Physics and Astronomy Colloquium 2019-2020

Thursdays, 4:00-5:00 pm

1-434 Physics and Astronomy (map)

Reception from 3:15-3:30
(unless otherwise posted)

For more information, contact Yaroslav Tserkovnyak

Fall 2019

Thursday, October 3, 2019

Saxon Lecture

How many numbers does it take to determine our Universe?

Michael S. Turner

Kavli Foundation and University of Chicago

Over the past three decades our understanding of the Universe has deepened.  The WMAP and Planck teams have asserted that just six numbers are needed to describe the whole Universe (fewer than the ten digits in a phone number), based upon their high-precision, all-sky maps of the Cosmic Microwave Background. Others have different opinions: one, two, a different six, and nine to determine our Universe. As I will discuss, the choice of numbers reveals much about what we know, our aspirations, and how we think about the Universe. After exploring the landscape, I will advocate for zero!


Thursday, October 10, 2019

On Ising's model of ferromagnetism

Peter Armitage

Johns Hopkins University

The 1D Ising model is a classical model of great historical significance for both classical and quantum statistical mechanics. Developments in the understanding of the Ising model have fundamentally impacted our knowledge of thermodynamics, critical phenomena, magnetism, conformal quantum field theories, particle physics, and emergence in many-body systems. Despite the theoretical impact of the Ising model there have been very few good 1D realizations of it in actual real material systems. However, it has been pointed out recently, that the material CoNb2O6, has a number of features that may make it the most ideal realization we have of the Ising model in one dimension.   In this talk I will discuss the surprisingly complex physics resulting in this simple model and review the history of "Ising’s model” from both a scientific and human perspective.  In the modern context I will review recent experiments by my group and others on CoNb2O6.  In particular I will show how low frequency light in the THz range gives unique insight into the tremendous zoo of phenomena arising in this simple model system.

Thursday, October 17, 2019

Building a quantum computer with neutral atoms

David Weiss

Penn State University

I will describe our work towards making a quantum computer using ultra-cold atoms trapped in a 3D optical lattice. In particular, I will explain: how we change the quantum state of individual atoms, even in the middle of the array, without affecting the quantum states of other atoms; how we sort atoms by realizing a Maxwell's demon; and how we reliably detect the internal states of the atoms without losing any.


Thursday, October 24, 2019


Thursday, October 31, 2019

Physics and the HIV Virus

Robijn Bruinsma

University of California, Los Angeles

The intense research effort dedicated to the HIV virus and to other retroviruses has revealed our fundamental lack of understanding how the HIV virus "works". The colloquium will discuss how a combination of the physics of soft matter and of numerical simulations provides us with important insights into the different stages of the life-cycle of HIV. Conversely, the study of the operation of HIV provides statistical physics with interesting challenges, such as the apparent violation of the Second Law of Thermodynamics during the assembly process.


Thursday, November 7, 2019

The Physics of Active Matter
M. Cristina Marchetti
University of California, Santa Barbara
In two-dimensional systems, such as thin films of superfluids, crystals, liquid crystals and magnets, topological defects are key to understanding the transition between ordered and disordered states.  Almost fifty years ago, Berezinskii, Kosterlitz and Thouless showed that these systems disorder through a topological phase transition associated with the proliferation of unbound pairs of vortices of opposite charge.  The essence of this transition relies on the mapping of the statistical physics of defects onto a Coulomb gas. In active liquid crystals, topological defects become motile particles and drive the transition from spontaneous laminar flow to self-sustained turbulent-like motion. In this talk I will outline the statistical physics of defects in active nematics and their possible role in materials science and biology. By viewing the active nematic as a collection of swarming and interacting active defects, the onset of active turbulence can be described as an activity-driven defect unbinding transition. A hydrodynamic theory of a gas of unbound defects captures a new state of hierarchically organized active matter - a defect flock where defects themselves line up and order into a collectively flowing liquid. The hydrodynamic treatment of active defects provides a framework to address fundamental questions of defect organization in active matter and paves the way for the design of active devices with targeted transport functionalities through the controlled variation of activity.

Thursday, November 14, 2019

Probing Dark Matter Throughout Cosmic History

Vera Gluscevic

University of Southern California

I will review the status of cosmological searches for dark matter-baryon interactions, summarizing the best current limits on scattering of light particle candidates with protons derived from the cosmic-microwave-background anisotropy measurements. I will then present stringent new bounds on the same physics, inferred recently from the observed population of the Milky Way satellite galaxies. I will highlight complementarities between different observations and laboratory searches for dark matter, and discuss the prospects for unveiling the physics of dark matter in the coming decade.


Thursday, November 21, 2019

Quantum decorating: Imaging novel electronic states in defect-engineered 2D materials

Christopher Gutierrez

University of California, Los Angeles

Two-dimensional (2D) quantum materials have attracted much excitement due to the many interesting physical properties that emerge when they are thinned down to single atomic layers. Graphene, for instance, is a single layer of the ordinary graphite found in your pencil lead, yet its electrons behave like relativistic massless Dirac fermions. This has allowed graphene to act as a tabletop testbed for exploring novel forms of symmetry breaking and for verifying longstanding theoretical predictions in relativistic quantum mechanics. 

Importantly, owing to its exposed surface, graphene’s electronic properties can be precisely tailored by the presence of atomic defects. In this talk I will present atomic scanning probe and photoemission spectroscopy experiments that highlight how the spatial arrangement of such defects can be harnessed to create novel electronic states in graphene. In the first part, I will show how different types of atomic scatterers peppered above (or below) graphene can self-assemble and drive the formation of new and topologically distinct collective density wave phases in graphene. In the second part, I will show that when substrate defects instead form large, amorphous clusters, they can create local potentials that can trap graphene’s quasi-relativistic electrons into quantized atomic-like orbitals, opening the door to studying 2D analogs of large, relativistic “Dirac atoms.”

Thursday, November 28, 2019

Thanksgiving Holiday

No Colloquium

Thursday, December 5, 2019, 4:00-5:00 p.m.

Kicking as a Route to Discovery: Condensed Matter Systems Away From Equilibrium

Anshul Kogar

University of California, Los Angeles

Traditionally, we have studied condensed matter systems at or near equilibrium using a variety of thermodynamic and spectroscopic measurements. Recently, through the advent of laser technology that has enabled intense ultra-short pulses, we have been able to gain access to material properties in a far-from-equilibrium regime. In this talk, I will describe what we have been able to learn using these technologies and how we went from studying phases of matter to being able to manipulate their properties with these intense laser pulses. Specifically, I will focus on a particular phase of matter called a charge density wave, where we have been able to visualize phase competition away from equilibrium and the writing and erasing of domain walls in these materials using light.


Winter 2020

Thursday, January 9, 2020, 4:00-5:00 p.m.

Gender, Equity, Power Structures and Implicit Bias in STEM

Elizabeth Simmons (University of California, San Diego)

University of California, San Diego

The presentation will start by reviewing data on the current status of gender equity in science, technology, engineering and mathematics (STEM) disciplines and summarizing social science research that illuminates some causes of gender disparities in STEM. With this context established, the focus will shift to how women enter into leadership roles in academic settings, what they experience and how gender impacts the way they exercise their authority. The final part of the talk will discuss how we can all contribute to changing the face of leadership for the future, to the benefit of all of us in STEM.


Thursday, January 16, 2020, 4:00-5:00 p.m.

"Twisting 2d materials: the magic and the mystery"
Leon Balents

University of California, Santa Barbara

Graphene, a single atom thick lattice of pure carbon, is an ideal material to study the physics of electrons in a two dimensional "flatland". A new twist - literally - on graphene physics arose in the last two years. Driven by a theoretical prediction from 2011, experiments in 2018 confirmed thats placing one layer of graphene atop another rotated by a tiny angle of about 1 degree completely changes the behavior of the electrons. The rotation forms a moiré pattern, which acts as a new artificial lattice within which electrons move. At this "magic" angle, this motion is highly correlated and very different from what occurs in the parent graphene. The resulting insulating, magnetic, topological, and superconducting states are the subject of intense current research. This talk will review this active area and describe some of the latest results and theoretical predictions for twisted graphene and beyond.


Thursday, January 23, 2020, 4:00-5:00 p.m.

"TBA" by Stefania Gori (University of California, Santa Cruz)


Thursday, January 30, 2020, 4:00-5:00 p.m.

"TBA" by Gregg Hallinan (Caltech)


Thursday, February 6, 2020, 4:00-5:00 p.m.

Neutrinos, Dark Matter, and the Quest for the New Standard Model

Ian Shoemaker

Virginia Tech

The observations that the Universe contains non-luminous Dark Matter and that neutrinos have mass are critical clues about the nature of physics beyond the Standard Model. In this talk, I'll review recent work on this front highlighting the complementarity between terrestrial and astrophysical probes of new physics.  


Thursday, February 13, 2020, 4:00-5:00 p.m.

Magic Angle Graphene: a New Platform for Strongly Correlated Physics

Pablo Jarillo-Herrero (Massachusetts Institute of Technology)

The understanding of strongly-correlated quantum matter has challenged physicists for decades. Such difficulties have stimulated new research paradigms, such as ultra-cold atom lattices for simulating quantum materials. In this talk I will present a new platform to investigate strongly correlated physics, based on graphene moiré superlattices. In particular, I will show that when two graphene sheets are twisted by an angle close to the theoretically predicted ‘magic angle’, the resulting flat band structure near the Dirac point gives rise to a strongly-correlated electronic system. These flat bands exhibit half-filling insulating phases at zero magnetic field, which we show to be a correlated insulator arising from electrons localized in the moiré superlattice. Moreover, upon doping, we find electrically tunable superconductivity in this system, with many characteristics similar to high-temperature cuprates superconductivity. These unique properties of magic-angle twisted bilayer graphene open up a new playground for exotic many-body quantum phases in a 2D platform made of pure carbon and without magnetic field. The easy accessibility of the flat bands, the electrical tunability, and the bandwidth tunability though twist angle may pave the way towards more exotic correlated systems, such as quantum spin liquids or correlated topological insulators.


Thursday, February 20, 2020, 4:00-5:00 p.m.

The Ghostly Messengers of the Universe

Irene Tamborra

Niels Bohr Institute

Neutrinos are key particles in a wide range of astrophysical sources. Neutrinos affect the stellar dynamics, drive the formation of new elements, and carry information about the physics of the most energetic events in our Universe. Recent developments on the role of neutrinos in cosmic sources will be reviewed. The detection perspectives of neutrino will be outlined.


Thursday, February 27, 2020, 4:00-5:00 p.m.

"TBA" by Katie Bouman (Caltech)


Thursday, March 5, 2020, 4:00-5:00 p.m.

"TBA" by Erik Petigura (University of California, Los Angeles)

Thursday, March 12, 2020, 4:00-5:00 p.m.

Shedding Light on the Nature of Dark Matter

Andrew Benson

Carnegie Institute for Science

In the 50 years since dark matter was confirmed to be a major component of our Universe, astronomical observations have reached a critical point, where they will soon have the power to either infer fundamental properties of the dark matter particle, or confirm that dark matter is essentially "cold" for most astrophysical purposes. Connecting this observations to dark matter particle properties requires careful modeling of the growth and destruction of dark matter halos. I will describe a program underway to predict key observables - such as the distribution of halo masses, and their spatial correlations with galaxies - and highlight some of the challenges that these predictions face. I will present current constraints on dark matter properties derived from this combination of observation and modeling, and discuss future prospects for furthering our understanding of the dark matter particle.

Thursday, June 6, 2019, 4:00-5:00 p.m.



Spring 2020

Thursday, April 2, 2020, 4:00-5:00 p.m

"TBA" by Steven Shenker (Stanford University)


Thursday, April 9, 2020, 4:00-5:00 p.m.

"TBA" by Hung-Hai Lee (University of California, Berkeley)


Thursday, April 16, 2020, 4:00-5:00 p.m.

"TBA" by Vinvenzo Vitelli (University of Chicago)


Thursday, April 23, 2020, 4:00-5:00 p.m.

"TBA" by Bradley Siwick (McGill)


Thursday, April 30, 2020, 4:00-5:00 p.m.



Thursday, May 7, 2020, 4:00-5:00 p.m.

"TBA" by Jessica McIver (LIGO)


Thursday, May 14, 2020, 4:00-5:00 p.m.

"TBA" by Mark Eriksson (University of Wisconsin-Madison)


Thursday, May 21, 2020, 4:00-5:00 p.m.

"TBA" by Annika Peter (Ohio State University)


Thursday, 28, 2020, 4:00-5:00 p.m.

"TBA" by Clifford Cheung (Caltech)


Thursday, June 4, 2020, 4:00-5:00 p.m.

"TBA" by Sera Markoff (University of Amsterdam)







Past Physics and Astronomy Colloquia