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]