The David and Edith Harris Physics Colloquium Archives

Spring 2011 Schedule

February 3, 2011
JULIANNE DALCANTON
University of Washington
Hosted by Josh Winn

"Dissecting Galaxies With the Hubble Space Telescope"

Galaxies are complex systems of stars, gas, and dark matter.  These three major components interact in many different ways, leading galaxies to have the structure and kinematics we see today.  I will discuss the current paradigm for galaxy formation, and show how Hubble Space Telescope observations can be used to extract detailed histories of the nearest galaxies.

February 10, 2011
YURI OGANESSIAN
Flerov Laboratory of Nuclear Reactions, JINR
Hosted by Janet Conrad

"Nuclei from the 'Island of Stability' of Super Heavy Elements"

One of the fundamental outcomes of the modern theory of atomic nucleus developed in the very end of 1960s was an uncommon prediction of "stability islands” in the domain of very heavy (super heavy) elements. This increased stability was expected for deformed nuclei near Z=108 and N=162, yet much stronger effect was predicted for heavier spherical nuclei close to the shells Z=114 and N=184.

This talk will be devoted to the experimental verification of these predictions - synthesis and study of properties of super heavy elements.

The role of "relativistic effect” on chemical properties of super heavy elements was experimentally demonstrated and will be briefly discussed as well.

February 17, 2011
DAVID DEMILLE
Yale University
Hosted by Martin Zwierlein

"Diatomic Molecules as Quantum Tools"

Our group is applying the techniques of modern atomic physics--cooling, trapping, and precise control and measurement--to the system of diatomic molecules.  Molecules are qualitatively more complex than atoms because of their vibrational and rotational degrees of freedom, and this complexity makes them difficult to control.  However, we have identified a variety of simple principles that allow us to make use of these "new" properties to provide powerful types of leverage on a broad range of problems.  These span fields all the way from particle physics, to quantum computation, to chemical physics. This talk will give an overview of the field, along with some specific examples of our recent work. These include the first-ever laser cooling of a diatomic molecule, and the search for the CP-violating electric dipole moment of the electron..

February 24, 2011
JOHN BUSH
MIT
Hosted by Ed Bertschinger

"Bouncing Droplets (and the Nature of Reality)"

Yves Couder and coworkers have recently reported the results of a startling series of experiments in which droplets bouncing on a fluid surface exhibit wave-particle duality and, as a consequence, several dynamical features previously thought to be peculiar to the microscopic realm, including single-particle diffraction, interference, tunneling and quantized orbits. We explore this fluid system in light of the Madelung transformation, whereby Schrodinger's equation is recast in a hydrodynamic form.

Doing so reveals a remarkable correspondence between bouncing droplets and subatomic particles, and provides rationale for the observed macroscopic quantum behavior. New experiments are presented, and indicate the potential value of this hydrodynamic approach to both visualizing and understanding quantum mechanics.

March 3, 2011
AMIR YACOBY
Harvard University
Hosted by Pablo Jarillo-Herrero

"Quantum Information Processing and Metrology Using Few Electron Spins in Solids"

Many different physical realizations of quantum bits have been studied over the past decade, including trapped ions, nuclear spins of molecules in solution, Josephson junctions and more. Among the different possible realizations, solid-state implementations have attracted considerable interest due to their promise in miniaturization and scaling, taking advantage of existing technology for fabrication.  The spin qubit is one such example where a quantum bit of information is encoded in the spin state of a single electron confined to a small spatial dimension.

In this talk I will discuss some of our recent work on single electron spin qubits in GaAs quantum dots and color centers in diamond. In these systems spin decoherence arises predominantly from the interaction with proximal paramagnetic spins such as nuclear spins of the host lattice. However, the slow dynamics of this environment lends itself to effective decoupling schemes that allow extending coherence to nearly a millisecond. Paradoxically, coupling to the seemingly random environment of nuclear spins provides valuable resources for storage, single shot readout and fast manipulation of quantum information with important applications to quantum information processing and metrology.

March 10, 2011
DANIEL EISENSTEIN
University of Arizona
Hosted by Paul Schechter

"Dark Energy and Cosmic Sound"

I will discuss how the acoustic oscillations that propagate in the photon-baryon fluid during the first million years of the Universe provide a robust method for measuring the cosmological distance scale.

The distance that the sound can travel can be computed to high precision and creates a signature in the late-time clustering of matter that serves as a standard ruler.  Galaxy clustering results from the Sloan Digital Sky Survey reveal this feature, giving a geometric distance to a redshift of 0.3 and an accurate measurement of Omega_matter.  I will review our recent work on the theoretical modeling of the shifts and scatter of the acoustic scale in N-body simulations.  I will then present SDSS-III, which will use the acoustic method to produce 1% distance measurements in order to map the curvature and expansion history of the Universe and measure the evolution of dark energy.

March 17, 2011
FRANÇOIS BOUCHET
Institut d'Astrophysique de Paris, CNRS & UPMC-Sorbonnes Universités
Hosted by Ed Bertschinger

"First Planck Results on CMB Foregrounds"

The Planck satellite mission from ESA was launched from French Guyana on May 19th 2009, and started surveying the microwave sky on August 13th 2009.
I will recall the mission goals and describe the mission status so far. We recently completed our first formal delivery to the community, the Planck Early Release Compact Source catalogue or ERCSC with about 15 000 objects from Cold Cores, to Galaxies, to Clusters detected by their Sunyaev-Zeldovich effect, that later sample being the current world's largest . I will also give an overview of some of the accompanying scientific analyses we performed on the Galactic ISM and the various Sources types, resolved or not. And I will conclude by our current anticipations for the rest of the mission.

March 31, 2011
CHARLES KANE
University of Pennsylvania
Hosted by Patrick Lee

"Topological Insulators and Topological Band Theory"

A topological insulator is a material that is an insulator on its interior, but has special conducting states on its surface.  These surface states are unlike any other known two dimensional conductor. They are characterized by a unique Dirac type dispersion relation and are protected by a topological property of the materials’ underlying bulk electronic band structure.   These materials have attracted considerable interest as a fundamentally new electronic phase with applications from quantum transport to quantum computing.   In this talk I will outline the theoretical discovery of this phase and describe recent experiments in which its signatures have been observed in both two and three dimensional systems.   I will close by arguing that the proximity effect between an ordinary superconductor and a 3D topological insulator leads to a novel two dimensional interface state which may provide a new venue for realizing proposals for topological quantum computation.

April 7, 2011
DAVID KLEINFELD
University of California at San Diego
Hosted by Sebastian Seung

"How Blood Flows in the Brain”

I will discuss how the combination of modern optical tools - particularly pulsed laser light to induce nonlinear optical effects - and modern physiological and anatomical tools reveal the architecture, flow dynamics, and neuronal control structure for the blood supply in the brain.

April 14, 2011
ANN NELSON
University of Washington
Hosted by Jesse Thaler

"The Neutrino Portal into Physics Beyond the Standard Model"

Because neutrinos are the most weakly interacting particles of the standard model, experiments with neutrinos offer special opportunities for the discovery of physics beyond the standard model. Neutrino oscillations provide a  window into the physics of Grand Unification, as well as into potential exotic new particles and forces. I will discuss a selection of past, current, and proposed neutrino experiments and how these may be used to find or constrain new physics.

April 21, 2011
STEVE SIMON
University of Oxford
Hosted by Eddie Farhi

"Topological (Non-Abelian) Phases of Matter and Why You Should Be Interested"

In two dimensional topological phases of matter, processes depend on gross topology rather than detailed geometry. Thinking in 2+1 dimensions, particle world lines can be interpreted as knots or links, and the amplitude for certain processes becomes a topological invariant of that link. While sounding rather exotic, we believe that such phases of matter not only exist, but have actually been observed in quantum Hall experiments, and could provide a uniquely practical route to building a quantum computer.   Possibilities have also been proposed for creating similar physics in systems ranging from superfluid helium to strontium ruthenate to spin systems to cold atoms to various superconducting interfaces.

April 28, 2011
RAPHAEL BOUSSO
University of California at Berkeley
Hosted by The Society of Physics Students

"The Multiverse of String Theory, the Measure Problem, and the Cosmological Constant"

The vacuum landscape of string theory can solve the cosmological constant problem, explaining why the energy of empty space is observed to be at least 60 orders of magnitude smaller than several known contributions to it.  It leads to a "multiverse" in which every type of vacuum is produced infinitely many times, and of which we have observed but a tiny fraction.  This conceptual revolution has raised tremendous challenges in particle physics and cosmology.  To understand the low-energy physics we observe, and to test the theory, we will need novel statistical tools and effective theories.  We must also solve a long-standing fundamental problem in cosmology: how to define probabilities in an infinite universe where every possible outcome, no matter how unlikely, will be realized infinitely many times.  This "measure problem" is inextricably tied to the quantitative prediction of the cosmological constant.

May 5, 2011
STEVE GIDDINGS
University of California at Santa Barbara
Hosted by The Physics Graduate Student Council

"Ultraplanckian Scattering, Black Holes, and the Problems of Quantum Gravity"

Reconciling quantum mechanics with gravity is perhaps the most conceptually profound unsolved problem from twentieth century physics.  Gedanken experiments have a long tradition in unraveling difficult problems.  One such experiment exposing a central issue in quantum gravity is that of scattering particles at energies above the Planck scale.  Such collisions might even be realized at LHC, in certain theories of nature.  In a classical description of this scattering, black holes form; Hawking showed quantum effects then cause their evaporation.  Attempts to give a complete quantum mechanical description of this process have lead to an apparent paradox, driving at the heart of the problem of quantum gravity, and which seems conceptually much deeper than the commonly-discussed issues of nonrenormalizability or singularities.  This has motivated new ideas in string theory, but the ultimate resolution may be beyond, and require new physical principles.  This problem particularly raises questions about the role of spacetime locality in physics and the possibility that locality only emerges as an approximate concept.  Related considerations are also expected to be relevant in inflationary quantum cosmology.

May 12, 2011
YVES COUDER
Laboratoire Matière et Systèmes Complexes
Université Paris Diderot -Paris7
Hosted by Leonid Levitov

"A Wave-Particle Duality at a Macroscopic-Scale: the Uncertainty Resulting from Attempts of Localisation"

The uncertainty principle is one of the central bases of physics at quantum scale. Directly linked with the wave-particle nature of quantum objects, it is usually thought to have no equivalent in macroscopic physics.

We found recently a classical system in which a droplet bouncing on a vibrated liquid interface becomes propagative when it couples to the surface wave it excites. Several experiments have been devoted to a single question. How can a continuous and spatially extended wave have a common dynamics with a localized and discrete droplet? They show that any attempt to confine spatially this wave-particle association results into a chaotic reaction so that a type of uncertainty appears in the droplet velocity. It will be shown that this classical uncertainty is linked with the structure of the wave field that drives the motion of the droplet. As it is generated by the successive collisions with the surface, it records the trajectory and thus contains what we called a "path-memory". This specific form of temporal non-locality is responsible for the observed chaos. The path memory also results in a quantization of the possible orbits of walkers submitted to a transverse force.