Seminars and Colloquia
Unless otherwise noted, all physics seminars and colloquia are held on Tuesdays 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 Jonathan Friedman with any questions about colloquia.
Tue, Sep 15, 2015
Tue, Sep 22, 2015
"Waves, Currents, Beaches, and All That: Fluid Dynamics of the Coastal Ocean"
How do ocean waves, currents, and coastlines evolve and interact? The answer lies in the fascinating dynamics of the coastal ocean: wind-generated ocean waves refract, steepen, and break as they enter shallow water, drive strong currents, transport sand, and change the shape of the beach. Improving our understanding of these processes is essential to making better predictions of flooding and erosion during storms like Hurricane Sandy. I’ll describe a set of experiments in which we “perturbed” the seafloor by dredging big holes and channels underwater at the beach, then studied the response to learn about the feedbacks between waves, currents, and seafloor change. The field observations, combined with theory and numerical simulations, reveal how gravity smooths out sandcastles and sandbars, and why rip currents turn on and off.
Tue, Sep 29, 2015
"Experimental Studies in 1D Quantum Magnetism: Old Physics, New Materials, New Physics"
Quantum physics is the study of the behavior of nature at very small length scales, atomic size and smaller. The explosive development of nanoscience over the past thirty years enables people to synthesize, manipulate, image, and control very small materials.
This presentation will offer a different perspective. Quantum behavior can also be studied and understood using appropriately-designed macroscopic materials. This premise will be illustrated by recent developments in one-dimensional magnetism in which magnetic behavior is dominated by purely quantum effects.
Tue, Oct 6, 2015
"Does the Big Bang Prevent Us from Being in Two Places at Once?"
Quantum mechanics tells us that atoms and even molecules can display both particle-like and wave-like properties. By wave-like properties, we mean for example that an atom can be in two different places at once. Only when we probe the atom does its position "collapse" into having one value or the other, and we have no way of knowing beforehand which value it will be. However, there is nothing in the theory of quantum mechanics that rules out larger objects, such as a ball or even you, being in two places simultaneously. So why don't we observe everyday objects in such bizarre quantum states? We shall argue that the answer may ultimately lie in the presence today of a largely invisible, leftover remnant from the Big Bang that created our Universe.
Tue, Oct 13, 2015
"Atomic Sensors for Precision Measurements"
Modern atomic physics techniques use lasers to interact with and manipulate atoms in a gas. Quantum mechanics predicts atomic structure to high precision and demonstrates that atoms of the same species are truly identical. These features provide an attractive platform for the use of atoms as sensors for a variety of fundamental and applied precision measurements. I will describe a fundamental symmetry test using warm atomic vapors of interacting K and 3He that set new limits on a Lorentz-violating background field interacting with the neutron spin. I will also describe instrument development of a novel atom interferometer in an optical cavity using Cs atoms in a cold atomic gas. Such an apparatus could be used for proposed fundamental gravity tests for use in inertial navigation without the aid of GPS.
Tue, Oct 20, 2015
"Breaking the Myth of the 'Non-Traditional' Physicist: Preparing Physics Graduates for the Real World of Employment"
Do you want to get a job after you graduate? Perhaps an internship? I will relay a recent talk by Crystal Bailey from the American Physical Society that detailed the statistics of employment for physics majors and how to land that perfect job (title, above, and abstract, below, are from Bailey's recent talk at an AAPT meeting). If you are a major in physics, biophysics, or a student in the Dartmouth 3-2 Engineering program, you won't want to miss this talk.
"Physics degree holders are among the most employable in the world, often doing everything from managing a research lab at a multi-million dollar corporation, to developing solutions to global problems in their own small startups. Employers know that with physics training, a potential hire has acquired a broad problem-solving skill set that translates to almost any environment, as well as an ability to be self-guided and -motivated so that they can learn whatever skills are needed to successfully achieve their goals. Therefore it's no surprise that the majority of physics graduates find employment in private sector, industrial settings. Yet at the same time, only about 25% of graduating PhDs will take a permanent faculty position--yet academic careers are usually the only track to which students are exposed while earning their degrees. In this talk, I will explore less-familiar (but more common!) career paths for physics graduates, and provide resources to help faculty mentors give their students better information and training for a broader scope of career possibilities."
Tue, Oct 27, 2015
"Physics Education Research on Laboratory Skills and Careers in Physics"
Physics education research (PER) offers a set of methods and ideas to better understand and improve students' learning of physics and has established itself as a vibrant and growing sub-field within the physics community. This talk will apply PER to study the professional practices of physicists in academic research and industrial physics careers and describe findings that can be applied to the undergraduate curriculum. One specific application will focus on the complexity of students' model-based reasoning in an upper-division physics laboratory, where students encounter both sophisticated apparatus and theoretical ideas . A second application will discuss on-going research on workplace usage of physics, math, and communication within academic and industry jobs in physics-related fields, such as photonics. The talk will provide a welcoming introduction to physics education research and approach PER in a way that draws many parallels to conducting research in the natural sciences.
Tue, Nov 3, 2015
"Interfacing Photons and Atoms with (really, really thin) Optical Fibers"
A major effort in quantum physics is the engineering of strong interactions between photons and atoms. The atoms need not be "real" and the photons need not be visible, but the underlying goal is the same. These strong interactions have applications in metrology, spectroscopy, quantum control, and quantum computation, to name a few. In this talk, I will summarize several implementations before focusing on one particular system: cold atoms interacting with photons via an optical nanofiber. An optical nanofiber has a diameter thinner than the wavelength of the light propagating through it, resulting in an evanescent field with relatively large amplitude that is the source of the atom-light interaction. I will outline how we make nanofibers with ultrahigh transmission, and how we use them for atomic-cloud thermometry, to measure atomic level decay, and to confine atoms for long times.
Tue, Nov 10, 2015
"Tabletop-Scale Probes for TeV Physics"
The Large Hadron Collider (LHC) is seeking to observe as-yet undetected, very massive particles. Their strategy involves colliding protons at unprecedentedly high energies, in order to directly create new particles according to E = mc^2. I will describe experiments using an alternate but powerful strategy to detect new particles. In quantum field theories, all ordinary particles are continuously emitting, and then quickly reabsorbing, every type of other particle that exists in nature; this “cloud” of “virtual particles” can modify the apparent properties of ordinary matter. We are searching for an asymmetric charge distribution of this cloud—an electric dipole moment—along the spin axis of an electron or a proton, which can be induced by the existence of certain types of new particles. Although our experiments can fit in a single room, they are sensitive to masses of 3 TeV or even higher, exceeding the direct reach of the LHC. This talk will explain the concepts and techniques of our experiments, including a new effort inspired by Prof. Hunter’s recent work at Amherst.
Tue, Nov 17, 2015
"Astrophysical Searches of Dark Matter Decay and Annihilation"
The abundance of ubiquitous dark matter is now well quantified by observations, yet its nature remains unknown. Dark matter is believed to be composed primarily of an elementary particle. Searches for the dark matter particle are one of the major efforts in particle physics and astrophysics today. X-ray observations of dark matter dominated objects have the potential to reveal a signal from decaying or self interacting dark matter. A well motivated dark matter candidate sterile neutrino oscillates into an active neutrino by emitting an X-ray photon. Another viable candidate is a self interacting dark matter, which could also produce an X-ray signal. I will summarize constraints on decaying and self interacting dark matter models with a focus on the detection of an unidentified emission line 3.55 keV in observations of clusters of galaxies.
Tue, Dec 1, 2015
"Investigating the Collective Motility of Dynein Motor Ensembles Using Structural DNA Nanotechnology"
Kinesin and cytoplasmic dynein are microtubule-based motors that drive intracellular cargo transport in eukaryotic cells. Many intracellular cargos are propelled by small groups of these motors working in ensembles. Yet many of the biophysical mechanisms that govern ensemble motility remain unknown. Building upon our previous work using the techniques of DNA origami (Derr & Goodman et al Science 2012), we have designed a programmable synthetic cargo “chassis” that allows us to control both the number of motors in the ensemble and the rigidity of the cargo chassis that links them. On this chassis, motors within an ensemble are conjugated together through variable length cargo “linker” regions comprised of parallel instances of either single- or double-stranded DNA. The configuration of these regions control the number of independent steps each motor can take before exerting forces on the other motors within the ensemble. This design enables us to investigate how the “communication" of motor stepping through the cargo structure affects interactions within the ensemble and how multiple linked, but independently acting, motors can coordinate to haul cargo. Using TIRF microscopy, we have observed dynein ensembles in vitro transporting these cargo chassis along microtubules. In contrast to our previous results using a rigid chassis (Derr & Goodman et al Science 2012) we find that ensembles of dynein on non-rigid cargos move faster as more motors are added. Our results suggest that cargo rigidity, and the ability for motors to communicate their steps to one another, play important roles in determining the collective motility of multiple molecular motors.