William and Mary

Fall 2014

September 5, 2014 (Friday) 4:00-5:00p.m. Small Hall 110
Speaker: Dr. Predrag Nikolic, GMU
Host: Prof. Enrico Rossi
Title: The rise of topological quantum entanglement

Abstract: Entanglement is at the heart of quantum mechanics, the fundamental theory of our world. Yet, it is hardly ever seen in macroscopic collections of particles. We presently know of only one real system that is macroscopically entangled in a non-trivial way beyond any doubt. This is the two-dimensional electron gas in a magnetic field strong enough to produce fractional quantum Hall effect. Several other material families may also realize macroscopically entangled quantum states of strongly interacting electrons. This talk will be devoted to one such family, known as "topological insulators" (TIs), which recently became a world-wide research focus. More specifically, samarium hexaboride (SmB6) and its subfamily of Kondo (heavy fermion) insulators are the first promising candidates for strongly correlated TIs. I will present a neutron scattering experiment combined with field-theory calculations that indeed paint SmB6 as a correlated topological material. Then, I will discuss the rich physics of exotic symmetry breaking and electron fractionalization that one can anticipate in Kondo TIs. With some luck, these and similar materials may provide a new playground for exploring fundamental phenomena in nature, and perhaps even a new setting for topological quantum computation.

September 19, 2014 (Friday) 4:00-5:00p.m. Small Hall 110
Speaker: Carl Carlson, William & Mary
Host: Prof. E. Rossi
Title: The Proton Radius Puzzle
Abstract: The puzzle is easy to state: different ways of measuring the proton charge radius give different results, and the difference is seven standard deviations. Now four years after the discovery of this puzzle, the explanation is still not known. We will discuss how the measurements are made, and then will outline a selection of both ordinary and exotic proposals to explain the phenomenon.

September 26, 2014 (Friday) 4:00-5:00p.m. Small Hall 111

Speaker: Prof. Michael Kohl, Hampton University
Host: Prof. C. Perdrisat
Title: The proton radius puzzle - how can it be resolved?
Abstract:  The proton is not an elementary particle, it has a substructure governed by quarks and gluons. The spatial extensions of the electric charge and magnetization determine the size of the proton and its response to electromagnetic interaction. Recently, contradicting observations have challenged our understanding of the proton. The disagreement between proton radius determinations from high-precision muonic hydrogen spectroscopy and numerous atomic hydrogen and electron scattering measurements has become known as the proton radius puzzle, which has received much attention even in public media. The puzzle has a variety of possible resolutions, including physics beyond the Standard Model, missing conventional physics, and errors or underestimated uncertainties in the extraction of the radius from the data. I will discuss ways that will eventually help to resolve the puzzle.

October 3, 2014  (Friday) 4:00-5:00p.m. Small Hall 111

Speaker:  Prof. James Eckstein, University of Illinois-Urbana
Host: Prof. M. Qazilbash
Title: The Superconducting Proximity Effect 
Abstract: The superconducting proximity effect arises when a superconductor “shares” its pairs with a nonsuperconducting layer with which it is in good contact.  It has been studied in many experiments, sometimes showing unexpected behavior.  Renewed interest in proximity coupled superconductivity has arisen due to experimental results that suggest Majorana Fermions can form in devices that include topological materials, such as topological insulators and devices made from certain semiconductors such as InAs.  I will review superconductivity and the proximity effect, and then discuss some recent experiments in which proximity induced changes in normal state properties of both semiconductors and topological insulators have been measured.

October 10, 2014  (Friday) 4:00-5:00p.m. Small Hall 111
Speaker:  Julia M. Phillips, Sandia National Laboratory
Host: Prof. P. Vahle
Title: Research and Technologies for National Security: A perspective from a national security laboratory

Abstract: Sandia National Laboratories is the Nation’s largest national security laboratory. The mission of the laboratory to deliver engineered solutions for national security needs is built on a broad and deep base of scientific research and expertise. I will motivate the research at Sandia by describing the Laboratories’ historical evolution, research accomplishments and priorities, and current mission. I will then discuss some of the exciting research challenges that the Laboratories are pursuing, including topics such as Beyond Moore Computing, First to High Yield Fusion, Engineering of Materials Reliability, and Science & Engineering of Quantum Information Systems.

October 30, 2014 (Friday) 4:00-5:00p.m. Small Hall 111 (Special Colloquium)
Speaker: J. Michael Klopf, College of William & Mary, Dept. of Applied Science
Host: Prof. Ale Lukaszew
Title: Using Light to Probe Ultrafast Dynamics
Abstract: The development of reliable ultrafast pulsed lasers – meaning lasers emitting picosecond or shorter pulses – has enabled unprecedented measurements of non equilibrium dynamics in matter. In particular, I will present how this type of laser in a pump-probe configuration can be used to measure the relaxation, thermalization, diffusion, and recombination processes of photoexcited electrons in thin film structures of direct gap semiconductors. These types of materials are the fundamental building blocks that emit, control, and sense light in optoelectronic devices, so it is critical to understand the carrier dynamics of these materials as a function of doping, alloying, film thickness, etc. I will also present how I model the effect of the photoexcited carrier dynamics on the optical properties of the film and use this to determine the scattering, diffusion, and recombination rates for a given sample. These processes play important roles in the performance of optoelectronic devices. The pump-probe method is also an effective tool to investigate the dynamics of the optically
induced insulator-metal transition in novel materials such as VO2 and NbO2. Recently we have configured a new setup to make these measurements in the Ultrafast Lab of Prof. Lukaszew and I will present some of our preliminary experimental results. These types of materials show great promise for passive light control and innovative all-optical sensing and switching. The nature of the ultrafast optical response of these materials though is not yet understood, and these types of measurements will be a key piece for solving this puzzle.

October 31, 2014 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Prof. Luis Orozco, University of Maryland
Host:  Prof. S. Aubin
Title: Atoms coupled to a superconducting circuit, a progress report.
Abstract: Coupling of a neutral atomic ensemble to superconducting circuits via a magnetic dipole transition forms an interesting hybrid system. Here we present progress towards trapping cold rubidium atoms within 10 micrometers of a superconducting circuit using a cryogenically-compatible atom trap and a tunable, high-Q superconducting resonator. Evanescent fields around an optical nanofiber with 99.95% transmission form an atom trap suitable for a 15 mK dilution refrigerator. We are developing the hardware and the tools to monitor the individual components of the system. Work supported by NSF though the PFC@JQI, the Atomtronics MURI, ONR, and DARPA.

November 7, 2014 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Gianpolo Carosi, LLNL
Host: Prof. A. Walker-Loud
Title: The Hunt for Dark Matter Axions 
Abstract: The nature of dark matter is one of the great mysteries of modern physics. It’s existence has been inferred by it’s gravitational effects over many distance scales but currently no known particle can account for the observed data. As a result new particles beyond the standard model have been suggested. The axion is one such particle that was originally devised as a solution to the strong-CP problem in nuclear physics (or the peculiar absence of a measurable electric dipole moment in the neutron). The Axion Dark Matter eXperiment (ADMX), and its sister experiment ADMX-High Frequency (ADMX-HF), are designed to detect axions by using large microwave cavities immersed in a strong magnetic field to resonantly convert the axion’s rest mass into detectable photons. In this talk I will describe the history of axion searches and the ADMX experiment in particular, which ran at LLNL for over a decade before being moved to the University of Washington. I will then discuss the upgrades to the ADMX experiment as it prepares for it’s upcoming search with orders of magnitude greater sensitivity. I will also outline R&D efforts that are currently being undertaken to expand the search range of ADMX further and ultimately determine if axions are, or are not, the major dark matter component of the Universe.

November 10, 2014 (Monday) 4:00-5:00p.m. Small Hall 110
Speaker: Dan Millison, P.E., P.G./Transcendergy, L.L.C.
Host: Physics Chair, Gene Tracy
Title: Saving the Forest and the Trees: A Conceptual Model of Sustainable Coal
Abstract: The global debate on climate change mitigation has focused on the single tree of climate change, blinding most policy- and decision-makers to the broader forest of sustainability. Although coal is public enemy number one in the war on climate change, it will remain one of the single largest sources of global energy supply for the foreseeable future. Nevertheless, a successful outcome of negotiations for a post-2012 climate change treaty framework would include a long term objective of leaving coal in the ground.
As most energy policy-makers believe that leaving coal in the ground is an unrealistic scenario for the foreseeable future, carbon capture and storage (CCS) has attracted significant research and development in an attempt to achieve some semblance of carbon neutrality. Commercially viable-CCS presents a potential moral hazard: “solving” the CO2 disposal problem will encourage greater use of coal, without addressing the upstream environmental and social impacts of coal mining, transport, and downstream waste disposal. “Clean coal” as currently envisioned – supercritical power with CCS bolted on – is not sustainable. CCS as end-of-pipe disposal is a non-starter in the absence of a robust regulatory framework for waste management including carbon pricing.
Bypassing the dual challenges of making coal “too expensive” or making low-carbon energy “too cheap to meter,” there is an intermediate solution to render coal more sustainable. Sustainable coal - not to be confused with “clean coal” – is possible by combining underground coal gasification (UCG, with the produced gas used in combined-cycle gas turbine power plants or other off-the-shelf systems including conversion to liquids) with carbon capture, reuse, and storage (CCR, preferably via carbonate mineralization or other utilization not involving additional hydrocarbon production). This end-to-end system is necessary to close the sustainability loop.
UCG is not a new technology, having been deployed in the former Soviet Union more than 60 years ago. There are several commercial UCG operations worldwide today, but it is not well-known even among energy specialists. UCG can remove most of the negative externalities associated with coal mining, transport, and conventional pollutant management. CCR would provide a positive market driver in place of a price on carbon. A commercially viable CCR system would also enable more sustainable exploitation of non-conventional gas resources (e.g., shale gas). An end-to-end system would facilitate the convergence of energy security and climate change objectives globally and particularly in developing countries which may rely increasingly on imported coal.
In the US, UCG offers the prospect of transforming the coal mining industry to a high-value-added sector supporting next-generation power plants and coal-to-liquids production, at the same time facilitating exports of natural gas.

November 14, 2014 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Dr. Vincent Liu, University of Pittsburgh
Host: Prof. Enrico Rossi
Title: Topological orbital bands: from optical lattices to oxide interfaces
Abstract: Do quantum particles in mixed orbital bands (such as p and d) organize themselves coherently at low temperature limit into topological states of matter by interaction? I will narrate, through simple and powerful models from cold atoms in optical lattices to electrons in LaAlO3/SrTiO3 oxide interfaces, how one may encounter exotic many-body states like quantum Hall-like  insulators without Landau level,  topological superconductivity/superfluidity by only s-wave scattering, and orbital-induced magnetic Skyrmions as ground state.  

November 21, 2014 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Dr. Marcus Diefenthaler (University of Illinois - Urbana)
Host: Prof. Wouter Deconinck
Title: The E-906/SeaQuest Experiment at Fermilab
Abstract: The nucleon is one the the fundamental building blocks of the visible universe. But many of its properties and how those properties can be deduced from its inner structure are not well understood. Deep-inelastic scattering (DIS) experiments have revealed that the inner structure of the nucleon consists of relativistic quarks that exchange gluons, and have established quantum chromodynanics (QCD) as the theory of the strong interaction between quarks and gluons. Due to the confinement feature of the strong interaction and the relativistic nature of the system, we cannot yet explain many properties of the nucleon from first principles. Our knowledge of the inner structure of the nucleon is to a large extent based on the measurement of electroweak processes such as DIS or the Drell-Yan process, which can be interpreted within QCD.

The E-906/SeaQuest experiment at Fermilab continues a series of Drell-Yan measurements to explore the antiquark content of the nucleon and to study the modifications to nucleon structure when the nucleon is embedded into a nuclei. To extend existing measurements to larger values of Bjorken-x - the momentum fraction of a quark within the nucleon - a 120 GeV proton beam extracted from Fermilab’s main injector is used, resulting in 50 times more luminosity than previous experiments and enabling access to values of x up to 0.9.

An overview will be presented of the key physics goals of the SeaQuest collaboration: These include investigation of the dramatic dbar/ubar flavor asymmetry in the nucleon sea and its behavior at high x; study of the EMC effect in Drell-Yan scattering and the unexpected absence of any antiquark excess in existing data; and measurements of the angular dependence of the Drell-Yan process, sensitive to spin-orbit correlations within the nucleon. Updates to the SeaQuest experiment with polarized beam (E-1027) and target (E-1039) will allow us to study the quarks' spin-orbit correlations within the nucleon and to provide complementary information to existing data from DIS. The talk will conclude with a status report on the ongoing data taking and analysis of this new experiment.