UMD CMNS Physics S1 Color


The Fall 2016 colloquia will be held in the lobby of the Physical Sciences Complex unless otherwise noted

Each week during the semester, the Department of Physics invites faculty, students and the local community to hear prominent scientists discuss intriguing physics research. The Fall 2016 colloquia will be held Tuesdays in the Physical Sciences Complex lobby at 4:00 p.m. (preceded by light refreshments at 3:30 p.m.)

Parking is available in the Regents Drive Parking Garage (PG2). An attendant will direct visitors within the garage. Additionally, a free ShuttleUM bus runs between the College Park Metro Station and Regents Drive at about eight-minute intervals.

For further information, please contact the Physics Department at 301-405-5946 or email This email address is being protected from spambots. You need JavaScript enabled to view it..

September 6
Carter Hall, University of Maryland

Down-to-earth searches for cosmological dark matter

Can we detect the Milky Way's dark matter halo in a laboratory experiment? If so, it would be a spectacular confirmation of modern cosmology, and would re-write the standard model of particle physics. A global campaign of such direct-detection experiments is rapidly exploring many theoretical models, and this talk will review where we stand and what may lie ahead, with emphasis on the LUX and LZ experiments.


September 13
Matt Goupell, University of Maryland

The Physics of Hearing: From Basics Physical Principles to Bionic Auditory Prostheses

Understanding the transformation of acoustical sound energy as it travels from a sound source to the ear to the brain requires a strong grounding in physical principles: from the between-the-ear differences used to help determine sound location, to the unique resonance properties of the inner ear that performs a frequency analysis of sound, to our present ability of the bypassing of typical electrochemical transduction of sound using a bionic auditory prosthesis. In this talk,we will discuss how sound is typically processed by the auditory system, as well as how physical acoustical sound properties correlate to sound perception. Then we will discuss how the typical transduction of sound can be bypassed for people who are deaf and require a bionic auditory prosthesis to hear and understand speech. While people with auditory prostheses can understand speech at high levels, substantial changes to the signals occur, which impacts many perceptions. Finally, we will discuss future technological directions for these devices and how they might better convey sound to the users’ auditory system.


September 20
Prange Prize Lecture
PHYS Room 1412
Frank Wilczek, MIT
Hosted by: Sankar Das Sarma

Some Intersections of Art and Science

There are profound reasons, rooted in the nature of human cognition and perception, why art and science have a lot to offer one another. Wilczek will display some important historical examples of their synergy, and point out some emerging opportunities. Several striking images are an integral part of the presentation.

September 27
Kaustubh Agashe, University of Maryland

Signals from a Composite Higgs boson and a Composite Top Quark

In the Standard Model of particle physics, a condensate of the Higgs boson determines the range of the weak nuclear force. However, one finds that quantum corrections generically shift this range to a much smaller value than what is observed. This "hierarchy problem'' can be solved by postulating that the Higgs boson is a composite particle, made up of constituents which are tightly bound by a new force. Such a framework necessitates that the closely related top quark is also composite. After briefly discussing the modeling of such a mechanism, I will describe in more detail how we can test this idea in a wide variety of experiments. These signals of Higgs/top compositeness include direct production of the associated new, heavy composite particles at the LHC, as well as modifications of the properties of the Higgs boson and the top quark themselves due to their composite nature. In this model, the idea of grand unification of the fundamental forces works very well and also naturally leads to an exotic particle that may be the dark matter of the universe. Such ambient dark matter can be detected and also produced at colliders in distinctive ways. I will highlight how some of this phenomenological work has triggered the development of novel experimental strategies, which have subsequently found applicability even beyond testing this framework.

October 4
Shih-I Pai Lecture
PHYS Room 1412
Carlos Bustamante, University of California, Berkeley
Hosted by: Chris Jarzynski

The Folding Cooperativity of a Protein is Controlled by the Topology of its Polypeptide Chain

Proteins are complex functional molecules that tend to segregate into structural regions. Throughout evolution, biology has harnessed this modularity to carry out specialized roles and regulate higher-order functions such as allostery. Cooperative communication between such protein regions is important for catalysis, regulation, and efficient folding; indeed, lack of domain coupling has been implicated in the formation of fibrils and other misfolding pathologies.  How domains communicate and contribute to a protein’s energetics and folding, however, is still poorly understood. Bulk methods rely on a simultaneous and global perturbation of the system (temperature or chemical denaturants) and can miss potential intermediates, thereby overestimating protein cooperativity and domain coupling.  I will show that by using optical tweezers it is possible to mechanically induce the selective unfolding of particular regions of single T4 lysozyme molecules and establish the response of regions not directly affected by the force.  In particular, I will discuss how the coupling between distinct domains in the protein depends on the topological organization of the polypeptide chain.  To reveal the status of protein regions not directly subjected to force, we determined the free energy changes during mechanical unfolding using Crooks’ Fluctuation Theorem. We evaluate the cooperativity between domains by determining the unfolding energy of topological variants pulled along different directions.  We show that topology of the polypeptide chain critically determines the folding cooperativity between domains and, thus, what parts of the folding/unfolding landscape are explored.  We speculate that proteins may have evolved to select certain topologies that increase coupling between regions to avoid areas of the landscape that lead to kinetic trapping and misfolding.

October 11
October 18
Peter Shawhan, University of Maryland

Probing physics and astrophysics with gravitational wave observations

The direct detection of gravitational waves by LIGO in 2015 was an amazing milestone. Our exquisitely constructed detectors have finally reached the sensitivity at which these exceedingly weak signals can be recorded and identified. LIGO detected two clear events, each from the merger of a pair of rather heavy black holes. Those events, plus a third candidate, are already informing us about stellar evolution and allowing us to test the general theory of relativity in detail. I will talk about the operational status of LIGO and Virgo and the prospects for capturing more events in the near future. Besides further binary black hole events, we are also eager to detect binaries containing neutron stars, and potentially other signals. I will outline the possibilities for detecting gamma-ray bursts and/or other electromagnetic signals associated with gravitational-wave events (with a possible hint already from the Fermi spacecraft).

THURSDAY, October 20
Democracy Then & Now Series
Tom Cohen, University of Maryland

American Democracy and Science

The philosophical movement known as the Enlightenment stressed the role of reason and in many deeps ways guided the development of modern science. In developing the political system of the United States, its founders were also profoundly influenced by the ideas of the Enlightenment. This talk explores the interactions between American democracy and science from their enlightenment beginnings to the present.

October 25
Paint Branch Distinguished Lecture
PHYS Room 1412
Eli Yablonovitch, University of California, Berkeley
Hosted by: Tom Murphy

A New Type of Heat Engine, Using LEDs as Refrigerators

Very efficient light emitting diodes (LEDs) actually become colder as they operate because the emitted light carries away entropy.  This surprising effect requires superb LED efficiency, which is achieved by using 2D photonic crystal structures to extract the luminescence.  2D photonic crystals have likewise been employed in photovoltaic cells to trap incident light.  We now know that the photovoltaic cell and the LED are reciprocals of one another. The maxim that “a great solar cell has to be a great LED” has led to solar cells with record efficiency.

What if the electrical output of a photovoltaic cell drives an LED, and the LED light in turn drives the photovoltaic cell?  You might fear that it would become a perpetual motion machine. Instead it becomes a heat engine in which a small amount electricity can efficiently provide refrigeration, or conversely a small temperature difference can generate electricity. Such an electro-luminescent heat engine, in which photons are the working fluid, can be more efficient than thermo-electrics, in which electrons are the working fluid.


MONDAY, October 31
Dean's Colloquium
4 p.m., 2136 PSC
Virginia Trimble, University of California, Irvine
Hosted by: Jayanth Banavar

Some Words, A Few Pictures & One Equation About the First Searches for Gravitational Waves


"Gosh, Prof. Trimble, Do You Really Remember Before Gravars?" This question derives from the last paragraph of a 1987 article Trimble wrote, at the editor's request, for Sky & Telescope. It is a good "vantage year," coming 28 years before the first report from the Laser Interferometer Gravitational-Wave Observatory (LIGO) and 28 years after the late Joseph Weber, who was a UMD physics professor, started talking in public about building a detector for gravitational waves/radiation. Earlier landmarks were papers by Poincare, Einstein and others saying that gravitational information must travel in wave form, to tell nearby masses how to react to changing quadrupole moments of masses in their vicinity. Curiously, it took many years before all the expert gravitation physicists could agree that such waves actually carried energy. Early "yes" votes included Weber & Wheeler in 1957, and the last mainstream opponent (until his death) was Leopold Infeld. Remarkably, the LIGO announcement brought at least two remaining doubters (from Italy) out of the haystack (the one in which you look for needles). This presentation will include some melange of the theoretical debates and the first designs and construction of laboratory detectors.

Virginia Trimble, professor of physics and astronomy at the University of California, Irvine. She was a visiting professor of astronomy at UMD from 1973 to 2003. She is also the widow of Joseph Weber, a pioneer in the search for gravitational waves who was a physics professor at UMD from 1961 until his retirement.

November 1 Special time: 3 p.m.
Laurens Molenkamp, University of Wurzburg
Hosted by: Mohammad Hafezi

Topological Insulators - A New State of Matter


Topological insulators are a novel class of materials that exhibit a novel state of matter – while the inside (bulk) of the materials are electrical insulating, their surface is metallic. This effect occurs because the band structure of the materials is topologically different (in a mathematical sense) from the outside world.

This talk describes our discovery of this type of behavior while studying the charge transport properties of thin, two-dimensional layers of the narrow-gap semiconductor HgTe. These layers exhibit the quantum spin Hall effect, a quantized conductance which occurs when the bulk of the material is insulating. Using various tricks one can show that the transport occurs along one-dimensional, spin-polarized channels at the edges of the sample.

Also thicker HgTe samples can be turned into topological insulators, but now the surface states are two-dimensional metallic sheets. The metal in these sheets is rather exotic in that the band structure is similar to that encountered for elementary particles – the charge is carried by so-called Dirac fermions. This means that experiments on these layers can be used to test certain predictions from particle theory that are difficult to access otherwise.

As an example, I will describe experiments where a supercurrent is induced in the surface states by contacting these structures with Nb electrodes. AC investigations indicate that the induced superconductivity is strongly influenced by the Dirac nature of the surface states. We present strong evidence for the presence of a gapless Andreev mode in our junctions.

Finally, by playing with the strain in the layers, we can turn HgTe into a Dirac semimetal, which exhibits the ‘axial anomaly’ known from particle physics when the Fermi level is tuned to the Dirac points.

Hosts: Mohammad Hafezi and Victor Yakovenko

November 8
Artur Ekert, University of Oxford
Hosted by: Charles Clark

The ultimate physical limits of privacy

Among those who make a living from the science of secrecy, worry and paranoia are just signs of professionalism. Can we protect our secrets against those who wield superior technological powers? Can we trust those who provide us with tools for protection? Can we even trust ourselves, our own freedom of choice? Recent developments in quantum cryptography show that some of these questions can be addressed and discussed in precise and operational terms, suggesting that privacy is indeed possible under surprisingly weak assumptions.


November 15
Distinguished University Professor Lecture
Rabindra Mohapatra, University of Maryland

Neutrino masses: where we are, where we are going and why is it important?


Discovery of neutrino oscillations in various experiments during the past two decades have established that neutrinos have mass, contrary to the common belief held for nearly half a century. The activities in experimental and theoretical as well as astrophysical and cosmological fronts have gone exponential following this discovery, uncovering many more details about neutrino properties. In this talk, after a brief overview of where we stand now in this field and where we are going, I will discuss some key theoretical hints that have emerged regarding physics beyond the standard model from the current results and suggest ways to test them experimentally.

November 22
Chris Monroe, University of Maryland

Building a Quantum Computer Atom by Atom

Laser-cooled and trapped atomic ions are standards for quantum information science, acting as qubits with unsurpassed levels of quantum coherence while also allowing near-perfect measurement. When qubit state-dependent optical forces are applied to a collection of ions, their Coulomb interaction is modulated in a way that allows entanglement operations that form the basis of a quantum computer. Similar forces allow the simulation of quantum magnetic interactions, and recent experiments have implemented tunable long-range interacting spin models with up to 25 trapped ions, the largest collection of interacting qubits yet demonstrated. Scaling to even larger numbers can be accomplished by coupling trapped ion qubits to optical photons, where entanglement can be formed over remote distances for applications in quantum communication, quantum teleportation, and distributed quantum computation. By employing such a modular and reconfigurable architecture, it should be possible to scale up ion trap quantum networks to useful dimensions, for future quantum applications that are impossible using classical processors

November 29
Distinguished Scholar-Teacher Lecture
Steven Anlage, University of Maryland

When Waves Meet Chaos: A Clash of Paradigms

The concept of duality, the fact that matter can either behave like a particle or a wave, has been around for 100 years, but few of us are completely comfortable with the idea. This clash of paradigms is illustrated by the field of ‘quantum chaos’ where one studies the quantum (wave) properties of systems that show classical chaos (a particle-like property) in the high energy (short wavelength) limit. ‘Wave chaotic’ systems appear in many contexts: nuclear physics, acoustics,two-dimensional quantum dots, and electromagnetic enclosures, for example. In this Distinguished Scholar Teacher lecture I will present the surprising results of experiments that my group has carried out to further explore the dual nature of matter from this unique perspective.



December 6
David Kaplan, Johns Hopkins University
Hosted by: Raman Sundrum

Macroscopic Physics, the Higgs Boson, and Cosmological Evolution of Parameters

In this talk, I present the Higgs Boson's Compton wavelength
(proportional to its inverse mass), as currently one of the few
fundamental length-scales in physics, from which much of macroscopic physics is derived. The Standard Model of particle physics predicts a direct relationship between the Higgs mass and the mass of all other fundamental particles, but it fails to predict the mass of the Higgs itself. In fact, the Higgs mass is a conundrum in the Standard Model, as simple (and very reasonable) scaling arguments it should be sixteen orders of magnitude bigger! I will summarize the different approaches to this problem (dubbed the 'hierarchy problem') and show that they all represent a single class of ideas. I will also summarize a second type of idea that relies on anthropic arguments and the existence of a multiverse. Finally, I will present a brand new approach that explains the smallness of the Higgs mass (and thus the largeness of atoms) as a result of cosmological evolution of parameters, and suggest that this fundamental scale in physics may have been result of something akin to self-organized criticality in the early universe.



December 13
Kate Scholberg, Duke University
Hosted by: Sarah Eno, Greg Sullivan

Neutrinos from the Sky and Through the Earth

The progress in neutrino physics over the past fifteen years has been tremendous: we have learned that neutrinos have mass and change flavor. This discovery won the 2015 Nobel Prize. I will pick out one of the threads of the story-- the measurement of flavor oscillation in neutrinos produced by cosmic ray showers in the atmosphere, and further measurements by long-baseline beam experiments. In this talk, I will present the latest results from the Super-Kamiokande and T2K (Tokai to Kamioka) long-baseline experiments, and will discuss how the next generation of high-intensity beam experiments will address some of the remaining puzzles.


Upcoming Events


Tue, Dec 6, 2016 1:15 pm - 2:15 pm


Wed, Dec 7, 2016 11:00 am - 5:30 pm


Wed, Dec 7, 2016 2:00 pm - 3:00 pm


Wed, Dec 7, 2016 3:00 pm - 4:00 pm


Thu, Dec 8, 2016 12:30 pm - 1:30 pm


Thu, Dec 8, 2016 2:00 pm - 3:30 pm


Thu, Dec 8, 2016 3:30 pm - 4:30 pm


Fri, Dec 9, 2016 11:00 am - 3:00 pm