Colloquia in Academic Year 2008-2009

Dept. of Physics & Astronomy, Stony Brook University


Colloquium committee: Meigan Aronson (chair), Abhay L. Deshpande, Hal Metcalf, Mike Zingale
Coffee & Tea served at 3:45 pm.  Talk begins at 4:15 pm.  Location: Harriman 137 (bottom of square C4 on the campus map)

Spring 2009 colloquia


(colloquia already given are listed here):

DateSpeakerTitleLocal Host

 

Colloquia already given in academic year 2008/2009:


DateSpeakerTitleLocal Host
Sept. 9 Peter Koch
Stony Brook University
Chair's Colloquium
 
Sept. 16 Seamus Davis
Cornell
How the Cooper Pairs vanish with approaching ‘Mottness’ in High-Tc Superconductors
Room temperature superconducting technology has been an aspiration of physicists and engineers for many decades. In conventional BCS superconductivity, the electron-like Landau quasiparticles of a metal form Cooper pairs, each having binding energy Δ. For such superconductors, if Δ >100meV the superconducting critical temperature Tc would be well above room temperature. This could revolutionize technologies of transport, power transmission, particle acceleration, computing and information technology, energy conservation and much more. Our best hopes for achieving this goal have been the hole-doped copper-oxide Mott insulators (MI) because they exhibit the highest Tc of any known material (165K). But the Tc of copper-oxides falls to zero as Δ increases to exceed 100meV with decreasing hole-density p - a frustrating disappointment and a profound and contentious mystery.

During the last year we have made several advances towards understanding the explanation. The key point is that when a copper-oxide MI is converted into a high temperature superconductor, the MI states localized in real-space must evolve into momentum-space eigenstates. Because of its unique capability to determine electronic structure simultaneously in real-space and momentum-space, quasiparticle interference (QPI) imaging using STM is ideal for studying such effects. We used superconducting QPI, techniques to study the canonical high-Tc superconductor Bi2Sr2CaCu2O8+δ as hole-density p is reduced towards zero. We discovered a progressive transformation of momentum-space states which are the excitations of delocalized Cooper pairs, into real-space states as the MI is approached3. It appears that the same ‘Mottness’ with causes electron pairing with high binding energy, extinguishes the momentum-space quasiparticles which are necessary for the superconductivity. We also demonstrate that the characteristic real-space electronic structure remaining after the quasiparticle extinction4 is that of the famous ‘pseudogap’ excitations.

[recorded movie]

Meigan Aronson
Sept. 23 Anand Sivaramakrishnan
AMNH
Planet-hunting with adaptive optics and interferometry
Extending particular frontiers of instrumentation can result in major advances in astronomical understanding. The study of planet and star formation is in the midst of such an expansion now. Bright speckles around a stellar image swamp any faint planetary companion's signal. This speckle noise results from tiny residual errors in the almost perfect optics of today's telescopes. Instruments dedicated to direct detection and characterization of extrasolar planets must combat this speckle noise to deliver science. I will explain the imaging problem, show how adaptive optics coronagraphy reduces speckle noise, and present some of our ground-breaking coronagraphic results. We recently captured the first image of a solar-system scale planet-forming disk around a young star, opening up search spaces inaccessible to even the Hubble Space Telescope. I will also describe a new approach, the non-redundant masking of a telescope aperture, which eliminates speckle noise. With such aperture masking we can peer closer to a star than has hitherto been possible. We hope to implement this technique on NASA's flagship mission, the 6.5-m IR James Webb Space Telescope, scheduled for launch in 2013.

[recorded movie]

Michael Zingale
Sept. 30 no colloquium -- Rosh Hashanah
Oct. 7 Piers Coleman
Rutgers
Qu-transitions. Phase transitions in the quantum era
Physicists are often so awestruck by the lofty achievements of the past, we end up thinking all the big stuff has been done. Unfortunately, this blinds us to the revolutions ahead, even when experiment clearly reveals the fault lines in our understanding. This is as true today as it was a hundred years ago.

We are still very much in the throes of the quantum revolution that began a hundred years ago. It took more than two centuries for the full impact of Galileo, Newton and Leibnitz to be felt by society: the Victorian era, with its clockwork view of reality, can be seen as the crowning peak of this epoch. Today, while the consequences of quantum physics on the atomic scale are well known, our understanding of its full ramifications are very much in a state of flux, in much the same way that classical physics was, more than a hundred years after Newton. Quantum gravity, quantum computers, qu-bits and quantum phase transitions, are all indications of this ongoing revolution. Nowhere is this more so than in the evolution of our understanding of the collective properties of quantum matter.

Just fifty years ago, physicists were profoundly shaken by the discovery of universal power-law correlations at thermal second-order phase transitions. This was, in many ways, one of the last great hurrahs of the classical era. Today, our understanding of phase transitions has entered a new stage, with the discovery of quantum phase transitions: phase transitions at absolute zero driven by the violent jigglings of quantum zero-point motion. Quantum phase transtiions have been discovered in a wide range of materials, including ferromagnets, helium-3, ferro-electrics, heavy electron and high temperature superconductors. I'll introduce you to some of these examples, and explain how a quantum critical point is a kind of "black hole" in the materials phase diagram: a singularity at absolute zero that profoundly influnces wide swaths of the material phase diagram at finite temperature.

I'll talk about some of the radical ideas in this field and we'll discuss the idea of " avoided criticality" - the possibility that high temperature superconductivity nucleates about quantum critical points. Does the electron fall apart a quantum phase transition, and if so... what is the associated Goldstone mode? These are some of the questions we'll touch upon in this colloquium.

[recorded movie]

Meigan Aronson
Oct. 14 Tom Hemmick and Vladimir Litvinenko
Stony Brook
The Center of Accelerator Science and Education
The Stony Brook Physics program benefits from a close connection to nearby Brookhaven National Laboratory in a number of ways. Among these are the opportunities for physics students to earn Ph.D. degrees advised by some of the world's top accelerator scientists. The university has recently established CASE (Center for Accelerator Science and Education) as a Type 1 institute both in recognition of the existing success and vitality of the accelerator physics program and as a means to support the growth of the program. The existence of CASE will not only affect students who receive advanced degrees in accelerator physics but all students in the department via new course offerings and new experiments in the senior and grad lab classes. This colloquium will include discussions of the educational mission of CASE, the past present and future directions of accelerator science, and a question/answer/suggestion period.

[recorded movie]

Michael Zingale
Oct. 21 Wesley Smith
University of Wisconsin at Madison
Startup of the Large Hadron Collider
The LHC at CERN will collide proton beams at 14 TeV center of mass energy and 100 times the luminosity of previous colliders. It will search for the mechanism of particle mass generation, supersymmetry that links mass particles with force particles, the dark matter making up most of the universe and extra dimensions. This facility is just starting operation and the latest information about first collisions at 10 TeV, the experiments and the machine will be presented.

[recorded movie]

Abhay Deshpande
Oct. 28 Wendy Zhang
University of Chicago
Asymmetry and Memory-Encoding Vibrations in a Disconnecting Bubble
Animals can be identified by the distinctive sounds they make. More generally, elementary excitations, or the vibrational spectra, can distinguish different shapes and materials. In this talk I describe the unusual vibrational spectrum associated with an experimentally accessible example of singularity formation: the disconnection of an air bubble while it is submerged under water. Slight initial asymmetries excite vibrations about the cylindrically-symmetric disconnection dynamics. As the singularity approaches, the amplitudes of the different vibrational modes freeze, thereby preserving half of the information about the initial state. In contrast, the phases chirp, changing more and more rapidly in time, thus scrambling the information about the initial phase relations between the different modes. This unusual vibrational spectrum is a consequence of the disconnection dynamics having to satisfy the competing demands of being nearly integrable and also evolving towards a singularity. As a result of these vibrations, the symmetric disconnection is always pre-empted by an asymmetric one. We have excited one of the vibrational modes directly in an experiment and found the measured dynamics to be in quantitative accord with that predicted. We have also conducted a survey of asymmetric disconnection for the simple limiting case of a long and slender bubble neck. The numerics reveals a variety of possible outcomes, the simplest being a smooth contact in which opposing sides of the air bubble collide at a finite speed.

[recorded movie]

Phil Allen / Michael Zingale
Nov. 4 Peter Nugent
Lawrence Berkeley Lab
The Search for Supernova: Past, Present and Future
The present Hubble diagram of Type Ia supernovae is anchored at low-redshift by an interesting hodgepodge collection of events spanning almost 40 years of observation. Starting from the last major photographic search for supernova, the Calan Tololo program in the early 1990's, I will outline the history of the search for supernovae and the inherent biases found in each survey. To address some of these issues, a new program called the Palomar Transient Factory is starting next year. I will describe PTF in detail as well as its recently completed predecessor, the Palomar-QUEST Survey. While the discovery of Type Ia supernovae for cosmology is often the driving force behind these efforts, these surveys find an equally interesting set of core-collapse supernovae. I will touch upon the diversity of these events and how some rare outliers are challenging our understanding of the core-collapse mechanism.

[recorded movie]

Michael Zingale
Nov. 5 (special date) Giulia Galli
UC Davis
Quantum Simulations of Nanostructures

[recorded movie]

Peter Koch
Nov. 11 John Thomas
Duke University
Searching for perfect fluidity in an Atomic Fermi Gas
An optically-trapped mixture of spin ½-up and spin ½-down 6Li atoms provides a new paradigm for exploring strongly interacting Fermi systems in nature. This ultracold atomic gas offers unprecedented opportunities to test theoretical techniques that cross interdisciplinary boundaries. A bias magnetic field is used to tune the gas near a Feshbach resonance, where the s-wave scattering length diverges and the interparticle spacing sets the only length scale. Even though it is dilute, an atomic Fermi gas near a Feshbach resonance is the most strongly interacting nonrelativistic system known, enabling tests of recent theories in disciplines from high temperature superconductors to nuclear matter. Strongly interacting Fermi gases also exhibit extremely low viscosity hydrodynamics, of great interest in the quark-gluon plasma and string theory communities, where it has been conjectured that the ratio of the shear viscosity to the entropy density has a universal lower bound, which defines a perfect fluid.

I will describe our all-optical cooling methods and our studies of the thermodynamic and hydrodynamic properties of the 6Li cloud. Our measurements of the entropy reveal a high temperature superfluid transition, which occurs at a large fraction of the Fermi temperature. Our most recent estimates of the shear viscosity are obtained from observations of the hydrodynamic expansion of a rotating cloud. Together, these results suggest that a strongly interacting Fermi gas may be the most perfect quantum fluid ever studied.

[recorded movie]

Hal Metcalf
Nov. 18 Xiangdong Ji
University of Maryland
What makes up the proton spin? Recent Advances
Twenty years after the "spin crisis", we are still looking inside the proton searching for the missing spin. Deeply virtual Compton scattering and lattice QCD calculations show that the quarks have substantial orbital motion, contrary to simple quark models. High-energy polarized proton collisions are putting significant constraints on the size of the gluon polarization. In this talk, I will give an update and outlook on theoretical and experimental efforts in answering the simple question "what makes up the proton spin"

[recorded movie]

Abhay Deshpande
Nov. 25 David DeMille
Yale
Diatomic Molecules as Quantum Tools
Our group has undertaken a program to apply the techniques of modern atomic physics--cooling, trapping, and ultra-precise control and measurement--to the more complex system of diatomic molecules. The vibrational and rotational degree of freedom in molecules makes these systems qualitatively different than atoms. Control over these properties is enabling new and powerful ways to attack a broad range of problems, ranging all the way from particle physics and cosmology to quantum information processing and quantum chemistry. This talk will give an overview of the field, along with some specific examples of our recent work.

[recorded movie]

Hal Metcalf
Dec. 2 Gordon Kane
Michigan
String Theory and the Real World
In this talk I'll describe how string theory is exciting because it can address most or all of the questions we hope to understand about the quarks and leptons and the forces that form our world. I’ll describe how string theory is testable and already being tested in a number of ways, with examples including issues about cosmology (including dark matter), LHC physics, neutrino physics and more, from the increasingly active subfield "string phenomenology".

[recorded movie]

Michael Zingale
Dec. 9 Jamie Nagle
University of Colorado at Boulder
Properties of the Quark Gluon Plasma and What They Tell Us
The high energy heavy ion collider at Brookhaven National Laboratory has been studying interactions of ultra-relativistic nuclei starting in 2000. Over the last eight years, the hottest nuclear matter on earth has been extensively probed and now we can describe some of the material properties of this matter, often termed the Quark Gluon Plasma. Amongst these properties are near perfect fluidity and extreme opacity. We will describe the experimental techniques, how the properties are constrained, and connections to other areas of physics.

[recorded movie]

Abhay Deshpande
 
Winter Break
 
Jan. 27 Peter Wolynes
UCSD
Landscapes of Matter
The tension between seeking the unity of the laws governing the Universe and appreciating the diversity of phenomena in the natural world has been a constant intellectual theme. Recently, discussions of this issue have reached a fever pitch in cosmology and high energy physics. The key idea is that of an "energy landscape." I will discuss the notion of energy landscapes in the contexts of condensed matter science and biochemistry. In these areas the mathematical description of landscapes has become relatively solid and also very fruitful. The specific examples of landscape theory I will discuss include glasses in the world of material science, the protein folding problem, and gene regulation.

[recorded movie]

Jin Wang/Michael Zingale
Feb. 3 John Marburger
Stony Brook
The Curious History of Heisenberg's Uncertainty Relation
In his famous 1927 paper Heisenberg derived the product of uncertainties in position and momentum for a Gaussian wave packet, and gave physical arguments for more general situations. Only later, in lectures at Chicago University, did Heisenberg derive the rigorous inequality we associate today with uncertainty relations. He cited a work by E.H. Kennard in connection with his derivation, and historians credit Kennard with the first proof. In 2007 I compared Heisenberg's Chicago proof with Kennard's and found they are completely different and that Kennard's version is fatally flawed. Probably the familiar proof based on Schwarz's inequality is due to Pauli. Heisenberg's intention for the uncertainty relations is obsolete, but they and their subsequent refinements are relevant to non-classical 'squeezed' states of light which are shifted ground states of the general linear quantum system.

[recorded movie]

Hal Metcalf
Feb. 10 Jim Simons
Renaissance Technologies Corporation
Mathematics, Common Sense, and Good Luck

[recorded movie]

Hal Metcalf
Feb. 17 Yimei Zhu
BNL
Exploring the Origin of Materials’ Functionality at the Nanoscale Using Advanced Electron Microscopy
Understanding of the fascinating behavior of the electronic, magnetic and atomic structure and the coexistence of strikingly diverse range of exotic electronic and magnetic structure and properties in strongly correlated oxides as well as nanostructured materials requires new measurement tools. Facing the challenges, we have developed unique electron microscopy instrumentation that allow us to study local structural imhomogeneity using quantitative atomic imaging, diffraction, energy-loss spectroscopy and electron holography as well as in-situ measurement by applying different stimulus (e.g., temperature, field, or electric bias) on sample in a transmission electron microscope. In this talk, I will present our recent studies of the correlated behavior, especially the charge/orbital and ferroelectric and ferromagnetic ordering in various systems using aberration corrected electron microscopes. I will focus on the interplay of the charge-, orbital-, lattice- and spin-orderings to understand the competing degree of freedom near the insulator-metal or antiferromagnetic-ferromagnetic phase transition in the systems, especially the role of interfaces and grain boundaries. Characterization of nanostructured materials including carbon nanotubes and nanoparticles will be highlighted. Switching behavior of patterned magnetic elements with various shapes and geometries will be presented. The work was support by the U.S. DOE, under contract No.DE-AC02-98CH10886.

[recorded movie]

Meigan Aronson
Feb. 24 Abby Stewart
U. Michigan
Advancing Faculty Diversity in Science and Engineering
Beginning in 2001, the University of Michigan undertook a campus-wide effort to increase the diversity of the faculty in science and engineering. Recognizing that organizational change was a necessary precondition for the success of these efforts, they have focused on recruitment, climate, and institutional policies. I will describe both areas in which we have been relatively successful and areas in which progress has been slow, and will conclude with suggestions about efforts that might be fruitful at other institutions.

[recorded movie]

 
March 3 Pat Looney
BNL
Science, Policy, Politics, and Money
Budgets are the most visible and essential element of public policy, and funding for research and development no exception. For federally funded R&D, there exists no policy or budgetary formula that fixes the appropriate level for the federal R&D budget, nor the relative priorities for the priorities of Federal Agencies and their programs. So, it is a remarkable fact that R&D spending has been a constant fraction of the Federal Budget for over 40 years; though the budgets for individual agencies and programs have risen and fallen and the relative mix of investments has changed in response to political forces and societal demands. In this talk, I will review the processes that drive the US agenda for basic science and their attendant budgets and how these processes influence and shape the agenda and directions of individual agencies and a look at how this may influence the climate for any particular area of research. I will provide a detailed look at R&D budgets, describe how policies debated and vetted across the Federal Government, the roles of various actors (Agencies, White House Offices, The Congress) and how political forces shape science policy and the appropriations process.

[recorded movie]

Meigan Aronson
March 10 Miles Padgett
U. Glasgow
Light's Twist
It is 15 years since Les Allen et al. recognised that light beams could be made in the laboratory which carried an Orbital Angular Momentum. Since that time much of my own group's work has been the exploration of this phenomenon, ranging from optical spanners and rotational frequency shifts to an angular form of Heisenberg's uncertainty principle. This lecture will, however, concentrate upon two of our current interests namely the role that angular momentum plays in the 3D structure of random speckle and most recently the quantum entanglement of spatial modes in parametric down-conversion.

[recorded movie]

Hal Metcalf
March 17 Adam Burrows
Princeton
Theories for the Mechanism of Core-Collapse Supernova Explosions
At the confluence of much of 20th-Century physics, lies an astrophysical puzzle that has taxed theorists and the computational arts for almost half a century. Supernova explosions, the source of much of the heavy elements in the Universe and the birthplace of neutron stars and stellar-mass black holes, are still not understood. However, using sophisticated numerical tools and platforms, theorists have been able to conduct multi-dimensional simulations with increasing physical fidelity that have provided insight into the variety of phenonoma that attend stellar death and explosion. The core of the emerging theoretical synthesis is the centrality of asphericity and the breaking of spherical symmetry. In this talk, I will review the state of the field, the contending explosion models, and the connections with other exotic objects, such as gamma-ray bursts and hypernovae. In the process, I will highlight the state-of-the-art computational astrophysics which has been applied to date, and which may be necessary in the future, to credibly unravel this mystery.

[recorded movie]

Michael Zingale
March 24 Wim Leemans
LBL
Accelerating electrons from 0 to 1 GeV in 3 cm: overview of laser-plasma acceleration science at LBNL
Accelerators are essential tools of discovery and have many practical uses. At the forefront of accelerator technology are the machines that deliver beams for particle physics, for synchrotron and free electron based radiation sources. The technology that drives these accelerators is extremely sophisticated but is limited by the maximum sustainable accelerating field. This impacts the size and cost of the device. More than two decades ago, lasers were proposed as power source for driving novel accelerators based on plasmas as the accelerating medium. An overview will be presented of laser accelerator research at LBNL, including the 2004 demonstration of high quality electron beams [1] and the 2006 demonstration of GeV class beams from a 3 cm long accelerating structure [2]. We then discuss the key challenges for broad applicability of this technology to advanced light sources and high energy physics.

[1] C.G.R. Geddes et al., Nature 431, 538-541 (2004).

[2] W.P. Leemans et al., Nature Physics 2, 696-699 (2006).

[recorded movie]

Abhay Deshpande
March 31 Dan Goldman
Georgia Tech
Walking and swimming on laboratory sand
Model locomotors (legged robots) have begun to achieve mobility comparable to biological organisms like cockroaches on hard ground, but these robots suffer significant performance loss on granular media like sand. We perform laboratory experiments on a model locomotor, a small (32 cm long) six-legged robot, SandBot, on a controlled trackway of granular media (poppy seeds) as a function of limb rotation frequency and material preparation (volume fraction). Kinematic limb parameters which generate a rapid (60 cm/sec) bouncing motion on hard ground result in a slow swimming motion in granular media (~ 1 cm/sec). With proper adjustment of the limb kinematics, SandBot achieves speeds of up to 30 cm/sec on granular media using a pendular-like walking gait. Walking speed depends sensitively on the packing fraction and the limb frequency, and a dramatic transition from walking to slow paddle swimming occurs when volume fraction becomes small enough and/or limb frequency becomes large enough. A model based on balancing inertial and granular forces reveals that properly tuned kinematics minimize inertial stresses and simultaneously maximize grain stresses. Journal paper: Li, Umbanhowar, Komsuoglu, Koditschek, Goldman, PNAS, 106, 3029 (2009).

[recorded movie]

Meigan Aronson
April 7no colloquium -- spring break
April 14 Sheila Tobias The Professional Science Masters Program

[recorded movie]

Hal Metcalf
April 21 Fred Raab
Caltech
the LIGO Scientific Collaboration
The Search for Gravitational Waves
There has been a significant advance in the sensitivity of broadband searches for gravitational waves, using an international network of kilometer-scale laser interferometers. Their sensitivity to strains in space of the order of 10-21 brings a variety of potential signals into range, from distortions of spinning neutron stars in our galaxy to the mergers of neutron stars and black holes in the Virgo cluster of galaxies. The design of these detectors seeks to reach and reduce fundamental noise sources, resulting from the quantum nature of light, the atomic nature of matter and the physical environments of the detectors. There are many additional opportunities for technical noise to adversely affect the instruments. Finally there is the challenge to engineer robust instrumentation that can run continuously at state-of-the-art sensitivity for years. This talk will describe the technical challenges of building and operating the current and future generations of detectors and will give some insight into what we have learned so far from observations and what we hope to learn in the future.

The LIGO Laboratory was constructed and is operated for the National Science by Caltech and MIT under cooperative agreements PHY-9210038, PHY-0823459 and PHY-0757058.

[recorded movie]

Hal Metcalf
April 28 Steve Kivelson Progress Report on the Theory of High Temperature Superconductivity
More than twenty years after the discovery of high temperature superconductivity in the cuprate superconductors, considerable progress has been made in understanding the material specific features of the superconductivity and related phenomena in these remarkable materials. Moreover, enormous progress has been made in the understanding of highly correlated electronic systems, in part due to dramatic progress in numerical studies of paradigmatic models, and in part due to a broadened perspective concerning the possible emergent behaviors of correlated electron fluids. In the last year, the discovery of high temperature superconductivity in another class of materials, the iron oxy-pnictides, has made it clear that high temperature superconductivity, in close association with antiferromagnetism, are not restricted exclusively to the cuprates. This discovery has reinvigorated the field, and increased optimism concerning the search for other high temperature superconductors, possibly with still higher Tc's.

[recorded movie]

Meigan Aronson
May 5 Laszlo Mihaly, Graduate Director Award Colloquium
student presentations by:
Jonathan Rameau, Soroff Prize Winner
Claire Allred, Wilcox Prize Winner

[recorded movie]