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Events: Departmental Colloquia

  • Urban Effects on Cloud Dynamics, Precipitation Physics, Thunderstorms, and Floods

    Guest: Marshall Shepherd, UGA Geography
    Thursday, January 31, 2013 4:00 pm - 5:00 pm
    Location: Physics Auditorium (202)

    Historical and current research continues to suggest that the urban environment itself (e.g., land cover, pollution) may initiate or alter convective storms. Additionally, impervious land cover in cities alters surface hydrological processes. Questions like "do cities create their own storms?" or "did Atlanta's urban land cover enhance historic flood levels?" are not only relevant and but increasingly well-understood.

    Precipitation is a key link in the global water cycle and a proxy for changing climate; therefore, proper assessment of the urban environment's impact on precipitation (land use, aerosols, thermal properties) will be increasingly important in ongoing climate diagnostics and prediction, Global Water and Energy Cycle (GWEC) analysis and modeling, weather forecasting, freshwater resource management, urban planning-design, and land-atmosphere-ocean interface processes. These facts are particularly critical if current projections for global urban growth are accurate. Dr. Shepherd will present the most current scientific thinking and methodologies for studying urban effects on the hydroclimate. He will provide a particular emphasis on how physical attributes of land cover, aerosols, and urban morphology modify precipitation processes (via cloud dynamics, microphysics, etc.). The discussion will also provide insight on future direction and implications for stakeholders and policymakers.

  • Colloidal liquids and glasses: Insights from microscopy

    Guest: Eric Weeks, Emory University, Department of Physics
    Thursday, January 24, 2013 4:00 pm - 5:00 pm
    Location: Physics Auditorium (202)

    What would we learn if we could clearly see individual atoms deep inside materials?  My group studies colloidal suspensions, which are solid micron-sized particles in a liquid.  In many ways, these particles are analogous to atoms.  At high particle concentration, the sample is a good model system for a glassy material, with the particles randomly packed together.  We use an optical confocal microscope to view the motion of these colloidal particles in three dimensions to see how the motion is changed as the glass transition is approached.  In particular, we will discuss two puzzles.  First, we'll examine how rotational and translational diffusion of tracers differ as the glass transition is approached. Second, we'll study how how the behavior of glassy samples change when they are confined, and how this depends on the nature of the confining boundaries.

  • Physics Puts New Lens On Major Eye Disease

    Guest: Fereydoon Family, Emory University, Department of Physics
    Thursday, January 17, 2013 4:00 pm - 5:00 pm
    Location: Physics Auditorium (202)

    The 21st Century promises a major expansion at the interface of physics with the life sciences. These areas fall outside the conventional boundaries of the scientific disciplines and require a collaborative, multidisciplinary approach. What I hope to show you in this talk is that we have built on techniques and inspirations from physics, particularly condensed matter physics and computational physics, to make exciting progress in understanding a disease called age-related macular degeneration (AMD), which is the leading cause of blindness in adults.

    We have developed a mechanistic model and studied the growth, patterning and progression of the disease. This allowed us to explore and quantitatively test many more combinations of hypotheses and parameter choices than would have been experimentally feasible. As a result, we have uncovered new mechanical instabilities that will have a significant effect on the future development of targeted intervention strategies and clinical treatment of AMD.

  • Discovery of a Higgs-like Boson with the ATLAS Experiment at the CERN LHC

    Guest: Kenneth Johns, University of Arizona
    Thursday, November 15, 2012 4:00 pm - 5:00 pm
    Location: 202

    The Standard Model of particle physics has been successfully tested experimentally for over 30 years with no discrepancies.
    Yet the Higgs boson, a key component of the Standard Model needed to provide mass to elementary particles, remained undetected. Now in 2012 the hunt for the Higgs boson is likely over. Experimental evidence from the ATLAS experiment at the CERN Large Hadron Collider (LHC) for the production of a new neutral boson will be presented.

    The production and decay of this particle is compatible with Standard Model Higgs boson. The future LHC and Higgs physics program will be discussed.

  • All-Dielectric Optical Metamaterials and Devices

    Guest: Prof. Jason Valentine, Mechanical Engineering Department, Vanderbilt University
    Thursday, November 8, 2012 4:00 pm - 5:00 pm
    Location: 202

    Ohmic loss in metal based metamaterials continues to be one of the primary impediments to their application at infrared and visible frequencies. Dielectric metamaterials offer one potential solution to this issue by eliminating ohmic loss as well as avoiding saturation in the magnetic response at high frequencies. In this talk, I will discuss our recent efforts to develop purely dielectric metamaterials at optical frequencies based on structured silicon including both non-resonant and resonant configurations. Non-resonant dielectric metamaterials are implemented for chip-based photonics using both nanostructured waveguides and adiabatically tapered waveguides. In both cases, a spatially varying refractive index profile is utilized for achieving transformation optics devices including highly efficient free-space couplers and massively parallel waveguide crossings. By avoiding resonances and metallic elements, the devices are both broadband and low-loss. I will also outline the development of resonant dielectric metamaterials for achieving near-zero refractive index at optical frequencies. These metamaterials are formed from unit cells exhibiting both electric and magnetic dipole Mie resonances. By overlapping these two resonances, we show how an impedance matched zero-refractive index can be achieved at optical frequencies. Such materials can be applied for a variety of applications including directional emitters, filters, and compact lens systems.

  • Strong Interaction and the Essence of Mass

    Guest: Ralf Gothe, University of South Carolina
    Thursday, November 1, 2012 4:00 pm - 5:00 pm
    Location: 202

    All visible matter that surrounds us is made of atoms, i.e. electrons and nuclei, and the latter are made of nucleons, which finally are made of quarks and gluons. Contrary to the recent discussions in the news, the Higgs boson, or frequently called the God Particle, is not responsible for the generation of all mass. In fact, if it exists, it only generates the mass of the elementary quarks and electrons amounting to less than 2% of the total visible mass. Somewhat counter intuitively, the biggest part of the mass is not ab initio mass at all but energy, or more physically, the energy of the strong fields that bind the quarks into nucleons. The mass-energy equivalence, E=mc2, formulated by Einstein allows us to understand that the more than 98% of the weight you see when you step on a scale is nothing, or more precisely vacuum filled solely with field energy. How Quantum Chromodynamics (QCD) generates these strong fields, and hence most of the mass, is still an unsolved problem that can be uniquely addressed by experiments at the Thomas Jefferson National Accelerator Facility (JLab) in Virginia.
    Pushing the idea of an electron microscope to higher and higher energies allows us to investigate nucleons and their excitations with higher and higher resolution via electron scattering experiments carried out at JLab. A close collaboration of theorists and experimentalists has already started to shed light on some of the remaining, overarching, and most important problems of QCD, as defined by Nuclear Science Advisory Committee’s Long-Range Plan, by providing new insights into the structure of the nucleon, the transition between meson/baryon and quark/gluon degrees of freedom, the nature of confinement, and the essence of mass.

  • Uncovering Molecular Relaxation Processes in Condensed Phases with Nonlinear Optical Spectroscopy

    Guest: Andy Moran, University of North Carolina at Chapel Hill
    Thursday, October 18, 2012 4:00 pm - 5:00 pm
    Location: 202

    Photoinduced electrocyclic ring opening of cylcoalkene molecules are among the most elementary processes in organic chemistry.  One prototypical light-activated reaction transforms cyclohexadiene into hexatriene.  It is known that a sequence of extremely fast non-radiative transitions precedes bond breaking in cyclohexadiene.  However, these excited state dynamics have never been directly monitored in solution.  We explore such photoinduced relaxation processes in a closely related derivative of cyclohexadiene, α-terpinene, using femtosecond four-wave mixing spectroscopies carried out in the deep UV spectral range.  Of particular interest are the primary molecular geometry changes induced by light absorption.  The importance of these nuclear motions for the ring opening process will be discussed.

    Intriguing fundamental physics surround photoinduced relaxation processes in DNA.  Non-radiative transitions deactivate the excited electronic states of the DNA bases in less than 1 picosecond.  Such ultrafast electronic relaxation holds implications for biological photoprotection because all slower excited state chemical reactions are necessarily suppressed.  Following ground state recovery, the nucleobases are left in “hot” quantum states, wherein a subset of vibrational modes possesses a highly non-equilibrium distribution of excitation quanta (i.e., >4 eV in excess energy).  We use laser spectroscopies to follow these dynamics in thymine model systems at temperatures ranging from 100K-300K.  Our data suggest a competition between internal conversion and vibrational cooling processes in this family of molecules. 

  • Science and a Journey of Extremes

    Guest: Francis Slakey, Georgetown University
    Thursday, October 11, 2012 4:00 pm - 5:00 pm
    Location: 202

    Talk Abstract:
    Physicist and adventurer Francis Slakey describes his decade long journey that led to his becoming the first person to both summit the highest mountain on every continent and surf every ocean. The talk reviews some of the people he encounters and the challenges he endures – a Lama who gives him an amulet etched with “life’s meaning”, an ambush in the jungles of Indonesia, a life-or-death choice atop Everest – that culminate in a recognition that science is the most powerful tool we have to build a better world. He will describe how that perspective now informs his work for the American Physical Society and Georgetown University.
     
    Bio:
    Francis Slakey received his PhD in physics from the University of Illinois, Urbana-Champaign in 1992. He is the Associate Director of Public Affairs for the American Physical Society where he oversees APS legislative activities, specializing in energy and security policy. He is also The Upjohn Lecturer on Physics and Public Policy and the Co-Director of the Program on Science in the Public Interest at Georgetown University. He is a Fellow of the APS, a Fellow of the AAAS, a MacArthur Scholar, and a Lemelson Research Associate of the Smithsonian Institution. In recognition of his adventures, in 2002, he was chosen to run the Olympic Torch from the steps of the US Capitol. He recounts his global journey in his best-selling adventure memoir, To The Last Breath.

  • Who Are the Stars? Where are the Planets?

    Guest: Todd Henry, Georgia State University
    Thursday, October 4, 2012 4:00 pm - 5:00 pm
    Location: 202

    Since 1994, RECONS (www.recons.org, REsearch Consortium On Nearby Stars) has been discovering and characterizing the Sun's neighbors. Because of their proximity, nearby stars are natural locations to search for other solar systems. The stars provide increased fluxes, larger astrometric perturbations, and higher probabilities for eventual resolution and detailed study of planets than similar stars at larger distances. We have been building a three-dimensional map of stars near the Sun since 1999 using a telescope in the Chilean Andes, and we are now beginning to add planetary companions orbiting the stars. Surprising results include the overwhelming number of red dwarf stars near the Sun ... and the amount of work it will take to search for planets orbiting so many stars. Examination of the nearby stellar sample will reveal the prevalence and structure of solar systems, as well as the balance of Jovian and terrestrial worlds. These are the stars and planets that will ultimately be key in our search for life elsewhere.

  • ThermoChemical NanoLithography (TCNL)

    Guest: Prof. Elisa Riedo, School of Physics, Georgia Institute of Technology
    Thursday, September 27, 2012 4:00 pm - 5:00 pm
    Location: 202

    Nanolithography has been recognized as an essential component of future technologies. However, many of the techniques employed today still have significant limitations in terms of resolution, speed of writing, and the chemical diversity of the materials that can be patterned on an arbitrary substrate. Achieving chemical patterning at resolutions of 100 nm and below has been a challenge because of the difficulty in spatially confining reactions and because of the need to control the interactions of the reactant and products with the substrates and stamps. Over the past few years, by using resistively-heated atomic force microscopy (AFM) tips, the ability to thermally activate a chemical reaction at the nm scale at the surface of a material has been demonstrated in our group. Local chemical changes with feature sizes down to 12 nm at scan speeds up to 1 mm/s have been obtained with this new technique, commonly referred to as ThermoChemical NanoLithography (TCNL). In this seminar I will review recent research on TCNL, which includes: i) acid and amine patterning on the surface of copolymers containing thermally labile groups, and subsequent functionalization with proteins and DNA, ii) nanofabricating poly(p-phenylene vinylene) (PPV) nanowires, a typical electroluminescence conjugated polymer, with a clear “turn-on” of luminescence, iii) producing reduced graphene oxide (r-GO) structures by local thermal reduction of insulating GO with a 104 increase in conductivity for features sizes as small as 12 nm, iv) crystallization of Pb(Zr0.52Ti0.48)O3 and PbTiO3 ferro/piezoelectric nanostructures on a variety of substrates including plastic, achieving lines with widths ≥ 30 nm, spheres with diameter  10 nm and densities up to 213 Gb/in2, and v) producing density gradients of functional groups on polymer surfaces with nanoscopic resolution.

  • Nanosheets from Superconducting and Ferroelectric Materials

    Guest: Tina Salguero, University of Georgia, Department of Chemistry
    Thursday, September 20, 2012 4:00 pm - 5:00 pm
    Location: 202

    Our research theme is inorganic nanosheets. Nanosheets are characterized as freestanding, two-dimensional materials from one to several monolayers thick (<10 nm total) and up to tens of microns in lateral dimensions. The nanosheet morphology has several features that put it at the frontier of materials development, and on a fundamental level, nanosheets provide an opportunity to better understand materials at the ultimate thickness limit—down to a single monolayer. We study a range of prototype material classes with diverse structure types, functional properties, and synthetic challenges. In this talk I will describe our results in two areas: (1) the preparation and chemistry of magnesium diboride nanosheets, which are derived from superconducting bulk magnesium diboride, and (2) the synthesis and structure of ternary oxide nanosheets, AXO3, which include a unique nanosheet form of the bulk ferroelectric material barium titanate.

  • "Particle Physics" for Today's (Geo)Archaeology

    Guest: Ervan Garrison, University of Georgia, Department of Geology & Anthropology
    Thursday, September 13, 2012 4:00 pm - 5:00 pm
    Location: 202

    The sub-discipline of archaeological geology aka geoarchaeology" makes use of several analytical tools based on many "particles" more common to physical inquiry. These include protons, neutrons, electrons (a close cousin - Muons) and high energy photons (x and gamma "rays").

    This talk is a brief survey of the utility of these particles for answering archaeological questions with instruments in earth science departments.

  • Majorana fermions: The emergence of a new quantum particle in condensed matter physics and its implications

    Guest: Sumanta Tewari, Clemson University
    Thursday, September 6, 2012 4:00 pm - 5:00 pm
    Location: 202

    Majorana fermions, proposed more than seven decades ago by E. Majorana in the context of high energy physics (to describe neutrinos), are finally beginning to be experimentally realized in condensed matter systems. Following our recent proposal to realize them in semiconductor-superconductor heterostructures, at least four experimental groups worldwide have claimed to observe them in various experiments. In this talk I will introduce the physics of the Majorana fermions, why they are technologically important (topological quantum computation), our proposal for Majorana fermions in solid state systems, and the subsequent experimental realizations that have been reported.

  • Physics of Twisted Bilayer Graphene

    Guest: Prof. Mei-Yin Chou, School of Physics, Georgia Institute of Technology
    Thursday, August 30, 2012 4:00 pm - 5:00 pm
    Location: 202

    Many interesting physical properties of graphene have been identified and investigated within the framework of massless relativistic fermions. When one stacks graphene layers on top of each other, modification of the physical properties occurs in an unexpected way. In this presentation, I will discuss our computational efforts that investigate the special electronic properties of twisted bilayer graphene (TBG). We have systematically mapped out the spectra of these Landau levels (LLs) as a function of the rotational angle and provided quantitative predictions of the fractal spectra in a certain angular range. In addition, the time-dependent wave-packet propagation demonstrates an anisotropic dynamical behavior of electrons in TBG, which is related to the specific interlayer coupling.

  • Kirkpatrick Award Colloquium

    Guest: Joydip Ghosh, UGA Physics and Astronomy
    Thursday, August 23, 2012 4:00 pm - 5:00 pm
    Location: Physics Auditorium (202)

    Quantum Computing with Superconductors

    A quantum computer, a computing device powered by the laws of quantum mechanics, would be capable of solving a class of problems exponentially faster than classical computers. The modern era of superconducting quantum computing began a decade ago with the demonstration of long-lived quantum states in Josephson junction devices. In this talk I travel through the timeline of quantum computing and discuss current challenges. A major problem is to understand how to perform quantum operations fault-tolerantly, and I will discuss the emerging subject of topological quantum error correction in this context.

  • Undergraduate Awards Day: Four Programs for Improving Undergraduate Physics Instruction at LSU

    Guest: Dr. Raymond Chastain, Department of Physics and Astronomy at Louisiana State University
    Thursday, April 26, 2012 4:00 pm - 5:00 pm
    Location: Physics 202

    As with many physics departments at public university across the country, the Department of Physics and Astronomy at Louisiana State University is in the process of dealing with increased pressure on our service courses due to rising enrollment numbers, significant decreases in the resources available for teaching, and increased pressure to demonstrate our instructional effectiveness.  In an effort to address the quality of our teaching in the service courses, the physics department at LSU is in the process of implementing four different programs designed to increase student understanding in the introductory level physics courses.  The first program uses undergraduate student instructors in recitation sections with students in the first semester, algebra-based course.  The second and third programs use metacognitive strategies with students taking the second semester, calculus-based course.  All three of these programs are being implemented for the first time this semester and I will describe the challenges we have faced with each and how we will attempt to assess their effectiveness.  In addition, I will also talk about the recent changes to the Masters of Natural Science program for middle and high school teachers in the Baton Rouge area designed to bridge the gap between "teaching science" and "doing science". 

  • Cummings Day Awards Ceremony

    Guest: TBA, UGA Physics
    Thursday, April 19, 2012 4:00 pm - 5:00 pm
    Location: Physics 202

    TBA

  • The NASA Kepler Mission

    Guest: Roger Hunter, NASA Ames Research Center
    Thursday, April 12, 2012 4:00 pm - 5:00 pm
    Location: Physics Auditorium 202

    NASA’s Kepler Mission spacecraft was launched in March 2009.  Its chief science objective is to answer some ancient questions:  How rare is the Earth?  What fraction of stars in our galaxy harbor potentially habitable planets?  The answers to these questions may offer a profound understanding on whether life is widespread in the galaxy or whether we are possibly alone.  I will present an overview of the Kepler Mission, its science objectives, the results discovered so far, and the expectations for the mission.

  • Mass generation for Dirac electrons in graphene

    Guest: Prof. Markus Kindermann, Georgia Institute of Technology School of Physics
    Thursday, March 29, 2012 4:00 pm - 5:00 pm
    Location: Physics 202

     

    Graphene, a two-dimensional allotrope of carbon, has drawn much attention since its first experimental isolation. Much of this fascination stems from its exotic low-energy dynamics that is governed by the ``Dirac equation,’’ a quantum mechanical law of motion that was originally discovered for relativistic particles such as neutrinos. Unlike for real neutrinos, however, the Dirac equation for electrons in graphene is generically massless. In this talk I discuss how a mass term can be induced in the material and what the consequences of such mass are. Also unlike the situation for real, relativistic particles, the mass for the charge carriers in graphene can be space-dependent. I will discuss the manifestations of this exotic property for the electrical characteristics of the material. I will discuss evidence of the discussed effects in scanning tunneling microscopy measurements.

     

  • Some secrets of swimming in sand

    Guest: Prof. Daniel I. Goldman, Georgia Institute of Technology School of Physics
    Thursday, March 22, 2012 4:00 pm - 5:00 pm
    Location: Physics 202

    I will summarize our recent progress in biophysical experiments and modeling of the locomotion of a sand-swimming lizard, the sandfish. We use high speed x-ray imaging to study how the 10 cm-long sandfish swims at 2 body-lengths/sec within sand, a granular material that displays solid and fluid-like behavior. Below the surface the lizard no longer uses limbs for propulsion but generates thrust to overcome drag by propagating an undulatory traveling wave down the body. To predict sandfish swimming speed in the granular ``frictional fluid", we develop an empirical resistive force model by measuring drag force on a small cylinder oriented at different angles relative to the displacement direction and summing these forces over the animal movement profile. The model correctly predicts the animal's wave efficiency (ratio of forward speed to wave speed) as approximately 0.5. The empirical model agrees with a more detailed numerical simulation: a multi-segment model of the sandfish coupled to a multi-particle simulation of the granular medium. We use the principles discovered to construct a sand-swimming physical model (a robot) which, like in our empirical and simulation models, swims fastest using the preferred sandfish wave pattern.

  • Novel Properties and Applications of Functionalized Fullerenes

    Guest: Vijay Krishna, Particle Engineering Research Center, University of Florida
    Tuesday, March 13, 2012 4:00 pm - 5:00 pm
    Location: 202

    We have discovered that certain functionalized fullerenes can be heated and ignited with low-intensity, continuous-wave laser irradiation. The laser induced ignition is observed with near-infrared, green and blue lasers. In absence of oxygen, functionalized fullerenes glow and transform into other carbon nanostructures, such as single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon onions.

    These novel optical properties of functionalized fullerenes have game-changing applications in energy, medical, electronics and advanced materials industries. In the energy sector, pyrotechnic charge was ignited with functionalized fullerenes and low-intensity laser (kW/cm2 vs. conventional GW/cm2). In the medical sector, we have demonstrated photoacoustic imaging and photothermal ablation of tumor in mice. For the electronics sector, we have developed methods for green and safe nanolithography. In the advanced materials sector, we have demonstrated ultra-rapid and catalyst-free optical transformation of functionalized fullerenes into carbon nanostructures.  This is the first catalyst-free process to create SWNTs and MWNTs under ambient conditions, and has the potential to produce next generation, high-performance nanocomposite coatings and thin films through in situ synthesis of carbon nanotubes. Water-soluble functionalized fullerenes have minimal eco-toxicity and have potential as a growth stimulant.

  • Plasmonics and Metamaterials for Extreme Light Manipulation

    Guest: Yongmin Liu, University of California, Berkeley
    Thursday, March 8, 2012 4:00 pm - 5:00 pm
    Location: 202

    Plasmonics has become a very important branch in nano optics, focusing on the new physical phenomena and exciting applications associated with metallic nanostructures. Plasmonics allows us to concentrate, guide, and manipulate light at the deep subwavelength scale, promising enhanced light-matter interaction, sub-diffraction-limited imaging, efficient solar energy harvesting, and ultrasensitive biomedical detection. Furthermore, the assembly of metallic nanostructures can be used to construct optical metamaterials with exotic properties and functionalities, including artificial magnetism, negative refraction, and invisibility cloak.

    In this talk, after the introduction of plasmonics and metamaterials, I will present some of my recent work on extreme light manipulation utilizing the two schemes. First, I will describe the design and demonstration of the first optical negative refraction in bulk metamaterials made of metallic nanowires, which exhibit low-loss, broad-band and all-angle advantages. Second, I will introduce a new concept of transformational plasmonics to mold near-field plasmon waves at the metal-dielectric interface in a prescribed manner. For instance, this approach enables surface plasmon waves to travel smoothly at uneven surfaces, where surface plasmons would normally suffer considerable scattering losses. Some plasmonic devices, such as a plasmonic bend and a plasmonic Luneburg lens, will also be presented. Finally, I will demonstrate a fully subwavelength and efficient nano-plasmonic source for unidirectional generation of surface plasmons, which is a key building block for the next generation of ultra-fast and ultra-compact integrated optical circuits. By tailoring the relative phase at resonance and the separation between two magnetic metamaterial resonators, surface plasmons can be steered to predominantly propagate along one specific direction. Such a device not only serves as a highly directional surface plasmon generator, but also could be useful for surface-plasmon-based nonlinear applications, active modulation and wireless communication.

  • TBA

    Guest: Prof. Robert B. Hawman, UGA Department of Geology
    Thursday, March 1, 2012 4:00 pm - 5:00 pm
    Location: Physics 202

    TBA

  • Coated Nanoparticles in Solution and at Interfaces

    Guest: Dr. Gary S. Grest, Sandia National Laboratories
    Thursday, February 23, 2012 4:00 pm - 5:00 pm
    Location: Physics 202

    Among the most prevalent ways to control the assembly and integration of nanoparticles is to coat them with organic molecules whose specific functionalized groups modifies their inter particle interactions as well as the interaction of nanoparticles with their surrounding, while retaining their inherent properties. While it is often assumed that uniformly coating spherical nanoparticles with short organic will lead to symmetric nanoparticles, I will show using explicit-atom molecular dynamics simulations of model nanoparticles that the high curvature of small nanoparticle and the relatively short dimensions of the coating can produce highly asymmetric coating arrangements. In solution geometric properties dictate when a coating’s spherical symmetry will be unstable and that the chain end group and the solvent play a secondary role in determining the properties of surface patterns. At the water-vapor interface the anisotropic nanoparticle coatings seen in bulk solvents are reinforced by interactions at the interface. The coatings are significantly distorted and oriented by the surface and depend strongly on the amount of free volume provided by the geometry, end group, and solvent properties. At an interface any inhomogeneity or asymmetry tends to orient with the surface so as to minimize free energy. These asymmetric and oriented coatings are expected to have a dramatic effect on the interactions between nanoparticles and can influence the structures of aggregated nanoparticles which self-assemble in the bulk and at surfaces

  • Coherent Optical Control of Rydberg States in Silicon

    Guest: Vinh Q. Nguyen, Department of Physics/Institute for Terahertz Science and Technology, University of California at Santa Barbara
    Thursday, February 16, 2012 4:00 pm - 5:00 pm
    Location: 202

    One of the great successes of quantum physics is the description of the long-lived Rydberg
    states of atoms and ions. Of particular interest, because they can be employed in quantum control of one atom by another, are excited Rydberg states, where wavefunctions are expanded from their ground-state extents of less than 0.1 nm to several nanometers and even beyond; this allows atoms far enough apart to be non-interacting in their ground states to strongly interact in their excited states. For eventual application of such states, a solid-state implementation is very desirable. I demonstrate here the coherent optical control of impurity wavefunctions in the most ubiquitous donors and acceptors in silicon. In our experiments, I take advantage of a terahertz radiation from a free-electron laser to stimulate and observe population lifetimes, photon echoes for coherent lifetimes - the orbital analogue of the Hahn spin echo, and Rabi oscillations familiar from magnetic
    resonance spectroscopy. As well as extending atomic physicists’ explorations of quantum
    phenomena to the solid state, the work adds coherent terahertz radiation, as a particularly precise regulator of orbitals in solids, to the list of controls, such as pressure and chemical composition, already familiar to materials scientists.
    [1]. N. Q. Vinh, et al., P. Natl. Acad. Sci. USA 105, 10649 (2008)
    [2]. P. T. Greenland, et al., Nature 465, 1057 (2010).

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