Physics and Astronomy Colloquia, Academic Year 2018-2019

Colloquium committee: Leonardo Rastelli (Chair), Will Farr, Marivi Fernandez-Serra, Krishna Kumar, Mengkun Liu, and Giacinto Piacquadio

Coffee & Tea served at 3:45 pm.

Talk begins at 4:15 pm.

Location: Harriman 137 (bottom of square C4 on the campus map)

Movies:  To watch the recorded movies, please  read the instructions here.


Fall 2018 colloquia

Sept. 4

Chair’s Colloquium

Chair’s Colloquium

   [recorded movies] on Firefox-ESR or VLC rtsp://

Sept. 11

Dominik Schneble

Stony Brook University

Exploring the physics of spontaneous emission with atomic matter waves

The quantitative understanding of spontaneous emission harks back to the early days of QED, when in 1930 Weisskopf and Wigner, using Dirac’s radiation theory, calculated the transition rate of an excited atom undergoing radiative decay. Their model, which describes the emission of a photon through coherent coupling of the atom’s dipole moment to the continuum of vacuum modes, reflects the view that spontaneous emission into free space, driven by vacuum fluctuations, is inherently irreversible.  In my talk, I will describe recent studies of the Weisskopf-Wigner model in a novel context that allowed us to go beyond the model’s usual assumptions. For this purpose, we created an array of microscopic atom traps in an optical lattice that emit single atoms, rather than single photons, into the surrounding vacuum. Our ultracold system, which provides a tunable matter-wave analog of photon emission in photonic-bandgap materials, revealed behavior beyond standard exponential decay with its associated Lamb shift. It includes partial backflow of radiation into the emitter, and the formation of a long-predicted bound state in which the emitted particle hovers around the emitter in an evanescent wave. My talk will conclude with an outlook on using our new platform for studies of dissipative many-body physics and (non)-Markovian matter-wave quantum optics in optical lattices.
  [recorded movies]  

Sept. 18

Will Farr

Stony Brook University 

The Emerging Population of Gravitational Wave Sources

The last three years have been a bonanza for gravitational wave astronomy.  The first gravitational wave signal ever detected---GW150914, the merger of a 30- and a 40-solar mass black hole---has been followed by five more announced black hole mergers (the latest, GW170814, observed for the first time by both the LIGO detectors and the Virgo detector).  Slightly more than a year ago, the first observed merger of two neutron stars (GW170817) was also detected in the electromagnetic spectrum, in a collective effort involving almost 4000 astronomers around the world.  Each of these events carries a wealth of information about the merging objects, their progenitors, their environment, and the universe; however, to extract this information we must often resort to statistical methods that extract features collectively from the entire population of events.  I will run through a few highlights from individual detections (including the measurement of the Hubble constant from GW170817), and then discuss recent results in modeling the population of merging compact objects including: using the distribution of spins in the population to distinguish among competing formation mechanisms; measuring the distribution of merger events in redshift to determine that we live---and gravity propagates---in three spatial dimensions (who knew?) and (eventually) measure the star formation rate to sub-percent precision; and measuring the maximum mass of stellar-mass black holes and using this feature in the mass spectrum for cosmography.

  [recorded movies] 


Sept. 25

David Miller
University of Chicago

Seeing the unseeable: boosting discoveries at the LHC by imaging quarks and gluons with jets and jet substructure

Quarks and gluons are ubiquitous in the debris of the proton-proton collisions of the Large Hadron Collider (LHC), but they can also signal the presence of massive particles that are signs of new physics: they are the needle in the proverbial haystack…of needles. However, for the first time in the history of particle physics, the collision energy at the LHC is often well above the scale of electroweak symmetry breaking. Not only did this allow for the discovery of the Higgs boson in 2012, but it also leads to exotic new features of the quarks and gluons that appear in the final states of those collisions. I will walk you through why the LHC is such a fantastic “quark and gluon” machine, how new techniques to image the events observed at the LHC allow us probe jets — the observable manifestation of quarks and gluons — in exquisite detail, and present the status of the jet substructure and Lorentz-boosted object tagging approaches in the ATLAS Experiment. These techniques are already being deployed successfully in searches for new particles and precision measurements of the Standard Model. I will then look toward the future and describe new instrumentation that we’re developing to identify and record Lorentz-boosted hadronic objects in future runs of the LHC.

  [recorded movies] 


Oct. 2

Joe Eberly

University of Rochester

What did Bohr need to know about complementarity?

By exploiting a quantum feature not recognized by Niels Bohr, one discovers a new identity among well-defined physical quantities [1]. The identity resolves the famously weird wave-particle dilemma of modern physics by showing how it becomes complete. The key quantum feature, also surprisingly useful in classical wave theory, is the other instrisically weird feature of quantum theory, namely entanglement. Experimental confirmation of the new identity will be presented [2]. 

[1] "Coherence Constraints and the Last Hidden Optical Coherence," Xiao-Feng Qian, Tanya Malhotra, A. Nick Vamivakas, and Joseph H. Eberly, Phys. Rev. Letters 117, 153901 (2016).

[2] "Entanglement limits duality and vice versa," X.-F. Qian, A.N. Vamivakas, and J.H. Eberly, Optica 5, 942 (2018).

  [recorded movies] 


Oct. 9

Fall Break

No classes and no colloquium

Oct. 16

Alexios Polychronakos

100 Years of Feynman and 30 without him: reminiscences from his last year

2018 marks the 100th anniversary of the birth and 30 years since the passing of Richard Feynman, a brilliantly creative physicist and a legendary personality in science and society at large. During the last year of his life at Caltech Feynman became fascinated by integrable models, his involvement and enthusiasm inspiring and motivating both experts and novices in the field. I will attempt to give a glimpse into Feynman's thinking and personality through the lens of personal memories and mementos from that last year.

  [recorded movies] 


Oct. 23

Robert Austin

Princeton University

No Light at the End of the Tunnel:  How Bacteria Solve Mazes

Bacteria often live in topologically complex environments. The path from a colony of bacteria which as exhausted its local supply of food to a source can have many branch points with false, dead-end leads. While chemotaxis can easily navigate bacteria to a food source in the presence of a food gradient, in a sufficiently complex and large maze chemotaxis will fail. Here we explore 3 ways that the bacterium E. coli can solve a complex maze where no clear gradient to food exists. 

  [recorded movies] 


Oct. 30

Adam Willard


Quantum Trajectory Ensembles: Applying Classical Statistical Mechanics to Open Quantum Systems

The dynamics of open quantum systems are inherently stochastic. This stochasticity originates from a combination of quantum uncertainty, due to the wave-mechanical nature of the system, and classical uncertainty, due to variations in the initial preparation of the system. In numerical simulation, the classical sources of probabilistic uncertainty are often integrated out by tracing over the bath degrees of freedom. This procedure yields a single trajectory that represents the average dynamics of the system. While this approach is efficient, tracing over the bath has the undesirable effect of combining quantum and classical uncertainty in such a way that their respective influences on system dynamics cannot be separated. As an alternative to tracing over the bath, quantum dynamics can be expressed as an ensemble of individual trajectories, each describing the deterministic evolution of a specific initial state of the system and bath. The statistics of such a trajectory ensemble can encode important information that is not available from a  bath-traced trajectory alone, including the information necessary to separate the quantum and classical sources of probabilistic uncertainty or to determine how the bath degrees of freedom contribute to a given reaction coordinate.

In this talk I will present recent efforts aimed at developing a framework for studying the trajectory statistics of quantum system. I will demonstrate that if the dynamics of quantum systems are expressed in the state-space of density operators, then they exhibit dynamical flow properties that are analogous to classical Hamiltonian systems. By applying this framework to the spin-Boson model I will show how trajectory ensembles expressed in this state-space can be analyzed and interpreted using the tools of classical statistical mechanics.

  [recorded movies] 


Nov. 6

Ashvin Vishwanath

Harvard University

Topology and Entanglement in Quantum Matter: Past, Present and Future

I will review recent developments in solid state physics that have compelled us to look more deeply at the role of topology and entanglement in quantum many particle systems. This has led to the prediction of entirely new strongly interacting phases and provided insights into existing states. Time permitting, I will discuss recent intriguing applications to graphene sheets twisted at a special `magic angle' where novel insulating and superconducting states have been experimentally observed.

The colloquium will take place in the Simons Center auditorium. 

Refreshments  at 3:45pm in the Simons Center lobby.

  [recorded movies] 


Nov. 13

Stuart Henderson

Jefferson Lab

Particle Accelerators: Legacy of discovery, ambition for the future

Particle accelerators have a remarkable legacy of scientific

discovery and societal impact, from powering our understanding of the

subatomic world to the treatment of cancer.   Next-generation accelerators

and their applications will be enabled by the developments underway right

now to increase the energy reach, intensity and phase space density of

particle beams.  This presentation will review both the legacy of particle

accelerators as well as some of the promising directions in accelerator

science and technology that hold the potential to revolutionize discovery

science, health, energy and security.

  [recorded movies] 


Nov. 20

Emylin Hughes

Columbia University

Cleaning up Teller's Mess: Nuclear weapons testing in the Marshall Islands 

In the 1940s and 1950s, the United States performed 67 nuclear weapon tests in the Marshall Islands, including the detonation of the largest US thermonuclear weapon (15 megatons), named Castle Bravo. Seventy years later, the impact of these tests on the Marshallese people is still apparent. The more recent challenge of rising sea levels, coupled with the remaining nuclear waste represents a particularly chilling problem. In this talk, we will discuss our recent work on this topic

  [recorded movies] 


Nov. 27

Washington Taylor IV


Physics and Energy

Energy plays a fundamental role in most natural systems, and in the physical theories we use to describe them.  Energy also plays a central role in human civilization; our choices related to energy use and technologies will have profound impact on the future of Earth and humanity over the coming centuries.  This colloquium will discuss some aspects of energy in science and society, and how energy and energy-related issues can be incorporated into the physics curriculum.  The speaker and colleague Robert Jaffe have been teaching a course at MIT on "The Physics of Energy" for the last 10 years, aimed at students across the spectrum of majors (but with some science and calculus background), and have recently completed a comprehensive text on energy science based on the course.

  [recorded movies] 


Dec. 4

Frank Petriello
Northwestern University

Exploring the frontiers of particle and nuclear physics using QCD

A deluge of data from the Large Hadron Collider (LHC) is allowing searches for physics beyond the Standard Model with remarkable reach.  Preparations are underway for a future Electron-Ion Collider (EIC) that will address outstanding riddles regarding the structure of nucleons and nuclei. The key needed to unlock the potential of both experiments is Quantum Chromodynamics (QCD), the strong force that describes the interactions of quarks and gluons.  Although QCD has been studied for decades, many of the emergent phenomena it predicts still puzzle us, and the need for a precision understanding of QCD is a central aspect of the LHC and a future EIC.  In this talk I discuss how a precision understanding of QCD links the programs of these two experiments that together represent the frontiers of both particle and nuclear physics.  I describe recent theoretical progress in our ability to understand QCD at the requisite level to help answer some of the most pressing questions facing the Standard Model.

  [recorded movies] 



Spring 2019 colloquia

Jan. 29

Thomas Allison

Stony Brook University

Ultrafast extreme ultraviolet photoemission without space charge

Time- and Angle-resolved photoelectron spectroscopy from surfaces can be used to record the dynamics of electrons and holes in condensed matter on ultrafast time scales. However, ultrafast photoemission experiments using extreme-ultraviolet (XUV) light have previously been limited by either space-charge effects, low photon flux, or limited tuning range. In this talk, I will discuss space-charge-free XUV photoelectron spectroscopy experiments with up to 5 nA of average sample current using a tunable cavity-enhanced high-harmonic source operating at 88 MHz repetition rate. The source delivers > 10^11 photons/s in isolated harmonics to the sample over a broad photon energy range from 18 to 37 eV with a spot size of 58 × 100 μm^2. From photoelectron spectroscopy data, we place conservative upper limits on the XUV pulse duration and photon energy bandwidth of 93 fs and 65 meV, respectively. The high photocurrent, lack of space charge distortions of the photoelectron spectra, and excellent isolation of individual harmonic orders allow us to observe laser-induced changes to the photoelectron spectrum at the 10^{-4} level in seconds of integration time, enabling time-resolved XUV photoemission experiments in a qualitatively new regime. I will discuss demonstration experiments on Au (111) showing the capabilities of the light source, and progress towards experiments on perturbatively excited molecular films.

  [recorded movies] 


Feb. 5

Anatoly Frenkel

Stony Brook University

Inverting the Structure-Spectrum Relationship in Nanoparticles by Supervised Machine Learning

Tracking the structure of nanocatalysts (and other functional nanomaterials) under operating conditions is a challenge due to the paucity of experimental techniques that can provide atomic-level information for active metal species. Here we report on the use of X-ray absorption spectroscopy (XAS) and supervised machine learning for determining the three-dimensional geometry of metal catalysts at the nanometer size scale. Artificial neural network is used to unravel the hidden relationship between the XAS features and catalyst geometry. In other words, we trained computer to learn how to ‘invert” the unknown spectrum and obtain the underlying structural descriptors. This method is demonstrated by reconstructing the average size, shape and morphology of nanoparticles with narrow size and composition distributions from the coordination numbers and interatomic distances obtained using the SML approach. First applications of this method to the determination of nanomaterial structure in operando conditions, such as studies of synthesis, nucleation, growth and reactivity of metal catalysts will be demonstrated.

  [recorded movies] 


Feb. 12

Lisa Miller

Brookhaven National Lab

The New X-Ray Microscopes at NSLS-II and Applications to Neurodegenerative Diseases
Synchrotron-based microscopy and imaging have grown in popularity over recent years due to rapid developments in X-ray sources, optics, and detectors.  One particular field that has benefited from these improvements is the area of neurodegeneration, where complicated tissue and cell heterogeneity demand micro- and nanoscale spatial resolution and sub-ppm detection sensitivity of metal distribution, concentration, and speciation. In this presentation, the new suite of X-ray microscope beamlines at Brookhaven’s NSLS-II will be introduced and examples will be described that involve the use of X-ray fluorescence microscopy (XFM) and spectroscopy (micro-XANES) for the study of metal homeostasis in neurological protein-folding diseases such as Alzheimer’s disease. These studies were performed in conjunction with behavioral studies of cognitive performance. The overall hypothesis is that elevated redox-active metal content in the misfolded aggregates is correlated with cognitive decline, hence identifying a potential mechanistic explanation for brain cell death in AD and providing a potential diagnostic marker and therapeutic target for ameliorating cognitive impairment. In addition to the current findings, the ongoing needs for high spatial resolution, data collection rates, tomography, and speciation will be presented. 

  [recorded movies] 


Feb. 19

Rouven Essig

Stony Brook University

Direct Detection of sub-GeV Dark Matter: A New Frontier

Dark matter makes up 85% of the matter in our Universe, but we have yet to learn its identity.  While most experimental searches focus on Weakly Interacting Massive Particles (WIMPs) with masses above the proton (about 1 GeV/c^2), it is important to also consider other motivated dark-matter candidates.  Indeed, over the last decade, the theoretical landscape of possible dark-matter candidates has expanded significantly to consider masses from 10^-22 eV/c^2 up to the Planck mass, and even higher in the case of composite dark matter.  At the same time, many novel dark-matter detection concepts have been put forward.  In this talk, I will discuss the search for dark matter with masses between about 500 keV/c^2 and 1 GeV/c^2.  This range of masses is theoretically well-motivated and presents a new frontier in the search for dark matter that has seen tremendous progress in the last few years.  I will describe a few direct-detection strategies that can probe this under-explored mass range.  In particular, I will highlight SENSEI, a funded experiment that will use new ultra-low-threshold silicon CCD detectors (“Skipper CCDs”).  I will describe the first results from SENSEI and show how this experiment will probe vast new regions of parameter space in the next few years.  

  [recorded movies] 

Feb. 26

Ruth Angus

Flatiron Institute

Planetary systems across time and space

How do you tell time in space? To place Earth and the solar system in an astrophysical context, we must first resolve the time axis in our galaxy by measuring the ages of its stars and the planets that orbit them. This is a long-standing challenge in astronomy. Thankfully, newly developed methods may allow us to read stellar clocks accurately enough to place the galactic population of extrasolar planets on a timeline. With sufficient time resolution, we can infer the evolutionary properties of the ensemble of planetary systems in our galaxy and reveal planet formation pathways that have remained shrouded in mystery. In this lecture, I will describe how the recent revolution in time-domain astronomy and the new era of large astrophysical surveys are leading to dramatic breakthroughs in time-resolved astrophysics. I will explain how to measure the ages of stars using statistical methods, and how new technology could lead to a new understanding of the evolution and formation of planetary systems and even the Milky Way galaxy itself.

  [recorded movies] 

March 5

Robyn Sanderson
University of Pennsylvania

Insights into dark matter from the stellar halos of galaxies 

Cosmological simulations can now make specific and detailed predictions for the shapes, masses, and substructure fractions in galactic dark matter halos that depend on the dark matter model assumed. Comparing these predictions to the observed mass distributions of galaxies should in principle lead to constraints on the nature of dark matter, but observable dynamical tracers can be scarce in regions where the dark matter distribution is best able to discriminate between models. One such region is the distant outskirts of galaxies, where the influence of baryonic matter on the dark matter halo is limited and the effect of dark substructures most prominent. New surveys of Milky Way stars like Gaia, alongside next-generation instruments and giant telescopes, are for the first time providing accurate positions, velocities, and abundances for large numbers of stars in faint tidal streams: remnants of tidally-disrupted satellite galaxies that trace out the mass distribution in the distant reaches of galaxy halos. I will show how state-of-the-art simulations play a crucial role in interpreting and analyzing this wealth of new information about stellar halos, and how stellar halo observations over the next decade will characterize the dark matter distribution in galaxies, test theories of the nature of dark matter, and illuminate the role of dark matter in galaxy formation.

  [recorded movies] 


March 12

Berndt Mueller

Brookhaven National Lab and Duke University


Emergence of ordinary matter from quarks and gluons

In our everyday world, quarks and gluons, forever hide inside protons and neutrons.  While their fundamental properties are encoded in the theory of quantum chromodynamics  (QCD), many phenomenological aspects of QCD dynamics remain poorly understood.  When gluons are massless and the quarks carry only a small fraction of the mass of

a nucleon, how do nucleons acquire their large mass? How does nuclear matter emerge from the hot quark-gluon plasma that permeated the universe shortly after the Big Bang? What are the limits of ordinary nuclear matter at high density, e.g. in the interior of neutron

stars or neutron star mergers? My talk will explain where our investigation of these questions  stands, aided by experiments at the Relativistic Heavy Ion Collider and elsewhere, and how future facilities, such as an Electron-Ion Collider can help us finding the answers.

  [recorded movies] 


March 19

Spring Break: No classes and no colloquium

March 26

Shirley Ho

Flatiron Institute

Machine learning the Universe: Opening the Pandora Box

Scientists have always attempted to identify and document analytic laws that underlie physical phenomena in nature. The process of finding natural laws has always been a challenge that requires not only experimental data, but also theoretical intuition. Often times, these fundamental physical laws are derived from many years of hard work over many generation of scientists. Automated techniques for generating, collecting, and storing data have become increasingly precise and powerful, but automated discovery of natural laws in the form of analytical laws or mathematical symmetries have so far been elusive. Over the past few years, the application of deep learning to domain sciences – from biology to chemistry and physics is raising the exciting possibility of a data-driven approach to automated science, that makes laborious hand-coding of semantics and instructions that is still necessary in most disciplines seemingly irrelevant. The opaque nature of deep models, however, poses a major challenge. For instance, while several recent works have successfully designed deep models of physical phenomena, the models do not give any insight into the underlying physical laws. This requirement for interpretability across a variety of domains, has received diverse responses. In this talk, I will present our analysis which suggests a surprising alignment between the representation in the scientific model and the one learned by the deep model.

  [movies not available.] 


April 2

Dmitri Kharzeev
Stony Brook University

Chiral matter: from quarks to quantum computing

Chirality is a ubiquitous concept in modern science, from particle physics to biology. In quantum physics, chirality is linked to the topology of gauge fields due to the quantum chiral anomaly. 

While the chiral anomaly is usually associated with the short-distance behavior, recently it has been realized that it affects also the macroscopic behavior of systems possessing chiral fermions. In particular, the local imbalance between left- and right-handed  fermions in the presence of magnetic field induces the non-dissipative transport of  electric charge ("the Chiral Magnetic Effect"). In heavy ion collisions, there is an ongoing search for this effect  at Relativistic Heavy Ion Collider at BNL, with a dedicated isobar run completed in June of 2018, and analysis results expected later in 2019.  Recently, the Chiral Magnetic Effect has been discovered in ZrTe5 and other materials possessing chiral quasi-particles. This observation opens a path towards a "chiral qubit" potentially capable of operating at room temperature, and at  much higher frequencies than the superconducting quantum qubits.

  [recorded movies] 

April 9

Leslie Schoop
Princeton University

Chemical principles of topological semimetals

Topological materials have been very intensively studied in the last decade, creating dreams and promises to be the building blocks for numerous novel technologies, ranging from quantum computing to optical sensors or switches. To fulfill these dreams, material development remains one of the most crucial challenges. In this talk, I will argue that the rules and laws we know from inorganic chemistry are extremely useful for finding and designing new quantum materials, including topological materials. I will introduce how we can bridge the language gap between chemistry and physics and how chemists can make an impact in the field of condensed matter physics. I will introduce several materials that we identified as topological semimetals based on these concepts. Further I will briefly discuss how these concepts also allow us to develop new two-dimensional materials.

  [recorded movies] 



April 16

Mark Tuckerman


Molecular simulation and Machine Learning as Routes to Exploring Structure and Phase Behavior in Atomic and Molecular Crystals

Organic molecular crystals frequently exist in multiple forms known as *polymorphs*.  Although there are no chemical differences among polymorphs, structural differences between them can influence desired properties, such as bioavailability of active pharmaceutical formulations, lethality or kill rate of pesticides, electrical conductivity of organic semiconductors, or detonation sensitivity of crystal explosives.  The conditions under which a crystal is grown can often influence which polymorph is obtained, a fact that makes an experimentally driven hunt for polymorphs  rather difficult. Experimental efforts are further complicated by the existence of so-called vanishing polymorphs, in which a polymorph initially obtained under a particular experimental protocol “disappears” in favor of another polymorph in subsequent repetitions of the experiment.  These experimental challenges create a need for theory and computational to play a vital role in mapping the landscape of crystal polymorphism.  However,  traditional theoretical methods, while sometimes achieving impressive successes, face their own challenges, and new approaches are needed to fill out the computational toolbox.  In this talk, I will suggest that such new approaches could come from an unexpected source:  statistical mechanics.  By leveraging concepts from statistical mechanics in combination with techniques of molecular simulation and machine learning, a new paradigm in crystal structure prediction may be emerging.
[ recorded movies]


April 23

Netta Engelhardt


Learning from Ignorance in Quantum Gravity

The physics of the most extreme regimes of the universe, from the big bang to the black hole interior, is expected to be described by quantum gravity, which currently has no explicit nonperturbative formulation. Since directly observing extreme gravity phenomena is challenging not just in practice but also in theory, we can instead attempt to make progress towards a better understanding of quantum gravity by constraining it based on its behavior in the semiclassical regime (that is, when it is approximately well described by General Relativity). I will introduce a remarkably useful tool, the coarse-grained gravitational entropy, which measures ignorance about a region of spacetime (e.g. the interior of a black hole), and use it to fully address the question (1) if we have complete knowledge of the black hole exterior, how ignorant do we remain of the black hole interior? and give evidence in favor of a negative answer to the question (2) if we can’t observe the singularity in the black hole interior, can we ever hope to learn about singularities by observing them in different systems in the universe?

  [recorded movies] 


April 30

Ulf Meissner

University of Bonn

Nuclear Physics as Precision Science 

Theoretical Nuclear Physics has entered a new era. Using the powerful machinery of chiral effective Lagrangians, the forces between two, three and four nucleons can now be calculated with unprecedented precision and with reliable uncertainties. Furthermore, Monte Carlo methods can be adopted to serve as a new and powerful approach to exactly solve nuclear structure and reactions. I discuss the foundations of these new methods and provide a variety of intriguing examples. Variations of the fundamental constants of Nature can also be investigated and the consequences for the element generation in the Big Bang and in stars are considered. This sheds new light on our anthropic view of the Universe. 

  [recorded movies] 


May 7

Graduate Director

Awards and Summary

  [recorded movies]