Colloquia & Seminars
  • CMTC Seminar
    Speaker Name: John Preskill

    Speaker Institution: Caltech

    Title: Fault-tolerant quantum gates for topological codes

    Abstract: TBD

    Host: Jay D. Sau

    http://www.physics.umd.edu/cmtc/seminars.html
    When: Thu, October 23, 2014 - 11:00am
    Where: 2205 Toll Physics Building
  • Applied Dynamics Seminar
    Speaker Name: Korana Burke

    Speaker Institution: UC-Davis

    Title: The Role of Geometric Structures in Chaotic Phase Space -- Ionization and Chaos Induced Energy Hopping from Mathematical Perspective

    Abstract : Humans interact with chaotic systems on everyday basis. Chaos plays a fundamental role on a wide span of length and time scales. Since it is hard to isolate a chaotic system from random interactions with the environment, the challenges in studying its behavior are both mathematical and experimental. In recent years, atomic gasses have emerged as experimentally accessible systems for observing chaos under controlled conditions. In this talk I will present the study of geometric structures in phase space that govern the chaotic transport in an atomic system. I will show how these results apply to understanding the chaotic ionization in Rydberg atoms. Theoretical results are based on the study of a homoclinic tangle and its corresponding turnstile. Understanding the relationship between the turnstile and the system parameters allows us to draw conclusions about the ionization process and to design the experiments for probing the structure of the chaotic phase space. Finally, I will present a set of recent results which show that this approach can be used to design an experimental protocol for nonadiabatic energy change of an electron ensemble.
    When: Thu, October 23, 2014 - 12:30pm
    Where: IREAP Large Conference Room, ERF 1207
  • Refreshments for CNAM Condensed Matter Colloquium

    When: Thu, October 23, 2014 - 1:30pm
    Where: physics room 1201, the "new" Toll Room
  • CNAM Condensed Matter Colloquium
    Speaker Name: Milton W. Cole, Department of Physics

    Speaker Institution: Penn State University

    Title: To wet or not to wet? That is the question!

    Abstract: If one looks at a leaf of a plant after a rain, one sees water droplets of varying sizes. What determines this behavior? The answer, known in principle for two centuries, involves the surface tension of the water itself, as well as surface tensions at the water-leaf interface. At the microscopic level, the “wetting” behavior depends on the interaction between two water molecules compared to that between a water molecule and the leaf.

    Understanding wetting is important for many technological applications, including adhesion, gas storage and separation and fluid flow in fine capillaries.

    My group has been studying the problem of wetting transitions on various surfaces. This transition is a two-dimensional analog of the familiar three-dimensional vapor-liquid transition, i.e. there is a line of first-order transitions in the P-T plane, ending with a critical point. The phenomenon can involve liquids as varied as superfluid helium, mercury and water, interacting with a wide variety of surfaces. The common characteristic is a very weak attractive interaction between the adsorbed molecules and the surface in question.

    Among the results presented will be evidence for the first wetting phase transition for water. We predicted this transition in 2004 and it was recently observed at UC Irvine [2,3]

    References:
    1. S. M. Gatica and M. W. Cole, "To wet or not to wet: that is the question", J. Low Temp. Phys., 157, 111-136 (2009)
    2. S. M. Gatica, Xiongce Zhao, J. K. Johnson and M. W. Cole, “Wetting transition of water on graphite and other surfaces”, J. Phys. Chem. B108, 11704-11708 (2004); Hye-Young Kim, Maria Cristina dos Santos and Milton W. Cole, Wetting transitions of water on graphite and graphene, J. Phys. Chem A118, 8237-8241 (2014)
    3. S. R. Friedman, M. Khalil and P. Taborek, Wetting transition in water, Phys. Rev. Lett. 111,226101 (2013)


    Host: T. Einstein
    When: Thu, October 23, 2014 - 2:00pm
    Where: physics room 1201
  • De Rham and Chevalley-Eilenberg cohomology, part 1
    Speaker: Paul Green (UMd)
    Abstract: We review the famous paper of Chevalley and Eilenberg on Lie algebra cohomology in Trans. Amer. Math. Soc. 63 (1948), http://www.ams.org/journals/tran/1948-063-01/S0002-9947-1948-0024908-8/S0002-9947-1948-0024908-8.pdf
    with a view toward understanding supersymmetric generalizations.
    When: Thu, October 23, 2014 - 3:30pm
    Where:
  • Materials Science and Engineering Seminar
    Speaker Name: Albert Davydov

    Speaker Institution : NIST

    Title : Low-Dimensional Semiconductors for Electronics, Sensors, and Energy

    Abstract : In addition to conventional thin film structures, 1D and 2D nanostructures such as semiconductor nanowires and graphene-like layers have attracted considerable attention due to their unique electronic, magnetic, optical, thermal and mechanical properties, complemented with superior structural quality and high surface-to-volume ratio. Nanowires and 2D layers represent nanoscale building blocks for on-chip integration for optoelectronic, sensor, and energy applications for portable ubiquitous electronics on flexible platforms.

    To realize new applications, the controlled fabrication of nanowires and 2D layers with defined geometries and electronic properties as well as their integration with planar device structures is required. This talk discusses fabrication and characterization of silicon and gallium nitride nanowire materials and devices, including single and arrayed nanowire transistors, chemical and bio- sensors, Li-ion batteries, and LEDs. A special case of developing periodic arrays of vertically aligned GaN core-shell nanostructures for p-i-n photodetectors, realized with a combination of top-down etch and subsequent chemical vapor deposition, is presented.

    The 2D research is illustrated by fabrication and testing of field-effect-transistors (FETs) composed of monolayer to few-layer MoS2 thin films, where device transport characteristics are governed by inter-layer coupling and electrically active surface states.
    When: Fri, October 24, 2014 - 1:00pm
    Where: Room 2108, Chemical and Nuclear Engineering Bldg
  • JQI Seminar
    Speaker Name: Donhee Ham

    Speaker Institution: Harvard

    Title: Manipulating light with mass of massless graphene electrons +

    Abstract: While one of the most celebrated physics of graphene is the behavior of its individual electrons as massless relativistic particles, they do exhibit mass when they move together, which is at the heart of graphene plasmonics. I will discuss our recent measurement of this mass of massless graphene electrons, and its application in ultra-subwavelength plasmonic devices at THz frequencies. And on a different topic, I will introduce our program for biomolecular NMR. NMR spectroscopy is one of the most powerful bio-analytical tools with its ability to elucidate 3D structure & function of bio molecules. Particularly, its use in structural biology and pharmaceutical screening has proven enormously fruitful. But it is inherently too slow while the workload of modern biology & medicine continues to increase. I will discuss our biomolecular NMR work using silicon chips and our vision to enable high-throughput biomolecular NMR.
    Host: James Williams
    When: Mon, October 27, 2014 - 11:00am
    Where: CSS 2400
  • EPT Seminar
    Title: Composite Higgs boson from top dynamics

    Speaker: Bogdan Dobrescu, Fermilab

    Abstract: The Higgs boson may be a composite particle, made of a top quark and a vectorlike quark. The binding should be non-confining, and may be provided by a new
    spontaneously-broken gauge interaction. I will show that the Higgs boon can arise as
    the pseudo Nambu-Goldstone boson of the chiral symmetry associated with the vector-like
    quark and the top quark. Its mass can be computed, and is consistent with the value of 125 GeV measured by the CMS and ATLAS collaborations.
    When: Mon, October 27, 2014 - 3:00pm
    Where: PSC 3150
  • Biophysics Seminar
    Speaker Name: Valeri Barsegov

    Speaker Institution : Barsegov

    Title: Fluctuating nonlinear spring model of mechanical deformation of biological particles

    Abstract : We present a new theory for modeling spectral lineshapes available from single-particle forced indentation experiments. The theory considers weakly non-linear Hertzian deformation due to a physical contact between the indenter and the biological particle, and bending deformations of other portions of the particle structure modeled as ‘vertical beams’. The bending of beams beyond the critical point sets in the particle dynamic transition to the collapsed state, an extreme event leading to the catastrophic force drop as observed in the force (F)-deformation (X) spectra (FX curves).
    The theory interprets fine features of the spectra, i.e. the slope of the FX curves and the force-peak signal, in terms of mechanical characteristics such as the Young’s moduli for Hertzian and bending deformations, and the Weibull probability distribution of the maximum strength with the scale parameter and shape parameter. The theory is applied to model the FX curves for several spherically shaped virus particles – CCMV, TrV, and AdV.
    When: Mon, October 27, 2014 - 4:00pm
    Where: 0112 Chemistry Building
  • CMTC Seminar
    Speaker Name: Kun Yang

    Speaker Institution: NHMFL & Florida State University

    Title: Entanglement Scaling Laws and Eigenstate Thermalization in Many-Particle Systems

    Abstract: Entanglement is perhaps the most counter-intuitive aspect of quantum mechanics, and provides the sharpest distinction between quantum and classical descriptions of nature. The most widely used measure of entanglement is the entanglement entropy. For extended quantum systems, ground states of local Hamiltonians are expected to follow the so called “area law”, which states that the entanglement entropy is proportional to the surface area of the subsystem. However, violations of the area law do exist, and it is important to understand their origin. In 1D they are found to be associated with quantum criticality. Until recently the only established examples of such violation in higher dimensions are free fermion ground states with Fermi surfaces, where it is found that the area law is enhanced by a logarithmic factor. In Ref. [1], we use multi-dimensional bosonization to provide a simple derivation of this result, show that the logarithimic factor has a 1D origin. More importantly the bosonization technique allows us to take into account the Fermi liquid interactions, and obtain the leading scaling behavior of the entanglement entropy of Fermi liquids. The central result of our work is that Fermi liquid interactions do not alter the leading scaling behavior of the entanglement entropy, and the logarithmic enhancement of area law is a robust property of the Fermi liquid phase.

    In sharp contrast to the fermioic systems with Fermi surfaces, quantum critical (or gapless) bosonic systems do not violate the area law above 1D (except for the case discussed below). The fundamental difference lies in the fact that gapless excitations live near a single point (usually origin of momentum space) in such bosonic systems, while they live around an (extended) Fermi surface in Fermi liquids. In Ref. [2], we studied entanglement properties of some specific examples of the so called Bose metal states, in which bosons neither condense (and become a superfluid) nor localize (and insulate) at T=0. The system supports gapless excitations around ``Bose surfaces", instead of isolated points in momentum space. We showed that similar to free Fermi gas and Fermi liquids, these states violate the entanglement area law in a logarithmic fashion. Our results demonstrate that perhaps area-law violation in high dimensions is more common than previously thought; in particular the existence of Fermi surface(s) is not a prerequisite for it.

    Compared to ground states, much less is known concretely about entanglement in (highly) excited states. Going back to free fermion systems, in [3] we show that there exists a duality relation between ground and excited states, and the area law obeyed by ground state turns into a volume law for excited states, something that is widely expected but very hard to prove. Most importantly, we find in appropriate limits the reduced density matrix of a subsystem takes the form of thermal density matrix, providing an explicit example of the eigenstate thermalization hypothesis. Our work [3] explicitly demonstrates how statistical physics emerges from entanglement in a single eigenstate.

    [1] Entanglement Entropy of Fermi Liquids via Multi-dimensional Bosonization, Wenxin Ding, Alexander Seidel, Kun Yang, Phys. Rev. X 2, 011012 (2012).

    [2] Violation of Entanglement-Area Law in Bosonic Systems with Bose Surfaces: Possible Application to Bose Metals, Hsin-Hua Lai, Kun Yang, N. E. Bonesteel, Phys. Rev. Lett. 111, 210402 (2013).

    [3] Entanglement entropy scaling laws and eigenstate thermalization in free fermion systems, Hsin-Hua Lai, Kun Yang, arXiv:1409.1224.

    Host: Bitan Roy

    http://www.physics.umd.edu/cmtc/seminars.html
    When: Tue, October 28, 2014 - 11:00am
    Where: 2205 Toll Physics Building
  • Physics Colloquium

    When: Tue, October 28, 2014 - 4:00pm
    Where: PSC Lobby
  • CMTC Seminar
    Speaker Name: Brian Swingle

    Speaker Institution: Stanford

    Title: Renormalization Group Constructions of Topological Quantum Liquids

    Abstract: I will discuss recent work with John McGreevy (1407.8203) on constructing ground state wavefunctions of general gapped Hamiltonians using a renormalization group approach. The formalism provides a number of results including a partial proof of the area law for entanglement entropy, efficient tensor network representations for wavefunctions, a definition of short- and long-range entanglement, and a classification scheme which we conjecture applies to all gapped phases. A special role is played by what we call topological quantum liquids which are gapped phases that are insensitive to the "shape" of space (like quantum Hall fluids).

    Host: Jay D. Sau

    http://www.physics.umd.edu/cmtc/seminars.html
    When: Thu, October 30, 2014 - 11:00am
    Where: 2205 Toll Physics Building
  • Applied Dynamics Seminar
    Speaker Name: Andrey Vilesov

    Speaker Institution : USC, Dept of Chemistry

    Title: X-ray diffraction imaging of quantum vortices in superfluid He droplets
    When: Thu, October 30, 2014 - 12:30pm
    Where: IREAP Large Conference Room, ERF 1207
  • Refreshments for CNAM Cond. Matter Colloquium

    When: Thu, October 30, 2014 - 1:30pm
    Where: physics room 1305F, the "new" Toll Room
  • CNAM Condensed Matter Colloquium
    Speaker: Dr. Mike Lilly, Sandia National Lab

    Title and Abstract: TBD
    When: Thu, October 30, 2014 - 2:00pm
    Where: physics room 1201
  • JQI Special Seminar
    Speaker Name: Kartik Srinivasan

    Speaker Institution: NIST

    Title: Quantum frequency conversion and nanocavity optomechanics”.

    Abstract to follow

    Host: Luis Orozco
    When: Mon, November 3, 2014 - 11:00am
    Where: CSS 2400
  • EPT Seminar
    Title: LHC phenomenology of exotic fermions

    Speaker: Tanumoy Mandal, HRI

    Abstract: Many BSM extensions predict the existence of exotic fermions near the
    TeV scale. I will discuss the LHC phenomenology of such heavy exotic
    fermions, namely the vectorlike quarks that arise in various warped
    extra dimensional theories and the color octet electrons which appear
    in some quark-lepton compositeness models. In this regard, I will
    present a generic coupling extraction method with a toy example of
    exotic b' and a generic combined search strategy in the context of
    color octet electron.
    When: Mon, November 3, 2014 - 3:00pm
    Where: PSC 3150
  • Space and Cosmic Ray Physics Seminar
    Speaker Name: Daniel Berdichevsky

    Speaker Institution: Goddard Space Flight Center

    Title: On a few properties of very dilute matter frozen in space magnetic fields

    Abstract: For a case study, the flux-rope (FR) that passed Earth on June 2, 2014 (1) (see also listing of magnetic clouds and their properties in the Wind SC MFI science team site at http://wind.gsfc.nasa.gov/mfi/mag_cloud_S1.html), we proceed to interpret plasma and magnetic field observations in the context of MHD. The observations used are 3s average interplanetary magnetic field (Wind/MFI instrument) and 3s plasma (Wind/SWE instruments) data (2). After identifying the observed correlation between electron density, temperature and pressure in the plasma frame of reference we proceed to establish the existence of a relationship between these plasma observables with the magnetic field pressure. By assuming ideal MHD conditions to be valid we proceed to confirm that the medium is diamagnetic, as is to be expected for the MHD state of matter and magnetic field which is assumed to be a superconducting medium. Additionally we infer the presence of magnetization work, as well as a few other constitutive properties of this state of matter.

    (1) Berdichevsky D. B., R. P. Lepping, and C. J. Farrugia, Geometric considerations of the evolution of magnetic flux ropes, Phys. Rev. E67, doi:10.1103/PhysRevE.036405. Lepping R. P. et al, A summary of Wind magnetic clouds for years 1995 – 2003: model-fitted parameters, associated errors and classifications, Ann. Geophysicae, 24, 215-245, 2006.

    (2) Ogilvie, K. W., et al, SWE, A comprehensive plasma instrument for the Wind spacecraft, Space Sci. Rev., 71, 55 – 77, 1995; Lepping R. P., et al , The Wind Magnetic Field Investigation, Space Sci. Rev., 71, 207 – 229, 1995.

    Notes: Coffee, Tea & Cookies 4:15-4:30 PM
    When: Mon, November 3, 2014 - 4:30pm
    Where: CSS Room 2400
  • CMTC Seminar
    Speaker Name: Titus Neupert

    Speaker Institution: Princeton

    Title: Interacting surface states of three-dimensional topological insulators

    Abstract: The surface states of three-dimensional topological insulators are celebrated for their robustness against perturbations, provided that time-reversal symmetry and particle number conservation are not violated. In my talk, I want to survey their possible phases in the limit where interactions between the surface electrons are strong. To that end, I choose a spherical topological insulator geometry to make the surface amenable to numerical studies of finite size systems. In this case, the single-particle problem maps to that of Landau orbitals on the sphere with a magnetic monopole at the center that has unit strength and opposite sign for electrons with opposite spin.

    Restricting the single particle Hilbert space to the small region in the surface Brillouin zone that is covered by the surface Dirac cone enforces a nontrivial quantum geometry on the problem, resulting in distinct real-space localization properties of the electron orbitals. Assuming density-density contact interactions, we find superconducting and anomalous (quantum) Hall phases for attractive and repulsive interactions, respectively. Our setup is ideally adapted to the search for recently proposed topologically ordered surface terminations that could be microscopically stabilized by tailored surface interaction profiles.

    Host: Philip Brydon

    http://www.physics.umd.edu/cmtc/seminars.html
    When: Tue, November 4, 2014 - 11:00am
    Where: 2205 Toll Physics Building
  • Physics Colloquium
    Speaker Name: Steve Kivelson

    Speaker Institution: Stanford University

    Title: Quenched Disorder and Vestigial Nematicity

    Abstract:
    When: Tue, November 4, 2014 - 4:00pm
    Where: PSC Lobby
 

Department of Physics


University of Maryland
College Park, MD 20742-4111
Phone: 301.405.3401
Fax: 301.314.9525