Spring 2021
Pappalardo Luncheon Speaker Series

Wednesdays // 12:00 PM via Zoom

A weekly series of Pappalardo Fellows ‘luncheon’ talks, featuring former, current and incoming Fellows from the program’s 21-year history.

All talks will be open to the MIT Physics community, and designed for broad appeal to researchers in all of the Department’s subfields, and across all constituencies, from students to staff, postdocs to faculty.

Questions? Email Carol Breen, Communications & Pappalardo Fellowships Program Administrator.

Speakers Series Schedule

Wednesday, February 10, 2021

Marin Soljačić, 2000-2003 Pappalardo Fellow; Professor of Physics, MIT
Introductory remarks: Joshua Foster, incoming 2021-2024 Pappalardo Fellow

“Photonics for AI and AI for Photonics”

The recent AI revolution presents a number of exciting opportunities for photonics, both to help with photonics research, but also for photonics to help further advances in AI.

Wednesday, February 17, 2021

Kevin Burdge, Incoming 2021-2024 Pappalardo Fellow
Introductory remarks: Steven Villanueva, 2018-2021 Pappalardo Fellow

Shedding Light on Millihertz Gravitational Wave Sources

Photons being collected today are powerful tools in identifying compact binary gravitational wave sources with orbital periods of minutes to hours. 

This talk will give an overview of an effort to use the Zwicky Transient Facility and other wide-field optical time-domain astronomical surveys to identify new sources of gravitational radiation detectable by the space-based gravitational wave detector LISA (Laser Interferometer Space Antenna).

Twenty new examples have been identified over the last two years, a rapid doubling of the known population of such sources. These sources can be used to experimentally probe general relativity, the degenerate Fermi gas equation of state, and tidal physics in white dwarfs, as well as shed light on astrophysical processes such as binary evolution and accretion physics.

Wednesday, February 24, 2021

Manki Kim, Incoming 2021-2024 Pappalardo Fellow
Introductory remarks: Rachel Carr, 2016-2018, 2020-2021 Pappalardo Fellow

“Towards Understanding Dark Energy in String Theory”

Dark energy has been the bedrock of modern cosmology. Despite its importance, it has been notoriously difficult to compute and understand dark energy in string theory.

In this talk, I will describe the recent progress on computing dark energy in string theory.

Wednesday, March 3, 2021

Henriette Elvang, 2005-2008 Pappalardo Fellow; Professor, University of Michigan, Ann Arbor
Introductory remarks: Washington Taylor, Professor of Physics

“Trajectories in the Theory Landscape”

The landscape of theoretical physics models described by field theories is vast and incredibly rich. It captures a wide range of physical phenomena, from the standard model of particle physics theories to critical phase transitions in water and helium.

In this talk, I will introduce the field theory landscape and give examples of interesting physical models.

I’ll also describe some very surprising connections between theories in the landscape. For example, low-energy graviton scattering can be computed as a “double-copy” of gluon scattering.

In conclusion, I’ll discuss new progress on a generalization of this double-copy map as an illustration of my recent work.

Wednesday, March 10, 2021

Sanfeng Wu, 2016-2019 Pappalardo Fellow; Assistant Professor, Princeton University
Introductory remarks: Mallika Randeria, 2019-2022 Pappalardo Fellow

“The “Dark” Condensed Matter”

In condensed matter physics, we are fascinated by a wide range of quantum phenomena associated with metallic states of matter, such as superconductivity and quantum Hall effects. The study of these wonderful phenomena has led to the advancement of a variety of experimental tools in probing quantum behaviors of metals. 

However, how good we are at probing metallic states of matter contrasts with how poor we are at probing insulating states of matter. In principle there must also be a wide range of interesting quantum phases hidden in electrical insulators, but we lack approaches to see them.

In this talk, I will introduce some of these challenging problems in condensed matter that may be thought of as the “dark matter problem” in solids. I will describe an example based on a surprising observation we made recently in my new lab at Princeton University. 

Wednesday, March 17, 2021

Walter Hofstetter, 2001-2004 Pappalardo Fellow; Professor, Institut für Theoretische Physik, Johann Wolfgang Goethe-Universität, Frankfurt am Main, Germany
Introductory remarks: Anna-Christina Eilers, 2019-2022 NASA Hubble Fellow; 2022-2024 Pappalardo Fellow

“Correlated Topological Quantum States in Ultracold Atoms”

Ultracold atoms in optical lattices are powerful quantum simulators for strongly correlated systems. With synthetic gauge fields, induced by time-periodic driving, they can simulate interacting topological states of matter. I will address the following open challenges.

Quantum gases are mesoscopic and have soft boundaries. We propose an interacting topological interface that allows experimentally observing edge modes via quantum gas microscopy.

We also show that the topology of an interacting Chern insulator is approximately encoded in the single-particle density matrix, which can be measured in time-of-flight experiments.

Disorder usually impedes coherent transport. Together with gauge fields it can remarkably induce a topological phase with quantized transport. We show that strong correlations can even enhance this effect. 

Wednesday, March 24, 2021

Richard Fletcher, 2016-2019 Pappalardo Fellow; Assistant Professor of Physics, MIT
Introductory remarks: Hoi Chun “Adrian” Po, 2018-2021 Pappalardo Fellow

“Quantum Hall physics in the quantum Foucault pendulum”

When charged particles are placed in a magnetic field, their single-particle energy states separate into discrete Landau levels, within which all states have the same energy. This degeneracy means that the behavior of the system is completely determined by the interparticle interactions and strongly-correlated behavior such as the fractional quantum Hall effect occurs. In contrast to transport measurements in condensed matter systems which probe the behavior of the entire sample, ultracold atomic quantum gases afford the ability to manipulate and observe the dynamics of single wavefunctions subject to a magnetic field. This offers a complementary, microscopic insight into the individual building blocks of quantum Hall systems. 

However, atomic quantum gases are electrically neutral, meaning one must engineer ‘synthetic’ magnetic fields for the atoms. Here, we present recent experiments on high-resolution microscopy of a rotating Bose-Einstein condensate, in which the Coriolis force felt by a massive particle in a rotating frame plays the role of the Lorentz force felt by a charged particle in a magnetic field. Remarkably, in a magnetic field the X and Y coordinates of a particle do not commute, leading to a Heisenberg uncertainty relation between spatial coordinates. We directly observe this uncertainty, and the resulting zero-point motion of atoms which sets a fundamental limit on their position. In a second experiment, we investigate the purely interaction-driven behavior of a Bose-Einstein condensate living entirely in the lowest Landau level, a strange world where kinetic energy is irrelevant. We reveal a spontaneous crystallization of the fluid, driven purely by the interplay of interactions and the magnetic field.

Wednesday, March 31, 2021

Jeongwan Haah, 2013-2016 Pappalardo Fellow; Researcher, Station Q, Microsoft Research
Introductory remarks: Hoi Chun “Adrian” Po, 2018-2021 Pappalardo Fellow

“Topological Phases of Discrete Time Evolution”
In the Heisenberg picture of quantum mechanics, time evolution is a one-parameter family of automorphisms of operator algebra. They are represented by a Hamiltonian and are arbitrarily accurately approximated by quantum circuits. Restricted to short times the equivalence between time evolution and quantum circuits, especially the property that it maps a local operator to another, has been implanted in theoretical studies of topological phases of matter.

In this talk, Jeongwan will explain recent findings that not all locality-preserving automorphisms, also called quantum cellular automata, can be written as quantum circuits—there exists a “discrete time dynamics” that cannot have a “Hamiltonian.” These are tightly related to static, topological many-body states.

Jeongwan will give results on the classification of these automorphisms.

Wednesday, April 7, 2021

Robert Simcoe, 2003-2006 Pappalardo Fellow; Francis L. Friedman Professor of Physics; Director, MIT Kavli Institute for Astrophysics and Space Research
Introductory remarks: Steven Villanueva, 2018-2021 Pappalardo Fellow

“Interpreting the Shadows of Unseen Galaxies in the Early Universe”

The first galaxies that emerged within t = 1 Gyr after the Big Bang were diminutive compared to present day galaxies like the Milky Way. Their low intrinsic luminosities and extreme distances make direct observation of starlight impossible with present facilities.

However, new surveys have uncovered a handful of ultra-luminous accreting black holes (quasars) at even earlier times, when the universe was just t = 700 Myr old (it is 13,787 Myr today).

I will describe discovery spectroscopy of the second-earliest quasar yet found, which was only recently dethroned as record holder. Its spectrum reveals foreground absorption from elements synthesized in the stars of a t = 794 Myr (redshift 6.84) galaxy that is too faint to be seen directly.

Our group will search for the as-yet unseen stellar populations of similar absorbers in the first year of operation for the anticipated James Webb Space Telescope, scheduled for launch on Halloween of this year.

I will offer some background on why the Webb telescope is so powerful for observing these early epochs, explain how we plan to use it, and share some of its operational idiosyncrasies.

Wednesday, April 14, 2021

Joshua Foster, 2021-2024 Pappalardo Fellow
Introductory remarks: Anna-Christina Eilers, 2019-2022 NASA Hubble Fellow; 2022-2024 Pappalardo Fellow

“The Direct and Indirect Detection of Axion Dark Matter”

The quantum chromodynamics axion is a well-motivated dark matter candidate that may also solve the strong CP problem related to the absence of the neutron electric dipole moment. Efforts towards the detection of the axion across a broad range of possible masses, through both precision laboratory measurement and astrophysical observation, are a critical component of the modern particle physics program. In this talk, I will discuss recent new results and future prospects of ongoing searches for axion dark matter performed by the ABRACADABRA collaboration in the Laboratory for Nuclear Science and through radio observations of neutron star populations at the Galactic Center.

Wednesday, April 21, 2021

Katelin Schutz, 2019-2020 Pappalardo Fellow; 2020 NASA Einstein Fellow
Pappalardo Symposium
Introductory remarks: Tracy Slatyer, Jerrold R. Zacharias Career Development Associate Professor of Physics

“Making Dark Matter Out of Light”

Dark matter could be a “thermal-ish” relic of freeze-in, where the dark matter is produced by extremely feeble interactions with Standard Model particles dominantly at low temperatures.

In this talk, I will discuss how sub-MeV dark matter can be made through freeze-in, accounting for a dominant channel where the dark matter gets produced by the decay of plasmons–photons that have an in-medium mass in the primordial plasma of our Universe. 

I will also explain how the resulting non-thermal dark matter velocity distribution can impact cosmological observables.

Wednesday, April 28, 2021

Anna-Christina Eilers, 2019-2022 NASA Hubble Fellow; 2022-2024 Pappalardo Fellow
Pappalardo Symposium
Introductory remarks: Robert Simcoe, Francis L. Friedman Professor of Physics; Director, MIT Kavli Institute for Astrophysics and Space Research

“The Formation and Growth of Supermassive Black Holes”

The existence of luminous quasars hosting supermassive black holes within the first billion years of cosmic history challenges our understanding of black hole growth. An important piece of the puzzle is the lifetime of quasars–the time that galaxies shine as active quasars and during which the bulk of the black hole growth occurs–but to date its value remains uncertain by several orders of magnitude. 

I will present a new method to obtain constraints on the lifetime of quasars based on the sizes of ionized regions around quasars known as proximity zones. These proximity zones act as a “quasar clock” and enable us to study the co-evolution of supermassive black holes and their host galaxies from a new perspective.

Surprisingly, our results indicate that black holes can grow several orders of magnitude faster than previously thought, which provides a potential solution to the long-standing puzzle of the rapid black hole growth and new insights into galaxy evolution across cosmic time.

Wednesday, May 5, 2021

Rachel Carr, 2016-2018, 2020-2021 Pappalardo Fellow
Pappalardo Symposium
Introductory remarks: Janet Conrad, Professor of Physics

“Chasing Anomalies with Reactor Neutrinos”

Nuclear reactors are the brightest sources of neutrinos on earth. Although built for quite different purposes, reactors have delivered a host of surprises, discoveries, and controversies in neutrino physics.

In the last decade, one intriguing anomaly launched a search for a new type of neutrino even more weakly interacting than the known types. That prize has not yet turned up, but the search is yielding other new facts and perhaps an unconventional nuclear technology. 

Six decades after the first quixotic–and ultimately successful–quest for neutrino signals at a reactor, the chase continues.

Wednesday, May 12, 2021

Nicholas Kern, 2020-2023 Pappalardo Fellow
Pappalardo Symposium
Introductory remarks: Jacqueline Hewitt, Julius A. Stratton Professor in Electrical Engineering and Physics

“Ushering in a New Era for High Redshift Astrophysics and Cosmology with the 21 cm Line​”

The next generation of large-scale cosmological surveys will use hydrogen, the most abundant baryonic species, and its 21-cm spin flip transition to systematically probe the cosmic web from the present day all the way back to the birth of the first stars and galaxies.

This will come from a new class of radio telescopes that have injected fresh energy into low-frequency radio astronomy. Such experiments will open an unprecedented window into high redshift galaxy formation physics, directly constraining the growth and spectral properties of the first stars and galaxies.

They will also present new stress tests of the cosmological standard model, and place novel constraints on the expansion history of the universe. However, in order to achieve these scientific goals, a revolution in precision radio data analysis is required in order to mitigate the giant levels of astrophysical and terrestrial contaminants.

In this talk, I will discuss the potential of the 21 cm line as a powerful probe of cosmology and astrophysics, and the promising work currently underway to detect the cosmological 21 cm signal. While I will touch on a variety of science drivers, I will focus mainly on the efforts to use the 21 cm line as a tool to map out the density, ionization, and temperature state of intergalactic gas during the Epoch of Reionization: the era marking the formation of the first stars and galaxies in the universe.

Wednesday, May 19, 2021

Hoi Chun “Adrian” Po, 2018-2021 Pappalardo Fellow
Pappalardo Symposium
Introductory remarks: Liang Fu, Lawrence C. (1944) and Sarah W. Biedenharn Career Development Associate Professor of Physics

“Topology at the Corner of the Table”

The influx of topological ideas in the past two decades has completely changed the way we think about materials. 

In this talk, we will discuss how the revolution reaches all the way to something we see and even taste every single day: sodium chloride, commonly known as table salt. 

We will show that an unnoticed topological aspect of the rock salt structure implies it is an example of the recently introduced notion of higher-order multipole insulators. 

As a consequence, the corners of salt crystals are sprinkled with fractions of electrons, which also form part of our daily meals. Bon appétit!

Wednesday, September 2, 2020

Or Hen, 2015-2017 Pappalardo Fellow; Assistant Professor of Physics, MIT
Introductory remarks: Prof. Robert Redwine, MIT Physics

“From radioactive nuclei to neutron stars: experimental probes of strongly interacting QCD matter”

Presenting first results from a new research program Or initiated as a Pappalardo Fellow, the program brings together concepts and tools from the atomic physics of strongly interacting many-body systems with nuclear ab-initio theory and experimental studies, using radioactive nuclear beams to shed new light on the properties of the highest density forms of visible matter in the universe.

Wednesday, September 9, 2020

Lu Li, 2008-2011 Pappalardo Fellow; Professor of Physics, University of Michigan, Ann Arbor
Introductory remarks: Mallika Randeria, Pappalardo Fellow

“Metal or insulator? That is the question.”

Lu will talk about the dual nature of the topological Kondo insulators. They are perfect insulators like pure silicon, and their electrical resistivity diverges by more than a million times during cooling down. Yet, they show a characteristic feature of good metal—oscillations in magnetization under magnetic fields.

In this talk, Lu will review his discovery of this contradiction: his quest to observe insulators’ oscillations, not only in magnetization but also in electrical resistivity. His experiments demonstrate that the oscillatory carriers are just like electrons, following the Fermi-Dirac distributions, even in this perfect insulator. So, can the compound be both metal and insulator? Or can a fermion exist in solids even without electrical charge? Let’s find the answer.

Wednesday, September 16, 2020

Mustafa Amin, 2008-2011 Pappalardo Fellow; Associate Professor of Physics, Rice University
Introductory remarks: Nick Kern, Pappalardo Fellow

“Smashing Solitons of Cosmology”

In Wednesday’s talk, Mustafa will explore what happens when cosmological solitons form, cluster, and smash into each other. He will argue that certain types of solitons, called oscillons, can arise in abundance both at the end of inflation, and in dark matter in the present day universe. 

He will then show that the formation, clustering, and collisions of such solitons can leave signatures in cosmological structure formation, give rise to gravitational waves, and potentially lead to highly energetic bursts of light.

Wednesday, September 23, 2020

Jacob Taylor, 2006-2009 Pappalardo Fellow; Fellow, Joint Quantum Institute, and Adjunct Professor, University of Maryland
Introductory remarks: Rachel Carr, Pappalardo Fellow

“Frontiers in Quantum Information Science”

Quantum information science (QIS) promises dramatic improvements in our ability to understand the physical world and in our capabilities for measurement, communication, and computation.

Over the past five years, a worldwide expansion of government-funded research and development has combined with an unprecedented investment from the private sector to dramatically accelerate progress in realizing the potential of quantum systems. In this talk, Jake will discuss the re-envisioning of the U.S. research and development approach to QIS enacted over the past two years through the National Quantum Initiative and other efforts, and consider future opportunities and challenges for academia, industry, government and the public.

Jake will also touch upon several research frontiers of personal interest in the space, specifically the interplay between quantum device development and physical understanding, from probing many-body systems with qubits to searching for dark matter using advanced quantum sensors to even exploring terrestrial tests of the quantum nature of gravity.

Wednesday, September 30, 2020

Guy Bunin, 2013-2016 Pappalardo Fellow; Assistant Professor of Physics, Technion-Israel Institute of Technology
Introductory remarks: Adrian Po, Pappalardo Fellow

“Ecosystems as Complex Systems”

Natural ecosystems exhibit astounding richness. This suggests that we treat them as many-variable interacting systems, but is there any evidence to support this perspective?

Guy will discuss two possible directions to address this question. The first looks for classical footprints of complex systems, such as phase-transitions. The second direction asks how species interact in complex ecosystems in order to coexist, and leads to theoretical predictions that are validated in data from plant-competition experiments.

Wednesday, October 7, 2020

Carlos Nunez, 2002-2005 Pappalardo Fellow; Professor of Physics, Swansea University, UK
Introductory remarks: Adrian Po, Pappalardo Fellow

“Aspects of Duality”

In physics, the idea of ‘duality’ is an old and elusive one. Examples of dualities appear scattered throughout various branches of theoretical physics. For a long time, dualities were seen as mere curiosities.

In this talk, Carlos will discuss the idea of duality, why it is interesting and how dualities can be useful in learning new physics, and perhaps put or see old physics under a new light.

Some dualities in string theory will also be discussed.

Wednesday, October 14, 2020

Carl Rodriguez, 2016-2019 Pappalardo Fellow; Assistant Professor of Physics, Carnegie-Mellon University
Introductory remarks: Christina Eilers, Pappalardo Fellow

“The Lives and Deaths of Star Clusters, and the Gravitational Waves They Make Along the Way”

The lives of star clusters are inextricably linked to the assembly and evolution of their parent galaxies. While significant progress has been made in understanding galaxy formation and the dynamics of star clusters as separate systems, our understanding of their symbiotic connection remains in its infancy. 

In this talk, Carl will describe how massive and old clusters, such as the globular clusters in the Milky Way, are an ideal site for the production of heavy binary black holes, and how repeated binary mergers in these environments can produce black hole masses that cannot be explained though the collapse of single stars.

Carl will then describe a recent project to model these clusters self-consistently from collapsing giant molecular clouds in an MHD simulation of a Milky Way-sized galaxy.

Finally, he will connect these results to the binary black holes formed from isolated binaries and dense star clusters, including GW190412 and GW190521, two recent gravitational-wave detections with unique masses and spins.

Wednesday, October 21, 2020

David Tong, 2001-2004 Pappalardo Fellow; Professor of Theoretical Physics and Fellow of Trinity College, University of Cambridge
Introductory remarks: Assistant Professor of Physics Or Hen, MIT

“Are we living in the matrix?”

No. Obviously not. And it’s got something to do with chiral fermions and the fact that our world does not respect the symmetry of parity.

David will explain and unveil the mystery.

Wednesday, October 28, 2020

Silviu Pufu, 2011-2014 Pappalardo Fellow; Associate Professor of Physics, Princeton University
Introductory remarks: Prof. Washington Taylor, Center for Theoretical Physics, MIT Physics

“What boiling water and magnets can teach us about Quantum Gravity”

The theory of phase transitions in statistical physics is an old subject. Nevertheless, the most precise calculations to date of the properties of certain critical points–including the properties of the critical point of the water-vapor transition–have been achieved only recently using the technique of conformal bootstrap.

In this talk, Silviu will start by describing some of the ideas behind these recent developments.

Afterwards, he will explain how the same ideas can give us insight into properties of Quantum Gravity in the presence of a negative cosmological constant.

Wednesday, November 4, 2020

Matthew Headrick, 2003-2006 Pappalardo Fellow; Professor of Physics, Brandeis University
Introductory remarks: Katelin Schutz, Pappalardo Fellow

“Black holes, quantum entanglement, and the geometry of spacetime”

Bekenstein and Hawking discovered 50 years ago that black holes carry an enormous entropy, suggesting that spacetime itself is a thermodynamic or emergent system built out of a vast number of underlying microscopic degrees of freedom.

What are these degrees of freedom, and how do they conspire to create a universe governed by general relativity?

String theorists studying certain models of quantum gravity have discovered an important clue, a beautiful and direct connection between quantum entanglement and the geometry of spacetime.

Matt will explain this connection, and how it has led to recent progress on old paradoxes concerning black holes.

Wednesday, November 18, 2020

Robert Penna, 2013-2016 Pappalardo Fellow; Fellow, Institute for Advanced Study
Introductory remarks: Steven Villanueva, Pappalardo Fellow

“Twistors and Integrability”

Roger Penrose (Nobel Prize 2020) created twistor theory as part of a program for quantizing gravity. Since then, twistors have found important applications in other areas of physics and mathematics, such as the theory of integrable systems.

In this talk, Bob will give an introduction to twistors and their role in the theory of integrable systems.

Wednesday, December 2, 2020

David Hsieh, 2009-2012 Pappalardo Fellow; Professor of Physics, Caltech
Introductory remarks: Aviram Uri, Pappalardo Fellow

“Magnetism far from thermal equilibrium”

Dynamically driven interacting many-body systems have the potential to exhibit exotic properties that defy the laws of equilibrium statistical mechanics.

David will describe such an occurrence in a strongly-correlated magnetic insulator that is driven far from equilibrium with an ultrashort burst of light. 

The transient system exhibits critical phenomena, but of a type that is forbidden in thermal equilibrium.

Wednesday, December 9, 2020

Taritree Wongjirad, 2014-2017 Pappalardo Fellow; Assistant Professor of Physics, Tufts University
Introductory remarks: Rachel Carr, Pappalardo Fellow

“From Pixels to Neutrinos”

The MicroBooNE experiment consists of a liquid argon time projection chamber(LArTPC) situated in the path of the Booster Neutrino Beam (BNB) at Fermilab.

The goals of the experiment are to (1) investigate the observation of an excess of a possible electron-neutrino and anti-neutrino events by the MiniBooNE experiment; (2) measure argon-nucleus cross sections; and (3) perform R&D for LArTPCs.

The data from MicroBooNE, and other LArTPCs, can be naturally arranged as high-resolution images of particle tracks traversing the detector. This has spurred effort on MicroBooNE towards applying convolutional neural networks (CNNs), a type of deep learning algorithm shown to be effective in numerous computer vision problems, to the data.