The David and Edith Harris Physics Colloquium Series

PAST SPRING 2012 COLLOQUIA

february 9, 2012
ADAM COHEN
Harvard University
Hosted by Jeremy England

“Bioelectricity and biomagnetism: shedding light on fringe fields”

Theories of biological function are biased toward what we can measure: in the age of bulk biochemistry, cells were viewed as complex systems of coupled reactions.  The development of laser tweezers and force probes showed that much of biochemistry is modulated by internal mechanical forces.  The role of electromagnetic fields in cell biology has remained mysterious, largely, I argue, because of the lack of good techniques to measure these fields.  My lab has been developing fluorescent molecular indicators with which we can observe electric and magnetic fields on the nanoscale.  Our voltage-indicating proteins (VIPs) enable, for the first time, robust imaging of electrical waves traveling through neurons and cardiomyocytes.  We also observed a surprising electrical pulsing behavior in bacteria.  I will also discuss possible roles of weak magnetic fields in biochemical processes.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (The Pappalardo Community Room)

february 16, 2012
MARTIN ZWIERLEIN
MIT
Hosted by Patrick Lee

"A Little Big Bang: Strong Interactions in Ultracold Fermi Gases"

Fermions, particles with half-integer spin such as electrons, protons and neutrons, are the building blocks of matter. When fermions strongly interact, complex collective behavior emerges, as seen for electrons in high-temperature superconductors, for neutrons in neutron stars or for quarks in the primordial matter of the early universe. Ultracold Fermi gases of atoms are a new type of strongly interacting fermionic matter that can be created and studied in the laboratory with exquisite control. Non-equilibrium processes are observable in real time. For example, we can study the collision of "spin up" and "spin down" Fermi gases with resonant, quantum limited interactions. In equilibrium, direct absorption images of the trapped atomic gas reveal the entire thermodynamics of the system, including the transition into the superfluid state. The specific heat of the gas displays a characteristic lambda-like feature at the critical temperature of 17% of the Fermi temperature. Scaled to the density of electrons, superfluidity would occur far above room temperature. We were recently able to follow the evolution of fermion pairing from three to two dimensions, connecting quite directly to models of layered superconductors. Our measurements in and out of equilibrium provide benchmarks for current many-body theories and will help to understand other strongly interacting Fermi systems, such as high-temperature superconductors and neutron stars.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (The Pappalardo Community Room)

february 23, 2012
XIAO-GANG WEN
MIT
Hosted by Patrick Lee

"Topological Order and Quantum Entanglements - from New Quantum Matter to a Unification of Light and Electrons"

What is the origin of fractional charges and fractional statistics in FQH states? What is the origin of light? What is the origin of Fermi statistics? It turns out that long range entanglement is the reason why fractional charges and fractional statistics can appear FQH state. Long range entanglement is also the reason why waves that satisfy the Maxwell equation can appear in some qubit (spin) systems. Long range entanglement also lead to a deeper understanding of gapped quantum phases. It allows us to obtain a classification of interacting bosonic/fermionic topological insulators/superconductors, as well as the much more general symmetry protected topological phases.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (The Pappalardo Community Room)

March 1, 2012
ROBERT GEROCH
University of Chicago
Hosted by MIT Physics Graduate Students Council

"Faster than Light?"

It is widely believed that relativity -- both special and general -- must require that no physical signal travel at a speed faster than that of light.  And there are good arguments – both mathematical and physical -- to support this belief.  For instance, the assumption that there could be superluminal signals in relativity gives rise to well-known paradoxes.  We suggest that this situation is not nearly as clear-cut as it appears at first sight.  Indeed, we shall argue that relativity -- precisely as it stands, but with superluminal signals allowed -- is as viable and self consistent as a physical theory as when such signals are excluded.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (The Pappalardo Community Room)

MARCH 8, 2012
DEBORAH JIN
NIST and University of Colorado
Hosted by MIT Graduate Women in Physics

"Ultracold Polar Molecules"

Gases of atoms can be cooled to temperatures close to absolute zero, where intriguing quantum behaviors such as Bose-Einstein condensation and superfluidity emerge.   A new direction in experiments is to try to produce an ultracold gas of molecules, rather than atoms.  In particular, polar molecules, which have strong dipole-dipole interactions, are interesting for applications ranging from quantum information to modeling condensed matter physics.  I will describe experiments that produce and explore an ultracold gas of polar molecules.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (The Pappalardo Community Room)

MARCH 15, 2012
RAY JAYAWARDHANA
University of Toronto
Hosted by Josh Winn

"Direct Imaging of Extra-Solar Planets: Progress, Missteps, and Prospects"

Twenty years ago, we knew of only one planetary system -- our own. Since then, astronomers have identified hundreds of others orbiting distant suns. These discoveries, made by measuring the subtle effects that planets induce on stars, have revealed a remarkable diversity of worlds. The picture is far from complete, however. Direct imaging, which is complementary to other techniques, will help by revealing planets in wide orbits and allowing us to characterize them. Despite daunting technological hurdles, we have now succeeded in taking images and spectra of a handful of extra-solar planets. I will discuss how these exciting findings challenge our preconceptions yet again, share a cautionary tale, and consider prospects for the near future.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (The Pappalardo Community Room)

MARCH 22, 2012
IAN SPIELMAN
Joint quantum institute; NIST and the University of Maryland
Hosted by Martin Zwierlein

"Bose-Einstein Condensates subject to Synthetic Gauge Fields"

Here I present our experimental work on Bose-Einstein condensates, systems of ultra-cold charge neutral atoms at a temperature of about 100 nano-Kelvin: one billion times colder than room temperature.  These condensates -- quantum gases -- are nearly perfect quantum mechanical systems, and here we demonstrate a technique by which these charge neutral particles are subject to effective (although static) gauge fields: vector potentials.  These vector potentials can be vectors of real numbers like the electromagnetic vector potential (with which we engineer synthetic electric and magnetic fields for our neutral atoms), or of matrices (creating artificial spin-orbit coupling).

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (The Pappalardo Community Room)

MARCH 29, 2012
SPRING BREAK - NO COLLOQUIUM SCHEDULED

APRIL 5, 2012
TONY F. HEINZ
Columbia University
Hosted by Nuh Gedik

"Seeing Electrons in Graphene: A Model 2-Dimensional Material"

The past few years have witnessed a surge of activity in the study of graphene, a stable sheet comprised of just a single atomic layer of carbon atoms in a honeycomb lattice structure.  Indeed, the recent Nobel Prize recognized two researchers for their pioneering contributions to this field.  We will describe some the reasons for the intense interest in this new material system, highlighting its unusual electronic dispersion and its distinctive chemical and mechanical properties.  We will then show how we can use light to probe the distinctive properties of excited electrons in this model 2-D material.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (The Pappalardo Community Room)

APRIL 12, 2012
NADYA MASON
University of Illinois at Urbana-Champaign
Hosted by Ed Bertschinger

"Using Graphene to study Superconductivity (new tricks for an old dog)"

Superconductors are materials that can have zero electrical resistance. They are thus of great interest for applications such as power transmission and energy storage. While the fundamental physics of standard superconductors has now been understood for over 50 years, questions remain about what happens when superconductors are coupled to other materials. For example, it was known that superconducting carriers could be transmitted through a normal metal, but the spectroscopy of the individual modes had not been measured. Graphene, a single atomic layer of carbon which has only recently been isolated for electrical measurements, is also of great interest for fundamental studies and applications. In this talk, I will discuss the new physics that emerges when “superlative” materials such as superconductors and graphene are put together in hybrid structures. In particular, I will show how the creation of a superconductor-nanoparticle -graphene sandwich structure enables a direct measurement of individual superconducting modes. Our measurements show that the spectra of these modes are sharp and tunable. These results may improve the understanding of how superconductivity is transmitted in materials, and may also be relevant to novel computing devices.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (The Pappalardo Community Room)

APRIL 19, 2012
ANDREAS KARCH
University of Washington
Hosted by Krishna Rajagopal

"Recent Progress in Applications of the Gauge/Gravity Correspondence"

I'll give a brief overview of the basic philosophy behind applying the gauge/gravity correspondence (or holography for short) to problems in nuclear and condensed matter physics. Recent progress regarding viscosities, energy loss, non-Landau phase transitions and non-Fermi liquids will be reviewed.

Time: 4:00 pm
Place: Room 34-101 *NOTE ROOM CHANGE

Refreshments @ 3:30 pm in 4-349 (The Pappalardo Community Room)

APRIL 26, 2012
TAEKJIP HA
University of Illinois at Urbana-Champaign
Hosted by Jeff Gore

"Revisiting the Double Helix"

Properties of DNA double helix have been studied for over 60 years. Yet as more sensitive tools become available, fundamental assumptions in our understanding of these properties are being challenged. One such question is over the flexibility of DNA. Looping or bending of DNA on short length scales is essential for many cellular processes but it is highly controversial exactly how flexible the DNA is. Using a new, single-molecule based method, we found that DNA of lengths as short as 50 base pairs can form a circle more than 108 times faster than theoretical predictions.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (The Pappalardo Community Room)

MAY 3, 2012
GUNTHER ROLAND
MIT
Hosted by Jesse Thaler

Time: 4:00 pm
Place: Room 10-250

"Trillion Degree Matter"

In this talk I will discuss a very simple question: What are the properties of matter at extremely high temperature, in excess of several trillion Kelvin?
Experiments at large particle colliders like RHIC at Brookhaven Lab and LHC at CERN have shown that such temperatures can be achieved in collisions of heavy nuclei, creating a soup of quarks and gluons resembling the universe shortly after the Big Bang. We have found that this unique state of matter exhibits fascinating and somewhat surprising properties: Although its density exceeds that of water by 16 orders of magnitude, the quark-gluon soup behaves like a near-perfect liquid.  I will review the most striking observations made in recent LHC data and discuss unexpected connections to strongly coupled systems in many areas of physics, ranging from string theory to ultra-cold atoms.

Refreshments @ 3:30 pm in 4-349 (The Pappalardo Community Room)

MAY 10, 2012
SETH LLOYD
MIT
Hosted by MIT Society of Physics Students

"The Quantum Goldilocks Effect: Optimal Design for Quantum Transport"

Energy transport in photosynthetic systems can be almost 100% efficient.  What are plants and bacteria doing to reach these high efficiencies?   In this talk, I show that this high efficiency can be understood in terms of the physics of quantum computation: excitons hopping through photosynthetic complexes are performing a quantum algorithm called a quantum walk.  Photosynthetic organisms orchestrated an interaction between quantum coherence and decoherence that is `just right' to optimize energy transport.  The quantum Goldilocks effect shows how we too can use the `just right' level of quantum coherence to build better energy transport systems.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (The Pappalardo Community Room)

MAY 17, 2012
ERIC MAZUR
Harvard University
Hosted by David Pritchard

"The Make-Believe World of Real-World Physics"

That physics describes the real world is a given for physicists. In spite of tireless efforts by instructors to connect physics to the real world, students walk away from physics courses believing physicists live in a world of their own. Are students clueless about the real world? Or are we perhaps deluding ourselves and misleading our students about the real world?

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (The Pappalardo Community Room)