Colloquia in Academic Year 2006-2007
Dept. Physics & Astronomy, Stony Brook University
Colloquium committee: Chris Jacobsen, Sasa Abanov (fall 2006), Meigan Aronson (spring 2007), Aaron Evans, Tom Weinacht

Coffee & Tea served at 3:45 pm.  Talk begins at 4:15 pm.  Location: Harriman 137, which is at the bottom of square C4 on the campus map.

Spring 2007 colloquia (colloquia already given in academic year 2006-7 are listed here):
Date
Speaker
Title
Local host
Apr. 24
Serge Luryi
Department of Electrical and Computer Engineering
Stony Brook University

Semiconductor scintillator and 3D integration

I will discuss a new scintillation-type detector in which high-energy radiation produces electron-hole pairs in a direct-gap semiconductor material that subsequently recombine producing infrared light to be registered by a photo-detector. The key issue is how to make the semiconductor essentially transparent to its own infrared light, so that photons generated deep inside the semiconductor reach its surface without tangible attenuation. I will discuss two novel ways to accomplish this, one based on doping the semiconductor with shallow donors to produce the Burstein shift between emission and absorption spectra in heavily doped direct-gap semiconductors, such as GaAs and InP, and the other on heterostructure bandgap engineering. The most innovative feature of the semiconductor scintillator is that it enables three-dimensional integration of standard semiconductor wafers, each provided with epitaxial photosensitive layer on its surface as well as amplifying and analog-to-digital electronic circuits. The detector stack can accommodate virtually any absorption length of high-energy radiation, without any loss in scintillator yield and speed of response. Three-dimensional pixellation of the scintillator response enables high-resolution angular discrimination. The semiconductor scintillator can be used for high-resolution spectroscopy of the high-energy radiation, accurate isotope identification, and rapid determination of the direction to source.

Kostya Likharev
May 1
Laszlo Mihaly
Dept. Physics Astronomy, Stony Brook University
Awards colloquium

For  academic year 2007-8 colloquia, go here.

Colloquia already given in academic year 2006-7:
Date
Speaker
Title
Local host
Sep. 12
(4:00 pm rather than 4:15 pm!!!)
Peter Koch
Department of Physics
Stony Brook University
Chair's colloquium (PDF of slides)
Tom Weinacht
Sep. 19
Clark McGrew
Department of Physics & Astronomy
Stony Brook University
Neutrino Oscillations: the Next Generation

The study of neutrino oscillations has rapidly moved from the first unambiguous observation by Super-Kamiokande in 1998, to confirmation in a wide variety of experiments looking at both terrestrial and astrophysical neutrinos.  The first and second generation of neutrino oscillation experiments are now either completed, or gathering data.  By observing "neutrino disappearance", these experiments demonstrated that  neutrino mixing is approximately "bi-maximal" between electron and muon neutrinos, and separately between muon and tau neutrinos.  The next generation of neutrino experiments will study oscillations using electron, or tau appearance.  I will describe the progress toward the next generation of neutrino experiments, concentrating on the T2K experiment in Japan.
Kostya Likharev
Sep. 26
Chris Monroe
University of Michigan
Quantum Networks and Ion Trap Quantum Computers

A quantum computer can process entangled quantum superpositions of information, providing exponential gains over conventional computers when applied to certain tasks.  Trapped atomic ions are among the most promising candidates for a future quantum information processor, with each ion storing a single quantum bit (qubit) of information.  Trapped ion qubits enjoy an unrivaled level of quantum coherence, and small numbers of ions can be entangled through a suitable interaction with optical fields.  The next generation experiments will transport and distribute trapped ion qubits to generate truly large-scale entangled quantum states.  I will discuss several options for networking trapped ion qubits, along with state-of-the-art experimental progress.
Tom Weinacht
Oct. 3
Laszlo Mihaly
Department of Physics & Astronomy
Stony Brook University
Ferromagnets, antiferromagnets and materials beyond

The ferromagnetic ground state, where the all of the spins are lined up in the same direction, is an exact solution to the Heisenberg model, a simple model of interacting spins. Quantum fluctuations are negligible in a ferromagnet. Such a simple solution does not exist for an antiferromagnet, where the magnetic order is often represented by two sublattices of spins.  Two ordered sublattices with opposite spin directions may correspond to the classical ground state, but this configuration is certainly not an exact (quantum mechanical) solution. Nature provides us with many more structures and interactions with complex magnetic order, and in some cases quantum fluctuations have a dominant role in the macroscopic properties. We will review a few unusual magnetic materials, and we will discuss a new way of doing electron spin resonance for the study of the elementary excitations in these systems. 
Aaron Evans
Oct. 10
Albert Bartlett
Department of Physics (Emeritus)
University of Colorado, Boulder
Future population and resource trends

The talk examines the exponential arithmetic of steady growth as it applies to costs (inflation) and population sizes, showing the enormous numbers that can result from modest growth rates and reasonable periods of time.  If the rate of consumption of a finite non-renewable resource grows steadily, the shortening of the life-expectancy of the resource is dramatic.  The concept of sustainability is examined to demonstrate that most sustainability "experts" avoid the central problem. We then look at the Hubbert Curves for U.S. and World petroleum production and the implications of these curves.  These facts are compared with the bland assurances of important and influential non-scientists.  The talk closes with recommendations for dealing with the problems our society faces.
Kostya Likharev
Oct. 17
Helen Quinn
SLAC
Sir Run Run Shaw Distinguished Lecture
The politics of science education, seen from a physicist's perspective

What are the forces that define how science education proceeds in your schools? How does the interplay of Federal, State and Local control over aspects of education work, particularly in the realm of science education? Who else plays a major role? If you wanted to improve science education nationally or locally what levers could you push? As a scientist with a strong interest in science education I have been trying to answer these questions for myself for some years. Among other efforts, I was deeply involved in the process that led to the California Science Standards. I also recently participated in a study by the National Academy whose report "Taking Science to School" will shortly be released. This talk is built from all my experiences, and gives a personal perspective.

George Sterman
Oct. 24
Bill Phillips
University of Maryland
A Bose Condensate in an Optical Lattice: cold atoms meet solid state

An atomic-gas Bose-Einstein Condensate, placed in the periodic light-shift potential of an optical standing wave, exhibits many features that are similar to the familiar problem of electrons moving in the periodic potential of a solid-state crystal lattice. Among the differences are that the BEC represents a wavefunction whose coherence extends over the entire lattice, with what is essentially a single quasi momentum and that the lattice potential can be turned on and off or accelerated through space. Experiments that are not easily done with solids are often straightforward with optical lattices, sometimes with surprising results.

Hal Metcalf
Oct. 31
Frederick M. Walter
Department of Physics & Astronomy
Stony Brook University
What Goes Down Must Blow Up? Stellar Accretion Studies Using SMARTS

SBU has been a member of the SMARTS consortium, with access to four one-meter class telescopes on Cerro Tololo, Chile, for the past 4 years. Following a short description of the facility and its operations, I shall give an overview of what Stony Brook astronomers have been doing with this telescope access, with heavy emphasis on my own research interests. The availability of year-round spectroscopic and photometric observations facilitated by the SMARTS consortium is proving a boon to the study of stellar accretion and its consequences, on timescales ranging from hours to years. Accretion is the primary driver of large scale variability in many stars. I will present an overview of some of the important questions concerning accretion in stellar systems, profusely illustrated with examples drawn from the realm of pre-main sequence stars, cataclysmic variables, and the galactic novae.

Aaron Evans
Nov. 7
Peter Sutter
Brookhaven National Laboratory
Low-Energy Electron Microscopy and Photoelectron Microscopy of Surface Reactions

Surface sensitive microscopy has become a key enabling technique for studying phenomena at the nanoscale. In contrast to widespread near-field scanning methods (STM, AFM) that are inherently slow, low energy electron microscopy (LEEM), a surface sensitive far-field electron microscopy technique, is capable of video-rate image acquisition and is ideally suited to study the lively dynamics of nanostructures at elevated temperatures.  Further, using synchrotron radiation, the LEEM instrument allows photoelectron microscopy (PEEM) that provides elemental or band structure maps with tens of nanometer resolution.
Chris Jacobsen
Nov. 14
Nima Arkani-Hamed
Department of Physics
Harvard University
Naturalness, the String Theory Landscape and the LHC
Tom Weinacht
Nov. 21
David Tannor
The Hermann Mayer Professorial Chair
Department of Chemical Physics
Weizmann Institute of Science
Optimal control of laser cooling:  A theory of purity increasing transformations

The powerful techniques of Optimal Control Theory (OCT), used in recent years to design laser pulse sequences to control chemical bond breaking, are applied to the problem of laser cooling in an open system. The result is a striking new mechanism in which spontaneous emission builds coherences between all the populated levels creating a pure state, only at the end of the process transferring the amplitude to the lowest energy state. This novel mechanism accelerates the cooling process by exploiting the cooling induced by spontaneous emission to all the ground electronic state levels, not just the lowest level. The mechanism suggests the calibration of cooling in terms of increasing purity of the system as measured by the quantity Tr(ρ2). An analytical theory of the cooling mechanism is developed in terms of a two-stage interplay between the control fields and the spontaneous emission. One of the main results of the analytical theory is a differential equation for the optimal cooling rate. The key components of the theory --- the definition of cooling as purity increase; the invariance of purity to control fields; and the maximum rate of approach to absolute zero --- correspond to the zeroth, second and third law of thermodynamics, providing a thermodynamic framework for laser cooling. The formulation of cooling in terms of the coherence measure Tr(ρ2) has an additional, interesting implication: that our results carry over immediately to the problem of control of quantum decoherence, suggesting both a new mechanism and fundamental limitations on the control of that process.

Tom Weinacht
Wed., Nov. 22
Talks at BNL
Anthony Leggett
University of Illinois at Urbana-Champaign
"Testing the limits of quantum mechanics: motivation, state of play, prospects"
Building 555 (Chemistry), Hamilton Seminar Room, 11 am

"Cuprate superconductivity: the current state of play"
Building 510 (Physics), large seminar room, 2 pm

Nov. 28
Ting Xu
Chemistry/U. Penn (present)
Materials Science/UC Berkeley (spring 2007)
De Novo Designed Peptides For Functional Biomolecular Materials

Nature builds proteins out of particular molecular sequences to achieve specific functions, while human manufactured polymeric materials are often involving just one or two molecules. Developing routes to use de novo designed peptides as building blocks and manipulate their assemblage, should allow us to not only mimic nature, but also construct functional biomolecular materials with non-proceeding performances. This talk will concern the development of designed amphiphilic 4-helix bundle peptides derived from natural photosynthesis proteins and their applications on controlling the vectorial orientation and local environment of extended conjugated chromophores. X-ray and neutron scattering techniques are used to understand the peptide/chromophore assembly in the Langmuir monolayer.
Chris Jacobsen
Dec. 5
Christian David
Laboratory for Micro- and Nanotechnology, Paul Scherer Institute
Villigen, Switzerland
Phase contrast imaging with hard x-rays and cold neutrons

An interferometic method to produce quantitative x-ray and neutron phase contrast images is presented. The interferometer is based on diffraction gratings fabricated using microlithography techniques. As opposed to existing techniques, the method requires only little coherence and can be scaled up to large fields of view. Its application is therefore not limited to be used at synchrotron light sources, but it can be used with standard x-ray tube sources. In addition recent experiments with cold neutron radiation are presented.

Chris Jacobsen
Dec. 12
Gene Sprouse
Department of Physics & Astronomy
Stony Brook University
Experimental Nuclear Physics at Stony Brook: Past, Present, and Future

The history of Experimental Nuclear Physics at Stony Brook will be presented, including tracing the first ideas to have an accelerator, the building of the Van de Graaff, acquiring the associated faculty, adding the superconducting LINAC, and forming a Relativistic Heavy Ion group that plays a key role at the Relativistic Heavy Ion Collider at BNL.  Many people have contributed to the Nuclear Physics program here who have gone on to important positions around the world, and some effort will be made to describe their impact on the field.
Chris Jacobsen
Jan. 30
Jim Truran
University of Chicago
Supernovae, Nucleosynthesis, and Cosmic Chemical Evolution

Movie of presentation

The Universe emerged from its first three minutes with a composition consisting of hydrogen, deuterium, 3He, 4He, and 7Li. These isotopes then constitute the primordial compositions of galaxies. Within galaxies, the synthesis of heavier elements from carbon through uranium is understood to occur during the normal evolution of stars and in supernova explosions of Types I and II. This history is written in the compositions of the stars and gas in our Galaxy and other galaxies as a function of time (metallicity). The contributions both from massive stars (M>10 solar masses) and associated Type II supernovae and from thermonuclear (Type Ia) supernovae are particularly noteworthy. We review both the nuclear processes by which this occurs and the compositions of the stellar components of our Galaxy as a function of time, and discuss how such observations inform us of the natures and nucleosynthesis products of the earliest stellar populations of galaxies and the Cosmos.

Aaron Evans
Feb. 6
Girsh Blumberg
Bell Labs


Collective phenomena in correlated electron systems: high-T superconductivity and high-T density waves

Movie of presentation

For doped two-dimensional quantum spin systems the competition between insulating states at low carriers concentration and superconductive pairing at higher densities has emerged as a key feature of the high-Tc problem. We study magnetic correlations in low-dimensional quantum systems and the carrier dynamics in doped antiferromagnetic environment with relevance to the phase diagram high-Tc cuprates. Magnetic correlations which give rise to a finite spin gap were predicted to generate an attractive interaction between doped carriers leading to superconductivity with a d-wave like order parameter. Novel ground states with broken translational symmetry in which single holes or hole pairs order in a crystalline pattern were observed.

Laszlo Mihaly
Feb. 13
Anton Barty
Lawrence Livermore National Lab
Coherent diffraction imaging with soft X-rays

Movie of presentation

Visualisation of the three-dimensional organisation of biological system component parts, be it cellular structures or proteins, is crucial to our understanding of the fundamental mechanisms involved in biological and biomolecular processes. The emerging field of coherent X-ray diffraction imaging offers the potential to open up new areas in biological imaging, particularly in the area of three-dimensional structure determination, and is achieved by dispensing with the need for complicated and inefficient X-ray optical systems. To date the technique has been demonstrated at soft X-ray wavelengths in both 2D and 3D on microfabricated test objects and materials science samples, and recent results and technique developments in this area will be discussed. In the longer term, coherent diffraction imaging may enable imaging of non-periodic objects at near-atomic resolution, using ultrafast pulses from hard X-ray free-electron lasers currently under development worldwide. These objects could include single macromolecules, protein complexes, or virus particles, and will be particularly valuable to determine the structures of proteins that cannot be crystallized. Recent results obtained at the FLASH facility in Hamburg confirm the basic principles of flash imaging and lend great confidence to achieving molecular imaging at future short-wavelength X-ray FELs.

Chris Jacobsen
Feb. 20
John Sipe
Department of Physics and Institute for Optical Sciences
University of Toronto
Quantum interference and the control of currents and spin-currents in semiconductors

Movie of presentation

The interference of quantum mechanical amplitudes, such as those for one- and two-photon absorption, can be used to optically inject electrical currents in semiconductors. The velocities of the injected carriers can be on the order of a thousand kilometers per second. The timescale of the process itself is limited only by the laser pulses, which with modern sources can typically be in the range of tens of femtoseconds. Recent work along these lines has focused on the optical injection of spin-currents, in which equal numbers of electrons are optically injected to the left and right, but spin-up electrons are injected preferentially in one direction, and spin-down in the opposite. These optical techniques form part of the "toolkit" of the developing subject of spintronics, in which one hopes to use the spin degree of freedom for information processing. I shall review our theoretical work on this subject and the experimental work of our colleagues. I shall also address the use of these processes to better understand transport phenomena in semiconductors, and their application to the study of related phenomena, such as the spin-Hall effect.

Tom Weinacht
Feb. 27
(15 minutes earlier: coffee 3:45, colloquium 4:00)
Marusa Bradac
KIPAC Institute
SLAC
Shedding Light on Dark Matter: Seeing the Invisible with Gravitational Lensing

Movie of presentation

The cluster of galaxies 1E0657-56 has been the subject of intense ongoing research in the last few years. This system is remarkably well-suited to addressing outstanding issues in both cosmology and fundamental physics. It is one of the hottest and most luminous X-ray clusters known and is unique in being a major supersonic cluster merger occurring nearly in the plane of the sky, earning it the nickname "the Bullet Cluster". In this talk I will present our measurements of the composition of this system, show the evidence for existence of dark matter, and describe limits that can be placed on the intrinsic properties of dark matter particles. In addition, I will explain how this cluster offers a serious challenge to MOdified Newtonian Dynamics (MOND) theories.

Fred Goldhaber
Mar. 6
Wenbing Yun
Xradia, Inc
From physics PhD to technology entrepreneur: a journey

Movie of presentation

Dr. Yun received his PhD from Stony Brook in 1987.  He will describe his path into academia, and then from there first to a national lab, and then to founding a company, Xradia, which currently employs three other Stony Brook PhD recipients as it brings new x-ray technologies to market.
Chris Jacobsen
Mar. 13
George Sterman
The Yang Institute for Theoretical Physics:  some of the history, some of the physics

Movie of presentation

No abstract provided.

Chris Jacobsen
Mar. 20
Deane Peterson
Stony Brook University
Vega is a rapidly rotating star

Movie of presentation

Astronomers have known almost since the invention of astronomical spectroscopy that stars significantly hotter than the sun tend to rotate rapidly. This lead to early investigations into the effects of rotation on the structure and shapes of stars by von Zeiple and Eddington, and predictions of flattening and substantial temperature gradients and in turn bright poles, dark equators and slowly circulating currents throught the stars. Eighty years later, through the use of a new generation of long baseline optical interferometers, and advances in microprocessors which allow us to deal with the atmosphere, we are finally beginning to test these predictions. We have for the first time resolved the surfaces of these hot stars, first Altair and next Vega and have found that the theory is at first glimpse in very good agreement with the observed (highly asymmetric) light distributions. Even then, the recognition that Vega, the long-time spectral and photometric standard, is rotating near breakup has sent tremors through the astronomical community. And with constantly improving precision, increasing baselines, and more sophisticated techniques to beat down the atmosphere, we expect to see the agreement with the simple theories begin to break down, which is when the fun will really begin.

Aaron Evans
Mar. 27
Gary Bernstein
University of Pennsylvania
Prospects for dark-energy and inflation experiments using precision cosmology

Movie of presentation

The apparent acceleration of the Hubble expansion is strong evidence for "new physics," either in gravitation or in a previously-unknown constituent of the Universe. I will explain the observable manifestations of this "dark-energy" physics. The extension of precision cosmological measurements from the era of recombination (as observed by WMAP) into more recent epochs can measure these manifestations, distinguish new constituents from modifications to gravity, and test the flatness of the Universe predicted by inflation theory. I will focus on the potential of weak gravitational lensing, and two large proposed US experiments, LSST and SNAP.

Aaron Evans
Apr. 3
No colloquium Spring Break
Apr. 10
Kostya Likharev
Stony Brook University
Hybrid semiconductor/nanoelectronic circuits

Movie of presentation

I will review the recent work on devices, circuits and architectures for possible hybrid semiconductor/nanodevice integrated circuits of the “CMOL” variety. Such a circuit combines a CMOS subsystem, fabricated with the usual lithographic patterning, and a two-layer nanowire crossbar (formed by an advanced patterning technique, e.g., nanoimprint), with an area-distributed pin-based interface connecting them. A rotation of the nanowire crossbar by a certain angle with respect to the interface pin grid allows the CMOS subsystem to address each and every of the similar, two-terminal nanodevices formed at each crosspoint of the crossbar, even without nanoscale alignment of the two subsystems. The CMOL concept enables one to combine the advantages of its components: the high reliability and functionality of MOSFET transistors and the minuscule footprint of nanodevices. This powerful combination may allow digital and mixed-signal CMOL circuits to reach an unparalleled device density (up to 1012 functions per cm2) and ultrahigh information processing performance, at manageable power dissipation, high defect tolerance, and modest fabrication costs.

The work has been supported in part by AFOSR, MARCO via FENA Center, and NSF.

Apr. 17
Dam Son
Institute for Nuclear Theory
University of Washington
Viscosity, black holes, and relativistic heavy ion collisions

Viscosity is a very old concept which was introduced to physics by Navier in the 19th century. However, in strongly coupled systems viscosity is extremely difficult to compute ab initio. In this talk I will describe some recent surprising developments in string theory which allow one to compute, easily and conveniently, the viscosity in a class of strongly interacting relativistic quantum field theories. I will describe efforts to measure the viscosity and other physical properties of the quark gluon plasma created at the Relativistic Heavy Ion Collider, and mention possible connections to the string-theory calculations.

Barbara Jacak

For  upcoming academic year 2006-7 colloquia, go hereFor  academic year 2007-8 colloquia, go here.