Physics and Astronomy Colloquia, Academic Year 2014-2015

Colloquium committee: Leonardo Rastelli (Fall Chair), Meigan Aronson (Spring Chair), Thomas Allison, Joanna Kiryluk, Alexandre Abanov, Rosalba Perna, and Abhay Deshpande.


Coffee & Tea served at 3:45 pm.

Talk begins at 4:15 pm.

Location: Harriman 137 (bottom of square C4 on the campus map)

 

Fall 2014 colloquia


Date

Speaker

Title

Local Host

Sept. 9

Arno Rauschenbeutel

Vienna Center For Quantum Science and Technology

Breaking the mirror symmetry of spontaneous emission via spin-orbit interaction of light

Light is often described as a fully transverse-polarized wave, i.e., with an electric field vector that is orthogonal to the direction of propagation. However, this is only valid in the framework of the paraxial approximation. Yet, in many physically relevant situations, like in strongly focused laser beams, plasmonic structures, nanophotonic waveguides or optical microresonators, light is transversally confined in the strongly non-paraxial regime and exhibits strong intensity gradients at the wavelength scale. According to Maxwell.s equations, this leads to a significant polarization component that points in the direction of propagation of the light. In contrast to paraxial light fields, the corresponding photon spin is position-dependent - an effect referred to as spin-orbit interaction of light. Remarkably, the photon spin can even be perpendicular to the propagation direction. I will discuss experimental situations in which this extreme condition occurs and will show that the interaction of emitters with such light fields leads to new and surprising effects. In particular, the intrinsic mirror symmetry of the emission of light by gold nanoparticles as well as by atoms near a silica nanophotonic waveguide is broken. This allowed us to realize chiral nanophotonic interfaces in which the emission direction of light into the waveguide is controlled by the polarization of the excitation light [1] or by the internal state of the atoms [2]. The additional control over light-matter interaction provided by spin-orbit interaction of light is thus highly interesting both from a fundamental point of view and for the implementation of next-generation communication and information processing devices.a

[recorded movie]

Allison/Metcalf

Sept. 16

Volker Schomerus

University

JOINT SCGP-PHYSICS Colloquium: The Yang-Baxter Equation in Yang-Mills Theory

Gauge theories provide a highly successful framework for the description of nature, even though precision calculations tend to become enormously complex. This complexity may not be a feature of gauge theory itself but of our computational schemes. In conventional Feynman graph expansions, for example, one often observes unexpected cancellations which can result from hidden symmetries. Where such hidden symmetries of gauge theory have been uncovered, they turned out to be well known from a seemingly unrelated area of physics: the study of solvable 1-dimensional quantum system. In my talk I will review some of these intriguing connections, and I will illustrate their powerful implications at the example of high energy scattering amplitudes.

Note: Special SCGP-Physics colloquium to be held in the Simons Center. Cookies in the SCGP lobby, talk following in the auditorium.

Abanov

Sept. 23

Steve Barwick

UC Irvine

The development of neutrino astronomy: past, present, and future

Do astrophysical sources produce high energy neutrinos? Dedicated neutrino telescopes based on optical Cherenkov techniques have been scanning the cosmos for about a decade to answer this question. Until recently, the answer was no, but IceCube has now observed more events with energies between 30 TeV and a few PeV than expected from modeled background mechanisms. I plan to discuss the development of high energy neutrino telescopes from AMANDA to IceCube and the neutrino events that led Physics World to declare IceCube the 2013 breakthrough of the year. To push to larger energies, an even larger detector is required to measure the flux of cosmogenic neutrinos, whose existence is relatively secure but the flux is frustratingly small. I'll outline our progress in the development of a new concept called ARIANNA, based on the radio Cherenkov technique, with the enough sensitivity to observe cosmogenic neutrinos.

[recorded movie]

Kyriluk

Sept. 30

Phil Armitage

JILA/CU

Turbulence in planet formation

The formation and early evolution of planetary systems occurs within the turbulent environment of protoplanetary disks. After reviewing our current understanding of the origin of extrasolar planetary systems, I will discuss our efforts to understand protoplanetary disk turbulence through first principles numerical simulation. Observations in the sub-mm now approach the acuity needed to test theoretical models, giving a glimpse at the environment within which the first gravitationally bound bodies in planetary systems may form.

[recorded movie]

Perna

Oct. 7

Juan Maldacena

IAS

Quantum mechanics and the geometry of spacetime

Quantum mechanics is important for determining the geometry of spacetime. We will review the role of quantum fluctuations that determine the large scale structure of the universe. In some model universes we can give an alternative description of the physics in terms of a theory of particles that lives on its boundary. This implies that the geometry is an emergent property. Furthermore, entanglement plays a crucial role in the emergence of geometry. Large amounts of entanglement are conjectured to give rise to geometric connections, or wormholes, between distant and non-interacting systems.

[recorded movie]

Rastelli

Oct. 14

David Reis

Stanford University

Lattice Dynamics with a big "D": a case for ultrafast x-ray scattering.

The x-ray free electron laser is a revolutionary tool for advancing our understanding of the dynamics of matter at the level of electrons and atoms. Their utility stems from extremely bright x-ray beams comprising a large number of photons concentrated in femtosecond pulses with a high-degree transverse coherence. A challenge for scientists is to devise experiments that make effective use of these unique properties. With large shot-to-shot fluctuations and potential for x-ray induced damage, this may seem like precisely the wrong source for high-resolution spectroscopy of elementary excitations in solids. In this colloquium, I will make a case for femtosecond x-ray scattering as a powerful new tool for studying lattice dynamics, particularly out of equilibrium. I will draw on two recent examples from my group where we perform high-resolution inelastic x-ray scattering in the time-domain using a femtosecond optical laser to prepare broadband two-phonon coherences in the sample. In the first experiment, we extract the transverse acoustic phonon dispersion in the prototypical semiconductor germanium with sub-meV resolution--- without the use of an analyzer. In the second experiment, we investigate the strongly anharmonic lattice dynamics in PbTe and present evidence for strong photo-induced mode-coupling spanning the Brillouin zone.

[recorded movie]

Allison

Oct. 21

Laszlo Mihaly

Stony Brook

Chair's Colloquium

[recorded movie]

Host

Oct. 28

Paul Steinhardt

Princeton University

Once Upon a Time in Kamchatka: The Search for Natural Quasicrystals 

Quasicrystals are exotic materials that were once thought to be impossible for matter. The concept was first introduced and examples were first synthesized in the laboratory 30 years ago. But could Nature have beaten us to the punch? This talk will describe the search to answer this question, resulting in one of the strangest scientific stories you are ever likely to hear.

[recorded movie]

Rastelli

Nov. 4

Margaret Murnane

JILA/University of Colorado

Science at the Timescale of the Electron: Tabletop X-ray Lasers and Applications in Nanoscience and Nanotechnology

Ever since the invention of the laser 50 years ago, scientists have been striving to extend coherent laser-like beams into the X-ray region of the spectrum. Very recently, we used tabletop mid-infrared femtosecond lasers to achieve this goal, and create bright X-ray beams at wavelengths spanning from the UV to <10Å.[1] The X‑ray supercontinua that are generate represent a coherent version of the Rontgen X-ray tube in the soft X-ray region. X-rays are powerful probes of the nanoworld. They penetrate thick samples and can image small objects with spatial resolution near the wavelength limit. Interest in this research area is booming worldwide, because of the critical need for better tools for a host of applications in science and technology. Moreover, the limits of this new light source are not yet known. 

[1] T. Popmintchev et al., Science 336, 1287 (2012).

[recorded movie]

Allison

Nov. 11

Bob Williams

STScI

Science from Hubble Space Telescope: Piecing Together the Universe

In orbit for 24 years and still operating well, in planning and development for 15 years before that, HST---at $7.5 billion---has been the most expensive scientific project in history until CERN’s LHC.  It’s unique features of high spatial resolution, ultraviolet sensitivity, and low sky background together with its unified, well calibrated, publicly available data archive have produced many notable astronomical discoveries.  Highlights of Hubble Telescope’s scientific mission will be discussed in the context of processes that have been key to our current understanding of the evolution of the universe from the earliest times to the present epoch.  These include gravitational lensing, the Hubble deep fields which have revealed early galaxy formation, galaxy mergers that form black holes, and the initial attempts of analysis of the atmospheres of planets around other stars.

[recorded movie]

Perna/Calder

Nov. 18

Mariangela Lisanti

Princeton University

Bringing Dark Matter into Focus

Although dark matter comprises the vast majority of the matter in the universe, its properties remain elusive.  Direct detection experiments are a promising avenue for discovering and characterizing the dark sector.  These experiments seek to identify dark matter particles as they scatter off nuclei in underground detectors.  The standard picture since the 1980s is that the scattering rate modulates annually due to the Earth's orbit around the Sun.  We have recently discovered a new modulation effect: Unbound dark-matter particles are focused by the Sun's gravitational potential, affecting their phase-space density in the lab frame.  This 'gravitational focusing' results in a significant overall shift in the phase of the annual modulation and provides a powerful new tool for characterizing the properties of the dark matter particle.

[recorded movie]

Perna

Nov. 25

Shamit Kachru

Stanford

Explorations in the Physics and Mathematics of Moonshine 

"Monstrous moonshine" is a beautiful phenomenon first discovered in the 1980s, providing startling and unexpected relations between several fundamental objects in mathematics and the physics of a (rather peculiar) string theory.  Very recently, physicists and mathematicians have started to uncover evidence of deep analogous "moonshine" connections between some of the more physically interesting solutions to string theory and important structures in group theory and number theory.  In this talk, I describe in an elementary way some of the fundamental mathematical and physical objects implicated in the moonshine conjectures, and the surprising and as yet mysterious connections between them.

Note: Special SCGP-Physics colloquium to be held in the Simons Center. Cookies in the SCGP lobby, talk following in the auditorium.

[recorded movie]

Rastelli

Dec. 2

Xu Du

SBU

Probing the Graphene Bridges

Graphene promises a wide spectrum of interesting properties from Dirac fermionic quantum transport to ultra-high mechanical flexibility/strength. Suspended graphene “bridges” offer opportunities for studying many of these properties. I will discuss two examples from completely different aspects of interest.  From the aspect of classical mechanics, graphene, as the strongest material, provides an excellent playground for studying nanoelectromechanical behaviors. By fabricating graphene nanomechanical resonators on flexible substrates, we are able to tune the mechanical resonance of these graphene “nano-strings” and study their non-linear dynamics.  From the aspect of quantum transport, the charge carriers in graphene are fundamentally different from that in the typical metals, due to their linear energy dispersion and the additional pseudospin degree of freedom. In high quality ballistic graphene-superconductor junctions, we demonstrate the impact of such Dirac fermionic electronic structure on the superconducting proximity effect.

[recorded movie]

Mihaly

 

 

 

 

Spring 2015 colloquia


Date

Speaker

Title

Local Host

Jan. 27

Sasha Abanov

Stony Brook

 Colloquium Rescheduled to 2/10   Due  to Winter Storm

Mihaly

Feb. 3

David Grier

NYU

Colloquium rescheduled to 4/28

Aronson

Feb. 10

Sasha Abanov

Stony Brook

Exotic Quantum Fluids: Geometry meets Quantum Physics

 

An interplay between quantum mechanics and strong inter-particle interactions in many body systems may result in a formation of exotic fluid like states. The well known such states are superfluids and superconductors. The understanding of properties of these states is very important in condensed matter physics. After a brief general review we will consider a somewhat less known quantum fluid --- the fractional quantum Hall state. We will see that some of the physical properties of this fluid can be described in a very geometric way.   

[recorded movie]

Mihaly

Feb. 17

George Sawatzky

U. British Columbia

The Role of atomic physics and non-uniform polarizability in correlated electron systems

I would like to discuss some rather elementary thoughts regarding  strongly correlated electron systems many but not all of which are not generally appreciated and therefore often forgotten in describing their atomic structure, electronic structure, and related physical properties. We start with the very simple models like the Hubbard model and demonstrate aspects which for some at least are rather strange such as spectral weight transfers from high to low energy scales quite different from mean field theories as also seen in XAS spectra of Cuprate superconductors. Following this we will look at why the 3d transition metal and rare earth compounds form quit a special class of materials and demonstrate the importance of electron correlations in Auger spectroscopy and photoelectron spectroscopy in which the full multiplet structure seen in gas phase optical spectroscopy is clear visible and basically unchanged in the solid. We need then to explain why the average coulomb interaction of two electrons on an atom is very strongly reduced in the solid compared to the gas phase but also why the multiplet spread is basically unaltered in the solid. This bring us to the question of screening or rather reductions of interactions in a polarizable medium quickly realizing that the convention assumptions of uniformly polarizable media as usually assumed in solid state physics is not applicable. Using this we come up with another surprise namely that in compounds involving large polarizable atoms short range interactions are strong reduced, intermediate range ones can even be increased and long range ones are reduced in the conventional way. With this background and adding in the non-spherical symmetry the atoms find themselves in in solids resulting crystal and ligand field effects as well as the atomic physics rules now applied to solids regarding the ground state or low energy state of atoms with open shells called Hunds’ rules we will build up our solids with translation symmetry and try to describe the wide range of properties exhibited by  3d and rare earth compounds leaving behind a huge amount of unexplained observations like high temperature superconductivity in the cuprates. However on the way we will also follow a different than conventional path emphasizing the explicitly important role of the other than narrow band state in the compounds ending up with a new way to look at the Cuprates, Nickelates, BaBiO3 as well as the so called topological Kondo Insulator SmB6. 

  

 

[recorded movie]

Aronson

Feb. 24

Jim Lattimer

Stony Brook

Determinations of the Properties and Internal Composition of Neutron Stars

Core-collapse supernovae lead to the formation of neutron stars, and both are sensitive to the dense matter equation of state. These supernovae sample matter up to about twice nuclear saturation density, but their end-products, neutron stars, are sensitive to the equation of state of matter both near the saturation density and at several times higher densities. Three important recent developments are the discovery of two-solar mass neutron stars, refined experimental determinations of the behavior of the symmetry energy of nuclear matter near the saturation density, and rapid cooling of the neutron star in the Cas A supernova remnant. Two-solar mass neutron stars and measurements of the nuclear symmetry energy, combined with the assumptions of general relativity and causality, imply that the radii of observed neutron stars are in the range of 11 to 13 km and largely independent of their masses. This is not only consistent with expectations from theoretical studies of pure neutron matter, but also accumulating observations of both bursting and cooling neutron stars. These studies furthermore severely limit the existence and properties of quark matter inside neutron stars. Observations of thermal emissionfrom the neutron star in Cas A are best explained by the existence of both proton superfluidity and neutron superconductivity in the stellar core. It is even possible to determine the critical temperatures of these superfluids, which are a million times larger than any terrestrial counterpart. In the future, continued X-ray, gamma-ray, radio and gravitational radiation observations will further refine our
knowledge.

[recorded movie]

Mihaly

Mar. 3

Boris Kayser

Fermilab

Neutrino Physics: What We Have Learned, and What We Would Like To Find Out

We review what has been learned about the neutrinos since the discovery of neutrino oscillation 17 years ago. We then identify open questions, and focus on several of them, including: Is the physics responsible for neutrino masses different from that responsible for the masses of all the other known particles?  Are we all descended from heavy neutrinos that lived briefly in the early universe, and then decayed in a way that led to a universe containing matter but no antimatter? What can the present-day neutrinos and the universe tell us about each other? Are there “sterile” neutrinos that do not experience any of the known forces of nature except gravity?  We briefly discuss plans to answer these questions

[recorded movie]

Kiryluk

Mar. 10

Alex Gaeta

Cornell University

Temporal Magnification, Compression, and Cloaking of Light


Recent research has shown that the properties of a light beam can be manipulated  to perform ultrafast all-optical signal processing in the time domain.  I will describe our recent work that uses nonlinear optics to create temporal lenses that can magnify, compress, and Fourier transform optical waveforms in the time domain.  Through use of more exotic lenses, temporal gaps in light beams can be opened and closed which can be used to cloak events over short periods of time.

 

[recorded movie]

Allison

Mar. 17

no colloquium—Spring Break

Mar. 24

David Spergel

Princeton

Cosmology After Planck

The Planck Telescope has made an accurate full-sky measurement of the cosmic microwave background (CMB) temperature, the leftover heat from the Big Bang. These measurements probe both the physics of the very early universe and the basic properties of the universe today. The Planck measurements confirm the earlier results from the WMAP telescope and rigorously test our standard cosmological model and provide an accurate determination of basic cosmological parameters (the shape of the universe, its age, and its composition). When combined with other astronomical measurements, the measurements constrain the properties of the dark energy and the nature of dark matter. The observations also directly probe the physics of first moments of the Big Bang: the current data are consistent with the idea that the early universe underwent a period of rapid expansion called inflation.    I will review the Planck data and preview the upcoming data from ground-based polarization experiments. I will also look forward to future measurements from LSST and WFIRST, the major ground and space-based surveys of the coming decade.

Many key cosmological questions remain unanswered: What happened during the first moments of the big bang? What is the dark energy? What are the properties of the dark matter?  The upcoming  combination of large-scale structure, supernova and CMB measurements may provide new insights into these key cosmological questions.





 

[recorded movie]

Perna

Mar. 31

Frans Pretorius

Princeton

Numerical Investigations of Black Hole Physics

 

The class of spacetimes with event horizons contain some of the most fascinating solutions to the equations of general relativity. Over the past few years numerical simulations have begun to reveal their properties in highly dynamical, non-linear regimes not amenable to exact analytical or perturbative treatments. In this talk, I will present two examples of what has been learnt, chosen from topics of arguably more theoretical interest (in contrast to astrophysical binary black hole mergers, of relevance to gravitational wave detection). First, I will describe the ultra-relativistic limit of black hole collisions and its connection to black hole formation in super-Planck scale particle collisions. The second topic will be on the instability of a 5-dimensional black string, its connection to an unstable fluid flow, and what it implies about Penroses' cosmic censorship conjecture.

[recorded movie]

Rastelli

Apr. 7

 Mats Selen

U. Illinois Urbana

The Evolution of Intro Physics at the University of Illinois

 About 17 years ago we significantly changed the way we taught intro physics at UIUC. The innovation, which is hindsight seems almost trivial, was to define these courses in terms of their content and associated infrastructure rather than in terms of the faculty assigned to teach them. Having our courses rest on a solid departmental foundation rather than on the shoulders of faculty means that faculty have the time and freedom to innovate, making incremental yet significant improvements to these courses over time. In this talk I will discuss this evolution as well as several of the resulting innovations, including prelectures, just in time teaching, peer instruction, and a new approach to labs.

 

[recorded movie]

Kelly

Apr. 14

Raju Venugopalan

Brookhaven

The glue that binds us all: imaging matter below the Fermi scale with an Electron-Ion Collider

 

A future Electron-Ion Collider (EIC) will probe the structure of strongly interacting matter down to distance scales as small as 10-18 meters (thousandth of a Fermi), with luminosities a hundred to a thousand times brighter than a previous such collider. High resolution images of the momentum, spatial, spin and orbital distributions of gluons and sea quarks in light and heavy nuclei will become available, many of these as first measurements. We outline how these images will help resolve outstanding puzzles in our understanding of the many-body dynamics of quarks and gluons that fundamentally make up the structure of nearly all visible matter in the universe.  

[recorded movie]

Deshpande

Apr. 21

Sergei Gukov

Caltech

The sound of knots and 4-manifolds

Barclay Prime is a restaurant in Philadelphia that became famous for its exquisite $100 cheesesteak. Served with a small bottle of Veuve Clicquot champagne, Barclay Prime’s cheesesteak is made of sliced Kobe beef, melted Taleggio cheese, shaved truffles, sauteed foie gras, caramelized onions and heirloom shaved tomatoes on a homemade brioche roll brushed with truffle butter and squirted with homemade mustard. Yet, in essence, it still is just a sandwich. The physics of new knot and 4-manifold invariants discussed at the SCGP program ``Knot homologies, BPS states, and SUSY gauge theories'' involves sophisticated ingredients from string theory and M-theory. Yet, at its heart, it is just a familiar quantum mechanics that I will present to you in this talk.

 


Note: Special SCGP-Physics colloquium to be held in the Simons Center. Cookies in the SCGP lobby, talk following in the auditorium.

[recorded movie]

Abanov

Apr. 28

David Grier

NYU

Practical Tractor Beams

A tractor beam is a traveling wave that transports illuminated objects back to its source, opposite to the direction that the wave’s energy flows. Long a staple of science fiction, tractor beams are one practical consequence of the recently developed theory of photokinetic effects, which casts the forces and torques exerted by electromagnetic waves in the language of experimentally accessible quantities.  They are readily projected using computer-generated holograms.  Among the manifestations of tractor beams are solenoidal waves, an interesting new family of solutions to the paraxial wave equation with surprising symmetries.  Related solutions include a knotted force field with potential applications for fusion power generation. 

 

[recorded movie]

Aronson/Metcalf

May 5

graduate director

Graduate Awards Colloquium

[recorded movie]

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