2011 - 2012 Physics Colloquia
Submitted by Ellen F. Feld
Unless otherwise noted, all physics seminars and colloquia are held on Thursdays from 4:45 to 6:00, in lecture room 3 of Merrill Science Center. Tea and snacks will be served before seminars at 4:15 in 204 Merrill. If you would like to be mailed seminar announcements, please send an email to Ellen Feld.
Contact colloquium organizer Ashley Carter with any questions about colloquia.
Click here for the spring semester schedule
Sept. 8 - No Seminar Sept. 15 - Welcome Back Pizza Party. Student lounge - Merrill 114-116, 4:30PM
Dr. Alexi Arango, Mount Holyoke College
"Next-generation photovoltaics utilizing unconventional semiconductors for low-cost, large-scale electricity generation"
Analysts are predicting that within four to seven years electricity generated from photovoltaics will cost less than grid electricity, making it the cleanest, cheapest, and most abundant form of energy generation. The rise of solar energy, however, could fail to materialize if current photovoltaic technologies cannot meet the staggering manufacturing volumes needed to meet anticipated demand. Next-generation photovoltaics fabricated from unconventional semiconductors -- such as organic molecular solids, conjugated polymers and inorganic semiconducting nanocrystals -- promise to solve existing manufacturing bottlenecks due to their superior processing advantages, low cost and earth-abundance. Unfortunately, power conversion efficiencies are currently too low for terrestrial energy applications. How can the efficiency be increased beyond the present limits? Using synthetically-grown nanocrystals, we have developed a new device structure that generates a record-high open-circuit voltage, a critical component of high efficiency. This result forces us to reconsider the mechanism responsible for voltage production in nanoscale heterostructures, and may ultimately lead to high-efficiency next-generation photovoltaics that are well-suited for wide-scale deployment.
Dr. Gerald Gabrielse, Harvard University
"The Surprising Electron"
The electron is a wonderfully surprising elementary particle. It may be a true point particle; at least no size has yet been detected. It has spin though nothing is rotating. It acts like a small magnet - its magnetic moment being the most accurately measured property of an elementary particle. Inside its vanishing size may be a charge distribution that is not spherically symmetric. This lecture tells the story of the modern, low energy probes of the properties of an electron.
Dr. Gabe Spalding, Illinois Wesleyan University
"Optical Momentum and Angular Momentum: Thinking about mechanical effects of light (and other wave/particle bombardments"
For microfluidic, "lab-on-a-chip" technologies and for research involving biomedical imaging, the components of interest are small enough that even the relatively weak forces (and torques) associated with light can be sufficient for mechanical manipulation, and offer extraordinary position control, and can measure interactions with three orders of magnitude better resolution than atomic force microscopy. This talk will include a discussion of the underlying physics and will extend our understanding of the angular momentum carried by light to clarify what orbital angular momentum means in the "stationary states" encountered in quantum mechanics. The talk will also detail some of the considerations that go into designing optical systems appropriate to micromanipulation of different types of micro- and nono-scale samples (dielectric solids or fluids, metals, semiconductors). Advanced methods, including the use of holographically structured optical fields, will also be introduced.
Dr. Tatsu Takeuchi, Virginia Tech, Department of Physics
"Galois Theory for Physicists: Spontaneous Symmetry Breaking and the Solution to the Quintic"
October 25, 2011 marks the 200th anniversary of the birth of Evariste Galois: October 25, 1811 - May 31,1832.
As you can see from the date of his death, he was a mere 20 years old when he died of wounds suffered during a duel. Anticipating his own death, he wrote two papers the night before the fateful duel in which he invents Group Theory, and applies it to the proof that the quintic equation cannot be solved by radicals. These papers were discovered posthumously by the French academy, and Galois' name has been immortalized.
Though the above story is well known to most math enthusiasts, and Group Theory is used in physics extensively, the details of Galois Theory remains unbeknownst to most physics students (and faculty), and one must take a course in advanced algebra to learn anything about it. And even then, the approach used my mathematicians is a very hard nut to crack.
In this talk, I attempt to remedy the situation by bringing in the idea of Spontaneous Symmetry Breaking from physics. I will review the solutions to the quadratic, cubic, and quartic equations using radicals, and show that the formulae accomplish the task of finding the solutions by implementing a sequence of symmetry breakings following a specific pattern. I then show why this cannot be done for the quintic.
Dr. Subir Sachdev, Harvard University Department of Physics
"Quantum phase transitions in condensed matter physics, with connections to string theory"
I will describe the importance of quantum phase transitions to the observable properties of a wide variety of modern quantum materials, including the high temperature superconductors. I will also discuss how insights from string theory have helped address some difficult questions arising in this context.
Dr. Erel Levine, Harvard University Department of Physics
"How to Worm Infection Dynamics out of Worms"
Infection by an intestinal pathogen is a complex dynamical process that occurs on multiple scales. The outcome of infection, and the evolution of pathogens and immune response, depends strongly on the processes responsible for the rise, dissemination, fall and evolution of infecting bacteria in the host. Quantitative understanding of these processes is limited in no small part due to the lack of clear experimental data.
In recent years host-pathogen interactions have been studied in simple invertebrate models such as the roundworm Caenorhabditis elegans. Remarkably, many of the virulence mechanisms used by microbes to infect C. elegans and other simple model hosts are also used in the infection of mammalian hosts. At the same time, the innate immune response of the invertebrate host is evolutionary conserved.
In this talk I will discuss experimental and theoretical approaches to study in-host population dynamics using C. elegans as a model host. Surprising connections will be made with concepts from systems biology and statistical mechanics.
Nov. 10 - 5-College Physics Talk
Dr. David Wineland, NIST Time and Frequency Division, Boulder, CO
"Quantum entanglement, quantum computers, and raising Schrodinger's cat"
Already in 1935, Erwin Schrödinger – one of the inventors of quantum mechanics - knew that when extended to the realm of our everyday experience, the theory permits rather bizarre situations. To illustrate his point, he introduced his well-known cat that can simultaneously be both dead and alive. That is, its quantum state is said to be a superposition of both possibilities, without either one being dominant. Now, 70 years later, we can create situations that have the same attributes of this unfortunate cat, although so far only on the microscopic scale of a few atoms, i.e., a very small Schrödinger kitten. As an example, first consider a marble placed in a bowl, rolling back and forth, but try to imagine what is classically impossible - a single marble that can be on the left side of the bowl and simultaneously on the right side! In the lab, we can make a micro-version of just such a marble. We confine a single atom in a region where it can't escape, and then by applying laser forces we can realize the situation where it is in two places at once.
It's true that this is just a kind of quantum parlor trick, but it might lead to something useful. The computer memory on a personal computer uses two electronic switch positions to store information. Two energy levels in an atom can serve the same function, and be labeled in the same way by "0" and "1". However, in analogy with the atomic marble in a bowl, we can arrange the quantum bit or "qubit" to be both "0" and "1" at the same time, thereby storing both states of the bit simultaneously. This property potentially leads to a memory and processing capacity that increases exponentially with the number of qubits. The power of this exponential scaling is apparent if we consider a quantum memory of only 300 qubits. For comparison, a classical computer memory of 300 bits could store about a line of text. However, a 300 qubit memory could store more information than an ensemble of PCs constructed of all the matter in the universe! This characteristic and a related property called quantum entanglement would enable a quantum computer to efficiently solve certain problems such as factorizing large numbers - an ability that could compromise the security of many encryption systems. So far, we have only realized a quantum computer composed of a few bits. However, although extremely challenging, there doesn’t seem to be any fundamental reason that we can’t build a useful device in the future.
Nov. 11 - (Friday)
Dr. David Wineland, NIST Time and Frequency Division, Boulder, CO
Atoms absorb electromagnetic radiation at certain precise frequencies. Knowing this, a recipe for making an atomic clock is fairly simple to state: we first need an oscillator to produce the radiation and a device that tells us when the atoms absorb it, thereby indicating that the oscillator is in synchronism with one of the atoms’ absorption frequencies. To make a clock from this setup, we then simply count cycles of the oscillator – the duration of a certain number of cycles defines a unit of time, for example, the second. In one of the world’s most accurate clocks, we count the cycles of an oscillator that has a frequency of 1,052,871,833,148,990.44 cycles per second – synchronous with an absorption frequency in 27Al+ ions. At this level of precision, many effects, such as those due to special and general relativity, can affect our measurements; therefore, our primary task is to determine and correct for these perturbing effects. For many centuries and still continuing today, a primary application of accurate clocks is for precise navigation.
Nov. 17 - Dr. Matthew LaHaye, Syracuse Deparment of Physics
There is a rapidly growing effort to integrate quantum technologies with mechanical structures in order to manipulate and measure quantum states of mechanics for applications ranging from quantum computing to sensing of weak forces to fundamental explorations of quantum mechanics at massive scales. A central focus of this effort, informally dubbed quantum electromechanical systems, has been the integration of superconducting electronics as control and measurement elements in nano and microelectromechanical systems (NEMS and MEMS). In fact, in just the last few years, spectacular advancements have been made in this area, providing researchers with a suite of tools for preparing, manipulating and measuring NEMS and MEMS near and even in the quantum domain. In my lecture, I will highlight the state-of-the-art of this exciting and nascent field, focusing in particular on recent work my colleagues and I have been engaged in to develop one such quantum electromechanical tool: the qubit-coupled mechanical resonator. I will discuss how qubit-coupled mechanical resonators are in many ways formally analogous to systems in cavity quantum electrodynamics that have been used for studying the quantum nature of light; and I will thus outline how qubit-coupled mechanics will similarly be an important test-bed for studying the quantum nature of mechanical structures.
Junior Orientation Meeting
Junior Orientation Meeting beginning at 4:30PM in the Student Lounge/116 Merrill. This will be an informational meeting for all juniors where we will discuss how to go about applying to graduate school and options and procedures for honors thesis projects. Pizza will be served.
Student Thesis Talks
Aftaab Dewan - "Probing Physics Beyond the Standard Model Through Neutrino Scattering"
Saugat Kanel - "Seeking a Dirac Monopole in a Spinor Condensate"
Benjamin Scheetz - "Diode Lasers for Beryllium Ions"
Dr. Dave Spiegel, Institute for Advanced Study, Princeton
"Worlds Around other Stars"
In the last 20 years, the science of extrasolar planets has blossomed from the dream of a few dedicated planet hunters to one of the core disciplines of astrophysics for the foreseeable future. We have moved from the first tentative detections of planet candidates to an era in which there are hundreds to thousands of known exoplanets. Moreover, we are in an era of characterizing planets, learning about their atmosphere and interior structures and compositions. I will review some highlights of exoplanet science to-date, and discuss what factors influence the climatic habitability of terrestrial planets around other stars.
Dr. Qi Wen, Department of Physics, Worcester Polytech Institute
"Nonlinear elasticity and non-affine deformation in biological polymer networks"
Mechanical properties of cells and tissues are largely determined by the cell cytoskeleton and extracellular matrix, which are essentially hydrogels of biological polymers such as actin, microtubule and collagen. Compared to synthetic rubber-like material, gels of these biological polymers show strong nonlinear elasticity in the form of strain-stiffening, which refers to a phenomenon that material elastic modulus becomes larger at larger deformation. A major challenge is to understand the physical mechanism of strain-stiffening. One way to probe the origin of strain-stiffening is measuring the non-affine deformations in biopolymer networks. Here, I show results of measuring the nonlinear elasticity and nonaffine deformation in biopolymer networks, and discuss the possible sources of nonaffine-deformation in polymer networks.
Dr. Anne Goodsell, Department of Physics, Middlebury
"Exciting Physics with Excited Atoms"
Atoms can be excited by light beams, when the energy of each photon matches the energy for a particular atomic transition. The resonant interaction between light and individual atoms in a gas can make those atoms heat up, cool down, or come to a nearly-complete stop in midair. With the technique of laser cooling, we can slow atoms from speeds of hundreds of meters per second to just a few centimeters per second. We are studying how electric fields can steer, manipulate, or capture these slow, laser-cooled atoms. I will describe the results of our experiments at Harvard in which we have captured and ionized individual atoms interacting with the electric field of a single charged nanotube. Looking toward the future, I will outline our plan for experiments at Middlebury to re-excite slow atoms and magnify the influence of external electric fields. Slow atoms in a highly-excited state can be tremendously sensitive probes to investigate the strength of electric fields near the surface of a material. As atoms in free flight move near a surface, their flight paths will be deflected by the force due to van der Waals attraction or by controlled fields near charged objects. While an atom in the ground state is fairly insensitive to these disturbances, an excited atom can be significantly influenced by these small fields.
Dr. Michael Durst, Department of Physics and Astronomy, Bates College
"Noninvasive Biomedical Imaging Using Nonlinear Optical Microscopy."
Biomedical optics entails using lasers, fluorescence, and other clever tools to extract images from beneath the surface of biological tissue. We are all familiar with MRI and ultrasound imaging, but these techniques suffer from poor resolution. Light-based microscopy provides superior resolution, allowing you to see details on the cellular level. This talk will describe efforts to look beneath the surface of the body without making an incision. Nonlinear optical microscopy techniques such as two-photon absorption, long-wavelength excitation, temporal focusing, and photothermal imaging will be discussed.
Dr. Frank Sup, Department of Mechanical and Industrial Engineering, University of Massachusetts
"Augmenting Human Mobility with Robotics"
Recent advances in power, actuation, and microelectronics technology over the past decade, have enabled new possibilities in the design and functionality of robotics. The combination of these advances has given rise to a new class of machines deemed ‘wearable robotics’. New possibilities in human-robot interactions are now being investigated into how best to augment or restore the physical abilities of humans. Doing so, however, creates new control challenges to seamless integrate humans and robots for coordinated and functional interaction. This talk will highlight the challenges in physical human-robot interaction and current approaches to in controlling the interaction. Examples in powered intelligent prostheses and orthoses from the field and the speaker’s own research will be used to demonstrate the progress in designing and controlling wearable robotics capable of transmitting human-scale joint torques and powers. An emphasis of the talk will be on the functional improvements such new technologies could provide to persons with disabilities and the elderly within the next decade.
Christopher Jones, Department of Physics, MIT
"Neutrinos Don't Lie: Using Neutrinos for Science and Peace"
Neutrinos; they can travel through a light-year of lead, they're produced in the sun, in reactors, and cosmic rays, and they always tell the truth. I'll give an overview about the elusive and intriguing neutrino, our latest efforts to measure its properties, and how they can help us with nuclear nonproliferation.
Carolyn Y. Johnson, Health/Science Reporter, Boston Globe
"Science writing: communicating complicated ideas to everyone"
Lessons in talking and writing clearly about science are rarely part of a scientist's formal education, yet they are essential skills in almost any future career. This talk will focus on the importance and difficulty of communicating science to a general audience, drawing on my unconventional path from Amherst physics major to science reporter for the Boston Globe. Those long hours spent in lab and working on problem sets will be useful later on, even in alternative careers! Topics will include how science journalism works, with a short primer on how a major daily newspaper functions (and what it feels like to be the lone person with a science background in the room). I will also explain the tactics I and others use to overcome the jargon and complexity that is part of the fabric of most scientific fields. Whether you will be writing grants to support research, teaching, pursuing a job in industry, or just trying to have a conversation at a party about your work, the ability to communicate a complicated idea -- and why it is interesting -- will always come in handy.
Dr. Robert W. Hyers, Department of Mechanical and Industrial Engineering, University of Massachusetts
"Computer-aided Experiments in Materials Processing"
Pervasive computing is changing not only our social world, but also our scientific approaches and capabilities. The particular strengths of computers can be employed to increase the scientific and technical return of experiments, and furthermore, to enable new classes of experiments. This talk will describe examples from the Materials and Processing Laboratory at the University of Massachusetts.
The first set of examples shows some of the advantages of predictive models as “virtual sensors” for quantities that are difficult or impossible to measure directly. In these cases, a model allows the magnetohydrodynamic flow field in electromagnetically levitated liquid metal drops to be used as an experimental variable. Control of the flow enables new experiments in the fundamental physics of nucleation in quasicrystals and metallic glasses, phase selection in stainless steels, and even transition to turbulence.
The second set of examples describes the use of machine vision for high-precision non-contact measurements of properties including density and thermal expansion. The very high resolution of this measurement, about 250 parts per million, makes it a very sensitive probe of changes in the nature and structure of undercooled liquids. This method has been extended to enable a new, non-contact method for measurements of creep of metals and ceramics, using electrostatic levitation. This method has been demonstrated up to 2400°C, for applications in extreme environments including next-generation jet engines, hypersonic flight, and rocketry.
The talk will conclude with a brief overview of the role of computers in other research being performed in our laboratory in diverse areas from detection of failures in oil-drilling equipment to lightweight radiators for nuclear-electric interplanetary spacecraft.
Dr. David Demille, Department of Physics, Yale University
"Diatomic Molecules as Quantum Tools"
Our group is applying the techniques of modern atomic physics to the system of diatomic molecules. Molecules are more complex than atoms because of their vibrational and rotational degrees of freedom, and this makes them difficult to control. However, we have identified a variety of simple principles that allow us to make use of these "new" properties to provide powerful types of leverage on a broad range of problems. These span fields all the way from particle physics, to quantum computation, to chemical physics. This talk will give an overview of the field, along with some specific examples of our recent work. These include the first-ever laser cooling of a molecule, and the search for the CP-violating electric dipole moment of the electron.
Dr. Jack Harris, Department of Physics, Yale University
"Dissipationless current in resistors: new measurements of persistent currents in normal metal rings"
One of the most remarkable predictions of the quantum theory of electronic circuits is that a small loop of resistive metal can have a perpetual current flowing in it in the absence of any applied voltage. This "persistent" current is directly analogous to the motion of electrons around the nucleus of an atom, and the prediction that it could be observed in realistic devices generated considerable excitement --- 25 years ago. Since then, experiments in this area have produced confusing results at odds with theory and even with other experiments. To address this long-standing controversy we developed a new type of detector for persistent currents that offers much greater sensitivity and a less-invasive measurement than was previously possible. Our results have made possible a painfully detailed comparison between experiment and theory. I will describe these results, which seem to give the clearest picture yet of persistent currents in resistive metals.
Dr. Arthur Zajonc, Department of Physics, Amherst College
"A Life in Physics and Beyond"
Looking back over three-decades of teaching, research and writing, Professor Zajonc will give highlights of his career not only as a physicist but also as author and social entrepreneur. His career has led him into the experimental foundations of quantum mechanics, active participation in teaching interdisciplinary courses with many Amherst colleagues, the founding of the Hartsbrook School in Hadley, Brookfield Farm in South Amherst, Director of the Center for Contemplative Mind in Society and most recently President of the Mind and Life Institute. Through slides and stories he will share aspects from each of these varied areas of his life. Arthur Zajonc retires from the Physics Department this year.
Student Thesis Talks
No Seminar - Departmental Meeting