# Faculty Publications: September, 2017

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

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

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Title: |
Braiding statistics and link invariants of bosonic/fermionic topological quantum matter in 2+1 and 3+1 dimensions | |

Authors: |
Putrov, Pavel; Wang, Juven; Yau, Shing-Tung | |

Publication: |
Annals of Physics, Volume 384, p. 254-287. | |

Publication Date: |
09/2017 | |

Origin: |
ELSEVIER | |

Abstract Copyright: |
(c) 2017 Elsevier Inc. | |

DOI: |
10.1016/j.aop.2017.06.019 | |

Bibliographic Code: |
2017AnPhy.384..254P |

### Abstract

Topological Quantum Field Theories (TQFTs) pertinent to some emergent low energy phenomena of condensed matter lattice models in 2+1 and 3+1 dimensions are explored. Many of our TQFTs are highly-interacting without free quadratic analogs. Some of our bosonic TQFTs can be regarded as the continuum field theory formulation of Dijkgraaf-Witten twisted discrete gauge theories. Other bosonic TQFTs beyond the Dijkgraaf-Witten description and all fermionic TQFTs (namely the spin TQFTs) are either higher-form gauge theories where particles must have strings attached, or fermionic discrete gauge theories obtained by gauging the fermionic Symmetry-Protected Topological states (SPTs). We analytically calculate both the Abelian and non-Abelian braiding statistics data of anyonic particle and string excitations in these theories, where the statistics data can one-to-one characterize the underlying topological orders of TQFTs. Namely, we derive path integral expectation values of links formed by line and surface operators in these TQFTs. The acquired link invariants include not only the familiar Aharonov-Bohm linking number, but also Milnor triple linking number in 3 dimensions, triple and quadruple linking numbers of surfaces, and intersection number of surfaces in 4 dimensions. We also construct new spin TQFTs with the corresponding knot/link invariants of Arf(-Brown-Kervaire), Sato-Levine and others. We propose a new relation between the fermionic SPT partition function and the Rokhlin invariant. As an example, we can use these invariants and other physical observables, including ground state degeneracy, reduced modular Sxy and Txy matrices, and the partition function on RP3 manifold, to identify all ν ∈Z8 classes of 2+1 dimensional gauged Z2-Ising-symmetric Z2f -fermionic Topological Superconductors (realized by stacking ν layers of a pair of chiral and anti-chiral p-wave superconductors [ p + ip and p - ip], where boundary supports non-chiral Majorana-Weyl modes) with continuum spin-TQFTs.

Title: |
Differential Zeros of Certain Special Functions | |

Authors: |
Chen, Jingyue; Huang, An; Lian, Bong H.; Yau, Shing-Tung | |

Publication: |
eprint arXiv:1709.00713 | |

Publication Date: |
09/2017 | |

Origin: |
ARXIV | |

Keywords: |
Mathematics - Algebraic Geometry | |

Comment: |
33 pages, minor corrections made | |

Bibliographic Code: |
2017arXiv170900713C |

### Abstract

In this paper, we study the zero loci of local systems of the form $\delta\Pi$, where $\Pi$ is the period sheaf of the universal family of CY hypersurfaces in a suitable ambient space $X$, and $\delta$ is a given differential operator on the space of sections $V^\vee=\Gamma(X,K_X^{-1})$. Using earlier results of three of the authors and their collaborators, we give several different descriptions of the zero locus of $\delta\Pi$. As applications, we prove that the locus is algebraic and in some cases, non-empty. We also give an explicit way to compute the polynomial defining equations of the locus in some cases. This description gives rise to a natural stratification to the zero locus.

Title: |
Observation of three-photon bound states in a quantum nonlinear medium | |

Authors: |
Liang, Qi-Yu; Venkatramani, Aditya V.; Cantu, Sergio H.; Nicholson, Travis L.; Gullans, Michael J.; Gorshkov, Alexey V.; Thompson, Jeff D.; Chin, Cheng; Lukin, Mikhail D.; Vuletic, Vladan | |

Publication: |
eprint arXiv:1709.01478 | |

Publication Date: |
09/2017 | |

Origin: |
ARXIV | |

Keywords: |
Physics - Atomic Physics, Quantum Physics | |

Bibliographic Code: |
2017arXiv170901478L |

### Abstract

Bound states of massive particles, such as nuclei, atoms or molecules, are ubiquitous in nature and constitute the bulk of the visible world around us. In contrast, photons typically only weakly influence each other due to their very weak interactions and vanishing mass. We report the observation of traveling three-photon bound states in a quantum nonlinear medium where the interactions between photons are mediated by atomic Rydberg states. In particular, photon correlation and conditional phase measurements reveal the distinct features associated with three-photon and two-photon bound states. Such photonic trimers and dimers can be viewed as quantum solitons with shape-preserving wavefunctions that depend on the constituent photon number. The observed bunching and strongly nonlinear optical phase are quantitatively described by an effective field theory (EFT) of Rydberg-induced photon-photon interactions, which demonstrates the presence of a substantial effective three-body force between the photons. These observations pave the way towards the realization, studies, and control of strongly interacting quantum many-body states of light.

Title: |
Theory of excitation of Rydberg polarons in an atomic quantum gas | |

Authors: |
Schmidt, R.; Whalen, J. D.; Ding, R.; Camargo, F.; Woehl, G., Jr.; Yoshida, S.; Burgdorfer, J.; Dunning, F. B.; Demler, E.; Sadeghepour, H. R.; Killian, T. C. | |

Publication: |
eprint arXiv:1709.01838 | |

Publication Date: |
09/2017 | |

Origin: |
ARXIV | |

Keywords: |
Physics - Atomic Physics, Condensed Matter - Quantum Gases | |

Comment: |
14 pages, 9 figures. arXiv admin note: substantial text overlap with arXiv:1706.03717 | |

Bibliographic Code: |
2017arXiv170901838S |

### Abstract

We present a quantum many-body description of the excitation spectrum of Rydberg polarons in a Bose gas. The many-body Hamiltonian is solved with functional determinant theory, and we extend this technique to describe Rydberg polarons of finite mass. Mean-field and classical descriptions of the spectrum are derived as approximations of the many-body theory. The various approaches are applied to experimental observations of polarons created by excitation of Rydberg atoms in a strontium Bose-Einstein condensate.

Title: |
E-String Theory on Riemann Surfaces | |

Authors: |
Kim, Hee-Cheol; Razamat, Shlomo S.; Vafa, Cumrun; Zafrir, Gabi | |

Publication: |
eprint arXiv:1709.02496 | |

Publication Date: |
09/2017 | |

Origin: |
ARXIV | |

Keywords: |
High Energy Physics - Theory | |

Comment: |
85 pages, 25 figures, harvmac | |

Bibliographic Code: |
2017arXiv170902496K |

### Abstract

We study compactifications of the 6d E-string theory, the theory of a small E_8 instanton, to four dimensions. In particular we identify N=1 field theories in four dimensions corresponding to compactifications on arbitrary Riemann surfaces with punctures and with arbitrary non-abelian flat connections as well as fluxes for the abelian sub-groups of the E_8 flavor symmetry. This sheds light on emergent symmetries in a number of 4d N=1 SCFTs (including the `E7 surprise' theory) as well as leads to new predictions for a large number of 4-dimensional exceptional dualities and symmetries.

Title: |
TASI Lectures on Collider Physics | |

Authors: |
Schwartz, Matthew D. | |

Publication: |
eprint arXiv:1709.04533 | |

Publication Date: |
09/2017 | |

Origin: |
ARXIV | |

Keywords: |
High Energy Physics - Phenomenology | |

Comment: |
33 pages | |

Bibliographic Code: |
2017arXiv170904533S |

### Abstract

These lectures provide an introduction to the physics of particle colliders. Topics covered include a quantitative examination of the design and operational parameters of Large Hadron Collider, kinematics and observables at colliders, such as rapidity and transverse mass, and properties of distributions, such as Jacobian peaks. In addition, the lectures provide a practical introduction to the decay modes and signatures of important composite and elementary and particles in the Standard Model, from pions to the Higgs boson. The aim of these lectures is provide a bridge between theoretical and experimental particle physics. Whenever possible, results are derived using intuitive arguments and estimates rather than precision calculations.

Title: |
Critical behavior of an impurity at the boson superfluid-Mott insulator transition | |

Authors: |
Whitsitt, Seth; Sachdev, Subir | |

Publication: |
eprint arXiv:1709.04919 | |

Publication Date: |
09/2017 | |

Origin: |
ARXIV | |

Keywords: |
Condensed Matter - Quantum Gases, High Energy Physics - Theory | |

Comment: |
25 pages, 4 figures | |

Bibliographic Code: |
2017arXiv170904919W |

### Abstract

We present a universal theory for the critical behavior of an impurity at the two-dimensional superfluid-Mott insulator transition. Our analysis is motivated by a numerical study of the Bose-Hubbard model with an impurity site by Huang et al. (Phys. Rev. B 94, 220502 (2016)), who found an impurity phase transition as a function of the trapping potential. The bulk theory is described by the $O(2)$ symmetric Wilson-Fisher conformal field theory, and we model the impurity by a localized spin-1/2 degree of freedom. We also consider a generalized model by considering an $O(N)$ symmetric bulk theory coupled to a spin-$S$ degree of freedom. We study this field theory using the $\epsilon = 3 - d$ expansion, where the impurity-bulk interaction flows to an infrared stable fixed point at the critical trapping potential. We determine the scaling dimensions of the impurity degree of freedom and the associated critical exponents near the critical point. We also determine the universal contribution of the impurity to the finite temperature compressibility of the system at criticality. Our results are compared with recent numerical simulations.

Title: |
Double light-cone dynamics establish thermal states in integrable 1D Bose gases | |

Authors: |
Langen, Tim; Schweigler, Thomas; Demler, Eugene; Schmiedmayer, Jörg | |

Publication: |
eprint arXiv:1709.05994 | |

Publication Date: |
09/2017 | |

Origin: |
ARXIV | |

Keywords: |
Condensed Matter - Quantum Gases, Condensed Matter - Statistical Mechanics, Quantum Physics | |

Comment: |
8 pages + 3 page appendix | |

Bibliographic Code: |
2017arXiv170905994L |

### Abstract

We theoretically investigate the non-equilibrium dynamics in a quenched pair of 1D Bose gases with density imbalance. We describe the system using its low-energy effective theory, the Luttinger liquid model. In this framework the system shows strictly integrable relaxation dynamics via dephasing of its approximate many-body eigenstates. In the balanced case, this leads to the well-known light-cone-like establishment of a prethermalized state, which can be described by a generalized Gibbs ensemble. In the imbalanced case the integrable dephasing leads to a state that, counter-intuitively, closely resembles a thermal equilibrium state. The approach to this state is characterized by two separate light-cone dynamics with distinct characteristic velocities. This behavior is rooted in the fact that in the imbalanced case observables are not aligned with the conserved quantities of the integrable system. We discuss a concrete experimental realization to study this effect using matterwave interferometry and many-body revivals on an atom chip.

Title: |
Experimental Targets for Photon Couplings of the QCD Axion | |

Authors: |
Agrawal, Prateek; Fan, JiJi; Reece, Matthew; Wang, Lian-Tao | |

Publication: |
eprint arXiv:1709.06085 | |

Publication Date: |
09/2017 | |

Origin: |
ARXIV | |

Keywords: |
High Energy Physics - Phenomenology, High Energy Physics - Experiment | |

Bibliographic Code: |
2017arXiv170906085A |

### Abstract

The QCD axion's coupling to photons is often assumed to lie in a narrow band as a function of the axion mass. We demonstrate that several simple mechanisms, in addition to the photophilic clockwork axion already in the literature, can significantly extend the allowed range of couplings. Some mechanisms we present generalize the KNP alignment scenario, widely studied as a model of inflation, to the phenomenology of a QCD axion. In particular we present new KSVZ-like realizations of two-axion KNP alignment and of the clockwork mechanism. Our "confinement tower" realization of clockwork may prove useful in a variety of model-building contexts. We also show that kinetic mixing of the QCD axion with a lighter axion-like particle can dramatically alter the QCD axion's coupling to photons, differing from the other models we present by allowing non-quantized couplings. The simple models that we present fully cover the range of axion-photon couplings that could be probed by experiments. They motivate growing axion detection efforts over a wide space of masses and couplings.

Title: |
Fragile Topology and Wannier Obstructions | |

Authors: |
Po, Hoi Chun; Watanabe, Haruki; Vishwanath, Ashvin | |

Publication: |
eprint arXiv:1709.06551 | |

Publication Date: |
09/2017 | |

Origin: |
ARXIV | |

Keywords: |
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science, Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory | |

Comment: |
(5.5+3) pages; 3 figures; 2 tables | |

Bibliographic Code: |
2017arXiv170906551P |

### Abstract

Topological phases, such as Chern insulators, are defined in terms of additive indices that are stable against the addition of trivial degrees of freedom. Also, such topology presents an obstruction to representing bands in terms of symmetric, exponentially localized Wannier functions. Here, we address the converse question: Do obstructions to Wannier representations imply stable band topology? We answer this in the negative, pointing out that some bands can also display a distinct type of "fragile topology." Bands with fragile topology admit a Wannier representation if and only if additional trivial degrees of freedom are supplied. We apply this notion to solve a puzzle in diagnosing band topology: A recent work [Nature 547, 298-305 (2017)] made the intriguing suggestion that whenever a so-called "elementary band representation" splits, the two sets of bands, separated by a band gap, are individually topological. Here, we construct a counterexample, defined on the honeycomb lattice, which features a split elementary band. We show that one of the two disconnected bands is completely trivial with exponentially localized, symmetric Wannier functions. This presents a conundrum regarding the nature of the second band, which is resolved by recognizing that it is topological, but in the fragile sense. Our model thus provides a physical example of fragile topology.

Title: |
Electronic Structure Theory of Strained Two-Dimensional Materials | |

Authors: |
Fang, Shiang; Carr, Stephen; Shen, Jiayu; Cazalilla, Miguel A.; Kaxiras, Efthimios | |

Publication: |
eprint arXiv:1709.07510 | |

Publication Date: |
09/2017 | |

Origin: |
ARXIV | |

Keywords: |
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science | |

Comment: |
2 figures; the code for generating the strain TMDC Hamiltonians will be available on the research group website | |

Bibliographic Code: |
2017arXiv170907510F |

### Abstract

We derive electronic tight-binding Hamiltonians for strained graphene, hexagonal boron nitride and transition metal dichalcogenides based on Wannier transformation of {\it ab initio} density functional theory calculations. Our microscopic models include strain effects to leading order that respect the crystal symmetry and local crystal configuration, and are beyond the central force approximation which assumes only pair-wise distance dependence. Based on these models, we also derive and analyze the effective low-energy k $\cdot$ p Hamiltonians. Our {\it ab initio} approaches complement the symmetry group representation construction for such effective low-energy Hamiltonians and provide the values of the coefficients for each symmetry-allowed term. These models are relevant for the design of electronic device applications, since they provide the framework for describing the coupling of electrons to other degrees of freedom including phonons, spin and the electromagnetic field. The models can also serve as the basis for exploring the physics of many-body systems of interesting quantum phases.

Title: |
A Realization of Thurstons Geometrization: Discrete Ricci Flow with Surgery | |

Authors: |
Alsing, Paul M.; Miller, Warner A.; Yau, Shing-Tung | |

Publication: |
eprint arXiv:1709.08494 | |

Publication Date: |
09/2017 | |

Origin: |
ARXIV | |

Keywords: |
Mathematics - Differential Geometry, General Relativity and Quantum Cosmology | |

Comment: |
8 pages, 6 figures. arXiv admin note: text overlap with arXiv:1308.4148 | |

Bibliographic Code: |
2017arXiv170908494A |

### Abstract

Hamilton's Ricci flow (RF) equations were recently expressed in terms of a sparsely-coupled system of autonomous first-order nonlinear differential equations for the edge lengths of a d-dimensional piecewise linear (PL) simplicial geometry. More recently, this system of discrete Ricci flow (DRF) equations was further simplified by explicitly constructing the Forman-Ricci tensor associated to each edge, thereby diagonalizing the first-order differential operator and avoiding the need to invert large sparse matrices at each time step. We recently showed analytically and numerically that these equations converge for axisymmetric 3-geometries to the corresponding continuum RF equations. We demonstrate here that these DRF equations yield an explicit numerical realization of Thurston's geometrization procedure for a discrete 3D axially-symmetric neckpinch geometry by using surgery to explicitly integrate through its Type-1 neck pinch singularity. A cubic-spline-based adaptive mesh was required to complete the evolution. Our numerically efficient simulations yield the expected Thurston decomposition of the sufficiently pinched axially symmetric geometry into its unique geometric structure -- a direct product of two lobes, each collapsing toward a 3-sphere geometry. The structure of our curvature may be used to better inform one of the vertex and edge weighting factors that appear in the Forman's expression of Ricci curvature on graphs.

Title: |
Further studies of the notion of differentiable maps from Azumaya/matrix supermanifolds I. The smooth case: Ramond-Neveu-Schwarz and Green-Schwarz meeting Grothendieck | |

Authors: |
Liu, Chien-Hao; Yau, Shing-Tung | |

Publication: |
eprint arXiv:1709.08927 | |

Publication Date: |
09/2017 | |

Origin: |
ARXIV | |

Keywords: |
Mathematics - Differential Geometry, High Energy Physics - Theory, Mathematics - Algebraic Geometry, Mathematics - Symplectic Geometry, 58A40, 14A22, 81T30, 51K10, 16S50, 46L87 | |

Comment: |
38+2 pages; 3 figures | |

Bibliographic Code: |
2017arXiv170908927L |

### Abstract

In this sequel to works D(11.1) (arXiv:1406.0929 [math.DG]), D(11.2) (arXiv:1412.0771 [hep-th]), and D(11.3.1) (arXiv:1508.02347 [math.DG]), we re-examine --- and reformulate when in need --- several basic notions in super $C^{\infty}$-algebraic geometry as guided by the mathematical formulation of Ramond-Neveu-Schwarz fermionic strings and of Green-Schwarz fermionic strings from the viewpoint of Grothendieck on Algebraic Geometry. Two theorems that are the super counterpart of Theorem~3.1.1 and Theorem~3.2.1 of D(11.3.1) are proved. They unify the notion of "smooth maps from an Azumaya/matrix super smooth manifold with a fundamental module to a super smooth manifold" introduced in D(11.2), making it a complete super parallel to the setting for D-branes in the realm of algebraic geometry in D(1) (arXiv:0709.1515 [math.AG]) and D(2) (arXiv:0809.2121 [math.AG]), and in the realm of differential or $C^{\infty}$-algebraic geometry in D(11.1) and D(11.3.1). A prototypical definition of dynamical fermionic stacked D-brane world-volume on a space-time in the same spirit of RNS fermionic strings or GS fermionic strings is thus laid down. Similar to D(11.3.1), which paved the path to the construction of non-Abelian Dirac-Born-Infeld action (D(13.1) (arXiv:1606.08529 [hep-th])) and the standard action (D(13.3) (arXiv:1704.03237 [hep-th])) for fundamental bosonic stacked D-branes, the current notes shall serve the same for the construction of supersymmetric action for fundamental fermionic stacked D-branes of various dimensions --- a theme of another subseries of the D-project. A notion of "noncommutative $C^{\infty}$-rings" and "morphism" between them is introduced at the end as a byproduct.

Title: |
Selective final state spectroscopy and multifractality in two-component ultracold Bose-Einstein condensates: a numerical study | |

Authors: |
Antal Werner, Miklós; Demler, Eugene; Aspect, Alain; Zaránd, Gergely | |

Publication: |
eprint arXiv:1709.08993 | |

Publication Date: |
09/2017 | |

Origin: |
ARXIV | |

Keywords: |
Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Quantum Gases | |

Bibliographic Code: |
2017arXiv170908993A |

### Abstract

We propose to use the method introduced by Volchkov et al., based on state dependent disordered ultracold bosons, to address the critical state at the mobility edge of the Anderson localization transition, and to observe its intriguing multifractal structure. An optimally designed external radio frequency pulse can be applied to generate transitions to eigenstates in a narrow energy window close to the mobility edge, where critical scaling and multifractality emerge. Two-photon laser scanning microscopy will be used to address individual localized states even close to the transition. The projected image of the cloud is shown to inherit multifractality and to display universal density correlations. Time of flight images of the excited states are predicted to show interference fringes in the localized phase, while they allow one to map equal energy surfaces deep in the metallic phase.

Title: |
Identification and rejection of pile-up jets at high pseudorapidity with the ATLAS detector | |

Authors: |
Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2856 coauthors | |

Publication: |
The European Physical Journal C, Volume 77, Issue 9, article id. #580, 32 pp. (EPJC Homepage) | |

Publication Date: |
09/2017 | |

Origin: |
SPRINGER | |

Abstract Copyright: |
(c) 2017: CERN for the benefit of the ALICE collaboration | |

DOI: |
10.1140/epjc/s10052-017-5081-5 | |

Bibliographic Code: |
2017EPJC...77..580A |

### Abstract

The rejection of forward jets originating from additional proton-proton interactions (pile-up) is crucial for a variety of physics analyses at the LHC, including Standard Model measurements and searches for physics beyond the Standard Model. The identification of such jets is challenging due to the lack of track and vertex information in the pseudorapidity range |η |>2.5. This paper presents a novel strategy for forward pile-up jet tagging that exploits jet shapes and topological jet correlations in pile-up interactions. Measurements of the per-jet tagging efficiency are presented using a data set of 3.2 fb^{-1} of proton-proton collisions at a centre-of-mass energy of 13 {TeV} collected with the ATLAS detector. The fraction of pile-up jets rejected in the range 2.5<|η |<4.5 is estimated in simulated events with an average of 22 interactions per bunch-crossing. It increases with jet transverse momentum and, for jets with transverse momentum between 20 and 50 GeV, it ranges between 49% and 67% with an efficiency of 85% for selecting hard-scatter jets. A case study is performed in Higgs boson production via the vector-boson fusion process, showing that these techniques mitigate the background growth due to additional proton-proton interactions, thus enhancing the reach for such signatures.

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: |
Journal of Cosmology and Astroparticle Physics, Issue 09, article id. 003 (2017). (JCAP Homepage) | |

Publication Date: |
09/2017 | |

Origin: |
IOP | |

DOI: |
10.1088/1475-7516/2017/09/003 | |

Bibliographic Code: |
2017JCAP...09..003K |

### 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 provide 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 2ΔlnScript L=12 with respect to the standard Λ cold dark matter (ΛCDM) model when only CMB, BAO, and LSS data are considered, the inclusion of Lyman-alpha data reduces the improvement of the fit to 2ΔlnScript L=6 relative to ΛCDM . 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, Δ Nfluid, will be improved by an order of magnitude compared to current bounds.

Title: |
Pretty good quantum state transfer in symmetric spin networks via magnetic field | |

Authors: |
Kempton, Mark; Lippner, Gabor; Yau, Shing-Tung | |

Publication: |
Quantum Information Processing, Volume 16, Issue 9, article id.210, 23 pp. | |

Publication Date: |
09/2017 | |

Origin: |
SPRINGER | |

Keywords: |
State transfer, Magnetic field, Symmetric spin network | |

Abstract Copyright: |
(c) 2017: Springer Science+Business Media, LLC | |

DOI: |
10.1007/s11128-017-1658-z | |

Bibliographic Code: |
2017QuIP...16..210K |

### Abstract

We study pretty good single-excitation quantum state transfer (i.e., state transfer that becomes arbitrarily close to perfect) between particles in symmetric spin networks, in the presence of an energy potential induced by a magnetic field. In particular, we show that if a network admits an involution that fixes at least one node or at least one link, then there exists a choice of potential on the nodes of the network for which we get pretty good state transfer between symmetric pairs of nodes. We show further that in many cases, the potential can be chosen so that it is only nonzero at the nodes between which we want pretty good state transfer. As a special case of this, we show that such a potential can be chosen on the endpoints of a spin chain to induce pretty good state transfer in chains of any length. This is in contrast to the result of Kempton et al. (Quantum Inf Comput 17(3):303-327, 2017), in which the authors show that there cannot be perfect state transfer in chains of length 4 or more, no matter what potential is chosen.

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: |
The Astronomical Journal, Volume 154, Issue 4, article id. 132, 24 pp. (2017). (AJ Homepage) | |

Publication Date: |
10/2017 | |

Origin: |
IOP | |

Astronomy Keywords: |
catalogs, globular clusters: individual: M2, methods: data analysis, methods: statistical | |

DOI: |
10.3847/1538-3881/aa8565 | |

Bibliographic Code: |
2017AJ....154..132P |

### 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 mag 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 mag. We also present an algorithm for reducing this catalog ensemble to a condensed catalog that is similar to a traditional catalog, except that 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 Survey Telescope era.

Title: |
Pretty good quantum state transfer in symmetric spin networks via magnetic field | |

Authors: |
Kempton, Mark; Lippner, Gabor; Yau, Shing-Tung | |

Publication: |
Quantum Information Processing, Volume 16, Issue 9, article id.210, 23 pp. | |

Publication Date: |
09/2017 | |

Origin: |
SPRINGER | |

Keywords: |
State transfer, Magnetic field, Symmetric spin network | |

Abstract Copyright: |
(c) 2017: Springer Science+Business Media, LLC | |

DOI: |
10.1007/s11128-017-1658-z | |

Bibliographic Code: |
2017QuIP...16..210K |

### Abstract

We study pretty good single-excitation quantum state transfer (i.e., state transfer that becomes arbitrarily close to perfect) between particles in symmetric spin networks, in the presence of an energy potential induced by a magnetic field. In particular, we show that if a network admits an involution that fixes at least one node or at least one link, then there exists a choice of potential on the nodes of the network for which we get pretty good state transfer between symmetric pairs of nodes. We show further that in many cases, the potential can be chosen so that it is only nonzero at the nodes between which we want pretty good state transfer. As a special case of this, we show that such a potential can be chosen on the endpoints of a spin chain to induce pretty good state transfer in chains of any length. This is in contrast to the result of Kempton et al. (Quantum Inf Comput 17(3):303-327, 2017), in which the authors show that there cannot be perfect state transfer in chains of length 4 or more, no matter what potential is chosen.

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: |
The Astronomical Journal, Volume 154, Issue 4, article id. 132, 24 pp. (2017). (AJ Homepage) | |

Publication Date: |
10/2017 | |

Origin: |
IOP | |

Astronomy Keywords: |
catalogs, globular clusters: individual: M2, methods: data analysis, methods: statistical | |

DOI: |
10.3847/1538-3881/aa8565 | |

Bibliographic Code: |
2017AJ....154..132P |

### 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 mag 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 mag. We also present an algorithm for reducing this catalog ensemble to a condensed catalog that is similar to a traditional catalog, except that 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 Survey Telescope era.

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