Past Department-wide Colloquia

Spring 2024

David Sing (JHU) “Exoplanet Atmospheric Spectroscopy in the Era of JWST”

Stephen Taylor (Vanderbilt University) “The Road Ahead for Gravitational-wave Astrophysics at Light-year Wavelengths“

Blakesley Burkhart “The Turbulent Life of Gas Across Cosmic Time: Unveiling the Hidden Drivers of Galaxy Growth”

Jami Valentine (AAWiP) “Diversity in Physics”

Meredith MacGregor (JHU) “Planet Formation Across the Electromagnetic Spectrum”

Alex Lupsasca (Vanderbilt) “The Black Hole Photon Ring”

Fall 2023

Bearden Lecture: Preeti Kharb “Jets in Radio-Quiet AGN and their Influence on the Host Galaxies”

Jason Hogan (Stanford) “Long baseline clock atom interferometry for gravitational wave and dark matter detection”

Ingo Waldmann (University College London) “Machine learning in exoplanet characterization”

Jill Tarter (SETI) “The 21st Century: The Century of Biology”

Charles L. Kane (Penn) “Symmetry, topology and electronic phases of matter”

Dave DeMille (U. of Chicago)

Spring 2023

DateSpeaker Title and abstract
February 2Nicole Yunger Halpern (UMD)

Video of the talk		What happens when conserved quantities fail to commute with each other in quantum thermodynamics

Starting in undergraduate statistical physics, we study small systems that thermalize by exchanging quantities with large environments. Such thermalization helps define time’s arrow; and the exchanged quantities—heat, particles, electric charge, etc.—are conserved globally. If quantum, the quantities are represented by Hermitian operators. We often assume implicitly that the operators commute with each other—for instance, in derivations of the thermal state’s form. Yet operators’ ability to not commute underlies quantum phenomena such as uncertainty principles. What happens if thermodynamic conserved quantities fail to commute with each other? This question, mostly overlooked for decades, came to light recently at the intersection of quantum thermodynamics and information theory. Noncommutation of conserved thermodynamic quantities has been found to enhance entanglement, decrease entropy-production rates, and potentially alter the nature of thermalization. This growing subfield illustrates how 21st-century quantum information science is reshaping 19th-century thermodynamics.
February 9Matthieu Wyart (EPFL, Paris)

Video of the talk		Landscapes and training in deep learning: insights from physics
 
Deep learning algorithms are responsible for a technological revolution in a variety of tasks, yet understanding why they work remains a challenge.  Puzzles include that (i) learning corresponds to minimizing a loss in high dimension, which is in general not convex and could well get stuck in bad minima. (ii) Its predictive power increases with the number of fitting parameters, even in a regime where data are perfectly fitted. (iii) Deep learning is also successful in high dimensions, where learning for generic tasks should be impossible.  I will review recent results on these questions based on analogies with physical systems and scaling arguments testable on real data.
February 16Andrea Liu (University of Pennsylvania)

Video of the talk		Machine learning concepts for inverse materials design 

In order for artificial neural networks to learn a task, one must solve an inverse design problem to determine the network that will give the desired output. The method by which this problem is solved by computer scientists can be harnessed to solve inverse design problems in materials design. I will discuss how we have used such approaches to design mechanical and flow networks that can perform functions inspired by biology. I will also show how we can exploit physics to go beyond artificial neural networks by using local rules rather than global gradient descent approaches to learn in a distributed way, so that we can solve machine learning tasks without a processor or external memory.
February 21James West (JHU)

Audio recording of the talk		For Black History Month, Johns Hopkins University’s National Society of Black Physicists (JHU-NSBP) student chapter and the Colloquium Committee have organized a special Colloquium series to highlight the excellence of Black and underrepresented scientists.
 
JHU-NSBP was charted in 2021 by a group of Physics and Astronomy graduate students as a platform to contribute and improve the experience of Black and under-represented minorities in tandem with the diversity initiatives taken by the Department of Physics and Astronomy.
 
Professor James West is a professor of electrical and computer engineering and of mechanical engineering at the Whiting School here at Johns Hopkins University.  After receiving his physics degree from Temple University in 1957, 

In 1962, while a scientist at Bell Laboratory, Professor West and his research partner, Gerhard (GARE-ard) Sessler, invented the foil electret microphone.  This invention has been the basis of the vast majority microphones used in telephones, sound and music recording equipment and hearing aids used today.  After 40 years at Bell Labs and Lucent Technologies, Professor West joined Johns Hopkins in 2001 (2002?) as a research professor of engineering, where he continues to work on a variety of projects and serves as a mentor to students and an advocate for addressing the underrepresentation of women and Minorities in STEM.

Professor West is a member of the National Inventors Hall of Fame, the  National Academy of Engineering, and a recipient of the US National Medal of Technology and the Benjamin Franklin Medal in Electrical Engineering from the Franklin Institute.  He is also a fellow of the Institute of Electrical and Electronics Engineers and a former president of the Acoustical Society of America.  

He holds over 260 US and foreign patents from his work, and his publication record spans the fields of acoustics, solid-state physics, and materials science. 
 
February 23Julia Mundy (Harvard)

Video of the Talk		Design and construction of an antiferromagnetic metal
 
Transition metal oxides exhibit almost every physical state known including photoconductivity, metallic conductivity, (high-temperature) superconductivity, colossal magnetoresistance, ferroelectricity, and ferromagnetism. Combined with the ability to epitaxially integrate these materials with silicon, they are leading candidates for applications spanning from photocatalysts to data storage. Here I will show how thin film epitaxy can be used to selectively stabilize materials which are not stable in the bulk form. I will show our results combining atomically-precise thin film deposition with band structure measurements to stabilize a new antiferromagnetic metal for spintronic applications.
February 28Anthony Johnson (CASPR & UMBC)

Video of the talk		Large Third-Order Nonlinearities in Atomic Layer Deposition (ALD) Grown Nitrogen-Enriched TiO2 Nanoscale Films & A Career Encompassing Optical Physics, Diversity and Mentoring

Joint NSBP-JHU colloquia for February & Black History Month:
The next-generation of high-speed photonics devices, such as ultrafast integrated modulators and wavelength converters, require materials with large third-order optical nonlinearities. Typically nonlinear materials are cut from bulk crystals or liquids that are not suitable for integration with complementary metal-oxide-semiconductor (CMOS) technology. In addition to all-optical on-a-chip device applications, materials that exhibit high nonlinear absorption and a fast response time are useful in optical limiting applications, for the protection of optical sensors and the human eye from high intensity light such as lasers. TiO2 films, with a 120-nm nominal thickness, were deposited by ALD at temperatures ranging from 100-300ºC on quartz substrates, and were studied using a femtosecond thermally managed Z-scan technique. TiO2 films prepared by physical vapor deposition (PVD) at room temperature were used as control samples. The as-grown ALD films deposited at 150-300ºC exhibited values for n2, the nonlinear index of refraction, between 0.6 x 10-10 and 10 x 10-10 cm2/W, which is 4-6 orders of magnitude larger than previously reported. Annealing the films for 3 hours at 450ºC in air reduced the nonlinearities below the detection limit of the experimental setup. Similarly, as-grown 100ºC ALD and PVD films did not produce a discernable Z-scan trace. The samples were also characterized by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD) and UV-Vis absorption. Compositional analysis using XPS reveals the presence of ~ 1 atomic % of Ti-O-N metallic bonds in the films that exhibit the largest nonlinearity. Annealing the samples results in the oxidation of the metallic bonding and is accompanied by a large decrease in the nonlinearity. XRD analysis indicates that the as-deposited films are amorphous and the annealed films are partially crystallized. These results demonstrate the possibility of a new class of thin-film nonlinear materials in which their properties can be tailored by controlling the film composition.
***
This talk is about my professional journey which started at AT&T Bell Laboratories in the early 1970s. The Bell Laboratories Cooperative Research Fellowship Program for Minorities (CRFP) founded in 1972, followed closely in 1974 by the Graduate Research Program for Women (GRPW) and the Summer Research Program for Minorities and Women (SRP), were among the first programs of their kind in the US to address the issue of underrepresentation of women and minorities in the STEM fields and had a particularly strong impact in Physics. In 1981, four PhDs were awarded to African-Americans in the US in Physics and two (including me) were Bell Labs CRFP Fellows. In addition to striving to produce leading edge research, these Diversity Programs (then called Affirmative Action) made me a strong proponent of the recruitment and retention of women and underrepresented minorities into the scientific enterprise.
March 2Xiaoxing Xi (Temple)


Video of the talk		Racial Profiling and the China Initiative: Challenges Facing Academics of Chinese Descent and Those Who Collaborate with Scientists in China

Collaborating with academics in China was once encouraged by the US government and universities. As tension between the two countries rises rapidly, those who did are under heightened scrutiny by the federal government. In 2015, I became a casualty of this campaign, being falsely charged by the Department of Justice for sharing American company technology with China. I never did, and the case was eventually dismissed. In 2018, the DOJ established the China Initiative, under which numerous university professors have been prosecuted for allegedly failing to disclose their activities in China. Although the China Initiative was terminated in February 2022, the DOJ continues to racial profile Chinese professors, scientists, and students as suspected spies for China. In this talk, I will describe the cases of Anming Hu, Charles Lieber, Gang Chen, Mingqing Xiao, and Franklin Tao, which exposed again and again the DOJ’s unfair targeting of academics of Chinese descent and those who collaborate with scientists in China. Not only are such policies contrary to America’s ideals, but they also weaken America’s innovation ecosystem and threaten its technological advantage. To protect American science and human rights from irreparable damages, it is imperative for the scientific community to speak up and push back.
March 16Open House

Nadia Zakamska

Video of the talk		Extragalactic astrophysics with the James Webb Space Telescope: from promise to practice

For years, we have been eagerly anticipating the promising capabilities that the JWST would bring to bear on scientific questions across all fields of astrophysics — from exoplanets, to Milky Way structure, to cosmology. The first science-quality JWST images were presented to the world in July 2022. How is the reality of using data from JWST shaping up to meet expectations? In this talk I will discuss how the major technical leaps of JWST — its spatial resolution, its sensitivity and its wavelength coverage — are impacting astrophysics. Specifically, I will focus on JWST advances in extragalactic astronomy and cosmology. My group is using JWST to unveil the evolution of supermassive black holes in centers of galaxies across cosmic time. I will present some early results from these programs, where JWST is revealing the complex physics of the interaction between the supermassive black holes and their host galaxies in unprecedented detail. Throughout the talk, I will present and discuss other extragalactic astronomy highlights from the first 8 months of data, especially those resulting from the efforts by JHU scientists.
March 30Dan Stamper-Kurn (Berkeley)

Video of the talk		Quantum simulation, sensing, and computation with ultracold atoms

Ultracold atomic gases are perhaps the coldest matter in the universe, reaching temperatures below one nano-kelvin.  At these low temperatures, noise is ironed out and the quantum mechanical properties of atoms, not only of their internal atomic states but also of their center-of-mass motion, become accessible and visible.  I will describe applications of this ultracold quantum material in the areas of quantum simulation, sensing, and computation.  Specifically, I will show how quantum gases far from equilibrium allow us to probe geometric singularities in band structure, a quantum simulation of condensed matter.  I will describe how single atoms, trapped tightly within optical tweezers, can be serve as quantum sensors within a scanning-probe microscope of optical fields.  Finally, I will explain how cavity-enhanced detection allows us to make mid-circuit measurements within an atoms-based quantum computing platform, a step toward quantum error correction.  And what’s next?  Feedback control of quantum systems?  Electromagnetic vacuum fluctuations serving as a chemical catalyst?  Telecom-frequency optical clocks?  Simulation of flat-band ferromagnetism?  Perhaps all of the above.
April 13Adam Kaufman (JILA)

Video of the talk		Programmable control of indistinguishable particles: from sampling to clocks to qubits

Quantum information science seeks to exploit the collective behavior of a large quantum system to enable tasks that are impossible (or less possible!) with classical resources alone. This burgeoning field encompasses a variety of directions, ranging from metrology to computing. While distinguished in objective, all of these directions rely on the preparation and control of many identical particles or qubits. Meeting this need is a defining challenge of the field. There are several promising platforms that are targeting these capabilities, and I will focus on one such platform — optically-trapped neutral atoms.  We have been developing a new suite of tools, based on the use of more exotic atomic species, new trapping architectures, and new control methods. I will provide an overview of these developments and a few specific examples of our recent results, which range from the use of bosonic atoms for sampling problems, a new kind of atomic clock, and a different kind of qubit.
April 20Peter Abbamonte (U. Illinois)

Video of the talk		Observation of Pines’ demon in Sr2RuO4 with momentum-resolved EELS

The characteristic excitation of a metal is its plasmon, which is a quantized sound wave in its valence electron density. In 1965, David Pines predicted that distinct type of plasmon, which he named a “demon,” could exist in multiband metals that contain more than one species of charge carrier. Unlike conventional plasmons, demons are acoustic excitations, meaning they are “massless,” i.e., their energy tends toward zero as the momentum q ® 0. So demons may play a central role in the low-energy physics of multiband metals. However, demons are neutral excitations that do not couple to light, so they have never been observed experimentally, at least in a 3D material.

In this talk I will present the discovery of a demon in the multiband metal Sr2RuO4. Formed of electrons in the β and γ bands, the demon is gapless with critical momentum qc = 0.08 reciprocal lattice units and room temperature velocity v = 1.065(120)×105 m/s. This study confirms a 67-year old prediction and suggests that demons may be a widespread feature of multiband metals.

*A. A. Husain, et al., arxiv:2007.06670 (to appear in Nature)
April 27Alex Sushkov (BU)

Video of the talk		Nuclear magnetic resonance at its quantum limit: fundamental science and applications

Magnetic resonance techniques are used in a broad range of scientific disciplines and practical applications, ranging from clinical magnetic resonance imaging and studies of protein structures to searches for new fundamental physics. Nuclear magnetic resonance (NMR) has an inherent limitation: the signals are notoriously weak, which constrains many applications. The fundamental limit on the sensitivity of NMR is set by quantum spin projection noise. I will describe our approach to achieving spin projection noise-limited NMR sensitivity, which may enable new NMR methodologies, with no need for spin polarization, and no tipping pulses. Our current work is focused on using quantum-limited NMR for a laboratory-scale search for ultra-light axion dark matter. A discovery in our search may solve several of the mysteries facing today’s physicists, including the nature of dark matter, the strong-CP problem, and the energy scale of inflation, providing insights into the earliest epochs of the universe and into fundamental physics at the highest energy scales, up to the Planck scale.
May 4Ingo Waldmann (University College London)Characterising extrasolar planets with machine learning
May 11Nick Hutzler (Caltech)

Video of the talk

Fall 2022

DateSpeaker Title and abstract
October 6Elena Donghia (U Wisc. Madison)

Video of the talk		When do disks become bars?

Sixtyfive percent of galaxies in the nearby Universe have a stellar bar. However, the criterion to establish when bars do form in disks is missing. Using high-resolution N-body simulations, we have investigated a stellar disk’s stability to a bar mode. To date, there is no convincing global criterion regulating the formation of bars in disk galaxies. The simulations show that two global dimensionless parameters in our study appear to control the instability of the bar modes, defining a plane with regions of stable and unstable disks to the bar formation. Unlike the Toomre Q parameter, which regulates the disk stability locally, the identified parameters in our study are global and play a crucial role in the stability of a broad class of disks to bar formation at all scales, from protostar disks to galaxies. The criterion should apply to high redshift galaxies visible with the James Webb telescope.
October 13Joe Silk (JHU, IAP: Bearden lecture)

Video of the talk		The Future of Cosmology
 
I will review the prospects for future progress in cosmology. I will give examples of two futuristic experiments. One seeks the dark ages signature via low frequency radio astronomy on the  far side of the Moon to  provide a  robust probe of inflationary cosmology. A second  involves a far infrared telescope in a permanently shadowed lunar crater to search for the elusive deviations from the blackbody spectrum of the cosmic microwave background that were generated  early in  cosmic history. These concepts could be implemented in the coming  decades of lunar exploration along with other, even more ambitious, telescope projects.
October 27

Jared Kaplan (JHU)AI Reasoning and Self-Supervision

I’ll briefly review how contemporary AI works and what sort of capabilities were possible, and what the limitations seem to be around the time I went on leave.  Then I’ll discuss recent progress removing these limitations and enabling AI to reason and do math at a level similar to a decent high school student, and to supervise itself in order to better align its behaviors with human preferences.
November 3Sean Carroll (JHU)

Video of the talk		From Quantum Mechanics to Spacetime

Nine decades in, the foundations of quantum mechanics remain mysterious. Meanwhile, modern physicists puzzle over how to reconcile quantum mechanics with gravity. I will suggest that these problems are related, and that a promising strategy suggests itself: rather than “quantizing gravity,” we should look for gravity within quantum mechanics. This approach has interesting consequences for how we think about the nature of space and time.
November 10

via Zoom		Qiuzi Li (Exxon, 2022 APS Distinguished Lectureship Award on the Applications of Physics Recipient)Industrial Experience and Technical Discussion on Induced Polarization for Subsurface Characterization
 
There has been substantial interest in applying induced polarization phenomena, which broadly include electrode and membrane polarization, to characterize organic contamination and biogeochemical environments. The presence of dispersed electronically conductive grains contributes to the electrode polarization, which arises due to the capacitive charging of the Stern Layer at the conductor-electrolyte interface. On the other hand, the membrane polarization is driven by spatial inhomogeneity in the ionic transferences, i.e., the proportion of current carried by the cation vs. the anion. Several phenomenological models, semi-quantitative models, and models for particular pore shapes have been proposed for understanding induced polarization. Here, we developed theoretical frameworks to quantitatively explain electrode and membrane polarization based on insights from experiments on model systems. We obtained quantitative agreement between experiment and theory, not just for characteristic frequencies and amplitudes, but for the entire spectral shape of the phase angle between electric field and current density.
November 17Bill Bialek (Princeton)

Video of the talk		Ambitions for theory in the physics of life
December 8Emanuela Del Gado (Georgetown)

Video of the talk		The physics of sustainable cement

Cement is the main binding agent in concrete, literally gluing together rocks and sand into the most-used synthetic material on Earth. However, cement production is responsible for significant amounts of man-made greenhouse gases—in fact if the cement industry were a country, it would be the third largest emitter in the world. It has become clear that even a slight reduction of cement carbon footprint will dramatically reduce the global anthropogenic CO2 emissions of the whole construction sector, and that meeting emission-reduction targets for new constructions calls for deeper scientific understanding of cement properties and performance. Cement cohesion originates from the accumulation and confinement of ions in solution between the surfaces of cement hydrates, surprisingly similar to a range of colloidal and biological matter, but surface charge densities and ionic compositions set cement outside the validity range of established mean field theories for electrostatics in solution. The progress made through experiments, simulations and theory over the years has left a knowledge gap in the fundamental understanding of how nanoscale cohesive forces emerge during cement hydration, and how they drive the gelation and solidification of cement based construction materials. I will discuss how, about one century after the early studies of cement hydration, we have quantitatively solved this notoriously hard problem and filled this gap, discovering how cement cohesion originates from water-ion interlocking when confined between the charged surfaces of calcium-silicate-hydrates. Starting from these new insights, I will analyze how statistical mechanics approaches and 3D numerical simulations studies open a new path to understand cement performance, durability and sustainability, and to scientifically grounded strategies of material design for greener cements.

Spring 2022

DateSpeaker Title and abstract
February 24 

Video of the talk		Jun Ye, JILA/University of ColoradoQuantum matter, clock, and fundamental physics 

Precise control of quantum states of matter and innovative laser technology are revolutionizing the performance of atomic clocks and quantum metrology, providing opportunities to explore emerging phenomena and probe fundamental physics. I will highlight recent work where the gravitation red shift within a single atomic ensemble is measured at the 2 x 10-20 level.  
March 3 (Prospective grad student Open House)

Video of the talk		Nhan Tran, FermilabFast machine learning for particles to the cosmos: from sensors to supercomputers

Pursuing answers to fundamental questions about our universe requires searches for the ultra-rare, very subtle, and the inspection of nature at extremely fine spatial and temporal scales. Cutting edge experiments are often confronted with massive amounts of very rich data. To accelerate scientific discovery, enabling powerful machine learning (ML) across the data processing continuum, from sensor front-ends to supercomputers, is becoming exceedingly valuable. This talk will introduce the motivations for “Fast” ML applications for physics, discussing in detail one example at the Large Hadron Collider, and introducing other applications more broadly. Then we will discuss how modern technology, tools, and techniques are being developed towards increasingly intelligent detectors and experiments.
April 7

Video of the talk		Dan Beller, JHULiquid crystalline order and defects in 3D active soft matter

Liquid crystals are phases of matter intermediate between typical liquids and crystalline solids, in terms of their molecular ordering and physical properties. In recent years, there has been a growing realization that liquid crystalline order emerges not just in equilibrium materials but also in the collective motions of many crowded, interacting objects far from thermal equilibrium—including in bacterial colonies, cellular tissues, and biofilament suspensions. In such “active matter” systems, the generic dynamics are determined to a great extent by the topological defects of liquid crystals, which in two dimensions are analogous to vortices in magnetic and superfluid systems. In this talk I will describe how this coupling of dynamics to topology manifests in three-dimensional active matter, and I will explore how these findings pose new questions for the mathematics and physics of liquid crystals.
April 21

Video of the talk

Yaojun Zhang, JHUWhy do biomolecular condensates ripen so slowly?

It has recently become clear that the interiors of cells are organized in both space and time by non-membrane bound compartments, many of which form via liquid-liquid phase separation. These phase-separated condensates play key roles in processes ranging from transcription to translation, signaling, and more. While the thermodynamic ground state of two immiscible liquids is a single droplet of one liquid immersed in the other, in cells natural and synthetic condensates typically appear as dispersed droplets. In this talk, I will focus on two potential mechanisms for a slowdown of droplet coarsening: (1) droplets’ coalescence and ripening can be mechanically suppressed in the cell nucleus due to the presence of the viscoelastic chromosomal DNA, (2) for molecules that are capable of self-collapsing into a “non-sticking” conformation, ripening can be further slowed by a bouncing effect, i.e., incident molecules can contact the interface without entering the dense droplet. More generally, I will discuss cellular strategies for regulating the number, size, and placement of condensates, with implications for both natural and synthetic systems.
April 28

Video of the talk		Yahui Zhang, JHUEmergent gauge fields in solid state systems

Condensed matter physics is usually dealing with electrons in crystalized solid, which are governed by non-relativistic quantum mechanics with static coulomb interaction. Most of the physics can be well captured by the “standard model”: Landau Fermi liquid theory+ Ginzburg-Landau theory of symmetry breaking. However, in the last several decades there appear systems beyond the standard framework due to strong correlation. In these systems, exotic phases emerge at low temperature, where the electron itself is not the correct starting point. Instead, the more fundamental building block seems to be a fraction of the electron, which is dubbed as “parton”. These partons further couple to dynamical U(1) or even SU(2) dynamical guage fields, like QED or QCD in high energy field theory. I will discuss (1) spin liquids with emergent gauge fields in a Mott insulator and (2) deconfined criticalities between spin liquids and conventional symmetry breaking phases (such as superconductor), through which the gauge field goes through a Higgs transition.
May 5David Krakauer, Santa Fe InstituteThe Problems of Complexity: domains, principles, & theories

Physical theory has made extraordinary progress under assumptions of model parsimony derived in large part from fundamental symmetries in nature. Let’s call this Wigner’s World. Complex systems – living systems (organic and cultural) – are characterized by huge numbers of largely irreducible broken symmetries. Let’s call this Darwin’s world. Complexity science seeks principled means of compressing or coarse-graining Darwin’s world into descriptions that allow for new forms of Wigner-like meta-parsimony: elegance defined at the level of algorithms or dynamical systems operating directly on emergent physical laws. You might think of these as the complex laws of nature modulating the physical laws observed in living systems. These forms of emergent regularity are the primary targets of both complexity science and machine learning. I shall illustrate these principles with data and theory related to animal collective computation.

Fall 2021

DateSpeaker InstitutionTitle and abstract
September 9


Video of the talk		Paul SteinhardtPrinceton University“Time to take the `Big Bang’ out of the Big Bang Theory?”

Although a wide range of empirical evidence supports the notion that the universe has been expanding and cooling for the last 14 billion years in accordance with the big bang theory, there is no evidence for the big bang itself. This talk will explain why it may be necessary to jettison the `big bang’ in favor of a `gentle bounce’ from a preceding phase of contraction in order to explain the observed properties of the universe. 
October 7


Video of the talk		Marcelle Soares-SantosUniversity of Michigan, Ann Arbor“Cosmology in the era of multi-messenger astronomy with gravitational waves”

Motivated by the exciting prospect of a new wealth of information arising from the first observations of gravitational and electromagnetic radiation from the same astrophysical phenomena, the Dark Energy Survey (DES) has established a search and discovery program for the optical transients associated with LIGO/Virgo events (DESGW). Using the Dark Energy Camera (DECam), DESGW has contributed to the discovery of the optical transient associated with the neutron star merger GW170817, and to the first cosmological measurements using gravitational wave events as standard sirens. After three successful observing campaigns, I present, in this talk, an overview of our results and their implications for the emerging field of multi-messenger cosmology with gravitational waves and optical data.
November 18Jon BaggerAPS“American Physical Society: what it is, where it is going, and why you (and I) should care”

Spring 2021

DateSpeaker InstitutionTitle and abstract
March 4Dan Scolnic

Video of the talk		Duke UniversityMeasuring the Expansion History of the Universe with Type Ia Supernovae

Type Ia Supernovae (SN Ia) were used to detect the acceleration of the universe, and are now being used today to make the most precise measurements of the equation-of-state of dark energy. SN Ia are also a critical pillar in measurements of the local value of the Hubble constant (H0), which has been found to be in tension with values inferred from measurements of the early universe. In this talk, I will discuss the progress made with these measurements since I was a graduate student at The Johns Hopkins University, and what are the top questions we have about SN Ia that impact our cosmological measurements. I will review recent controversies with how SN Ia are used to measure dark energy, and discuss the puzzling H0 tension and what happens next. I will also go over what makes JHU such a special center of cosmology, and how it prepared me to be in the middle of some of the most exciting questions in physics today.
March 18John Doyle 

Video of the talk		Harvard University Cold and ultra-cold molecules for quantum science 

Polar molecules, due to their intrinsic electric dipole moment and their controllable complexity, are a powerful platform for precision measurement searches for physics beyond the standard model (BSM) and, potentially, for quantum simulation/computation. This has led to many experimental efforts to cool and control molecules at the quantum level. I will discuss our results on the laser cooling of molecules into the ultracold regime, the search for the electric dipole moment of the electron (EDM), and future prospects for molecules in Quantum Science. In particular, I will discuss the creation of an optical tweezer array of ultracold CaF molecules, the study of ultracold CaF collisions, the search for the EDM using cold ThO molecules, and the laser cooling of the polyatomic molecules SrOH, YbOH, CaOH and CaOCH3. As the field of cold and ultracold molecules has grown, polyatomic molecules in particular have attracted new focus as potential novel quantum resources that have distinct advantages (and challenges) compared to both atoms and diatomic molecules. I will discuss how some key features of polyatomic molecules can be used to enhance applications in quantum simulation/computation, fundamental symmetry tests, searches for dark matter, and the search for T-violating BSM physics.
April 8Matthew Fisher

Video of the talk

UC Santa BarbaraQuantum Many-body Theory in the Quantum Information Era

Traditionally, quantum many-body theory has focused on ground states and equilibrium properties of spatially extended systems, such as electrons and spins in crystalline solids. In recent years “noisy intermediate scale quantum computers” (NISQ) have emerged, providing new opportunities for controllable non-equilibrium many-body systems. In such dynamical quantum systems the inexorable growth of non-local quantum entanglement is expected, but monitoring such open systems (by making projective measurements) can compete against entanglement growth. In this talk I will describe recent theoretical work exploring the behavior of “hybrid” quantum circuits consisting of both unitary gates and projective measurements. These circuits can be shown to exhibit a novel quantum dynamical phase transition between a weak measurement phase and a quantum Zeno phase. Detailed properties of the weak measurement phase – including relations to quantum error correcting codes – and of the critical properties of this novel quantum entanglement transition will be described.
April 15Alessandra Lanzara

Video of the talk		UC BerkeleyMaterials engineering via local symmetry breaking

The 20th century has been dominated by the realization that symmetry and symmetry breaking influence the forces that govern our universe and are keys to much of the novel phenomena observed in materials today. Recently it has been realized that, even if the global symmetry of a system is retained, a local symmetry breaking can still drive a variety of novel fascinating behaviors. In this talk I will present the effect that local breaking of inversion, translational and rotational symmetry can have in defining fundamental properties of matter from topological phases to superconductivity and how it can be used as a tuning parameter to control novel properties in van der Waals heterostructures.
April 22David AwschalomUniversity of ChicagoCreating quantum technologies with spins in semiconductors

Our technological preference for perfection can only lead us so far: as traditional transistor-based electronics rapidly approach the atomic scale, small amounts of disorder begin to have outsized negative effects. Surprisingly, one of the most promising pathways out of this conundrum may emerge from current efforts to embrace defects to construct quantum devices and machines that enable new information processing and sensing technologies based on the quantum nature of electrons and atomic nuclei. Recently, individual defects in diamond, silicon carbide, and other wide-gap semiconductors have attracted interest as they possess an electronic spin state that can be employed as a solid-state quantum bit at room temperature. These systems have a built-in optical interface in the visible and telecom bands, retain their coherence over millisecond timescales, and can be polarized, manipulated, and read out using a simple combination of light and microwaves. With these well-characterized foundations in hand, we discuss merging electronic, photonic, magnetic, and phononic degrees of freedom to develop coherent atomic-scale devices for transducing information to create multifunctional quantum technologies. We present demonstrations of gigahertz coherent control, single nuclear spin quantum memories, entangled quantum registers, and advances in extending the quantum coherence in both commercial and custom CVD-grown electronic materials for emerging applications in science and technology.
April 29Kathryn (Kam) Moler

Video of the talk		Stanford UniversityQuantum Rings of Many Things

Electrons create magnetic fields, so materials that manifest quantum-mechanical and strongly correlated electron behavior must have magnetic signatures. Although distinctive, interesting, and informative, these magnetic signals are hard to measure. In this talk, I will take you on a tour of mesoscopic magnetic phenomena. We will visit metallic rings that exhibit persistent currents despite having a finite resistance; see images of superfluid density that provides clues to the origin of superconductivity; view landscapes of paramagnetism, ferromagnetism, conductivity and superconductivity in exotic materials; and manipulate quantum vortices, one-dimensional elastic objects moving through energy landscapes. These advances in nanomagnetic imaging provide insight into the interplay of disorder, order, and dimensionality in quantum-mechanical phase-coherent states in real materials.

Fall 2020

September 3:  Jared Kaplan

Title: Neural Scaling Laws and GPT-3
Video of the talk

September 10:  Kevin Schlaufman

Title: The Formation, Structure, and Evolution of the Most Commonly Found Planets in the Galaxy
Video of the talk

September 17:  Collin Broholm

Title: Spooky action at a distance in a solid?
Abstract: The quantum spin liquid is a hypothesized state of matter characterized by long range quantum entanglement of spin degrees of freedom. Exactly solvable theoretical models indicate that physical realization of a quantum spin liquid within a crystalline solid may be possible. While they lack a symmetry breaking order parameter, quantum spin liquids support exotic quasi-particles that could be the basis for technological applications including topologically protected quantum computing. I shall describe the exotic magnetic properties of spin liquid candidate materials and new experimental methods to access their entanglement.

September 24:  Danielle Speller

Title: Bringing darkness to light: Searching for new physics at low energies
Video of the talk

October 1:  Nadia Zakamska

Title: The complex life stories of stellar binaries
Video of the talk

October 8:  Yi Li

Title: Topological Superconductivity 2.0
Video of the talk

October 15:  Andrei Gritsan

Title: Understanding the emptiness: the Higgs field and beyond
Video of the talk
Abstract: The quantum theory of the matter and energy that surrounds us, the standard model of particle physics, has been hugely successful in describing both the microscopic world and some of the earliest moments of our Universe. Yet, it appears to be incomplete, as it cannot explain several puzzles of our Universe. One of the last breakthroughs in completing the full picture of the standard model was the discovery of the Higgs boson, measured to have the quantum numbers of the empty space, or vacuum. Understanding the vacuum filled with the Higgs field requires deep experimental measurements and has implications for solving cosmological puzzles of our Universe. We will review what we have learned and what we would like to learn from the Higgs boson interaction with gauge bosons, with fermions, and self-interaction. Prospects of the Higgs physics at future runs of LHC and other facilities will be discussed. 

October 22: Fall Break
October 29: Peter Armitage

Title: On Ising’s model of ferromagnetism
Video of the talk

November 5: Ibou Bah

Title: Bubbling Spacetime
Abstract: An important problem in physics is what are the make ups of black holes?  Addressing this question undoubtedly requires a quantum theory of gravity. For black holes in supersymmetric theories of gravity, the states that make up the black can be reliable described in string theory.  Interestingly, there exist a class of coherent quantum gravity states that admit classical descriptions in classical theories of gravity.  Motivated by such results from string theory, one can look for classical and non-supersymmetric solutions of gravity that can describe states of black holes.  I will discuss recent constructions along this line and their potential implications for black hole physics. 

November 12: Oleg Tchernyshyov
Video of the talk

Title: Mechanics of magnetic solitons

November 19: Francesca Serra

Title: Living cells as liquid crystals
Video of the talk

December 3: Surjeet Rajendran

Title: Understanding Dark Energy
Video of the talk
Abstract: The nature of dark energy is one of the most pressing problems confronting particle physics. What is the dark energy and how can we experimentally probe it?  It is usually assumed that the dark energy is simply a cosmological constant. But, the observed value of the dark energy requires an extra-ordinary fine tuning that defies a natural explanation. In this talk, I will discuss new theoretical approaches to solve this problem and point to experimental opportunities that can be pursued to test these solutions. The theoretical ideas involve independently motivated phenomena such as bouncing universes and I will present controlled solutions within general relativity that accomplish these goals.  Some of the experimental methods can be immediately pursued in CMB polarization and Lorentz violation experiments, while others can be implemented in emerging  techniques such as proton storage rings. A third class of measurements require new sensors that operate in the THz regime.

December 8: David Neufeld
Video of the talk

Title: Probing Galactic Cosmic Rays with Small Molecules and Giant Atoms
Abstract: In the century following their discovery by Victor Hess in 1912, cosmic-rays have been recognized as an important constituent of the Galaxy. With a total energy density somewhat larger than that of starlight, cosmic-rays are the dominant source of ionization within cold, neutral interstellar gas clouds.  In the densest, coldest parts of the interstellar medium – the molecular cloud cores where stars can ultimately form – cosmic-rays are also the dominant source of heating. 

In this talk, I will discuss recent estimates for the cosmic-ray ionization rate (CRIR) in the Galactic disk, obtained by using detailed astrochemical models for interstellar gas clouds to interpret terahertz observations of three interstellar molecular ions, ArH+, OH+, and H2O+; infrared observations of H3+; and radio observations of hydrogen atoms in highly-excited “Rydberg” states.  The resulting estimates for the CRIR – obtained by three independent methods – are in excellent agreement with each other but present a curious puzzle: they are all an order-of-magnitude higher than expectations based on direct measurements of cosmic-rays by the Voyager spacecraft.

At the end, I will discuss a  recently-selected Legacy Program, “HyGAL,”  to be performed with NASA’s SOFIA airborne observatory, which will greatly expand the number of sight-lines on which ArH+, OH+, and H2O+ have been observed.

Spring 2020 Department-wide Colloquia

  • February 20 Aleksander Madry (MIT)

Fall 2019 Department-wide Colloquia

  • September 12 Emanuele Berti (JHU/P&A)
  • September 26 Jason Kalirai (JHU/APL)
    • Title: Space Exploration at the JHU Applied Physics Laboratory
    • Abstract: Space exploration has been a part of APL since its inception in 1942. The Civil Space program is focused on providing critical contributions to some of the biggest challenges facing our understanding of the Sun, Earth and other Solar System planets, and deep space.  In this presentation, I will first give a brief summary of APL’s history in space science and then focus on some of our new space missions, technology programs, and research priorities.  This will include new scientific discovery from the New Horizons and Parker Solar Probe missions, and a look forward to the DART mission that will deflect an asteroid and the Europa Clipper mission that will investigate potential habitability on Jupiter’s moon Europa.  I will also highlight a mission concept that would enable a new chapter in humanity’s quest to explore; to travel beyond our Solar System. (No video was captured for this talk)
  • October 10 Alison Sweeney (Penn)
  • October 24 Massimo Mascaro (Google)
    • Title: The Era of AI: How Deep Learning is revolutionizing Science
    • Video of the talk
  • November 7 David Keith (Harvard)
  • November 21 Prof. Greg Eyink (JHU Applied Math and Statistics Dept.)
  • December 5 Vidya Madhavan (Illinois)

Spring 2019 Department-wide Colloquia

  • February 21 Eliza Kempton (University of Maryland)
    Title: “Revealing Exoplanet Atmospheres in 3-D”
    Video of the talk
  • March 7 Mark Kasevich (Stanford)
    • Title: “Quantum measurements for bio-imaging and precision sensing”
      Video of the talk
  • March 14 Tin-Lun Ho (Ohio State University)
  • March 28Adam Riess (JHU)
    • Title: “A New Measurement of the Expansion rate of the Universe, Hints of New Physics?”
      Video of the talk
  • April 11 Resnick Lecture: France Cordova (National Science Foundation)
    • Title: “Thinking Big: Promoting the Progress of Science Through NSF’s 10 Big Ideas” 
    • Video of the talk
  • April 18 Tom Lubensky (University of Pennsylvania)
  • April 25 Natalia Drichko (JHU)
    • Title: Organic Mott insulators as hosts of spin and dipole liquids.
    • Video of the talk
  • May 2 Karin Öberg (Harvard University)
    • Title: Astrochemical origins of planets and planetary habitability
    • Abstract: Planets form in disks around young stars, and the outcome of planet formation is therefore regulated by structures and processes active in these disks. The chemical disk composition and how molecules are distributed throughout the disk affect all stages and aspects of planet formation, from initial grain sticking probabilities to the acquisition of hydrospheres and atmospheres. In the age of ALMA we can directly observe some of the key chemical structures in disks, including snowlines, signs of non-uniform C/O/N ratios, and non-uniform distributions of organics implicated in origins of life scenarios. Together these results imply that both the composition and chemical habitability of a nascent planet will depend sensitively on where in the disk it acquires its volatile inventory. I will review these observations, as well as the frameworks that have developed to interpret them. I will also suggest some paths going forward, to better connect the compositions and chemistry we observe in disks with the compositions and chemistry we observe on planets.

Fall 2018 Department-wide Colloquia Schedule

  • Associate Professor Jared Kaplan (JHU)
    • October 4, 2018
    • Title: Machine Learning and Why I’ve Been Thinking About It
    • Abstract: In the last six years there has been an explosion of progress in Machine Learning.  In this colloquium I’ll explain the (very simple) ideas underlying Neural Networks, and give a few examples of their structure and current capabilities.  Then I’ll survey the increasing scales of data and computation in this field, and make some comparisons and projections to see where it could be headed.
  • Principal Research Scientist and Engineering Manager of the Instrument Development Group, Steven Smee (JHU)
    • October 18, 2018
    • Title: The Instrument Development Group: The First Twenty Years
    • Abstract: For the past twenty years the Instrument Development Group, an engineering research and development group within the Department of Physics and Astronomy, has been developing instruments for physics and astronomy research. I’ll talk about the history of the group, how it got started, and discuss numerous projects the IDG has been involved in over the years, with some emphasis on our work for the James Webb Space Telescope (JWST) and the Subaru Prime Focus Spectrograph (PFS).
  • Planetary Scientist Elizabeth Turtle (JHU APL)
    • November 1, 2018
    • Title: Dragonfly: Exploring prebiotic chemistry and habitability on Titan by rotorcraft
  • Consensus (a.k.a. Antoine Gittens-Jackson)
    • November 15, 2018
    • Title: Examining the Intersection of Art and Science
    • Abstract: South London-based hip-hop artist Consensus (a.k.a Antoine Gittens-Jackson) will present a multimedia presentation about the intersection of art and science using examples of his work around the globe introducing new audiences to complex scientific concepts through music.

  • Assistant Professor Brian Camley (JHU)
    • November 29, 2018
    • Title: Collective gradient sensing: how can cells cooperate to sense signals?