Physics

2008 - 2009 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 William Loinaz with any questions about colloquia.


 Fall 2008

Sept. 4

beginning-of-semester pandemonium

Sept. 11 

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

Sept. 18

Professor Jonathan Friedman  
Department of Physics 
Amherst College

Phonon-Bottleneck-Driven Relaxation and Tunneling in Single-Molecule Magnets

A single-molecule magnets is – true to the name – a magnet made out of a single molecule. The magnetic moment of such a system shows hysteresis like a classical magnet, yet it can tunnel between different orientation states. This talk will focus on recent experiments to study the spin relaxation in single-molecule magnets when subjected to pulsed microwave radiation. We find that, for the Fe8 single-molecule magnet, intense, short pulses of radiation induce a phonon bottleneck with decay time ~5 microseconds. This allows us to observe the thermally assisted resonant tunneling process in real time down to ~100 ns time scales. Detailed numerical modeling of the process quantitatively agrees with our data.

Sept. 25

Professor Frederick Strauch
Department of Physics

Williams College

Perfect Quantum State Transfer with Superconducting Qubits

Superconducting quantum bits (qubits) are artificial atoms that can be wired up into complex structures.  Recently, experimenters have demonstrated quantum state transfer between two superconducting phase qubits and a resonant cavity.  I will present a theoretical proposal to implement perfect quantum state transfer between any two nodes of a hypercube network. This example of novel quantum transport in an artificial solid has applications for both quantum computing and fundamental tests of quantum mechanics at the macroscopic level.

Oct. 2

Professor Albion Lawrence
Department of Physics
Brandeis University

String Theory and Gravity

A principal motivation for work in string theory is to solve outstanding problems in gravitational physics. In this talk I will discuss some of these problems, why string theory provides a fairly natural solution, and what some of the implications are.

Oct. 9

Russell Anderson
Centre for Atom Optics and Ultrafast Spectroscopy
Swinburne University of Technology
Australia

All the Bells and Whistles of Two Component Bose-Einstein Condensate

A common train of thought in physics is "Now we understand one thing, what happens when two (or more) of them interact?". This is precisely the case for macroscopic matter waves, Bose-Einstein condensates (BECs). In the exploding inquiry of multi-component BEC, there exists a huge disparity between the number of theoretical studies to experimental observations. Here, in the BEC laboratory at Amherst College, surprising discoveries have illuminated the rich dynamics achievable in two-component condensates. I will discuss new investigations of two-component BEC, whereby the experimentalist can tune the interaction between the components. Another important feature of two-component quantum systems is relative phase. Here I outline two proposed methods of imaging this phase spatio-temporally; with a Ramsey like technique, and a non-interferometric phase retrieval technique. The latter presents a novel atom-optical analogue to the traditional retrieval of an optical phase imprinted by matter, as used in classical optics and x-ray microscopy.

Oct. 16  no speaker

Oct. 23

Professor Howard Berg
Dept. of Molecular and Cellular Biology
Harvard University

Using Fluorescence to Study Bacterial Chemotaxis

Escherichia coli swims by rotating long, thin, helical filaments that arise at different points on the cell surface.  Each filament is driven at its base by a rotary motor only 45 nm in diameter made from about 20 different kinds of parts.  Cells are able to swim up gradients of chemical attractants by controlling the direction of rotation of these motors, a process known as chemotaxis.  Our aim is to understand how chemoreceptors and flagella work, and how they talk to one another.  I will touch upon the history of this subject, tell you about some of the physics that E. coli knows, and describe some recent experiments that involve measurements of fluorescence, fluorescence resonance energy transfer, and fluorescence anisotropy.

Oct. 30 no speaker

Nov. 6

Professor Anne Gershenson
Department of Chemistry
Brandeis University

Enzyme Activity at Surfaces:  Interactions Between Proteins and Lipids

Peripheral membrane proteins are water soluble proteins that bind to lipid surfaces, a biological example of binding to an interface.  Using bacterial phosphatidylinositol specific phospholipase C (PI-PLC) as a model system and a large variety of biophysical techniques, we are investigating the interactions between soluble proteins and the membrane surface.  Questions of particular interest include: (i) How altering the charge of the membrane surface and/or the protein affects binding (studied by fluorescence  correlation spectroscopy (FCS)) and enzyme activity.  (ii) How protein binding affects lipid dynamics (studied by field cycling nuclear magnetic resonance (NMR)).

 Nov. 13

Dr. Alex Sushkov
Department of Physics
Yale University

Why Does the Universe have more Matter than Anti-Matter? A Condensed-Matter Search for a Violation of Parity and Time-Reversal Symmetries

This year’s Nobel Prize in physics was awarded to Nambu, Kobayashi, and Maskawa for their study of nature’s broken discrete symmetries (charge conjugation C, parity P, and time reversal T). However what we know about the breaking of these symmetries is not enough to explain the matter-antimatter asymmetry of the universe. One of the ways to study the breaking of parity and time reversal symmetries is to search for the permanent electric dipole moment (EDM) of the electron. I will describe an experimental search for this EDM, based on a solid paramagnetic ferroelectric. We expect to improve the current EDM limit by a factor of 100, with the sensitivity gain originating from large densities

22cm−3, and from large effective electric fields E* = 10 MV/cm due to the ferroelectric displacement of the ions in the crystal lattice field.

Nov. 20

Dr. Steve Maxwell '00
National Institute of Standards and Technology (NIST)

Dynamics of a Sodium Spinor Condensate

In the Laser Cooling and Trapping Group at the National Institute of Standards and Technology, we have an ongoing experimental and theoretical effort to understand the dynamics of Bose-Einstein condensates of atomic sodium in an optical trap. In an optical trap, atoms in any spin state can be confined. Collisions between atoms in different spin states can give rise to collective oscillations in the spin of all atoms in the condensate. These collisions, which are antiferromagnetic in nature, also lead to a phase transition which can be seen by changing the orientation of the atoms or by changing the value of an applied magnetic field.

In this talk, I will discuss the features of this system observed by our group and explain how some of them can be understood in the context of a simple approximation. I will also introduce our efforts to build a computational model to understand the aspects of the system not explained by current theory.

Nov. 27 

Thanksgiving Break

Dec. 2

Student Thesis Talks

- Tim Ripper
- Michael Chernicoff

Dec. 4

Student Thesis Talks

- Ted Pudlik
- Jonathan Tucker
- Dylan Bianchi 

Dec. 9

Student Thesis Talks

- Adam Kaufman
- Max Urmey
- Jeff Grover

Dec. 11 

Reading Period

Dec. 18 

Examination Period

Spring 2009

Jan. 29

no speaker

Feb. 5

Professor Lori Goldner
Department of Physics
University of Massachusetts at Amherst

Biomolecules in Nanodroplets

Biomolecular function can now be studied with unprecedented detail by
optically observing the motion and conformational changes of single
molecules.  In a typical experiment, molecules are tethered to a
surface and studied on an individual basis utilizing the optical
properties of attached dyes or nanoparticles. This works well for
studying single molecules in equilibrium and long-lived molecular
complexes.  However, for more commonly occurring short-lived
complexes, other methods for molecular confinement are needed.  I will
describe how we use single fluorescent dye molecules to study
biomolecules, and then describe a new method for biomolecular
confinement that utilizes nanodroplets.  This method is particularly
good for studying molecules and molecular complexes that are sticky
(denature on surfaces), that fall apart (are short-lived) or that go
"boom" (are out of equilibrium).  Applications to the study of protein
folding and/or protein/RNA interactions will be discussed.

Feb. 12

no speaker

Feb. 19

Matt Hummon '02
Department of Physics
Harvard University

Cold Collisions:  Magnetic Trapping of Atomic Nitrogen and Imidogen (NH)

In John Doyle's group at Harvard University we have a research effort
geared toward the cooling, trapping, and study of collisions of atoms
and polar molecules at temperatures of less than 1Kelvin.
Understanding these collisions and interactions is important for
applications of polar molecules to quantum computing and tests of
physics beyond the standard model.  In addition, reactions in cold
gas-phase atom-molecule systems play an important role in interstellar
chemistry

In this talk, I will present our observations of cotrapping atomic
nitrogen with the polar molecule imidogen (NH) using the buffer gas
loading technique.  This is a first step toward studying cold N - N
and N - NH collisions.  By understanding these collisions we hope to
evaporatively cool atomic nitrogen and in turn sympathetically cool NH
to higher densities and colder temperatures.  I will also discuss our
recent progress toward extending the trap lifetimes of NH to times
greater than 1 second.

Feb. 26

Ian Gregory
Evergreen Solar

The future of solar power in America

The US economy is facing unprecedented challenges.  The solar power industry is no exception.  But the federal stimulus bill, the prospect of new energy policy and the track record of innovation in America is shining a bright light on the near and long-term prospects for solar power.  Evergreen Solar, America's largest manufacturer of solar panels, is positioned at the forefront of this coming revolution.  This seminar will discuss the latest state of the solar industry and what Massachusetts based Evergreen Solar is doing to prepare itself for the future of solar power in America.

Mar. 5

no speaker

Mar. 12

Jared Hertzberg '98E
Department of Physics
University of Maryland

Making Quantum Mechanics Really Big: High-Precision Measurement of a Micron-Scale Mechanical Oscillator

Quantum mechanics is fundamental to physics, but everyday objects behave classically. Key signatures of quantum behavior such as energy eigenstates and superposition states were first observed only at the atomic scale, and in recent years have been demonstrated "macroscopically" in systems such as bose-einstein condensates and superconducting circuits. In this vein, we would like to treat the motion of a macroscopic or nearly-macroscopic object as a quantum observable. A simple harmonic oscillator offers a good candidate. We have fabricated oscillators consisting of a micron-scale mass and spring with resonant frequencies of 5 to 25 MHz, and measured their motion in a dilution refrigerator at temperatures < 100 mK. In this talk, I will discuss two promising experimental goals: preparing the oscillator in its quantum ground state, and demonstrating the limits on position measurement set by the Heisenberg uncertainty principle.

Mar. 19

Spring Break

Mar. 26

no speaker

Apr. 2

Professor Kyungwha Park
Department of Physics
Virginia Tech

Electron Transport Through A Single-Molecule Magnet

Recently, there have been a great amount of experimental efforts
to build and characterize nanoscale single-molecule magnets
deposited on surfaces and bridged between electrodes aiming at
applications for information storage devices or quantum computing
materials.  Single-molecule magnets showed magnetic quantum
tunneling and quantum interference, and may exhibit an intriguing
effect of the coupling between spin and charge degrees of freedom
on transport.  Reported transport measurements through the prototype
single-molecule magnet Mn12 demand theoretical inputs on the roles
of the interfaces and molecular geometries on the transport, and
on whether electronic and magnetic properties are maintained in
low-dimensional structures.  To provide such theoretical inputs,
large-scale simulations at the atomistic level are required.  We
simulate semi-infinite electrodes and different molecular geometries
and interfaces which would mimic experimental set-ups.  Then we
compute transport properties through the single-molecule magnet
Mn12, using the non-equilibrium Green's function method
in conjunction with density-functional theory.  We discuss the
coupling between the Mn12 and the electrodes, as well as charge
distribution of conduction electrons over the Mn12 depending on
molecular geometries and interfaces. We also present a possibility
of the Mn12 being used as a spin filter at low bias voltages.

Apr. 9

Professor Jon McGowan
Department of Mechanical and Industrial Engineering
University of Massachusetts at Amherst

Windpower:  Kilowatts to Megawatts to Gigawatts in 20 years!  What's next?

Apr. 16

Professor Annette (Peko) Hosoi
Department of Mechanical Engineering

Massachusetts Institute of Technology

Optimizing Locomotion: From Biology to Robotics

In this talk I will discuss various projects in which we take inspiration from nature to advance technology.  The key idea behind these bio-inspired design projects is the belief that, thanks to natural selection, if a structure exists in nature that performs a desired function, it is tough for engineers to dramatically improve upon the natural design.  Yet, historically, the countless failures in biomimetics have been more notorious than its successes (e.g. airplanes with flapping wings).  There are many reasons for these failures -- impractical energy requirements and complexity of controls, among others.  To avoid these pitfalls, our biomimetic studies focus on simple biological systems (preferably organisms with primitive or, better yet, non-existant central nervous systems) in which the energy requirements are low and the biological solutions to challenging questions are grounded in mechanics rather than in neurological controls.

Apr. 23

student thesis talks

1. Tim Ripper - An Investigation of Precursors in Fluid Surface Waves

2. Tadeusz Pudlik - Lattice Simulations of the φ4 Theory and Related Systems

Apr. 28 (Tuesday)

student thesis talks

1. Maxwell Urmey - Interference of Flux Tunneling Paths in a Superconducting Qubit 

2. Jeffrey Grover - Using Repeated Landau-Zener Transitions to Factor Integers in a Superconducting Qubit

3. Adam Kaufman - Three Interspecies Feshbach Resonances in 87Rb

Apr. 30

student thesis talks

1. Michael Chernicoff - Automated Phenomenological Calculations for High Energy Electroweak Neutrino Scattering on a Fixed Target

2. Jonathan Tucker - LIBS analysis of geological samples for ChemCam Calibration

3. Dylan Bianchi - Characterizing a Crossed-Beam Optical Dipole Trap for Ultra-cold 87Rb Atoms

May 7

no speaker

May 14

 Exam Period

Student attendance at talks

Administrative notes

 

Physics and Astronomy Department

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

Particle Paths