Colloquia & Seminars
  • JQI Special Seminar
    Speaker Name: Dr. André Eckardt

    Speaker Institution: Max-Planck-Institut

    Title: Topological insulators in optical lattices and their tomography

    Abstract: Band insulators constitute a fascinating form of quantum matter. Their very existence relies on band structure and quantum statistics, and the geometric phase inherent in their wave function gives rise to, e.g., a quantized Hall conductance (topological insulator) or quantized matter transport in adiabatic cycles (topological charge pumping). After an introduction, I will compare different schemes for the realization of topological insulators in optical lattices that are based on periodic driving. In the second part I will then present a method for the complete tomography of (topological) band insulators in optical lattices with two sublattice states.

    Host: Brandon Anderson
    When: Mon, July 28, 2014 - 2:00pm
    Where: CSS 2115
  • Special Seminar
    Speaker Name: Dr. Carey King

    Speaker Institution: University of Texas at Austin

    Title: Quantifying the Energy-Complexity Spiral

    Abstract: This talk presents ideas related to understanding the relationship between energy (or natural resources) and economic organization and differentiation (or complexity). Researchers such as Joseph Tainter posit the “energy-complexity spiral”. He posits that as societies grow, they (i) must become more complex to solve new problems, (ii) in order to become more complex, they must consume more energy, and (iii) increasingly complex technologies are required to extract lower quality resources. Here Dr. King presents recent work regarding how to measure and track complexity in the U.S. economy to find evidence for or against the “energy-complexity spiral”. He compares information theory and other existing metrics of economic transactions to metrics of energy and net energy. Initial calculations show that when U.S. primary energy consumption grew exponentially until 1970, the U.S. domestic economic structure (Use and Make matrices) became less complex. However, after 1970, U.S. primary energy consumption grew more linearly, and the domestic economic structure grew more complex.

    Speaker Bio: Dr. Carey W King performs interdisciplinary research related to how energy systems interact within the economy and environment as well as how our policy and social systems can make decisions and tradeoffs among these often competing factors. The past performance of our energy systems is no guarantee of future returns, yet we must understand the development of past energy systems. Carey’s research goals center on rigorous interpretations of the past to determine the most probable future energy pathways.
    Carey is Assistant Director at the Energy Institute at The University of Texas at Austin, and Research Associate with the Center for International Energy and Environmental Policy within the Jackson School of Geosciences.

    Hosted by Victor Yakovenko and Safa Motesharrei
    When: Tue, July 29, 2014 - 1:15pm
    Where: Computer and Space Sciences Building (CSS), Room 4301
  • Christopher H. Marrows - Special Seminar in CM Physics and Materials Science
    Wednesday July 30, 2014 at 11:00 AM
    Domain Wall Motion in Multilayer Films

    Christopher H. Marrows
    School of Physics & Astronomy
    University of Leeds

    Domain walls (DWs) in magnetic nanowires have been proposed as the basis of memory, logic, and sensor technologies. Until recently the fruit-fly structure for the study of current-driven DW motion was the in-plane magnetised Permalloy nanowire. In this structure, DWs are move by the conventional spin-transfer torque, but critical current densities for the onset of motion are typically ~1012 A/m2, too high for application [1]. Here we show that it is possible to form narrow Néel-type DWs in synthetic antiferromagnets (SAFs) formed by sandwiching two CoFe magnetic nanowires on either side of a thin Ru layer, which provides strong antiferromagnetic coupling that markedly changes the micormagnetics that determines the wall structure. Current-driven DW motion has been measured in these systems using magnetotransport measurements, and a critical current density for the onset of DW motion ~1×1011 A/m2. An extended 1D model suggests that the antiferromagnetic coupling can markedly reduce extrinsic pinning of the DW [2]. Meanwhile, recent experiments in materials with out-of plane anisotropy suggest that the fast DW velocities are caused by the presence of Néel walls rather than Bloch walls [3], generated by the presence of an interfacial Dzyaloshinskii-Moriya interaction (DMI). Here we show that we are able to measure the DMI even in the creep regime using a field-driven Kerr-imaging method [4]. We show that by inserting an atomically thin layer of Ir (which has opposite DMI [5]) at a Co/Pt interface we are able to switch the DM field from -60 mT in the case of Pt/Co/Pt to about +60 mT for tIr ~ 0.5 nm. We also comment on the origin of the DMI in the Pt/Co/Pt stack, showing that this nominally symmetric system can show strong effects due to changes in growth quality breaking the symmetry of Pt/Co and Co/Pt interfaces [6].

    [1] C. H. Marrows, Advances in Physics 54, 585 (2005). [2] H. Saarikoski et al., arXiv:1407.5805 [cond-mat.mes-hall]. [3] S. Emori et al., Nature Mater. 12, 611 (2013); K.-S. Ryu et al., Nature Nano. 8, 527 (2013). [4] S.-G. Je et al., Phys. Rev. B 88, 214401 (2013). [5] G. Chen et al., Nature Comm. 4, 2671 (2013). [6] A. Hrabec et al., Phys. Rev. B 90, 020402(R) (2014).

    Christopher Marrows is Professor of Condensed Matter Physics, and was previously a Reader in the same subject, a lecturer, and before that an 1851 research fellow, funded by the Royal Commission for the Exhibition of 1851. He has published almost 190 articles in peer-reviewed journals since the completion of his thesis in 1997, and is regularly a speaker at conferences around the world. He has published with over 200 other scientists from 70 institutions in 16 countries. Recent pieces of work have been selected as a scientific highlights by ISIS, the Diamond Light Source, and the National Synchrotron Light Source at Brookhaven National Laboratory on Long Island in New York State.
    Attachments area
    Preview attachment Marrows Advert.pdf
    When: Wed, July 30, 2014 - 11:00am
    Where: Room 2136 in the New Physical Sciences Complex
  • JQI Special Seminar
    Speaker Name: Vandna Gokhroo

    Speaker Institution: Okinawa Institute of Science and Technology Graduate University, Okinawa, Japan

    Title: Experiments on two-photon absorption in cold 87Rb atoms using an optical nanofiber

    Abstract: Optical nanofibers (ONFs), with subwavelength diameters, have a strong evanescent field around them. When an ONF is combined with a cold atom setup, the surrounding cold atoms can couple to guided modes of the fiber via evanescent field coupling. Here, I will talk about experiments on cold atoms and an optical nanofiber (ONF) to probe 2-photon absorption at a few nanowatts of power. Apart from its spectroscopic importance, this study will be useful for all optical switching and quantum logic gates at low powers.
    In our experiment, the ONF is fabricated by the heat-and-pull technique using a hydrogen:oxygen flame. Laser-cooled 87Rb atoms are excited from 5S1/2 →5D5/2 via a 2-photon excitation process using 5P3/2 as an intermediate level. Using a few nanowatts of 780 nm (5S1/2 →5P3/2) and 776 nm light (5S1/2 →5D5/2) through the ONF, the atoms are excited to the 5P3/2 state and thereby spontaneously emit 5.2 µm (5D5/2 →6P3/2) and 420 nm (6P3/2→5S1/2) photons which are coupled to the ONF. We detect the 420 nm fluorescence photons via the ONF and study effects such as Autler-Townes splitting and power broadening in this process for such a system. Two-photon experiments on a Rb vapor will also be discussed.

    Host: Luis A. Orozco
    When: Thu, July 31, 2014 - 11:00am
    Where: CSS 2115
  • JQI Special Seminar
    Speaker: Juan-Jose Garcia-Ripoll (Instituto de Física Fundamental, Madrid)

    Title: Some results on the spin-boson m

    Abstract: In this talk I will discuss various applications and results on this well know model, which has found a new life in a variety of experimental systems that combine two-level systems with bosonic degrees of freedom, such as circuit-QED and trapped ions. The ideas I will discuss are related mainly to (i) the propagation of quantum information and correlations in the system and (ii) the existence of quantum phase transitions in regimes of “ultra-strong” coupling, where the counter-rotating terms of the spin-boson interaction play a relevant role. In passing I will review the theoretical and numerical tools we use to solve these problems.
    Lieb-Robinson bounds for spin-boson lattice models and trapped ions, J. Juenemann, A. Cadarso, D. Perez-Garcia, A. Bermudez, J.J. Garcia-Ripoll
    Phys. Rev. Lett. 111, 230404 (2013)
    Hybrid quantum magnetism in circuit-QED: from spin-photon waves to many-body spectroscopy, Andreas Kurcz, Alejandro Bermudez, Juan José Garcìa-Ripoll, Phys. Rev. Lett. 112, 180405 (2014)

    Host: Chris Monroe
    When: Wed, August 20, 2014 - 11:00am
    Where: CSS 2115
  • JQI Seminar
    Speaker: Nathalie de Leon
    Institution: Harvard
    Hosts: Luis Orozco, Steve Rolston
    Title and Abstract to follow
    When: Mon, September 8, 2014 - 11:00am
    Where: CSS 2400
  • Physics Colloquium
    Speaker Name: Jaeyoung Park

    Speaker Institution: E=mc2

    Title: TBA
    When: Tue, September 9, 2014 - 4:00pm
    Where: Lobby of the Physical Sciences Complex
  • JQI Special Seminar
    Speaker Name: Michal Lipson

    Speaker Institution: Cornell

    Title and Abstract to follow
    Host: Luis Orozco
    When: Mon, September 15, 2014 - 11:00am
    Where: CSS 2400
  • Physics Colloquium
    Speaker Name: Mark Dykman

    Speaker Institution: Michigan State University (East Lansing)

    Title: TBA
    When: Tue, September 16, 2014 - 4:00pm
    Where: PSC Lobby
  • JQI Seminar
    Speaker Name: Brian DeMarco

    Speaker Institution: University of Illinois

    Host: James Williams

    Title and Abstract to follow
    When: Mon, September 22, 2014 - 11:00am
    Where: CSS 2400
  • Physics Colloquium
    Speaker Name: Brian DeMarco

    Speaker Institution: University of Illinois at Urbana
    When: Tue, September 23, 2014 - 4:00pm
    Where: PSC Lobby
  • JQI Seminar
    Speaker: Gleb Findelstein
    Institution: Duke
    Title: "Quantum critical behavior and Majorana fermions in a resonant level coupled to a dissipatie environment"

    Abstract: to follow
    Host: James Williams
    When: Mon, September 29, 2014 - 11:00am
    Where: CSS 2400
  • EPT Seminar
    Title: tk

    Speaker: Daniel Stolarski

    Abstract: tk
    When: Mon, September 29, 2014 - 3:00pm
    Where: PSC 3150
  • Physics Colloquium
    Speaker Name: Johnpierre Paglione

    Speaker Institution: University of Maryland
    When: Tue, September 30, 2014 - 4:00pm
    Where: PSC Lobby
  • JQI Seminar
    Speaker: Leon Balents
    Institution: U. California Santa Barbara
    Host: Jimmy Williams
    Title and Abstract to follow
    When: Mon, October 6, 2014 - 11:00am
    Where: CSS 2400
  • Physics Colloquium-Shih-I Pai Lecture
    Speaker Name: Anneke Levelt Sengers

    Speaker Institution: NIST
    When: Tue, October 7, 2014 - 4:00pm
    Where: PSC Lobby
  • JQI Seminar
    Speaker: Von Kiltzing
    Institution: Max Planck, Stuttgart
    Host: Sankar Das Sarma
    Title and Abstract to follow
    When: Mon, October 13, 2014 - 11:00am
    Where: CSS 2400
  • Prange Prize Lecture
    Speaker Name: Klaus Von Klitzing
    When: Tue, October 14, 2014 - 4:00pm
  • JQI Seminar
    Speaker Name: David DeMille

    Speaker Institution: Yale University

    Host: Luis Orozco
    Title and Abstract to follow
    When: Mon, October 20, 2014 - 11:00am
    Where: CSS 2400
  • Physics Colloquium
    Speaker Name: John Preskill

    Speaker Instituion: California Institute of Technology
    When: Tue, October 21, 2014 - 4:00pm
    Where: PSC Lobby

Department of Physics

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