Fall 2018 Colloquium Schedule

<p>Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.</p>

<p>Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.</p>

<h3>December 12 — "<strong>Mixed Conduction in Polymeric Materials: Electrochemical devices for Biosensing and Neuromorphic Computing"</strong></h3>

<ul>
<li>Presenter: Alberto Salleo, Stanford University</li>
<li>Host: Sean Shaheen</li>
<li>Abstract: Organic semiconductors have been traditionally developed for making low-cost and flexible transistors, solar cells and light-emitting diodes. In the last few years, emerging applications in health case and bioelectronics have been proposed. A particularly interesting class of materials in this application area takes advantage of mixed ionic and electronic conduction in certain semiconducting polymers. Indeed, the ability to transduce ionic fluxes into electrical currents is useful when interacting with living matter or bodily fluids. My presentation will first discuss the fundamental aspects of how mixed conduction works in polymeric materials and then focus on two families of devices made with such materials: electrochemical transistors and artificial synapses.<br />
<strong>1- Biosensing using electrochemical transistors:</strong> The continuous monitoring of human health can greatly benefit from devices that can be worn comfortably or seamlessly integrated in household objects, constituting “health-centered” home automation aka "domotics". I will describe electrochemical transistors that detect ionic species either directly present in body fluids or resulting from a selective enzymatic reaction (e.g. ammonia from creatinine) at physiological levels. Additionally, I will show that non-charged molecules can be detected by making use of custom-processed polymer membranes that act as “synthetic enzymes”. Using these membranes in conjunction with electrochemical transistors we demonstrate that we are able to measure physiological levels of cortisol in real human sweat. Finally, I will show a more biomimetic approach where the sensing layer is a lipid membrane stabilized at a liquid-liquid interface, which we use to detect antimicrobial compounds. The same basic device that we use for sensing can also be used for computing.<br />
<strong>2- Polymer-based artificial synapses:</strong> The brain can perform massively parallel information processing while consuming only ~1 - 100 fJ per synaptic event. I will describe a novel electrochemical neuromorphic device that switches at record-low energy (<0.1 fJ projected, <10 pJ measured) and voltage (< 1 mV, measured), displays >500 distinct, non-volatile conductance states within a ~1 V operating range. Furthermore, it achieves record classification accuracy when implemented in neural network simulations. Our organic neuromorphic device works by combining ionic (protonic) and electronic conduction and is essentially similar to a concentration battery. The main advantage of this device is that the barrier for state retention is decoupled from the barrier for changing states, allowing for the extremely low switching voltages while maintaining non-volatility. I will show that the device can rival commercial flash memory in terms of endurance and possibly switching time. When accessed with an appropriate switching device it exhibits excellent linearity, which is an important consideration for neural networks that learn with blind updates.<br />
<strong>Speaker Bio:</strong> Alberto Salleo is currently an Associate Professor of Materials Science at Stanford University. Alberto Salleo holds a <em>Laurea </em>degree in Chemistry from <em>La Sapienza </em>and graduated as a Fulbright Fellow with a PhD in Materials Science from UC Berkeley in 2001. From 2001 to 2005 Salleo was first post-doctoral research fellow and successively member of research staff at Xerox Palo Alto Research Center. In 2005 Salleo joined the Materials Science and Engineering Department at Stanford as an Assistant Professor and was promoted to Associate Professor in 2013. Salleo is a Principal Editor of MRS Communications since 2011.While at Stanford, Salleo won the NSF Career Award, the 3M Untenured Faculty Award, the SPIE Early Career Award, the Tau Beta Pi Excellence in Undergraduate Teaching Award, and the Gores Award for Excellence in Teaching, Stanford’s highest teaching award. He has been a <em>Thomson Reuters Highly Cited Researcher</em> since 2015, recognizing that he ranks in the top 1% cited researchers in his field.</li>
</ul>

<h2>Previous Colloquia</h2>

<h3>August 29 — "Tales from the Cold: New Science from Superconducting Sensors"</h3>

<ul>
<li>Presenter: Joel Ullom, NIST Boulder</li>
<li>Host: Scott Diddams</li>
<li>Abstract: In the last decade, superconducting sensors operating at milliKelvin temperatures have evolved from laboratory curiosities to powerful tools for performing science.  These sensors are now essential for fields of science such as studies of the cosmic microwave background, and they are beginning to impact research areas previously thought unsuitable such as beamline science at large x-ray lightsources.  In this seminar, I will cover three interrelated topics: (1) the growing scope of application for superconducting sensors, (2) recent advances in performance enabled by better fundamental understanding of their behavior, and (3) some examples of recent science enabled by these devices, including demonstrations of tabletop ultrafast x-ray emission and absorption spectroscopy.  Timely background information is available in ref. 1.
<p>[1] K. Morgan, Physics Today 71, 8, 28 (2018); doi: 10.1063/PT.3.3995</p>
</li>
</ul>

<h3>September 5 — "Whispering-gallery-mode microresonators: fundamentals and applications"</h3>

<ul>
<li>Presenter: Lan Yang, Washington University</li>
<li>Host: Juliet Gopinath</li>
<li>Abstract: Light-matter interactions are the fundamental basis for many phenomena and processes in optical devices. Whispering-Gallery-Mode (WGM) optical resonators trap light in a manner similar to a phenomenon found in the gallery spaces of St. Paul’s Cathedral dome in London, where a single whisper (i.e., a sound wave) can be heard along the circular boundary of the architecture. Ultra-high-quality WGM optical micro-resonators provide unprecedented capability to trap light in a highly confined volume smaller than a strand of human hair; a light beam can travel around the boundary of a WGM resonator over 10⁶ times, significantly enhancing light-matter interactions, creating the potential for a wealth of new scientific discoveries and technological breakthroughs difficult to achieve by other devices. They have shown a great promise for a variety of fields of science, spanning from optomechanics to communication, non-Hermitian physics, sensing and metrology. In this talk, I will report the recent research discoveries from my group in this exciting field. I will present a few cases demonstrating the great potentials of high-Q WGM microresonators and microlasers for both fundamental science and engineering applications. Specifically, I will discuss ultra-high-Q microresonators and microlasers for ultra-sensitive detection of nanoscale objects. I will explain a self-referencing sensing scheme for detection and sizing of single virion, dielectric and metallic nanoparticles. These recent advancements in WGM microresonators will enable a new class of ultra-sensitive and low-power sensors for investigating the properties and kinetic behaviors of nanomaterials, nanostructures, and nanoscale phenomena. Afterwards, I will discuss our recent exploration of fundamental physics, such as parity-time symmetry (PT-symmetry) and light-matter interactions around exceptional points (EPs) in high-quality WGM resonators, which can be used to achieve a new generation of optical system enabling unconventional control of light flow. Examples including nonreciprocal light transmission, loss engineering in a lasing system, directional lasing emission, and EPs enhanced sensing, will be introduced. A non-Hermtian phonon laser tuned in the vicinity of EPs will be discussed briefly. In the end, I will present a new generic and hand-held microresonator platform transformed from a table-top setup, which will help release the power of high-Q WGM resonator technologies.
<p><em>Short bio:</em> Professor Lan Yang is the Edwin H. and Florence G. Skinner professor in the Preston M. Green Department of Electrical and Systems Engineering at Washington University, St. Louis, MO, USA. She received B.S. from the University of Science and Technology of China and received her Ph.D. in applied physics from Caltech in 2005. Her research interests have been focusing on the fundamental understanding of high-quality photonic whispering-gallery-mode (WGM) resonators and their applications for sensing, lasing, light harvesting, and communications. Recently, her research interests expanded to parity-time-symmetry and non-Hermitian physics in high-quality WGM resonators, which have led to a series of new discoveries for unconventional control of light transport in photonic structures. She received NSF CAREER Award in 2010 for her work on single nanoparticle detection and sizing using an on-chip optical resonator. She is also the recipient of the 2010 Presidential Early Career Award for Scientists and Engineers (PECASE). She is a fellow of the Optical Society of America (OSA).</p>
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</ul>

<h3>September 12 — "Picoastronomy: an electron microscopist's view of the history of the Solar System"</h3>

<ul>
<li>Presenter: Rhonda Stroud, U.S. Naval Research Laboratory</li>
<li>Host: Mihaly Horanyi</li>
<li>Abstract: A wide range of astrophysical processes, from condensation of dust particles in circumstellar envelopes to space weathering on airless bodies, are inherently pico-to-nanoscale phenomena. Thus, an electron microscope, used for direct observation of planetary materials in the laboratory, can be as much of an astronomical tool as a telescope pointed at the sky. The energy resolution of state-of-the-art monochromated scanning transmission electron microscopes (STEMs), as low as 10 meV, makes it possible to directly observe the infra-red optical properties of individual cosmic dust grains in the 2 to 25 um range. Thus, distinguishing the 10-um and 18-um features of individual bonafide astrosilicates is now possible. Furthermore, the spatial resolution and sensitivity of the STEM enables imaging and at spectroscopy at scales down to the single atom. Samples of nanomaterials from diverse classes of stars from red giants to supernovae, from asteroids and comets, and the surface of the Moon are all available for laboratory studies. Results of these studies can help aid in the understanding of the formation and evolution of solar systems, and even provide clues for advancing the development of technologically important materials, such as doped nanodiamonds, SiC and graphene.</li>
</ul>

<h3>September 19 — "Magnetism and spin in quantum materials"</h3>

<ul>
<li>Presenter: Minhyea Lee, University of Colorado Boulder</li>
<li>Host: John Cumalat</li>
<li>Abstract: Quantum materials are crystalline solids with exotic physical properties arising from the quantum mechanical nature and interactions of electrons.  Quantum phenomena such as fluctuations, topology, tunneling and interference are at the heart of exciting developments in the fundamental science of quantum materials. At the same time, these phenomena have the potential to play a key role in future technologies.
<p>In this colloquium I will give some examples from my research on magnetism, illustrating the discovery of novel phenomena in quantum materials, and the development of frameworks that can guide the search for new materials and devices with advanced functionality.</p>
</li>
</ul>

<h3>September 26 — "<strong>Quantum Nanophotonics from Ultrathin Metallic Junctions"</strong></h3>

<ul>
<li>Presenter: Maiken Mikkelsen, Duke University</li>
<li>Host: John Bohn</li>
<li>Abstract: Tiny gaps between metals enables extreme field enhancements and strongly modified light-matter interactions promising for ultrafast optoelectronics, energy applications and on-chip components for quantum information processing. We use creative nanofabrication techniques at the interface between chemistry and physics to realize nanostructures with critical dimensions on the atomic- and molecular-scale (~1-10 nm), together with advanced, ultrafast optical techniques to probe the emerging phenomena. Here, I will provide an overview of our recent research demonstrating tailored light-matter interactions by leveraging ultra-small plasmonic cavities fabricated with bottom-up techniques. Examples of our demonstrations include 1,000-fold Purcell enhancements [Nature Photonics 8, 835 (2014)], ultrafast single photon sources [Nano Letters 16, 270 (2016)], tailored emission from two-dimensional semiconductor materials [Nano Letters 15, 3578 (2015), ACS Photonics 5, 552 (2018)], perfect absorbers and combinatorial plasmonic colors [Advanced Materials 27, 7897 (2015), Advanced Materials 29, 1602971 (2017)].    
<p><u>Bio:</u></p>

<p>Maiken H. Mikkelsen is the James N. and Elizabeth H. Barton Associate Professor at Duke University in the Departments of Physics, Electrical & Computer Engineering, and Mechanical Engineering & Materials Science. Currently, she is a Visiting Associate Professor at Stanford University in the Department of Materials Science & Engineering. She received her B.S. from the University of Copenhagen in 2004, her Ph.D. in Physics from the University of California, Santa Barbara in 2009 and was a postdoctoral fellow at the University of California, Berkeley. Her research focuses on nanophotonics and quantum materials to enable transformative breakthroughs for optoelectronics, the environment and human health. Her awards include the Maria Goeppert Mayer Award from the American Physical Society, the Early Career Achievement Award from SPIE, the NSF CAREER award, the Cottrell Scholar Award from the Research Corporation for Science Advancement and Young Investigator Program Awards from the ONR, ARO and AFOSR.</p>
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</ul>

<h3>October 3 — "The physics, biology, and technology of resonance energy transfer"</h3>

<ul>
<li>Presenter: Philip Nelson, University of Pennsylvania</li>
<li>Host: Loren Hough</li>
<li>Abstract: Resonance energy transfer has become an indispensable experimental tool for single-molecule and single-cell biophysics, and a conceptual tool to understand bioluminescence and photosynthesis. Its physical underpinnings, however, are subtle: It involves a discrete jump of excitation from one molecule to another, and so we regard it as a strongly quantum-mechanical process. And yet its first-order kinetics differ from what many of us were taught about two-state quantum systems; quantum superpositions of the states do not seem to arise; and so on. The key step involves acknowledging quantum decoherence.
<p>Ref: P C Nelson, Biophys J 115: 167(2018) <a href="http://doi.org/10.1016/j.bpj.2018.01.010">http://doi.org/10.1016/j.bpj.2...
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</ul>

<h3>October 10 — "Front and center: physics and the large size of whales"</h3>

<ul>
<li>Presenter: Jean Potvin, Saint Louis University</li>
<li>Host: Tom DeGrand</li>
<li>Abstract: Large baleen whales such as the humpback and blue whales have become the shining stars of a great number of popular nature documentaries. Paradoxically, much of their physiology remains poorly understood. Generally one must look into a complex web of relationships between morphology, physiology, ecology and bio-mechanics to explain the whys and hows of, for example, body architecture. In this presentation I show that the blue whales and their baleen-bearing cousins represent shining examples of the central role played by physics in shaping their evolution into the largest and most massive life forms to have ever lived on Earth. The peculiarities of their feeding strategies permit the use of simple formulations of the work-energy and momentum conservation principles to estimate swimming metabolic energetic expenditures over size and demonstrate how body gigantism can not only become an advantage but also a disadvantage. This presentation will also show the results of an ongoing NSF-funded and inter-disciplinary study aimed at collecting kinematic and video data on humpback and blue whales foraging off the coast of California, with the goals of further understanding their feeding behavior as well as providing data for physical modeling validation.</li>
</ul>

<h3>October 17 — "Observing quantum materials in real time by pump-probe Raman Scattering"</h3>

<ul>
<li>Presenter: Dmitry Reznik, University of Colorado Boulder</li>
<li>Host: Mihaly Horanyi</li>
<li>Abstract: Pump-probe experiments open a completely new way to study and control quantum materials. Their behavior away from thermal equilibrium, generation of metastable phases, photoexcited states, quantum computing-related phenomena, chemical reactions, energy dissipation, etc. can now be measured in real time with unprecedented precision due to rapid advances in ultrafast lasers and x-ray sources. In this talk I will give an overview of several representative pump-probe techniques and then focus on time-resolved Raman scattering. I will then discuss a demonstration project elucidating how energy from hot electrons cascades through different vibrational modes on the way to the thermal bath in graphite. Finally, to illustrate the diversity of problems that can be addressed, I will show how pump-probe Raman scattering is used to probe relaxation of the magnetic state in an antiferromagnetic Mott insulator.</li>
</ul>

<h3>October 24 — "From the Big Bang to Signs of Alien Life, with the James Webb and Future Telescopes"</h3>

<ul>
<li>Presenter: John Mather, Goddard Space Flight Center</li>
<li>Host: Jason Glenn</li>
<li>Abstract: Planned for launch in 2021 on an Ariane 5 from French Guiana, the James Webb Space Telescope (JWST) will observe at wavelengths from 0.6 to 28 µm with a full suite of imagers, spectrometers, and coronagraphs. JWST will extend the discoveries of the Hubble and Spitzer observatories in all areas from cosmology, galaxies, stars, and exoplanets to our own Solar System. With a 6.5 m primary mirror it has a collecting area 7 times that of Hubble and 50 times that of Spitzer. Inventions were required ranging from deployment and in-flight focusing of its segmented telescope, to greatly improved infrared detectors, to a 6 Kelvin refrigerator for one of the instruments.  I will outline the planned observing program and the major scientific challenges being addressed. What were the first objects that formed in the expanding universe? How do the galaxies grow? How are black holes made, ranging from stellar mass to supermassive, over a billion solar masses, and what is their effect on the neighborhood? How are stars and planetary system formed? What governs the evolution of planetary systems, with the possibility of life? How did the Earth become so special? But the most important discoveries will be those we have not even imagined today.
<p>I will also describe the new telescopes being built on the ground and proposed for space, ranging from far infrared to X-rays.  And now for something completely different, I am developing a radical idea to observe exoplanets with ground-based telescopes and extreme adaptive optics, using an orbiting starshade. Since it does not require a space telescope, it could reveal an Earth twin with signs of life within the next 15 years. Not easy, but not impossible!</p>
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</ul>

<h3>October 31 — "Searching beyond the Standard Model at the LHC"</h3>

<ul>
<li>Presenter: Kevin Stenson, University of Colorado Boulder</li>
<li>Host: John Cumalat</li>
<li>Abstract: With the discovery of the Higgs boson in 2012 by the CMS and ATLAS collaborations, all of the fundamental particles in the standard model of particle physics have been observed.  Nevertheless, the many open questions in particle physics make it clear that the Standard Model is not a complete theory, and the main goal now is to discover what lies beyond the Standard Model.  I will describe some existing searches from the CMS experiment at the LHC and how the accelerator and detectors will be upgraded over the next decade to increase our sensitivity to new phenomena.</li>
</ul>

<h3>**CANCELLED** November 7</h3>

<h3>November 14 — "Active Matter: from colloids to living cells"</h3>

<ul>
<li>Presenter: M. Cristina Marchetti, University of California, Santa Barbara</li>
<li>Host: Leo Radzihovsky</li>
<li>Abstract: Collections of self-propelled entities, from living cells to engineered microswimmers, organize in a rich variety of active fluid and solid states, with unusual properties. For instance, active fluids can flow with no externally applied driving forces and active gases do not fill their container. In this talk I will describe the behavior of such “active materials” and highlight two examples of active phase transitions. The first is the formation of cohesive matter with no cohesive forces in collections of purely repulsive active colloids. The second is a model of epithelial tissues that exhibit a liquid-solid transition at constant density driven by cell motility, contractility, and cell-cell adhesion.</li>
</ul>

<h3>November 21 — Fall Break; No Colloquium</h3>

<h3>November 28 — "Nanoscale Lasing: A Conundrum?"</h3>

<ul>
<li>Presenter: Teri Odom, Northwestern University</li>
<li>Host: Scott Diddams</li>
<li>Abstract: Metal nanostructures concentrate optical fields into highly confined, nanoscale volumes that can be exploited in a wide range of applications. However, the use of plasmonic structures as cavities for generating coherent emission seems counter-intuitive based on conventional designs of macroscopic lasers. This talk will describe how arrays of nanoparticles can support a unique open-cavity architecture that can be used to interrogate the mechanisms of energy transfer processes and plasmon amplification in confined systems. First, we will describe how single band-edge lattice plasmons in metal nanoparticle arrays can contribute to single-mode lasing at room-temperature with directional emission. Second, we will discuss how ultra-narrow resonances from superlattice plasmons, collective excitations in hierarchical nanoparticle arrays, can support multi-modal nanolasing. Finally, we will describe challenges in and approaches to differentiating among competing energy transfer in the lasing action based on coherence, cavity size, and ultra-fast characteristics.</li>
<li>Biography: <strong>Teri W. Odom</strong> is Charles E. and Emma H. Morrison Professor of Chemistry and Chair of the Chemistry Department at Northwestern University. She is an expert in designing structured nanoscale materials that exhibit extraordinary size and shape-dependent optical properties. Odom has pioneered a suite of multi-scale nanofabrication tools that has resulted in flat optics that can manipulate light at the nanoscale and beat the diffraction limit, plasmon-based nanoscale lasers that exhibit tunable color, and hierarchical substrates that show controlled wetting and super-hydrophobicity. She has also invented a class of biological nanoconstructs that are facilitating unique insight into nanoparticle-cell interactions and that show superior imaging and therapeutic properties because of their gold nanostar shape. 
<p>Odom is a Fellow of the American Physical Society (APS), the American Chemical Society (ACS), the Materials Research Society (MRS), the Optical Society of America (OSA), the Royal Society of Chemistry (RSC), and is an OSA Senior Member. She has received numerous other honors and awards, including a Research Corporation TREE Award; a U.S. Department of Defense Vannevar Bush Faculty Fellowship; the Associated Student Government Faculty Honor Roll; the Carol Tyler Award from the International Precious Metals Institute; a Blavatnik Young Scientist Finalist in Chemistry and Physical Sciences and Engineering; a Radcliffe Institute for Advanced Study Fellowship at Harvard University; the ACS Akron Section Award; an National Institutes of Health (NIH) Director's Pioneer Award; the MRS Outstanding Young Investigator Award; the National Fresenius Award from Phi Lambda Upsilon and the ACS; the Rohm and Haas New Faculty Award; an Alfred P. Sloan Research Fellowship; a DuPont Young Investigator Grant; a NSF CAREER Award; the ExxonMobil Solid State Chemistry Faculty Fellowship; and a David and Lucile Packard Fellowship in Science and Engineering. Odom was founding Chair of the Noble Metal Nanoparticles Gordon Research Conference (2010) and founding Vice-Chair of Lasers in Micro, Nano, Bio Systems (2018). She is on the Editorial Advisory Boards of <em>ACS Nano, Materials Horizons</em>, <em>Annual Reviews of Physical Chemistry</em>, <em>ChemNanoMat, Chemical Society Reviews</em>, <em>Bioconjugate Chemistry</em>, and <em>Nano Letters</em>. She was founding Associate Editor for <em>Chemical Science </em>(2009-2013) and serves as founding Executive Editor of <em>ACS Photonics</em> (2013 - ). Odom’s <a href="http://axial.acs.org/2018/02/26/teri-odom-discovery/">Personal Story of Discovery</a> was featured by ACS Publications.</p>
</li>
</ul>

<h3>**Special Colloquium: Monday, December 3** — "An Introduction to Quantitative Finance from the Viewpoint of an Experimental Physicist"</h3>

<ul>
<li>Presenter: Joseph Mitchell, former researcher at Renaissance Technologies</li>
<li>NOTE SPECIAL LOCATION: DUAN G125</li>
<li>Host: Jerry Peterson</li>
<li>Abstract: During the past several decades it has become common for Wall Street firms to hire workers trained in Physics, Mathematics and other technical fields. Given this, it is perhaps interesting for physicist to learn a bit about quantitative finance. We will discuss some properties of financial data and the very basics of risk and cost models. Along the way we will contrast some aspects of financial data analysis with the data analysis of physics experiments. Finally, time permitting, we will discuss a textbook example of a trading strategy.</li>
</ul>

<h3>December 5 — "<b>Watching Chemical Reactions Happen One Molecule at a Time"</b></h3>

<ul>
<li>Presenter: Heather Lewandowski, JILA, Department of Physics, University of Colorado Boulder</li>
<li>Host: John Cumalat</li>
<li>Abstract: Reactions between ions and radical molecules play an important role in the chemistry that drives dynamics in the interstellar medium and during combustion of hydrocarbons. Unfortunately, experimental measurements of these reactions are very challenging, and thus very rare. We use tools borrowed from the cold atom community to measure ion-molecule reactions in a well-controlled environment. Here, we can study reactions between atoms and molecules in single quantum states at low temperatures. Our high sensitivity allows us to study reactions where the reaction rate can be as low as one reaction per minute. I will present the capabilities of this cold ion-molecule reaction apparatus and some example reactions we have been able to study using this new system.</li>
</ul>

<p>For more information about colloquia this semester, contact: <a href="/physics/node/786">Mihaly Horanyi</a>.</p>