Physics Department

Spring 2004 Colloquium Schedule

Speaker:   Dr. Bruce Knuteson (MIT)
Title:     Systematic Analysis of HEP Collider Data

Abstract:  Run II of the Fermilab Tevatron presents an excellent opportunity
           for discovering physics beyond the Standard Model.  Unforntunately,
	   predictions for what that new physics may be are all over the map.

	   How can we search for new physics when we only vaguely know what is 
	   should look like?  Is there a way to perform an unbiased yet
	   data-drive search?  Can we quantify the "interestingness" of apparent
	   anomalies after looking at the data?  Is it possible to automate the
	   testing of specific hypotheses against those data?  Can we publish HEP
	   data in a more genuinely and generally useful form, following the lead
	   of our colleagues in astronomy and astrophysics?

	   Algorithms are presented that answer these and related questions.

Host:      Eric Zimmerman 






 



Speaker:   Dr. Steve Wagner (SLAC)
Title:     Interference from Above:  The e+e- -> mu+mu- "Electroweak"
           Asymmetry from 10-1000 GeV

Abstract:  

The $e^+e^-\rightarrow \mu^+\mu^-$ forward-backward asymmetry,
caused above and below the $Z^0$ by the interference of the photon and
$Z^0$ propagators and on the $Z^0$ by the intrinsic parity violation
of the $Z\mu\mu$ coupling, has been studied for the past 25 years.
In the 1980's this asymmetry was used to elucidate
the electroweak interaction.
In the post-LEP era, combined with other fermion asymmetries,
it gives limits on possible ``new physics'' (contact interactions,
additional Z bosons) which might occur at mass scales higher
than the available center-of-mass energy.
I will review the measurements and the models,
and investigate what can be learned with the huge samples
of mu-pairs being collected at high-luminosity B-Factories.
Polarized electron-electron and electron-proton scattering
are also sensitive to similar types of new physics, so I
will discuss recent progress there, together with existing
results from neutrino scattering, atomic parity violation, and
the Tevatron. The sensitivity of these asymmetries to new physics
at the proposed TeV-linear $e^+e^-$ collider will be compared
with the reach of the Large Hadron Collider, which will run years
earlier at a higher center-of-mass energy.

Host:      Bill Ford






 



Speaker:   N. J. Halas, Stanley C. Moore Professor of Electrical and Computer Engineering and Professor of Chemistry, Rice University, Houston, TX, USA
Title:     Plasmon Hybridization: a Design Principle for the Realization of Practical Nanophotonic Architectures
           

Abstract:  

The collective electronic resonance response, or plasmon frequency, of a metal nanostructure 
is dependent both on the constituent metal and on its shape.  Systematic variations in the 
shape of metal nanostructures, when achievable, allows one to control and tune the near and far 
field optical properties of these structures in ways in which we can effectively predict.  This 
combination of nanofabrication chemistry and electromagnetic theory, grounded in time dependent 
local density approximation calculations, allows us to develop simple design rules for new nanoscale 
plasmonic architectures with tailorable and optimizable properties. Over the past few years in our 
laboratory we have developed a concentric layered nanoparticle, known as a nanoshell, whose plasmon 
resonance can be tuned across a large region of the optical and infrared spectrum by varying its internal 
geometry. We have recently shown that the Surface Enhanced Raman Scattering (SERS) response of molecules 
adsorbed onto a nanoshell  surface can be precisely controlled and optimized for a specific pump 
wavelength, and that enhancements of the Raman response greater than 1012 are obtainable for nonresonant 
adsorbates.  A new concentric nanoshell architecture, or “nano-matryushka”, which permits the 
controlled interaction between inner and outer shell plasmons on the same nanostructure, will also be 
discussed. Generalization of the plasmon hybridization concept to planar architectures, where certain 
propagation characteristics of surface plasmon waves can be controlled, will be addressed.  Applications 
of rationally designed plasmonic nanostructures to problems in biotechnology, where in vivo plasmon resonant 
nanostructures tuned to the near infrared region of the optical spectrum can be accessed by light penetrating 
through skin and tissue by as much as 10 cm, will be described. 


Host:      Margaret Murnane 






 



Speaker:   Shijie Zhong
Title:     Thermal Evolution of Oceanic Upper Mantle and Its Implications for Seafloor Heat Flux and Topography
           
Abstract:  

The half-space cooling model explains well the heat flux and
topography (ocean depth) on relatively young seafloor, significant
deviations exist on old seafloor.  In this tlak, I review the 
basic observations and previous attempts in resolving this 
discrepancy.  I propose a new idea that involves thermal boundary
instabilities and trapped heat to explain the observations.










 



Speaker:   Scott C. Hsu (Physics Division, Los Alamos National Laboratory)
Title:     Laboratory Plasma Astrophysics:  What Spheromak Formation
           Teaches Us About Galactic Jet Collimation (and Vice Versa)
           
Abstract:  

The exciting, fast-growing research area of "laboratory plasma astrophysics"
uses laboratory plasma experiments to improve understanding of
astrophysical objects and processes.  This field is spurred by (1) recent
precision astrophysical observations which demand better understanding of
underlying physical processes and (2) advances in experimental
plasma capabilities.  The field addresses research problems at the forefront
of three disciplines:  basic plasma physics, magnetic fusion plasma physics,
and plasma astrophysics, resulting in many opportunities for synergistic
exchange of ideas.  After a brief introduction to laboratory plasma
astrophysics, this talk will focus on one specific example:  the related
problems of spheromak formation and galactic jet collimation (the
spheromak is a plasma configuration studied for its promise as a magnetic
fusion confinement scheme).  Leading theories of galactic jet collimation are
based on magnetohydrodynamic (MHD) treatments of the evolution of a
force-free plasma above a differentially rotating accretion disk which
continuously twists the ambient magnetic field, a process known as
"magnetic helicity injection" and remarkably similar to laboratory spheromak
formation.  Recently, magnetic collimation in accretion disk geometry was
demonstrated experimentally for the first time in a spheromak formation
experiment, providing compelling evidence in support of the MHD
theoretical models.  However, the experiments also raised key questions,
such as how actual jet collimation overcomes magnetic helicity injection
limits and also plasma instabilities expected to arise due to magnetic field
twisting.  These questions also relate to spheromak sustainment, a key
problem holding back the spheromak as a fusion energy concept.  The talk
will conclude with a brief discussion of further experiments being planned.


Host:  Scott Robertson




 



Speaker:   J.L. Kline
Title:     Investigation of Laser Plasma Instabilities in a 
           Single Laser Hot Spot Applicable for the National Ignition Facility
           
Abstract:  

There are a few key obstacles standing in the way of achieving 
thermonuclear ignition at the National Ignition Facility (NIF). 
One of them is controlling parametric instabilities, especially 
Stimulated Raman Scattering (SRS), where the light wave decays 
into a scattered light wave and an electrostatic plasma wave (EPW). 
Parametric instabilities can spoil laser power coupling into the 
target, and can accelerate electrons which preheat the target. The 
linear-theory thresholds for significant SRS activity are routinely 
exceeded in experiments on ignition-relevant quasi-homogeneous 
plasmas.  Experimental results from existing lasers make it clear 
that SRS saturates via non-linear processes. One possible saturation 
mechanism for SRS is coupling of energy from the SRS daughter EPW 
to other non-resonant EPWs [Baker et al., Phys. Rev. Lett. 77 (1996) 67].  
If the amplitude of the daughter SRS EPW is large enough, it can decay 
into a counter-propagating EPW and an ion acoustic wave (IAW), i.e., 
the Langmuir Decay Instability (LDI).  Damping of all these waves 
ultimately saturates SRS.  Another possible saturation mechanism is 
electron trapping by the SRS EPW.  On the one hand, the process 
greatly reduces collisionless EPW damping from classical levels, 
promoting instability growth above linear theory predictions.  On 
the other hand, the trapped electrons dynamically detune the EPW, 
and SRS saturates as a result [H.X. Vu et al., Phys. Plasmas 9, 1745 (2002)].  Theoretical considerations indicate that the dominant saturation mechanism 
should transition from the former to the latter at some value of the 
Debye length.  Whether this theoretical framework is correct, and 
whether we can quantitatively predict the transition is a key question, 
and will help lead to a quantitative, predictive understanding of SRS.


Host:  Scott Robertson






 



Speaker:   Deborah Jin (University of Colorado)
Title:     Making Condensates with a Fermi Gas of Atoms
                      
Abstract:  

An ultracold gas of fermionic atoms provides a unique model 
system in which to investigate fundamental quantum phenomena.  In 
particular, a novel superfluid phase is predicted for a Fermi gas of 
atoms near a Feshbach resonance.  I will discuss recent experiments at 
JILA where we trap and cool fermionic potassium atoms in the quantum 
degenerate regime and create condensates by varying the interactions in 
the Fermi gas.






 



Speaker:   Tobin Munsat (Princeton Plasma Physics Laboratory)
Title:     Plasma Fluctuation Measurements using Microwave Imaging Techniques
                      
Abstract:  

A new instrument for measuring turbulent density and temperature
fluctuations in high temperature plasmas has been developed and 
installed on the TEXTOR tokamak.  This is a combined Microwave 
Imaging Reflectometer (MIR) and Electron Cyclotron Emission Imaging 
(ECEI) system, and is expected to extend the range and detail of 
turbulence measurement capability in magnetically confined plasmas.  
Both the MIR and ECEI techniques take advantage of large aperture 
optics to form an image of the reflecting/emitting layer onto an 
array of detectors located at the image
plane, enabling localized sampling of small plasma areas.

The MIR instrument has been fully characterized in the laboratory 
using a series of corrugated reflecting targets.  16 channels cover a ~9 cm
poloidal region of the cutoff layer.  The MIR technique should enable
poloidally and temporally resolved fluctuation measurements even in the
presence of 2-D turbulence, without reliance on complicated 
computational data analysis or a-priori knowledge of the turbulence 
characteristics.

The ECEI instrument simultaneously samples a 2-D cross-section of 
the plasma with 8 horizontally distributed vertical observation chords, each
with 16 vertically distributed spatial channels.  Poloidal resolution 
of ~1 cm can be achieved for all receiver channels by imaging the ECE 
radiation onto a Schottky barrier diode array.

This research is an attempt to develop an instrument capable of
providing a comprehensive description of short-scale fluctuations, 
widely believed to be a primary driver of cross-field transport 
in magnetically confined plasmas.









 



Speaker:   J. Egedal, W. Fox, A. Fasoli and M. Porkolab
Title:     A laboratory study of fast collisionless reconnection 
           and its relevance to space observations
           
Abstract:  

Plasmas, the ionized gas in lightning bolts, tube lights, 
and most of interstellar space, are generally an excellent 
conductor of electricity. A result is that plasmas interact 
strongly with electric and magnetic fields, and in fact are 
generally “frozen” to magnetic field lines.  Many plasmas, 
however, ranging from the sun to those confined in nuclear fusion 
experiments, can occasionally and rapidly break free, in a process 
called magnetic reconnection. This process controls the evolution 
of solar flares, it allows the solar wind to enter the Earth's 
magnetosphere, and it is an integral part of magnetic sub-storms 
and the aurora phenomena. The fast time scales under which 
reconnection occurs are still poorly understood. 

Magnetic reconnection in the collisionless regime is studied on 
the Versatile Toroidal Facility (VTF). The detailed evolution of 
the profiles of plasma density, current density, and electrostatic 
potential at the onset of driven reconnection is reconstructed 
experimentally. Our analysis reveals a new mechanism, particle 
trapping, efficiently facilitates fast reconnection. We also provide 
an analysis of a unique data set obtained by the Wind spacecraft 
during its recent observation of magnetic reconnection in the 
Earth’s magnetotail. Also in the latter case is electron 
trapping the cause of the fast reconnection process observed. 


Host:  Scott Robertson





 



Speaker:   Steven M. Girvin (Yale University)
Title:     Qubits and Cavity QED with Electrical Circuits
           
Abstract:  

   Recent experimental breakthroughs have led to the construction 
of artificial superconducting ‘atoms’: electrical circuits 
whose state variables (voltages and currents) are intrinsically 
quantum mechanical.   This talk will give an introduction showing 
how these two-state systems can be used as quantum bits for computation 
and will describe an experiment now being performed at Yale to perform 
the analog of strong coupling ‘cavity QED’ measurements on these 
artificial atoms placed in a superconducting resonator.


Host: Leo Radzihovsky










 



Speaker:   Dr. Darren Link (Harvard University)
Title:     Generating and manipulating droplets in microfluidic devices
Abstract:  

The ability to engineer emulsion droplets of precise size and composition is
fundamental to the development of new materials and offers great potential for
the study of chemical kinetic processes. We use microfluidic devices to both
generate and to further manipulate dispersions one drop at a time. One
strategy for doing this is electrified flow-focusing. This technique offers
two important advantages over other emulsification strategies in that it both
allows for a significant reduction in the smallest drop size that can be
obtained, and also it generates droplets that have an electrostatic charge
that can be further used in their manipulation for droplet positioning and
controlled coalescence. Additional strategies for manipulating drops involve
techniques for putting drops inside of drops to create controlled multiple
emulsions.



Host: Leo Radzihovsky










 



Speaker:   Ronald K. Thornton, Center for Science and Math Teaching, 
Departments of Physics and Education, Tufts University, Medford, MA 02155  
CSMT@Tufts.edu

Title:     IMPROVING PHYSICS UNDERSTANDING WITH INTERACTIVE LECTURE 
DEMONSTRATIONS, MICROCOMPUTER-BASED LABS, MODELING, AND VISUALIZATION 

Abstract:  

We have created active learning environments in the introductory 
physics laboratory by developing real-time microcomputer-based 
laboratory (MBL) tools and student-oriented laboratory curricula like 
RealTime Physics: Active Learning Laboratories and Tools for Scientific 
Thinking.  By making use of the results of physics education research, 
we have created environments that have been demonstrated to promote 
significant conceptual learning gains.  One reason for the success of 
these materials is that they engage students and allow them to take an 
active part in their learning.  Such an active learning environment is 
more difficult to achieve in large lecture sessions.  This presentation 
will demonstrate the use of sequences of interactive, 
microcomputer-based lecture demonstrations using real experiments to 
create an active learning environment in large lecture classes.  Actual 
interactive lecture demonstrations will be done in the area of dynamics 
using MBL motion and force probes that will also illustrate the types 
of experiments done by students in laboratory groups.  The Visualizer® 
(part of our modeling suite of software) will be used to display the 
real-time data in vector form.  Videos of students involved in 
interactive lecture demonstrations will be shown and the results of 
research studies will be presented.

  *This work was partially funded by the NSF under the Student-Oriented 
Science and the Modeling Project and by The Fund for the Improvement of 
Postsecondary Education (FIPSE, US Department of Education) under the 
Tools for Scientific Thinking and Interactive Physics Project at Tufts 
University.



Host: Noah Finkelstein










 



Speaker:   Vladan Vuletic (MIT)
Title:     Collective laser cooling due to spatial self-organization of 
           classical atoms: From Rayleigh to Bragg scattering
 
Abstract:  

We demonstrate that classical atoms illuminated by sufficiently intense
laser light self-organize into a density grating. This grating then
efficiently diffracts the incident light, giving rise to strong
collective light-induced friction forces. Since the observed cooling
mechanism is independent of the atomic level structure, it may be
applicable to new atomic species, molecules, or even structureless
scatterers.




Host:  Jun









 



Speaker:   Mikhail Lukin
Title:     Quantum control of photons and atoms     
           
Abstract:  

The work described in this Colloquium is part of the broad effort,
currently under way, to  develop new techniques for manipulating
quantum states of light and matter. Here we will discuss
how the tools from quantum optics and atomic physics  can be used to
attain this goal but these developments are  related to diverse areas of
science  ranging from quantum information  to physics of strongly
correlated systems.

Specifically, we will discuss our recent work involving atomic ensembles
for controlling light propagation. It is based on the technique known as
Electromagnetically Induced Transparency. This technique allows to
coherently
trap photonic states in atomic medium and to convert the stored atomic
excitation into  light pulses with localized, stationary  electromagnetic
energy. Furthermore, it  enables new mechanims for controlled generation,
storage and manipulation of few photon quantum states of light as well
as new approaches to long-distance quantum communication.
We will describe recent experimental progress towards realization of these
ideas.

Finally, the application of the related ideas to mesoscopic systems
will be discussed, pointing to one of the emerging interfaces between
quantum optics and condensed matter physics.





Host:  Jun









 



Speaker:   Prof. Gary Glatzmaier (UC Santa Cruz)
Title:     Numerical Simulations of the Geodynamo:
           Current Results and Future Challenges
           
Abstract:  

Three-dimensional computer simulations of the geodynamo, the mechanism
in the Earth's fluid outer core that maintains the geomagnetic field, now
span more than a million years, using an average computational time step
of about 15 days.  At the surface of the model Earth, the simulated
magnetic field has an intensity, an axial dipole dominated structure,
and a westward drift of the non-dipolar structure that are all similar
to the Earth's. Several spontaneous reversals of the magnetic dipole
polarity have occurred during the simulations, similar to those seen in
the Earth's paleomagnetic record.  However, no global convective dynamo
simulation has yet been able to afford the spatial resolution required to
simulate strongly turbulent convection, which surely must exist in the
Earth's low-viscosity fluid core.  A series of short movies will
illustrate the current results and the challenges involved in developing
improved, turbulent models.


Host:  Shijie Zhong













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