Physics and Astronomy Colloquium 2017-2018

Fall 2017 and Winter 2018:  Thursdays, 4:00-5:00 pm

Spring 2018:  Thursdays, 3:30-4:30

1-434 Physics and Astronomy (map)

Reception from 3:30-4:00 p.m.
(unless otherwise posted)

For more information, contact Jay Hauser

 

Fall 2017

 

Thursday, October 5, 2017
 

APS Bridge Program: Changing the Face of Physics Graduate Education

Theodore Hodapp

American Physical Society (APS)

 

In nearly every science, math, and engineering field there is a significant falloff in participation by underrepresented minority (URM) students who fail to make the transition between undergraduate and graduate studies.  The American Physical Society (APS) has realized that a professional society can erase this gap by acting as a national recruiter of URM physics students and connecting these individuals with graduate programs that are eager to a) attract motivated students to their program, b) increase domestic student participation, and c) improve the diversity of their program.  Now in its fifth year the APS has placed enough students into graduate programs nationwide to eliminate this achievement gap.  The program has low costs, is popular among graduate programs, and has inspired other departments to adopt practices that improve graduate admissions and student retention. This presentation will review project activities, present data that demonstrate effectiveness, and discuss future actions.

This material is based upon work supported in part by the National Science Foundation under Grant No. (NSF-1143070).

 

 
Thursday, October 12, 2017 - 4:00pm to 5:00pm
 

Searches for new TeV resonances decaying to electroweak bosons with the CMS detector at the highest LHC energies

Michalis Bachtis

University of California, Los Angeles

 

After the discovery of the Higgs boson in 2012, the priority of the experiments at CERN’s large hadron collider is to search directly for new physics beyond the Standard Model at the highest energies attainable. The current data-taking at  the LHC is at a center of mass energy of 13 TeV, about 1.6 times higher than in 2012, and has been extremely successful with twice as many proton collisions already recorded. This opens new frontiers in both energy and intensity enabling searches for heavy new particles with masses of several  TeV, more than ten times heavier than the heaviest known elementary particle, the top quark. Meanwhile, precision measurements of Standard Model processes indicate that searching mass scales at least this high is probably required to find new physics. My group’s latest results using the full dataset of the Compact Muon Solenoid experiment will be presented along with an overview of my group’s plans for upgrading the capabilities of the CMS detector that are essential to maintain good quality physics output in even higher beam intensities.

 


Thursday, October 19, 2017

Cancelled


 
Thursday, October 26, 2017 - 4:00pm to 5:00pm
 

Seeking ultra-high energy neutrinos in Antarctica with the radio detection technique

Amy Connolly

The Ohio State University

 

Ultra-high energy neutrinos ($>10^{18}$~eV) are uniquely capable of probing the most energetic astrophysics sources at cosmic distances, and fundamental physics at center-of-mass energies beyond what is probed by current particle accelerators.  The IceCube Neutrino Observatory at South Pole has announced the first measurements of a neutrino flux of astrophysical origin up to approximately $10^{15}$~eV through an optical signature.  In the last two decades, the radio technique has emerged as the most promising way to detect enough neutrinos in the UHE regime to extract the wealth of information that they carry about astrophysics and particle physics. I will present the latest developments in the field in terms of the experiments, analytical techniques and theoretical groundwork that are bringing us ever closer to the era of UHE neutrino astronomy.  I will also present some first attempts to study the radio sky with our antenna arrays, and I will also introduce some new ideas that our group at OSU is developing to use genetic algorithms in both the design of our projects and in data analysis.  


 
Thursday, November 2, 2017 - 4:00pm to 5:00pm
 

Ultrashort meets Ultracold (in the Ultraviolet)

Wesley Campbell

University of California, Los Angeles

 

By using narrow-band lasers to damp atomic motion, samples of atoms and a few molecules can be produced routinely at sub-millikelvin temperatures. These "ultracold" atoms can be used as quantum sensors, simulators of quantum many-body physics, and precision probes of fundamental physics.  Likewise, "ultrashort" pulse broadband lasers have been employed to study vibrational and electronic motion on extremely short timescales.  The contrast between the spectral widths (or, equivalently, timescales) of these two types of lasers has largely led to the development of separate ultracold and ultrashort communities.  However, progress in merging these two fields has already yielded some unexpected advances, and new work along these lines shows further promise.  Among the surprises, we will discuss the extension of laser-cooling to chemically-prevalent atoms, the non-destructive observation of harmonic electron motion in a single atom, phonon lasing ("phasing?") from trapped ions, and the generation of strong, stimulated optical forces for the deceleration of molecular beams.


 
Thursday, November 9, 2017 - 4:00pm to 5:00pm
 

New Windows into the Strong Interaction

Iain Stewart

Massachusetts Institute of Technology

 

The strong interaction is described by a remarkable theory called Quantum Chromodynamics (QCD), a fully consistent quantum field theory at all distance scales which gives rise to interesting emergent phenomena.  It plays a crucial role in a variety of interesting physical processes, from binding together quarks and gluons in the proton, to the evolution of matter in the early universe, to producing streams of collimated particles called jets in high energy collisions.  Precise control over the strong interaction is necessary for studies of the Higgs boson, as well as for measuring the fundamental parameters of the standard model of particle and nuclear physics.   In this talk I will describe modern developments that enable precision control of the strong interaction in certain situations, as well as a number of important open questions.   Examples will include enhancing our understanding of jet data to dramatically improve the measurement of one of the fundamental parameters of nature, the strong interaction coupling constant, and improving predictions for proton collisions to strengthen our ability to hunt for new particles and forces at very short distances.

 


 

Thursday, November 16, 2017 - 4:00pm to 5:00pm
 

Rewards are worth the Risk: Working in Direct Dark Matter Detection

Kimberly Palladino

University of Wisconsin - Madison

 

For particle physicists, determining the nature of Dark Matter is one of the greatest open mysteries. An abundance of astrophysical evidence indicates that the matter density of the universe is dominated by a new form of matter, which played a key role in growth of large scale structure. One candidate for Dark Matter is the Weakly Interacting Massive Particle (WIMP). We hope to detect WIMPS by seeing them scattering off of the target materials in our detectors. Liquid xenon has proved itself an excellent target, and LZ is a dual-phase TPC that will begin taking science data in 2020.  Much of the originally proposed parameter space for WIMPS has been excluded over the past few decades, so I will also delve into the sociology of working on direct dark matter searches.

 

Thursday, November 23, 2017 - Thanksgiving break

 


Thursday, December 7, 2017 - 4:00-5:00 p.m.

Cancelled

 

 


Winter 2018


Thursday, January 18, 2018 - 4:00-5:00 p.m.

 

What happened 13.8 billion years ago?

Paul Steinhardt

Princeton University)

 

According to the prevailing view, the universe sprang into existence 13.8 billion years ago in a sudden violent event known as the big bang; and this was soon followed by a brief period of accelerated expansion, known as inflation, which set the large-scale properties of the universe.  In this talk, we will explain the reasons why this idea fails and present a simple alternative – replace the big bang with a bounce and eliminate the need for inflation.   

 


Thursday, January 25, 2018 - 4:00-5:00 p.m.

 

Cell mechanical phenotype in cancer: from screening cells to disease biophysics

Amy Rowat

University of California, Los Angeles

 

Cell mechanical phenotype, or ‘mechanotype’, determines how physical forces are transduced into the cell, and can also signal a transformation in a cell’s physiological state, such as in malignant transformation. If we could obtain higher throughput measurements of cell mechanotype, this would enable a deeper understanding of the molecular origins of cell mechanical properties, as well as screening based on mechanotype. To address these needs, we have used insights from physics to develop a mechanotyping platform that enables us to extract measurements of single cell elastic modulus and fluidity, and to screen cells based on their mechanotype. I will discuss how we are applying our fluidic-based deformability methods to develop a deeper understanding of cell mechanotype in cancer progression. One example application is our discovery that stress hormones, which promote metastasis in mice, also elicit changes in cell mechanical properties: we find that breast cancer cells treated with isoproterenol become stiffer due to actin remodeling, myosin II activity, and increased calcium. Using assays to measure cell invasion through in vitro protein networks, we also discovered that these stiffer isoproterenol-treated breast cancer cells are more invasive. Taken together, our results provide insight into how the mechanical phenotype of cancer cells is associated with their functional behavior.

 
 

 
Thursday, February 1, 2018 - 4:00pm to 5:00pm

Black holes gold rush.

Alexander Kusenko

University of California, Los Angeles

 

Recent discoveries promise to revolutionize our understanding of black holes, their origin, and their signals.   I will discuss the signals of giant black holes, as well as the possibility that small black holes created in the early universe make up the cosmological dark matter and contribute to synthesis of heavy elements, including gold. 

 


Thursday, February 8, 2018 - 4:00pm to 5:00pm

Physics of the auditory system

Dolores Bozovic

University of California, Los Angeles

The inner ear constitutes a remarkable biological sensor that exhibits nanometer-scale sensitivity of mechanical detection. The first step in auditory processing is performed by hair cells, which act as transducers that convert minute mechanical vibrations into electrical signals that can be sent to the brain. This conversion involves the opening of ion channels, which are mechanically gated. The hair cells operate in a viscous environment, but can nevertheless sustain oscillations, amplify incoming signals, and even exhibit spontaneous motility. The thermodynamic requirements of this indicate the presence of an underlying active process that pumps energy into the system. Theoretical models have proposed that a hair cell constitutes a nonlinear system, and allow us to describe and predict how they respond to incoming sound.

Our experiments explore the physical mechanisms behind the detection of very weak signals, and describe them using models based on dynamical systems theory. We explore the different bifurcations that characterize hair bundle activity, and study how they affect phase-locking to incoming signals. We demonstrate experimentally that bundles can phase-lock to a broad range of frequencies, in various mode-locking ratios. Further, we demonstrate the presence of chaos in the underlying dynamics of active bundles, and explore its impact on the sensitivity of detection. Secondly, we explore the interaction between active bundle mechanics and the electrical circuit comprised of somatic ion channels. Finally, we study the fluctuation dynamics of actively oscillating hair bundles.


Thursday, February 15, 2018 - 4:00-5:00 p.m.

CANCELLED - There is no colloquium scheduled for this week.


Thursday, March 1, 2018 - 4:00-5:00 p.m.

Statistical Mechanics, Localization and Periodically Driven Quantum Systems
Shivaji Sondhi

Princeton University

The statistical mechanics of equilibrium systems is characterized by two fundamental ideas: that closed systems approach a late time thermal state and that of phase structure wherein such late time states exhibit singular changes as various parameters characterizing the system are changed. Recent progress has established generalizations of these ideas which apply to periodically driven, or Floquet, closed quantum systems. I will describe this progress, which centrally uses other recent advances in our understanding of many body localization. I will describe how it has resulted in the discovery of entirely new phases such as the Pi-spin glass/Floquet time crystal which exist only in driven quantum system.

 


Thursday, March 8, 2018 - 4:00-5:00 p.m.

Atomic Resolution Analysis of Single Atoms in 2D Materials using Transmission Electron Microsco

Jamie Wagner

Oxford University

 

Measuring a material atom-by-atom provides unrivalled insights into its structure and how this impacts its properties. Transmission electron microscopy is one of the leading approaches to probe individual atoms in solids to measure their position, elemental type, bond length, charge state, and local electric field. I will discuss our recent advances in sub-Angstrom resolution measurements of nanomaterials using aberration corrected transmission electron microscopy (TEM). I will show how state-of-the-art electron-optics provide electron probes that can interact with single atoms, using a combination of annular dark field scanning TEM with electron energy loss spectroscopy (EELS). The main materials of focus are 2D systems, such as graphene, MoS and WS2. I will show how we can measure the local electric field around single atoms in MoS2 using direct electron detectors to capture 4D data sets that are rich with information. Analysis around defects and dopants in 2D materials will be presented, with atom-by-atom EELS mapping and measurements of local perturbations to electric fields. In-situ TEM is also shown for nanoelectronic devices to understand the mechanisms of electrical breakdown in monolayer MoS2, and how high temperature transformations occur in 2D materials in real time. I will discuss grain boundaries, single atom dopants, vacancy defects, dislocations, buckling, strain maps, interlayer stacking structures, atomically sharp cracks, inversion domains, 1D nanowires, and nanopores in 2D materials at the atomic level. 


Thursday, March 15, 2018 - 4:00-5:00 p.m.

Quantum Magnetism from the Iron Age to Today

Daniel Arovas

University of California, San Diego

 

The quantum theory of magnetism has provided many durable paradigms for quantum phases of matter, including intrinsically quantum disordered states, symmetry-protected topological phases, and quantum spin liquids.  In this lecture, I will review some of the history and highlights of this very rich field.

 

 

 

 


Spring 2018 -- New start time:  3:30 p.m.

 Thursday, April 5, 2018 - 3:30pm to 4:300pm

Old Galaxies, New Surprises

Alexie Leauthaud

University of California, Santa Cruz

 

I will present new results from the ongoing Hyper Suprime Cam survey currently being carried out by Subaru. The HSC survey is an unprecedented effort to map 1400 deg^2 in 5 bands to i~26. This unique combination of depth and area enables us to study the individual light profiles of several thousand super massive galaxies (M*>11.6 Msun) to 100 kpc and beyond. We show that massive galaxies are not self similar and that instead their light profiles are diverse. This diversity is not random: using weak gravitational lensing we make a remarkable discovery. There is a tight correlation between the shapes of galaxy light profiles and their host dark matter halo mass. Deep imaging is critical for measuring the total light from these galaxies. With better luminosity measurements in hand, I will show that there is a much tighter relation between the luminosities of super massive galaxies and dark matter halo mass that previously recognized.  Finally, I will discuss how our results have the potential to transform optical galaxy cluster detection and the way we use cluster surveys to constrain dark energy.

 


Thursday, April 12, 2018 - 3:30pm to 4:300pm

Hydrodynamics of topological fields in insulators

Yaroslav Tserkovnyak

University of California, Los Angeles

 

I will discuss recent progress on understanding and harnessing collective transport in magnetic insulators. Central to this talk will be conservation laws that are rooted in a topological invariant rather than a global symmetry. In one example, the emergent hydrodynamics closely mimics neutral superfluidity, which may allow to establish and utilize superflows in solid-state devices at room temperature. Other examples will include magnetic films harboring skyrmionic textures and, surprisingly, disordered glassy spin systems. Recently developed magnetoelectric and thermoelectric techniques are now allowing us to systematically access this physics in a range of materials, both old and new.

 


Thursday, April 19, 2018 - 3:30pm to 4:300pm
 

Is Basketball Scoring Just a Random Walk?

Sid Redner

Boston University and Santa Fe Institute

 

Watching basketball is nearly the same as watching repeating coin tossings!  By analyzing recently available data from recent NBA basketball seasons, basketball scoring during a game is well described by a continuous-time anti-persistent random walk, with essentially no temporal correlations between successive scoring events.  We show how to calibrate this model to account for many statistical season-long metrics of NBA basketball.  As further fillustrations of this random-walk picture, we show that the distribution of times when the last lead change occurs and the distribution of times when the score difference is maximal are both given by the celebrated arcsine law -- a beautiful and surprising property of random walks.  We also use the random-walk picture to construct the criterion for when a lead of a specified size is "safe" as a function of the time remaining in the game.  The obvious application to game-time betting is left as an exercise for the interested.


Thursday, April 26, 2018 - 3:30pm to 4:30pm

Directed Energy for Relativistic Propulsion Enabling the First Interstellar Missions

Philip Lubin

University of California, Santa Barbara

 

All propulsion systems that leave the Earth are based on chemical reactions. Chemical reactions, at best, have an efficiency compared to rest mass of 10-10 (or about 1eV per bond). All the mass in the universe converted to chemical reactions would not propel even a single proton to relativistic speeds. While chemistry will get us to Mars it will not allow interstellar capability in any reasonable mission time. Barring new physics we are left with few realistic solutions. None of our current propulsion systems, including nuclear, are capable of the relativistic speeds needed for exploring the many nearby stellar systems and exo-planets. However, recent advances in photonics and directed energy systems now allow us to realize the ability to develop systems capable of relativistic flight. From fully-functional wafer-scale spacecraft capable of speeds greater than 0.25c  that could reach the nearest star in 20 years to 10 kg spacecraft travelling at 0.02 c to  large missions capable of supporting human life for rapid interplanetary transit. Photonics, like electronics, and unlike chemical propulsion is an exponential technology with a current double time of about 20 months. Additionally the same system can be used for many other purposes including planetary defense, space debris mitigation among many others. This would be a profound change in human capability. The FY 2017 congressional appropriations request directs NASA to study the feasibility of an interstellar mission to coincide with the 100th anniversary of the moon landing. Seen from a different perspective this technology has significant implications for SETI searches with visibility of this technology beyond redshift 20 should there exist another civilization trying to beacon its existence. We will discuss the many technical challenges ahead, our current laboratory prototypes and recent data on kilometer baseline arrays as well as the many transformative implications of this program.

 

For technical information on this program see our website:

http://www.deepspace.ucsb.edu/interstellar

http://www.deepspace.ucsb.edu/projects/implications-of-directed-energy-f...

http://arxiv.org/abs/1604.02108


Thursday, May 3, 2018

CANCELLED


Thursday, May 17, 2018 - 3:30pm to 4:30pm

How Fermi Became Fermi.

David Schwartz

D N Schwartz & Co

Enrico Fermi was one of the most significant figures of 20th century physics, with major contributions across a wide range of sub-disciplines. How did Fermi become Fermi? Drawing on research undertaken in preparation for his recently published biography of Fermi, “The Last Man Who Knew Everything: The Life and Times of Enrico Fermi, Father of the Nuclear Age” (Basic Books, December 2017) David N. Schwartz will discuss the development of Fermi as a physicist; the role of nature, nurture, and historical circumstance in his career; and the characteristics behind both his strengths and his weaknesses. Are great physicists born, do they make themselves, or do others make them? How does the accident of one’s birth influence a career like Fermi’s? What was it that enabled Fermi to continue to contribute to the field well beyond the age when many great physicists are content to rest on their previous achievements?


Thursday, May 24, 2018 - 3:30pm to 4:30pm

Opportunities, dangers and destiny in the Solar System... and beyond.

David Brin

Near term debates over "moon vs. asteroids" may determine the commercial/industrial viability of space. But many other factors could affect whether (and which varieties of) humans venture outward. Preliminary concepts for interstellar travel include a plausible intermediate gaol, the sun's gravitational focal distance. Is travel beyond that possible? If so, what are the implications for life in the universe?  Come for a free-ranging discussion led by astrophysicist and science fiction author David Brin.


Thursday, June 7, 2018 - 3:30pm to 4:30pm

Quantum Indistinguishability in Chemical Reactions
Leo Radzihovsky

University of Colorado Boulder


I will discuss a role of quantum indistinguishability in chemical bond-breaking processes. Specifically, I will argue that chemical reactions involving small symmetric molecules require a full quantum treatment of collective nuclear degrees of freedom beyond the conventional Born-Oppenheimer description. I will present physical arguments for a “Quantum Dynamical Selection” (QDS) conjecture that precludes processes that involve direct transitions from orbitally non-symmetric molecular states. QDS leads to a number of striking experimental predictions, such as e.g., a differential chemical reactivity of para- and ortho-hydrogen, a mechanism for inducing inter-molecular quantum entanglement of nuclear spins, and a new mass-independent isotope fractionation mechanism, among others.


Thursday, May 31, 2018 - 3:30pm to 4:30pm

Quantum sensing and imaging with diamond spins

Ania Bleszynski Jayich

University of California, Santa Barbara

 

The nitrogen-vacancy center is a point defect in the diamond lattice. It consists of a nearest-neighbor pair of a nitrogen atom, which substitutes for a carbon atom, and a lattice vacancy.  This atomic-scale defect that exhibits remarkably coherent quantum properties in a uniquely accessible way: at room temperature, in ambient conditions, and even immersed in biological environments. NV centers are being explored for a variety of quantum technologies, including quantum sensing and quantum information processing. In this talk, I introduce the physics and materials science behind the success of the NV center as a quantum sensor. Here I discuss an NV-based imaging platform where we have incorporated an NV center into a scanning probe microscope and used it to image vortices in superconductors and skyrmions, nanoscale topological spin textures, in thin film magnetic multilayers. I also discuss recent experiments that utilize the NV center’s sensitivity to fluctuating magnetic fields to image the conductivity of a proximal sample with nanoscale spatial resolution. A grand challenge to improving the spatial resolution and magnetic sensitivity of the NV is mitigating surface-induced quantum decoherence, which I will discuss in the second part of this talk. These studies guide the ongoing development of quantum control and diamond surface preparation techniques, pushing towards the ultimate goal of NV-based single nuclear spin imaging.


Thursday, June 7, 2018 - 3:30pm to 4:30pm

Quantum Indistinguishability in Chemical Reactions
Leo Radzihovsky

University of Colorado Boulder


I will discuss a role of quantum indistinguishability in chemical bond-breaking processes. Specifically, I will argue that chemical reactions involving small symmetric molecules require a full quantum treatment of collective nuclear degrees of freedom beyond the conventional Born-Oppenheimer description. I will present physical arguments for a “Quantum Dynamical Selection” (QDS) conjecture that precludes processes that involve direct transitions from orbitally non-symmetric molecular states. QDS leads to a number of striking experimental predictions, such as e.g., a differential chemical reactivity of para- and ortho-hydrogen, a mechanism for inducing inter-molecular quantum entanglement of nuclear spins, and a new mass-independent isotope fractionation mechanism, among others.