Physics

2007 - 2008 Physics Colloquia

Submitted by Ellen F. Feld

Sept. 13

Alex Rimberg, Dartmouth College

The Quantum Limit for Electrical Amplifiers: Can We Reach It?

Any scientific instrument, including an electrical amplifier, necessarily adds noise in the process of performing a measurement. As might be expected from knowledge of Heisenberg's uncertainty principle, quantum mechanics sets strict limits on how little noise a measurement can add. There is a great deal of current interest in performing measurements at the quantum limit on such systems as qubits and nanomechanical resonators. This talk will introduce the notion of quantum limited electrical measurement, and discuss recent progress toward this goal at Dartmouth.

Sept. 20

Welcome Back Pizza Party. Student lounge - Merrill 114-116, 4:30PM

Sept. 27

David Haviland, KTH (Sweden) and University of Massachusetts

Nonlinearities, Parametric Amplification and Noise Squeezing in Superconducting Microresonators

Superconducting microresonators are key components in the emerging field of Circuit Quantum Electrodynamics (QED). These circuits are made with planar lithography, and their electrodynamics can be well described by the simple model Hamiltonians of QED, where both field and "atom" degrees of freedom must be treated quantum mechanically. The talk will discuss the intrinsic non-linear properties of coplanar microresonators, demonstrating how this non-linearity can be controlled and used to realize parametric amplification of microwave signals. A brief introduction to parametric amplifiers will be given, and results on squeezing of a microwave signal with the phase-sensitive parametric amplifier will be shown. It is also possible to squeeze noise, and even quantum zero-point fluctuations, creating squeezed vacuum states. Such states can be used for noise-free measurement. 

Oct. 4

Eric Mazur, Harvard University - There will be two talks:

4PM in Merrill 3 - Subcellulary Surgery and Nanosurgery  

We use femtosecond laser pulses to manipulate sub-cellular structures inside live and fixed cells. Using only a few nanojoules of laser pulse energy, we are able to selectively disrupt individual mitochondria in live bovine capillary epithelial cells, and cleave single actin fibers in the cell cytoskeleton network of fixed human fibro-blast cells. We have also used the technique to micromanipulate the neural network of C. Elegans, a small nematode. Our laser scalpel can snip individual axons without causing any damage to surrounding tissue, allowing us to study the function of individual neurons with a precision that was not achievable.

8PM in Merrill 2 - Dr. Mazur will deliver Amherst College’s Phi Beta Kappa lecture, on “How the Mind Tricks Us: Visualizations and Visual Illusions.” The lecture and a reception that follows are open to the public at no charge. Neurobiology and cognitive psychology have made great progress in understanding how the mind processes information—in particular, visual information. The knowledge we can gain from these fields has important implications for the presentation of visual information and student learning. A member of the Harvard faculty since 1984, Eric Mazur holds appointments as Harvard College Professor, Gordon McKay Professor of Applied Physics and professor of physics. His research is in optical physics. He also devotes time to finding ways to improve science education. This research has led to the publication of Peer Instruction, a manual that offers methods for teaching large lecture classes interactively. In 1988 Mazur received a National Science Foundation Presidential Young Investigator Award and, in 2001 he received the NSF Director’s Award for Distinguished Teaching Scholars. A fellow of the American Physical Society and its Centennial Lecturer in 1998-99, he has been a visiting professor or distinguished lecturer at the University of Leuven in Belgium, the National Taiwan University, Carnegie Mellon University, Hong Kong University and Vanderbilt University. He is the author of hundreds of scientific publications and serves on the editorial board of Journal of Science Education and Technology.

Oct. 11

John Doyle, Harvard University

Cold Molecules the Old Fashioned Way

Over the past ten years we have developed the technique of buffer-gas cooling and loading of atoms and molecules into magnetic traps. Buffer-gas cooling relies solely on elastic collisions (thermalization) of the species-to-be-trapped with a cryogenically cooled helium gas. This makes the cooling general and potentially applicable to any species trappable at the temperature of the buffer gas (as low as 240 mK). Using buffer-gas loading, paramagnetic atoms and polar molecules were trapped at temperatures around 300 mK. In conjunction with evaporative cooling, buffer-gas loaded magnetic traps offer a means to further lower the temperature and increase the density of the trapped ensemble. Future directions include the production of polar molecule chips for quantum information.

Oct. 18

Keith Schwab, Cornell University

Probing the Foundations of Quantum Mechanics with Mechanical Objects Over the past 10 years, researchers have made enormous progress in the area of quantum measurement in quantum optics and condensed matter settings. This has transformed what scientists have thought was impossible and absurd to the ordinary and routine; for instance it is now common-place to produce coherent superposition states in electronic circuits. Recently there has been a wave of progress in the efforts to produce and measure the quantum properties of mechanical objects. I will discuss recent measurements in my lab and others which approach the Heisenberg Uncertainty Principle and the quantum ground state, and efforts around the world to produce a superposition in space of a mechanical structure: an object located in two places simultaneously. These experiments are designed to shed light on the boundaries of quantum mechanics and the quantum decoherence of macroscopic objects.

Oct. 25

Solomon Diamond, Dartmouth College

How Your Brain May End Up in My Computer: Modeling Cerebrovascular Physiology in Functional Neuroimaging

Neuroimaging technologies have revolutionized our ability to noninvasively image the dynamics brain function but our ability to interpret these data still lags behind. A specific challenge with functional magnetic resonance imaging (fMRI) and near-infrared spectroscopy (NIRS) is to isolate an evoked response from significant background physiological fluctuations. Data analysis approaches typically use averaging or linear regression to remove this physiology with varying degrees of success. An alternative solution is to apply biophysical models of the underlying physiology to interpret the data. In the present study, we compare model-based predictions of cerebrovascular physiology with NIRS measurements from 10 human subjects measured at rest. We found significantly higher correlations with the NIRS data for our model predictions compared to linear regression with the blood pressure fluctuations (multifactor ANOVA, p<0.0001). This finding supports the further development and use of physiological models for neuroimaging analysis. Future extensions of this work could model changes in cerebrovascular physiology that occur during development, aging and disease.  

Nov. 1

Chen-Yu Liu, Indiana University

Hunting for the Evidence of Time Reversal Symmetry Breaking: An electric dipole moment search using a paramagnetic insulator The physics that generates a permanent electric dipole moment (EDM) in fundamental particles, like electrons, requires breaking of both parity and time reversal symmetries. While parity violation has been verified in a wide range of experiments, the direct time reversal process seems much rarer. A non-zero result of the electric dipole moment measurement will provide insights into mechanisms that produce T violation, which is believed to link intimately to the physics of CP violation. I will discuss one such EDM searches at Indiana University. This experiment looks for an induced magnetization in a garnet sample polarized by an external electric field. The technique complements the ongoing EDM search at Amherst.

Nov. 8

Noah Graham, Middlebury College

An Introduction to Solitons and Oscillons Ordinary waves, like a musical note, the beam of a flashlight, or ripples on a pond, tend to dissipate. We can understand this behavior by breaking the wave into components of different amplitudes, each with a definite wavelength and frequency. By plucking a string, turning on a light, or dropping a rock in a pond, one typically creates a superposition of many such waves, each of which propagates independently, leading to spreading and dissipation. In the Standard Model of particle physics, there appear nonlinear effects through which waves can interact, rather than simply passing through each other and dispersing. This modification opens up the possibility of waves forming coherent lumps that do not disperse. These objects can take the form of static configurations, called solitons, and configurations that undergo regular oscillations, called oscillons or breathers. Such objects could be of particular interest in the early universe, when the higher energies available facilitate their formation.

Nov. 15

Fred Cooper, National Science Foundation

Time Dependent Variational Methods: The Dynamics of Solitary Waves in Classical and Quantum Field Theories

By parametrizing solitary waves in terms of a few shape parameters and the position of the wave, the behavior of these waves in a wide variety of non-linear dynamical systems can be understood by using a time dependent variational method to obtain a simple Hamiltonian dynamical system for the shape parameters. The exact relationship between the Height, Width, Energy, Momentum, and velocity of the waves can be obtained without ever constructing the exact solution. Also critical indices during cases where the solitary waves "blowup" (width goes to zero) at finite time can be determined. In Quantum Field theories the use of variational methods and appropriate shape functions reduce the problem to coupled classical field equations and we study the collision of a kink and an antikink in 1+1 dimensional quantum field theory as an example of these methods.

Nov. 22

Thanksgiving Break

Nov. 27 at 7:30 pm in Merrill 1. (Note unusual day, time, and place)

Steve Chu, Lawrence Berkeley National Laboratory (Five College "What's New in Physics" lecture)

The World's Energy Problem and What We Can Do to Solve It Among America's most serious concerns are (i) national security, which is intimately tied to energy security, (ii) economic competitiveness, and (iii) the environment. These issues transcend our national boundaries and have serious implications for the world.  At the core of these problems is need to secure, clean, affordable and sustainable sources of energy. Solutions must come from a combination of improvements on both the demand and supply side, and  science and technology will be an essential part of the solution.  After briefly describing the energy problem, the remainder of the talk will describe areas of research that may lead to transforming technologies.

Dec. 4, 6 and 11

Senior Honors Thesis Talks

Tuesday, Dec. 4 - 5PM

- Don Kun Kim: Test of Local Lorentz Invarience

- PeiDa Guo - The Hydrodynamics Model and Quantitative Experiments for Bacillus Swarming

Thursday, Dec. 6 - 5PM

- Jesse Rasowsky - Quantifying Entanglement

- Kyle Virgien - Applied Magnetization Even Effects in a Solid-State Electron Electric Dipole Moment Measurement

Tuesday, Dec. 11 - 4:30PM

- Elizabeth Petrik - Vortices in an Optically Trapped Bose-Einstein Condensate

- Michael Goldman - Spin BECs Through Landau-Zener Transitions

- Eduardo H. Da Silva - Abrupt Changes in the Tunneling Levels for Mn12-tBuAc Induced by a Transverse Magnetic Field

Jan. 31

Laura Cadonati, University of Massachusetts - Amherst

Gravitational Waves and LIGO: A New Probe into the Universe

The Laser Interferometer Gravitational-wave Observatory (LIGO) has the ambitious goal of the first direct detection of gravitational waves. As predicted by General Relativity, gravitational waves are ripples in the fabric of space-time generated by accelerating masses: black hole and neutron star collisions, supernova explosions, rotating systems and the Big Bang itself. Their detection will provide a fundamental new tool for the understanding of the universe.

To achieve this goal, LIGO uses three Michelson laser interferometers, two in Hanford, WA, and one in Livingston, LA. Each interferometer monitors changes in the relative separation of mirrors at the ends of each of two perpendicular arms of km-scale length, in response to the space-time distortions induced by the passage of gravitational waves.
The goal for the initial phase of LIGO is to measure differences in length of one part in 10^{21}, or 10^{-18} m, one thousand times smaller than the nuclear diameter.
The LIGO detectors have successfully completed a 2-year run at design sensitivity and the LIGO Scientific Collaboration is actively searching for gravitational wave signatures in the interferometers’ data, while upgrades have started to improve the detectors' sensitivity by one order
of magnitude over the next decade.

This talk will give an overview of the status and the science of LIGO, with current results and the expected reach of the initial and advanced LIGO configuration.

Feb. 7

Dmitry Garanin, CUNY Lehman College

The Phonon Bottleneck

The problem of phonon bottleneck (PB) in relaxation of two-level systems (henceforth spins) via direct phonon emission/absorption processes, first recognized by Van Vleck in 1941, remains unsolved until now. In short, if the emitted phonons have nowhere to go, they can be absorbed by spins again and thus the spins cannot relax efficiently. However transparent this picture might appear, is not easy to propose a theoretical description of the effect based on first principles. Here the PB problem is considered in the weak-excitation limit where the Schroedinger equation for the spin-phonon system simplifies and becomes numerically tractable. The solution for the relaxing spin excitation p(t), emitted phonons n_k(t), etc. is obtained in terms of the exact many-body eigenstates. In the absence of phonon damping Gamma_{ph}, p(t) approaches the bottleneck plateau p_\infty > 0 with strongly damped oscillations, the frequency being related to the spin-phonon splitting Delta at the avoided crossing. For any Gamma_{ph} > 0 one has p(t) -> 0 at T = 0 but in the case of strong bottleneck the spin relaxation rate is much smaller than Gamma_{ph} and p(t) is nonexponential.

Feb. 14

Zvonimir Dogic, Brandeis University

Order through Disorder: Entropy Driven Phase Transitions in Colloidal Systems

Although the idea that entropy alone is sufficient to produce an ordered state is an old one, the notion remains counter-intuitive and it is often assumed that attractive interactions are necessary to generate phases with long-range order. Over the past 20 years entropy driven phase transitions have been experimentally demonstrated in both colloidal suspensions of rods and spheres.  In the first part of this talk I will provide a general overview of these experiments. I will also introduce an entropy driven isotropic-nematic phase transition of colloidal rods, first described in a seminal work by Lars Onsager in 1949.  In the second part of the talk I will discuss recent extensions of entropy driven phase transitions to binary mixtures. In this context I will focus on recently discovered highly complex yet very regular structures found in mixtures of monodisperse rods and non-adsorbing polymers. 
Feb. 21

Anthony Dinsmore, University of Massachusetts

How Crystals Melt: Colloids as a Tool to Study Phase Transitions The freezing and melting of crystals are fascinating phenomena that are very common in nature yet difficult to study in the laboratory. Micron-sized particles suspended in solution (colloidal particles) serve as a useful model of these phenomena. Colloidal particles obey the same laws of statistical mechanics that govern how ice melts into water, but they are much larger and slower than molecules, and are thus visible with optical microscopy. By tracking the motions of thousands of individual particles, one can observe phase transitions at the single-'atom' level - and uncover some surprises.

Feb. 28

Jennifer Ross, University of Massachusetts

Single Molecule Biophysics: Cellular Highways and Big Rigs

Microtubules form a polarized network that is primarily radial, but microtubules intersect at a variety of angles both near the nucleus and at the cell periphery. The behavior of kinesin and dynein at these intersections may affect long-range transport efficiency, targeting, and accuracy. Intersecting microtubules serve as crossroads and also possibly as obstacles. In order to test motor function at microtubule intersections, cross-overs of microtubule tracks were arranged in vitro using flow to orient successive layers of filaments. Single molecules of GFP-labeled kinesin and cytoplasmic dynein-dynactin-GFP were observed using total internal reflection fluorescence microscopy.  Motors were also bound to artificial bead cargos at various concentrations. Dynein-dynactin coated beads exhibited a strong dependence on motor density. At low density, the behavior at intersections was highly variable, similar to that of single molecules. At high dynein-dynactin decoration, bead cargos stopped, anchoring dynein-bound beads at every intersection. This result implies that a simple mechanism of regulating dynein motor number could change a motile cargo into one that is constrained at an intersection, consistent with dynein’s proposed tethering functions in the cell, for instance at the Golgi apparatus. The different behaviors of dynein-dynactin and kinesin at intersections most likely reflect their structural differences, and provide insight into the functional specialization of these motors in the complex cellular environment. 

March 5

What's New in Physics? - 5 College Talk, 7:30PM, Merrill Science Center, Lecture Room 2 

Dan Greenberger, The City College of New York

What Did Max Planck Actually Do in 1900? (Big Surprise)

Max Planck is rightly honored as the father of quantum theory.  But what he actually did bears little resemblance to what he is given credit for.  Prof. Greenberger will explore the problems and background of that period, and the contributions of Planck and others to the early days of the theory, and try to put the various pieces, and many ironies, into perspective.

March 6

Dan Greenberger, The City College of New York

New Approaches to the Einstein-Podolsky-Rosen (EPR) Paradox, Since John Bell

I will review some of the key issues of the Einstein-Podolsky-Rosen debate, and emphasize why the questions raised still haunt us, even though they have pretty much been experimentally resolved.  Then I will briefly review Bell's work, and the Greenberger-Horne-Zeilinger (GHZ) innovation for three particles, where there are no inequalities.  Finally, I will show how new experimental techniques have allowed the GHZ approach to be extended down to two particles, and even to the use of inefficient counters, closing many of the remaining loopholes.

March 20 -

Spring Break

March 27

Tatsu Takeuchi, Virginia Polytechnic Institute

The Physics of Color

Color is something we see all around us. Everything we see has some color or another. But do you know how each object acquires those colors? In this talk, I will discuss how the colors of living organisms are often created. The answer simple and, at the same time, surprising.

April 3

Thomas Powers, Brown University

'Life at Low Reynolds Number' Revisited 

At the scale of a cell, viscous effects dominate and inertia is unimportant.  We discuss what it is like to swim in the overdamped regime, using a few simple problems to illustrate the physics of fluid-structure interactions for a slender body, hydrodynamic synchronization, and propulsion in a viscoelastic fluid.

April 10

Kiko Galvez, Colgate University

Quantum Interference of Light: From "Which Way" to "Spooky Action at a Distance"Quantum Mechanics is the most successful physical theory. Yet for all its successes it also makes troubling predictions. At the heart of these mysteries is the nature of light. Deliberations about these have remained academic for decades, but recent technological advances have allowed us to address some of those fundamental issues experimentally. In this talk I will discuss a series of experiments with light that confirm quantum mechanics but not without deepening the mystery of the nature of light.

April 24

Senior Thesis Talks 5PM

Dong Kun Kim - Test of Local Lorentz Invariance

PeiDa Guo - Measuring the Swarm Expansion Rate of B. subtilis: Does chemotaxis play a role in swarm expansion? 

April 29 - Tuesday

Senior Thesis Talks 5PM

Jesse Rasowsky - Quantifying Entanglement

Michael Goldman - Landau-Zener Transitions and Feshbach Resonance in a Spinor Bose-Einstein Condensate

May 1

Senior Thesis Talks 4:30PM

Elizabeth Petrik - Optically Trapped Vortex Lattices in a Bose-Einstein Condensate

Kyle Virgien - Minimizing Systematic Effects in a Solid-State Electron Electric Dipole Measurement

Eduardo H. da Silva Neto - Abrupt Changes in the Tunneling Levels for Mn12-tBuAc Induced by a Transverse Magnetic Field

 

 

Physics and Astronomy Department

AC# 2244
Amherst College
Amherst, MA 01002-5000
413-542-2251
Larry Hunter, Chair

Particle Paths