Spring 2018

January 26, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Kevin Cox, JILA, University of Colorado at Boulder, Army Research Lab
Host: I. Novikova
Title:  Is Entanglement Useful?
Abstract: Entanglement—non-local quantum correlation--is the most “quantum” part of quantum mechanics.  But is it useful for anything?  For most of us, the answer is “not yet”.  I will discuss experiments at the JILA research institute in Boulder, CO and the US Army Research Laboratory in Adelphi, MD that are pushing the boundaries of creating useful entanglement in a way that will soon impact real world applications.

February 9, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Hadar Steinberg, Racah Institute of Physics, Hebrew University, Jerusalem, Israel
Host: E. Rossi
Van-der-Waals integration of hybrid devices
Abstract: Progress in solid state physics is often tied to the emergence of material systems hosting new electronic properties. Specifically, the interface between different materials can yield new way to control the band-structures and interaction effects, giving rise to new potential functionalities. Particular recent interest is given to “van der Waals materials”. Here, weak inter-layer bonds allow exfoliation into ultra-thin layers. Moreover, such materials can be vertically stacked with high precision, creating a range of new types of heterostructure. In my talk I will describe a number of experiments based on such van der Waals stacks. Specifically, I will discuss the interface between graphene, a single layer of carbon, and a topological insulator (TI), which is a material hosting protected states at its surface. At the graphene-TI interface, strong spin-orbit band-modifications are expected to take place, which makes it an attractive model system for probing proximity effects involving topological states. We show how parameters such as relative crystallographic orientation between the two materials strongly affect the physics of such devices.

February 16, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Francis Halzen, Wisconsin IceCube Particle Astrophysics Center and Department of Physics, University of Wisconsin–Madison
Host: M. Sher
Title: IceCube and the Discovery of High-Energy Cosmic Neutrinos
Abstract: The IceCube project has transformed a cubic kilometer of natural Antarctic ice into a neutrino detector. The instrument detects more than 100,000 neutrinos per year in the GeV to PeV energy range. Among those, we have isolated a flux of high-energy cosmic neutrinos. I will discuss the instrument, the analysis of the data, the significance of the discovery of cosmic neutrinos, and the recent multimessenger observation of a flaring TeV blazar in coincidence with the IceCube neutrino alert IC170922. The large cosmic neutrino flux observed implies that the Universe’s energy density in high-energy neutrinos is the same as that in gamma rays, suggesting that the sources are connected and that a multitude of astronomical objects await discovery.

Marc 2, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Joshua Magee, Lawrence Livermore National Lab
Host: D. Armstrong
Title: Precision Measurements of Neutron Induced Fission Cross Sections of Actinides
Abstract: Neutron induced fission of actinides is of great interest in nuclear applications (for example, nuclear energy and security). Fission reaction rates, or cross sections, have traditionally been made using fission chambers, which provide limited information on the fission products, and report results good to only a few percent. These are inadequate for next generation reactor simulations which require sub-percent knowledge of these cross sections. To meet this need, the Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) collaboration designed and built the fission Time Projection Chamber (fissionTPC), which provides additional information on the fission products through full 3-dimensional tracking and improved particle identication. Ultimately, this should provide the first sub-percent measurements of the (n,f) cross sections of 239Pu and 238 relative to 235U.

An overview of neutron induced fission cross sections will be given, and the fissionTPC will be discussed. Additionally, preliminary results from recent fissionTPC analysis will be presented.

March 23, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Maura McLaughlin, West Virginia University
Host: D. Armstrong
Title: A Galactic Scale Gravitational Wave Observatory
Abstract: Pulsars are rapidly rotating neutron stars with phenomenal rotational stability that can be used as celestial clocks in a variety of fundamental physics experiments. One of these experiments involves using an array of precisely timed millisecond pulsars to detect perturbations due to gravitational waves at much lower frequencies than those probed by LIGO. The gravitational waves detectable through pulsar timing will most likely result from an ensemble of supermassive black hole binaries.  I will describe the efforts of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), a collaboration which monitors an array of over 70 millisecond pulsars with the Green Bank Telescope and Arecibo Observatory. The most recent limits on various types of gravitational wave sources will be presented, and I will show how these limits are already constraining models for galaxy formation and evolution. I will then describe the dramatic gains in sensitivity that are expected from discoveries of millisecond pulsars, more sensitive instrumentation, improved detection algorithms, and international collaboration and show that detection is possible before the end of the decade.

March 30, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Bahram Roughani, Loyola
Host: W. Deconinck
Title: Raman scattering correlation with crystallographic orientation of Si cut off axis
Abstract: Raman spectroscopy is the inelastic scattering of light by matter, a process which provides important insight into the structure and properties of materials.  This laser spectroscopy technique provides non-destructive and non-contact analysis with high spatial resolution up to sub-micron scale and requires no sample preparation.  Raman scattering of solids represent vibrational modes that are directly linked to the crystal symmetry.  Therefore, intensity analysis of Raman modes provides information about crystal properties.  We have leveraged this characteristics to develop a new approach in polarized backscattered Raman spectroscopy that can identify the crystallographic orientation of silicon cut off axis.  Our theoretical model is developed using Raman tensors for backscattering geometry that predicts variations in the backscattering polarized Raman intensity profiles as a function of the rotating wafers about the lab z-axis.  A comparison between the experimental spectra and theoretical model will be presented, and specific Raman spectra signatures that are correlated with the degree of off-axis cut for single crystals of Si wafers will be discussed.  Our model suggests a quick and nondestructive approach for determining the off-axis cut of single crystal Si wafers, which is the most commonly used substrate material in semiconducting device fabrications.

April 6, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Teppei Katori, Queen Mary University of London
Host: M. Kordosky

April 13, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Nathan Kidwell, William & Mary
J. Stevens
Lights, Camera, Action! Taking a Molecular-Level Snapshot of Atmospheric Photochemistry
Abstract: The Earth's atmosphere has experienced an unprecedented transformation in its chemical composition due to anthropogenic and biogenic emissions.  This presents a challenge to the scientific community seeking to provide a molecular-scale understanding of the impact on the atmosphere.  The development of accurate models to predict atmospheric reactions relies on experimental data encompassing the spectroscopy, dynamics, and kinetics of photoinitiated and bimolecular chemical events.  I will discuss recent results from our laboratory on the photodissociation dynamics of atmospherically-relevant molecules that serve as temporary reservoirs of reactive species, which may further react with ambient compounds or participate in new particle formation.  In particular, we utilize laser spectroscopy and advance particle imaging methods accompanied by high-level theory and reaction modeling to address atmospheric chemistry problems.  Our experimental measurements provide important benchmarks for theoretical studies in order to determine detailed mechanisms for the first few nucleation events towards aerosol formation, which are necessary for predictive atmospheric chemistry modeling.

April 20, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
John Delos, William & Mary Physics
E. Rossi
47@74, a Swan Song

April 27, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Anton Burkov, Waterloo
E. Rossi