Physics & Astronomy Colloquium

Thursdays, 4:00-5:00 pm

Virtual Colloquium Meetings are held via Zoom, in-person events in PAB 1-434. Meeting information will be sent in email. You may watch past presentations by clicking the title link when available.

For more information, contact Katsushi Arisaka.

Click here for the 2020-2021 archived Physics & Astronomy Colloquium.

Click here for the 2019-2020 archived Physics & Astronomy Colloquium.

Fall 2021
Thursday, October 7, 2021

Where's Waldo in Biology
Keisuke Goda
University of Tokyo

A fundamental challenge of biology is to understand and exploit the vast heterogeneity of cells, particularly how the spatial architecture of cells is linked to their identity and physiology. However, it is challenging to address the need because it is analogous to “Where’s Waldo (Wally in the UK and Walter in Germany)?” In this talk, I introduce a new type of technology known as “Image-Activated Cell Sorting” that performs real-time, intelligent, image-based sorting of cells at an unprecedented rate of >1000 cells per second (Nitta et al, Cell, 2018; Nitta et al, Nature Communications, 2020). This technology integrates high-throughput fluorescence microscopy, cell focusing, cell sorting, and deep learning on a hybrid software-hardware data-management infrastructure, enabling real-time automated operation for data acquisition, data processing, intelligent decision-making, and actuation. I show a new class of biological, medical, and pharmaceutical applications of the technology.

Biography: Keisuke Goda is a professor in the Department of Chemistry at the University of Tokyo, an adjunct professor in the Institute of Technological Sciences at Wuhan University, and an adjunct professor in the Department of Bioengineering at UCLA. He obtained a B.A. degree from UC Berkeley summa cum laude in 2001 and a Ph.D. from MIT in 2007, both in physics. At MIT, he worked on the development of quantum-enhanced gravitational-wave detectors in the LIGO group. After several years of work on ultrafast photonics and microfluidics at Caltech and UCLA, he joined the University of Tokyo as a professor. His research group focuses on the development of serendipity-enabling technologies based on molecular imaging and spectroscopy together with microfluidics and computational analytics to realize Louis Pasteur’s statement “Chance favors the prepared mind” ( He has published >300 papers and received >30 awards.

Thursday, October 14, 2021

Building a quantum world with trapped ions
Norbert M. Linke
University of Maryland

Trapped ions give us a high degree of detailed control of their various quantum degrees of freedom, which has enabled a large number of experiments in quantum optics, quantum computing, simulation and networking as well as precision metrology and others. We describe our quantum architecture consisting of a linear chain of trapped 171 Yb+ ions with individual laser beam addressing and readout. The collective modes of motion in the chain are used to efficiently produce entanglement between any qubit pair. In combination with a classical software stack, this becomes in effect an arbitrarily programmable, fully connected quantum computer. Over the past five years, we have employed this experiment to demonstrate a variety of quantum algorithms with the help of a community of academic partners, including cross-hardware comparisons with commercially developed systems and digital quantum simulations of models from high-energy physics and other areas. We also use the same level of control to study interesting quantum phenomena using the motional degrees directly, such as exotic para particles. This talk will give recent highlights from both of these approaches and discuss improvements in trap technology for scaling up as well as other ideas for the future.

Norbert M. Linke is a Fellow of the Joint Quantum Institute at the University of Maryland, working on quantum applications with trapped ions, including quantum computing. Born in Munich, Germany, he graduated from the University of Ulm, and received his doctorate at the University of Oxford, UK, working on micro-fabricated ion-traps and microwave-addressing of ions. Before becoming a faculty member in 2019, he spent four years as a post-doc and research scientist in the group of Chris Monroe at the JQI where he led a project that turned a physics experiment into a programmable quantum computer.

Thursday, October 21, 2021

Broken symmetries in living matter
Nikta Fakhri
Massachusetts Institute of Technology

Active processes in living systems create a novel class of non-equilibrium material composed of many interacting parts that individually consume energy and collectively generate motion or mechanical stress. In this talk, I will discuss experimental tools and conceptual frameworks we develop to uncover laws governing order, phase transitions and fluctuations in systems in which individual components break time reversal symmetry.

Thursday, October 28, 2021

Neutrinos from the Sky and Through the Earth
Kate Scholberg
Duke University

The progress in neutrino physics over the past quarter century has been tremendous: we have learned that neutrinos have mass and change flavor. This discovery won the 2015 Nobel Prize. I will pick out one of the main threads of the story -- the measurement of flavor oscillation in neutrinos produced by cosmic ray showers in the atmosphere, and further measurements by long-baseline beam experiments. In this talk, I will present the latest results from the Super-Kamiokande and T2K (Tokai to Kamioka) long-baseline experiments, and will discuss how the next generation of high-intensity beam experiments will address some of the remaining puzzles.

Thursday, November 4, 2021

Attosecond X-ray movies: the frontier of ultrafast science
Agostino Marinelli
SLAC National Accelerator Laboratory

Electron motion initiates most chemical reactions, and it is an essential component of fundamental light-matter interactions. The dynamics of bound electrons in atoms, molecules and solids happen on very fast time scales, from few femtoseconds down to the sub-femtosecond regime. Therefore, the study of electronic processes on their natural timescales requires pulses of light faster than one femtosecond, and of sufficient intensity to interact with their sample with high probability.

The recent generation of attosecond pulses from an X-ray free-electron laser (at the Linac Coherent Light Source at SLAC) marks the beginning of a new era of attosecond science. XFELs can generate pulses that are more than a million times brighter than conventional attosecond light sources and pave the way to molecular pump/probe movies with sub-fs resolution.

In my talk I will briefly describe the physics of X-ray free-electron lasers and report our recent advances in attosecond X-ray pulse generation. I will then show our recent experimental results in measuring attosecond coherent electron motion in molecules. Finally, I will discuss possible avenues towards brighter and shorter X-ray pulses using the next generation of particle accelerators.

Biography: Ago Marinelli is an assistant professor of Photon Science and Particle Physics and Astrophysics at Stanford University and the SLAC National Accelerator Laboratory. He received his PhD in physics in 2012 from UCLA, working under the supervision of Prof. Jamie Rosenzweig. His research is focused on X-ray free-electron lasers and their applications, with special emphasis on the development of capabilities for ultrafast time-resolved experiments. He is the head of the free-electron laser physics department in the accelerator research division of SLAC and leads the accelerator research and development program at the Linac Coherent Light Source.

Thursday, November 18, 2021

Unlocking Dark Matter Physics out of Astrophysical Data Sets
Cora Dvorkin
Harvard University

Cosmological observations and galaxy dynamics seem to imply that 84% of all matter in the universe is composed of dark matter, which is not accounted for by the Standard Model of particles. The particle nature of dark matter is one of the most intriguing puzzles of our time. The wealth of knowledge which is and will soon be available from astrophysical surveys will reveal new information about our universe. I will discuss how we can use new and complementary data sets to improve our understanding of the particle nature of dark matter both at large and small scales.

Winter 2022
Thursday, January 20, 2022

The Ultra-Compact X-ray Free-Electron Laser
James Rosenzweig

Recent advances in high gradient cryogenic RF research have opened the door to use of surface electric fields between 250 and 500 MV/m. Such structures can enable a host of new, transformative applications, ranging from TeV-scale linear colliders to an X-ray free-electron laser (XFEL), which has a cost and size more than an order of magnitude below that of the current state-of-the-art instruments. In this talk, we discuss the crisis of success in the XFEL, where the expense and availability of ultra-fast, coherentXx-rays greatly constrains the scientific output of these powerful machines. We present a resolution of this problem through use of very high field accelerators, which have the capacity to enhance the electron beam brightness, and through judicious miniaturization of electromagnetic devices, to create a full XFEL in less than 40 m, as opposed to the km-scale presently found in only a handful of national labs worldwide. In the context of a burgeoning project centered at UCLA to develop this ultra-compact X-ray FEL (UC-XFEL), we review physics and technological challenges currently being confronted in the beam, accelerator, magnetics.

Thursday, January 27, 2022

The Hubble tension: hints of new physics?
Tommaso Treu
Available via Zoom

The standard LCDM model gives a successful description of many astrophysical observations. However, in the past few years a tension has developed between local determinations of the Hubble constant and the value predicted from early universe probes. If confirmed, this so called Hubble Tension, would require additional physical ingredients beyond LCDM, e.g. early dark energy, on new particles. After describing the tension, I will provide an update of our 20-year long effort to measure the expansion history of the universe and thus the Hubble constant using gravitational time delays, highlighting recent results based on lensed quasars from the TDCOSMO collaboration (the union of H0licow/STRIDES/SHARP collaborations), and from the multiply imaged supernova Refsdal. I will conclude my talk by discussing the prospects for achieving 1-2% precision and accuracy on H0 in the next few years and thus resolving the Hubble tension.

Thursday, February 3, 2022

Searching for dark matter with current detectors and beyond
Alvine Kamaha

Numerous astronomical and cosmological observations indicate that about 85% of the matter in our universe is in an unknown and yet to be discovered form, so-called dark matter. Identifying the nature of this dark matter has arguably become one of the most important questions in physics research today. Many worldwide experiments (telescopes, colliders, underground based detectors) are in the race to answer this question, utilizing various detection techniques. Among them, is the dual-phase liquid xenon time projection chambers (LXe-TPCs) currently used by some underground based experiments. An example of these experiments is the LUX-ZEPLIN (LZ) experiment, the flagship dark matter experiment in the US which has been designed to reach unprecedented sensitivity in dark matter search.

In this talk, I will first discuss the various detector technologies searching for dark matter with an emphasis on the LZ detector and the UCLA group contribution to LZ. I will then review the status and outlook of the current experiments. I will end by talking about the search for dark matter beyond the scope of current detectors and some R&D efforts for the next generation of dark matter detectors.

Thursday, February 10, 2022

Neurophysics of space, time and memory
Mayank Mehta

How does the brain create abstract ideas? This has intrigued us for many years, with renewed interest due to the resurgence of AI. While there are plenty of theories and experiments that address this, including the Nobel Prize of 2014 about the "GPS system of the brain", experimentally validated biophysical theories are lacking. Hence, we investigate how neurons create universal, abstract concepts of 3D space, time, distance, angle and causality from 2D stimuli on the walls and the retina. We develop minimal biophysical theories with only a handful of parameters to have strong predictive power. We test these theories by measuring activities of many neurons at unprecedented resolution while rats navigate the real world and virtual reality and then sleep and dream. This approach has provided surprising insights that rewrite textbook ideas of how neurons compute and point to exciting opportunities in the Neurophysics of abstraction.

Thursday, February 17, 2022

Supermassive black holes, fundamental physics, machine learning, and beyond
Tuan Do

In this talk, I will discuss three major research themes: (1) the frontiers of our understanding of supermassive black holes and how we can use Sgr A*, the supermassive black hole at the center of the Milky Way as a laboratory to test fundamental physics. (2) The formation and evolution of the stars around our supermassive black hole. I will show how the long time-baseline of Galactic center observations, improved instrumental capabilities, and use of statistical methods to combine many types of data have led us to new insights into how the centers of galaxies form. (3) The use of machine learning in astrophysics to help answer big questions such as: what is the nature of dark energy? What kind of universe do we live in? I will also discuss how we are preparing to take advantage of upcoming major facilities like the James Webb Space Telescope, the Thirty Meter Telescope, and the Vera Rubin Telescope to advance these three research areas.

Thursday, February 24, 2022

Designing and probing quasi-particles in flatlands
Qianhui Shi

While electrons are the main characters of condensed matter physics, their interactions with lattices, external fields and other electrons often leads to collective behaviors that are conveniently described by quasi-particles. The two-dimensional van der Waals materials are platforms that are highly tunable by external fields and stacking order, and provide a playground for various types of quasi-particles. In this talk, I will discuss our experiments in such platforms that explores different types of quasi-particles, from electronic-polarons, plasmons to merons and paired composite fermions.

Thursday, March 3, 2022

Grand Unified Theory of Mind and Brain: Space-Time Approach to 3D Vision
Katsushi Arisaka
1-434 PAB and on Zoom

Animals have brains to perceive and navigate the external 3D space for survival. But how can we reconstruct the allocentric space in 3D from the egocentric 2D visual stimulation while constantly moving eyes/head/body? To solve this question, I imposed the fundamental principle of physics, “causality and locality,” onto every single synaptic connection. Consequently, I have constructed the space-time “Feynman” diagram of the entire human brain, where the signals flow in the order of MePMoS (Memory-Prediction-Motion-Sensing). In this model, the external 3D space is holographically reconstructed in the frequent-time domain by the multi-frequency brainwaves. It follows the concept of Neural Holographic Tomography (NHT) and is memoried by the engram named Holographic Ring Attractor Lattice (HAL). These new concepts of MePMoS, NHT, and HAL can be applied universally to all five senses for any animal, forming the “Grand Unified Theory of Mind and Brain.”

Spring 2022
Thursday, April 7, 2022

The Missing Link: Mentorship as The Key to Success
Sherard Robbins
Visceral Change, LLC
1-434 PAB

This particular workshop will focus on the importance of mentorship for students, staff, and faculty. Using a multicultural lens, this session will explore the ways in which cultural and social identities impact how people connect with one another while providing helpful tips to create space to celebrate our diversity; when done correctly, this will lead to a collectivist approach to growth and development.

Thursday, April 21, 2022

Observational Signatures of Quantum Gravity
Kathryn Zurek
1-434 PAB

Traditionally observational signatures of quantum gravity have been considered far out of reach of observation. We consider how non-perturbative effects in quantum gravity could give rise to observational effects in interferometer experiments, and we describe an effort underway to search for such effects.

Thursday, April 28, 2022

The Journey of the James Webb Space Telescope -- and Ours
Alan Dressler
Carnegie Observatories
1-434 PAB

The James Webb Space Telescope had an unconventional beginning, and it faced and overcame many challenges, technical, managerial, and political, on its way to what we hope will be a long and scientifically bountiful life. Clearing these hurdles have also taught us much about how to tackle such projects in the future, including the large UV-optical telescopes that that Astro2020 favors in the search for life on extrasolar planets. In this colloquium I will describe some of my experiences in decadal reviews and the NASA missions they recommended. I will also describe a program on the star formation histories of the first galaxies that I hope to carry out as a member of the NIRCam team.

Thursday, May 5, 2022

Probing the heart of neutrinos in the coldest cubic meter in the Universe
Yury Kolomensky
University of California, Berkeley
1-434 PAB

Neutrinos, the enigmatic weakly interacting particles, may hold the keys to some of the fascinating puzzles in particle physics and cosmology. On one hand, they demonstrate the quantum mechanical effect of flavor mixing -- on macroscopic distance scales -- and thereby violate a conservation law thought to be valid only two decades ago -- the conservation of lepton flavor. On the other hand, neutrino is the only known particle that may be a Majorana fermion, or identical to its antiparticle. Processes involving Majorana neutrinos could violate the lepton number conservation -- an empirical property of the Standard Model that, unlike other conservation laws, is not explained by a known symmetry principle. Neutrinoless Double Beta Decay (0nuDBD) is a rare nuclear process that is possible only if neutrinos are Majorana fermions. Observation of 0nuDBD would change our understanding of the nature of neutrinos, may provide a strong evidence for the role of neutrinos in generating matter-antimatter asymmetry in the early Universe, and set the scale for the absolute values of neutrino masses. CUORE, a cryogenic experiment constructed jointly by the US and Italy at Gran Sasso National Laboratories, is one of the most sensitive currently operating 0nuDBD experiments. We will review the history of DBD searches, discuss the unique features of CUORE and its upgrade, CUPID, and also outline what the next decade may bring to this exciting field.

Thursday, May 12, 2022

Solving A Century-Old Problem: Three-Dimensional Atomic Structure of Amorphous Solids
Jianwei (John) Miao
University of California, Los Angeles
1-434 PAB

Liquids and solids are two fundamental states of matter. Although the structure of crystalline solids has long been solved, amorphous solids such as glass, rubber and plastics are more ubiquitous in our daily life and have broad applications ranging from telecommunications to electronics and solar cells. However, due to the lack of long-range order, the 3D atomic structure of amorphous solid had defied direct experimental determination for more than a century. As a graduate student, I aspired to solve this grand challenge in the physical sciences. In 1999, I pioneered coherent diffractive imaging (CDI) to extend X-ray crystallography to allow imaging of non-crystalline systems. In 2012, I applied CDI methods to tomography and pioneered atomic electron tomography (AET) to resolve the 3D atomic structure of matter without assuming crystallinity. In 2021, after more than 22 years of relentless pursuit, we finally advanced AET to determine the 3D atomic structure of a metallic glass and quantitatively characterized the short- and medium-range order. We discovered that, although the 3D atomic packing of the short-range order is geometrically disordered, some short-range-order structures connect with each other to form crystal-like superclusters and give rise to medium-range order. We identified four types of crystal-like medium-range order - face-centred cubic, hexagonal close-packed, body-centred cubic and simple cubic - coexisting in the amorphous sample, showing translational but not orientational order. These observations provide direct experimental evidence to support the general framework of the efficient cluster packing model for metallic glasses. Furthermore, we also used AET to resolve the 3D atomic packing in monatomic amorphous solids. We observed that pentagonal bipyramids are the most abundant atomic motifs in these amorphous solids. Instead of forming icosahedra, the majority of pentagonal bipyramids arrange into pentagonal bipyramid networks with medium-range order. Molecular dynamics simulations further reveal that pentagonal bipyramid networks are prevalent in monatomic metallic liquids, which rapidly grow in size and form more icosahedra during the quench from the liquid to the glass state. We expect that these results pave the way for the determination of the 3D atomic structure of a wide range of amorphous solids, which could transform our fundamental understanding of non-crystalline materials and related phenomena.

Thursday, May 19, 2022

The Biocybernetics of Insect Vision
Mark Frye
University of California, Los Angeles
1-434 PAB

In the 1950’s, a group of German physicists used psychophysical approaches in a quest for the elementary algorithms and neural circuits for the perception of visual motion. They reasoned that an insect with a ‘cortex’ the size of a poppy seed, which nevertheless showed exquisite motion vision, could shed light on fundamental mechanisms common among all seeing animals, including humans. Advances in electronics, genetics, and neuroscience have enabled my own research to build upon their classical findings, and also to expose profound weaknesses. We show that panoramic motion and objects are processed by parallel yet interacting neural pathways in the brain, and that visual control of flight maneuvers uses a hybrid controller in which the visual panorama is stabilized by smooth steering movements, while salient objects are pursued with rapid body saccades.

Thursday, May 26, 2022

Diffractive Optical Networks & Computational Imaging Without a Computer
Aydogan Ozcan
University of California, Los Angeles
1-434 PAB

Abstract: We will discuss diffractive optical networks designed by deep learning to all-optically implement various complex functions as the input light diffracts through spatially-engineered surfaces. These diffractive processors complete their computational task at the speed of light propagation through thin, passive optical layers and will find various applications in e.g., all-optical image analysis, feature detection, object classification, computational imaging and sensing, also enabling task-specific camera designs and new optical components.

Biography: Dr. Ozcan is the Chancellor’s Professor and the Volgenau Chair for Engineering Innovation at UCLA and an HHMI Professor with the Howard Hughes Medical Institute, leading the Bio- and Nano-Photonics Laboratory at UCLA and is also the Associate Director of the California NanoSystems Institute. Dr. Ozcan is elected Fellow of the National Academy of Inventors (NAI), holds more than 50 issued/granted patents and >20 pending patent applications, and is the author of one book and the co-author of >700 peer-reviewed publications in major scientific journals and conferences. Dr. Ozcan is the founder and a member of the Board of Directors of Lucendi Inc., Pictor Labs, Hana Diagnostics and Holomic/Cellmic LLC, which was named a Technology Pioneer by The World Economic Forum in 2015. Dr. Ozcan is also a Fellow of the American Association for the Advancement of Science (AAAS), the International Photonics Society (SPIE), the Optical Society of America (OSA), the American Institute for Medical and Biological Engineering (AIMBE), the Institute of Electrical and Electronics Engineers (IEEE), the Royal Society of Chemistry (RSC), the American Physical Society (APS) and the Guggenheim Foundation, and has received major awards including the Presidential Early Career Award for Scientists and Engineers, International Commission for Opstics Prize, Biophotonics Technology Innovator Award, Rahmi M. Koc Science Medal, International Photonics Society Early Career Achievement Award, Army Young Investigator Award, NSF CAREER Award, NIH Director’s New Innovator Award, Navy Young Investigator Award, IEEE Photonics Society Young Investigator Award and Distinguished Lecturer Award, National Geographic Emerging Explorer Award, National Academy of Engineering The Grainger Foundation Frontiers of Engineering Award and MIT’s TR35 Award for his seminal contributions to computational imaging, sensing and diagnostics. Dr. Ozcan is also listed as a Highly Cited Researcher by Web of Science, Clarivate.

Thursday, June 2, 2022

Topological Superconductivity in Superconductor-Semiconductor Hybrids
Chetan Nayak
University of California, Santa Barbara
1-434 PAB

Topological superconducting nanowires are characterized by Majorana zero modes, which can form the basis of topological qubits. In this talk, I will present some recent theoretical and experimental progress on these systems.