wrinkling instability can be entirely suppressed when the surface tension is large enough relative to the magnitude of the in-plane stress. Finally, we present an operating diagram that indicates regions of the parameter space that result in a required outlet sheet thickness upon stretching, while simultaneously minimizing or suppressing the out-of-plane buckling; a result that is relevant for the glass redraw method used to create ultrathin glass sheets.

 

Title:
Mechanical detection and imaging of hyperbolic phonon polaritons in hexagonal Boron Nitride
Authors:
Ambrosio, Antonio; Jauregui, Luis A.; Dai, Siyan; Chaudhary, Kundan; Tamagnone, Michele; Fogler, Michael; Basov, Dimitri N.; Capasso, Federico; Kim, Philip; Wilson, William L.
Publication:
eprint arXiv:1704.01834
Publication Date:
03/2017
Origin:
ARXIV
Keywords:
Condensed Matter - Materials Science, Physics - Optics
Bibliographic Code:
2017arXiv170401834A

Abstract

Mid-infrared nano-imaging and spectroscopy of two-dimensional (2D) materials have been limited so far to scattering-type Scanning Near-field Optical Microscopy (s-NSOM) experiments where light from the sample is scattered by a metallic-coated Atomic Force Microscope (AFM) tip interacting with the material at the nanoscale. These experiments have recently allowed imaging of plasmon polaritons in graphene as well as hyperbolic phonon polaritons (HP2) in hexagonal Boron Nitride (hBN). Here we show that the high mechanical sensitivity of an AFM cantilever can be exploited for imaging hyperbolic phonon polaritons in hBN. In our imaging process, the lattice vibrations of hBN micrometer-sized flakes are locally enhanced by the launched phonon polaritons. These enhanced vibrations are coupled to the AFM tip in contact to the sample surface and recorded during scanning. Imaging resolution better than {\lambda}/20 is showed, comparable to the best resolution in s-NSOM. Importantly, this detection mechanism is free from light background and it is in fact the first photon-less detection of phonon polaritons.

 

Title:
spectral ID of supernova AT2017cfb
Authors:
Bieryla, A.; Carmichael, T.; Challis, P.; Cordova, R.; Finkbeiner, D.; Gilchrist, R.; Komorowski, E.; Alonso-Monsalve, E.
Publication:
The Astronomer's Telegram, No. 10178
Publication Date:
03/2017
Origin:
ATEL
Keywords:
Supernovae
Bibliographic Code:
2017ATel10178....1B

Abstract

Spectra (range 350-760 nm) of supernova AT2017cfb (=ATLAS17cof) was obtained on Mar 17, 2017 UT with the F. L. Whipple Observatory 1.5-m telescope (+ FAST).

 

Title:
Superrotations and black hole pair creation
Authors:
Strominger, Andrew; Zhiboedov, Alexander
Publication:
Classical and Quantum Gravity, Volume 34, Issue 6, article id. 064002 (2017). (CQGra Homepage)
Publication Date:
03/2017
Origin:
IOP
DOI:
10.1088/1361-6382/aa5b5f
Bibliographic Code:
2017CQGra..34f4002S

Abstract

Recent work has shown that the symmetries of classical gravitational scattering in asymptotically flat spacetimes include, at the linearized level, infinitesimal superrotations. These act like Virasoro generators on the celestial sphere at null infinity. However, due to the singularities in these generators, the physical status of finite superrotations has remained unclear. Here we address this issue in the context of the breaking of a cosmic string via quantum black hole pair nucleation. This process is described by a gravitational instanton known as the C-metric. After pair production, the black holes are pulled by the string to null infinity with a constant acceleration. At late times the string decays and the spacetime settles into a vacuum state. We show that the early and late spacetimes before and after string decay differ by a finite superrotation. This provides a physical interpretation of superrotations. They act on spacetimes which are asymptotically flat everywhere except at isolated singularities with cosmic string defects.

 

Title:
Search for triboson W^{± }W^{± }W^{∓ } 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 2854 coauthors
Publication:
The European Physical Journal C, Volume 77, Issue 3, article id. #141, 28 pp. (EPJC Homepage)
Publication Date:
03/2017
Origin:
SPRINGER
Abstract Copyright:
(c) 2017: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-017-4692-1
Bibliographic Code:
2017EPJC...77..141A

Abstract

This paper reports a search for triboson W^{± }W^{± }W^{∓ } production in two decay channels ({W^{± }W^{± }W^{∓ } → ℓ ^± ν ℓ ^± ν ℓ ^∓ ν } and {W^{± }W^{± }W^{∓ } → ℓ ^± ν ℓ ^± ν jj} with ℓ =e, μ ) in proton-proton collision data corresponding to an integrated luminosity of 20.3 fb^-1 at a centre-of-mass energy of 8 {TeV} with the ATLAS detector at the Large Hadron Collider. Events with exactly three charged leptons, or two leptons with the same electric charge in association with two jets, are selected. The total number of events observed in data is consistent with the Standard Model (SM) predictions. The observed 95% confidence level upper limit on the SM W^{± }W^{± }W^{∓ } production cross section is found to be 730 fb with an expected limit of 560 fb in the absence of SM W^{± }W^{± }W^{∓ } production. Limits are also set on WWWW anomalous quartic gauge couplings.

 

Title:
Search for new phenomena in events containing a same-flavour opposite-sign dilepton pair, jets, and large missing transverse momentum in \varvec{√{s}=13} {TeV} \varvec{pp} collisions with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.; ... Franklin, M.;... Huth, J.;... Morii, M.;... and 2835 coauthors
Publication:
The European Physical Journal C, Volume 77, Issue 3, article id. #144, 40 pp. (EPJC Homepage)
Publication Date:
03/2017
Origin:
SPRINGER
Abstract Copyright:
(c) 2017: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-017-4700-5
Bibliographic Code:
2017EPJC...77..144A

Abstract

Two searches for new phenomena in final states containing a same-flavour opposite-sign lepton (electron or muon) pair, jets, and large missing transverse momentum are presented. These searches make use of proton-proton collision data, collected during 2015 and 2016 at a centre-of-mass energy √{s}=13 {TeV} by the ATLAS detector at the large hadron collider, which correspond to an integrated luminosity of 14.7 fb^{-1}. Both searches target the pair production of supersymmetric particles, squarks or gluinos, which decay to final states containing a same-flavour opposite-sign lepton pair via one of two mechanisms: a leptonically decaying Z boson in the final state, leading to a peak in the dilepton invariant-mass distribution around the Z boson mass; and decays of neutralinos (e.g. \tilde{χ }_2^0 → ℓ ^+ℓ ^- \tilde{χ }_1^0), yielding a kinematic endpoint in the dilepton invariant-mass spectrum. The data are found to be consistent with the Standard Model expectation. Results are interpreted in simplified models of gluino-pair (squark-pair) production, and provide sensitivity to gluinos (squarks) with masses as large as 1.70 {TeV} (980 {GeV}).

 

Title:
Optical Nanoscopy of High Tc Cuprate Nanoconstriction Devices Patterned by Helium Ion Beams
Authors:
Gozar, A.; Litombe, N. E.; Hoffman, Jennifer E.; Božović, I.
Affiliation:
AA(0000-0002-3233-0990)
Publication:
Nano Letters, vol. 17, issue 3, pp. 1582-1586
Publication Date:
03/2017
Origin:
CROSSREF
DOI:
10.1021/acs.nanolett.6b04729
Bibliographic Code:
2017NanoL..17.1582G

Abstract

Helium-ion beams (HIB) focused to sub-nanometer scales have emerged as powerful tools for high-resolution imaging as well as nano-scale lithography, ion milling or deposition. Quantifying irradiation effects is essential for reliable device fabrication but most of the depth profiling information is provided by computer simulations rather than experiment. Here, we use atomic force microscopy (AFM) combined with scanning near-field optical microscopy (SNOM) to provide three-dimensional (3D) dielectric characterization of high-temperature superconductor devices fabricated by HIB. By imaging the infrared dielectric response we find that amorphization caused by the nominally 0.5 nm HIB extends throughout the entire 26.5 nm thickness of the cuprate film and by about 500 nm laterally. This unexpectedly widespread structural and electronic damage can be attributed to a Helium depth distribution substantially modified by internal device interfaces. Our study introduces AFM-SNOM as a quantitative nano-scale tomographic technique for non-invasive 3D characterization of irradiation damage in a wide variety of devices.

 

Title:
Unbalanced Hole and Electron Diffusion in Lead Bromide Perovskites
Authors:
Elbaz, Giselle A.; Straus, Daniel B.; Semonin, Octavi E.; Hull, Trevor D.; Paley, Daniel W.; Kim, Philip; Owen, Jonathan S.; Kagan, Cherie R.; Roy, Xavier
Affiliation:
AB(0000-0003-2977-5590), AG(0000-0001-5502-3267), AI(0000-0002-8850-0725)
Publication:
Nano Letters, vol. 17, issue 3, pp. 1727-1732
Publication Date:
03/2017
Origin:
CROSSREF
DOI:
10.1021/acs.nanolett.6b05022
Bibliographic Code:
2017NanoL..17.1727E

Abstract

Not Available

 

Title:
Microfluidic Fabrication of Colloidal Nanomaterials-Encapsulated Microcapsules for Biomolecular Sensing
Authors:
Xie, Xi; Zhang, Weixia; Abbaspourrad, Alireza; Ahn, Jiyoung; Bader, Andrew; Bose, Suman; Vegas, Arturo; Lin, Jiaqi; Tao, Jun; Hang, Tian; Lee, Hyomin; Iverson, Nicole; Bisker, Gili; Li, Linxian; Strano, Michael S.; Weitz, David A.; Anderson, Daniel G.
Publication:
Nano Letters, vol. 17, issue 3, pp. 2015-2020
Publication Date:
03/2017
Origin:
CROSSREF
DOI:
10.1021/acs.nanolett.7b00026
Bibliographic Code:
2017NanoL..17.2015X

Abstract

Not Available

 

Title:
Observation of a discrete time crystal
Authors:
Zhang, J.; Hess, P. W.; Kyprianidis, A.; Becker, P.; Lee, A.; Smith, J.; Pagano, G.; Potirniche, I.-D.; Potter, A. C.; Vishwanath, A.; Yao, N. Y.; Monroe, C.
Publication:
Nature, Volume 543, Issue 7644, pp. 217-220 (2017). (Nature Homepage)
Publication Date:
03/2017
Origin:
NATURE
Abstract Copyright:
(c) 2017: Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
DOI:
10.1038/nature21413
Bibliographic Code:
2017Natur.543..217Z

Abstract

Spontaneous symmetry breaking is a fundamental concept in many areas of physics, including cosmology, particle physics and condensed matter. An example is the breaking of spatial translational symmetry, which underlies the formation of crystals and the phase transition from liquid to solid. Using the analogy of crystals in space, the breaking of translational symmetry in time and the emergence of a ‘time crystal’ was recently proposed, but was later shown to be forbidden in thermal equilibrium. However, non-equilibrium Floquet systems, which are subject to a periodic drive, can exhibit persistent time correlations at an emergent subharmonic frequency. This new phase of matter has been dubbed a ‘discrete time crystal’. Here we present the experimental observation of a discrete time crystal, in an interacting spin chain of trapped atomic ions. We apply a periodic Hamiltonian to the system under many-body localization conditions, and observe a subharmonic temporal response that is robust to external perturbations. The observation of such a time crystal opens the door to the study of systems with long-range spatio-temporal correlations and novel phases of matter that emerge under intrinsically non-equilibrium conditions.

 

Title:
Observation of discrete time-crystalline order in a disordered dipolar many-body system
Authors:
Choi, Soonwon; Choi, Joonhee; Landig, Renate; Kucsko, Georg; Zhou, Hengyun; Isoya, Junichi; Jelezko, Fedor; Onoda, Shinobu; Sumiya, Hitoshi; Khemani, Vedika; von Keyserlingk, Curt; Yao, Norman Y.; Demler, Eugene; Lukin, Mikhail D.
Publication:
Nature, Volume 543, Issue 7644, pp. 221-225 (2017). (Nature Homepage)
Publication Date:
03/2017
Origin:
NATURE
Abstract Copyright:
(c) 2017: Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
DOI:
10.1038/nature21426
Bibliographic Code:
2017Natur.543..221C

Abstract

Understanding quantum dynamics away from equilibrium is an outstanding challenge in the modern physical sciences. Out-of-equilibrium systems can display a rich variety of phenomena, including self-organized synchronization and dynamical phase transitions. More recently, advances in the controlled manipulation of isolated many-body systems have enabled detailed studies of non-equilibrium phases in strongly interacting quantum matter; for example, the interplay between periodic driving, disorder and strong interactions has been predicted to result in exotic ‘time-crystalline’ phases, in which a system exhibits temporal correlations at integer multiples of the fundamental driving period, breaking the discrete time-translational symmetry of the underlying drive. Here we report the experimental observation of such discrete time-crystalline order in a driven, disordered ensemble of about one million dipolar spin impurities in diamond at room temperature. We observe long-lived temporal correlations, experimentally identify the phase boundary and find that the temporal order is protected by strong interactions. This order is remarkably stable to perturbations, even in the presence of slow thermalization. Our work opens the door to exploring dynamical phases of matter and controlling interacting, disordered many-body systems.

 

Title:
Chern-Simons theory and Wilson loops in the Brillouin zone
Authors:
Lian, Biao; Vafa, Cumrun; Vafa, Farzan; Zhang, Shou-Cheng
Publication:
Physical Review B, Volume 95, Issue 9, id.094512 (PhRvB Homepage)
Publication Date:
03/2017
Origin:
APS
Abstract Copyright:
2017: American Physical Society
DOI:
10.1103/PhysRevB.95.094512
Bibliographic Code:
2017PhRvB..95i4512L

Abstract

Berry connection is conventionally defined as a static gauge field in the Brillouin zone. Here we show that for three-dimensional (3D) time-reversal invariant superconductors, a generalized Berry gauge field behaves as a fluctuating field of a Chern-Simons gauge theory. The gapless nodal lines in the momentum space play the role of Wilson loop observables, while their linking and knot invariants modify the gravitational theta angle. This angle induces a topological gravitomagnetoelectric effect where a temperature gradient induces a rotational energy flow. We also show how topological strings may be realized in the six-dimensional phase space, where the physical space defects play the role of topological D-branes.

 

Title:
Non-Hookean statistical mechanics of clamped graphene ribbons
Authors:
Bowick, Mark J.; Košmrlj, Andrej; Nelson, David R.; Sknepnek, Rastko
Publication:
Physical Review B, Volume 95, Issue 10, id.104109 (PhRvB Homepage)
Publication Date:
03/2017
Origin:
APS
Abstract Copyright:
2017: American Physical Society
DOI:
10.1103/PhysRevB.95.104109
Bibliographic Code:
2017PhRvB..95j4109B

Abstract

Thermally fluctuating sheets and ribbons provide an intriguing forum in which to investigate strong violations of Hooke's Law: Large distance elastic parameters are in fact not constant but instead depend on the macroscopic dimensions. Inspired by recent experiments on free-standing graphene cantilevers, we combine the statistical mechanics of thin elastic plates and large-scale numerical simulations to investigate the thermal renormalization of the bending rigidity of graphene ribbons clamped at one end. For ribbons of dimensions W ×L (with L ≥W ), the macroscopic bending rigidity κR determined from cantilever deformations is independent of the width when W <ℓth , where ℓth is a thermal length scale, as expected. When W >ℓth , however, this thermally renormalized bending rigidity begins to systematically increase, in agreement with the scaling theory, although in our simulations we were not quite able to reach the system sizes necessary to determine the fully developed power law dependence on W . When the ribbon length L >ℓp , where ℓp is the W -dependent thermally renormalized ribbon persistence length, we observe a scaling collapse and the beginnings of large scale random walk behavior.

 

Title:
Photon emission near extreme Kerr black holes
Authors:
Porfyriadis, Achilleas P.; Shi, Yichen; Strominger, Andrew
Publication:
Physical Review D, Volume 95, Issue 6, id.064009 (PhRvD Homepage)
Publication Date:
03/2017
Origin:
APS
Abstract Copyright:
2017: American Physical Society
DOI:
10.1103/PhysRevD.95.064009
Bibliographic Code:
2017PhRvD..95f4009P

Abstract

Ongoing astronomical efforts extract physical properties of black holes from electromagnetic emissions in their near-vicinity. This requires finding the null geodesics which extend from the near-horizon region out to a distant observatory. In general these are given by elliptic integrals which are often studied numerically. In this paper, for the interesting special case of extremally spinning Kerr black holes, we use an emergent near-horizon conformal symmetry to find near-superradiant geodesics analytically in terms of elementary functions.

 

Title:
Publisher's Note: Supersymmetric Sachdev-Ye-Kitaev models [Phys. Rev. D 95, 026009 (2017)]
Authors:
Fu, Wenbo; Gaiotto, Davide; Maldacena, Juan; Sachdev, Subir
Publication:
Physical Review D, Volume 95, Issue 6, id.069904 (PhRvD Homepage)
Publication Date:
03/2017
Origin:
APS
DOI:
10.1103/PhysRevD.95.069904
Bibliographic Code:
2017PhRvD..95f9904F

Abstract

Not Available

 

Title:
Depolarization Dynamics in a Strongly Interacting Solid-State Spin Ensemble
Authors:
Choi, Joonhee; Choi, Soonwon; Kucsko, Georg; Maurer, Peter C.; Shields, Brendan J.; Sumiya, Hitoshi; Onoda, Shinobu; Isoya, Junichi; Demler, Eugene; Jelezko, Fedor; Yao, Norman Y.; Lukin, Mikhail D.
Publication:
Physical Review Letters, Volume 118, Issue 9, id.093601 (PhRvL Homepage)
Publication Date:
03/2017
Origin:
APS
Abstract Copyright:
2017: American Physical Society
DOI:
10.1103/PhysRevLett.118.093601
Bibliographic Code:
2017PhRvL.118i3601C

Abstract

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

 

Title:
Cooperative Resonances in Light Scattering from Two-Dimensional Atomic Arrays
Authors:
Shahmoon, Ephraim; Wild, Dominik S.; Lukin, Mikhail D.; Yelin, Susanne F.
Publication:
Physical Review Letters, Volume 118, Issue 11, id.113601 (PhRvL Homepage)
Publication Date:
03/2017
Origin:
APS
Abstract Copyright:
2017: American Physical Society
DOI:
10.1103/PhysRevLett.118.113601
Bibliographic Code:
2017PhRvL.118k3601S

Abstract

We consider light scattering off a two-dimensional (2D) dipolar array and show how it can be tailored by properly choosing the lattice constant of the order of the incident wavelength. In particular, we demonstrate that such arrays can operate as a nearly perfect mirror for a wide range of incident angles and frequencies, and shape the emission pattern from an individual quantum emitter into a well-defined, collimated beam. These results can be understood in terms of the cooperative resonances of the surface modes supported by the 2D array. Experimental realizations are discussed, using ultracold arrays of trapped atoms and excitons in 2D semiconductor materials, as well as potential applications ranging from atomically thin metasurfaces to single photon nonlinear optics and nanomechanics.

 

Title:
Enantiomer-Specific State Transfer of Chiral Molecules
Authors:
Eibenberger, Sandra; Doyle, John; Patterson, David
Publication:
Physical Review Letters, Volume 118, Issue 12, id.123002 (PhRvL Homepage)
Publication Date:
03/2017
Origin:
APS
Abstract Copyright:
2017: American Physical Society
DOI:
10.1103/PhysRevLett.118.123002
Bibliographic Code:
2017PhRvL.118l3002E

Abstract

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

 


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