The Tuesday JFI Seminar - Mohammad Hafezi, Joint Quantum Institute, University of Maryland
Topological Photonics: From Classical to QuantumThere are tremendous efforts underway to better understand systems with topological features --- global properties that are not discernible locally. The best-known examples are quantum Hall effects in electronic systems, where insensitivity to local properties manifests itself as conductance through edge states that are insensitive to defects and disorder. In this talk, I demonstrate how similar physics can be observed for photons; specifically, how various quantum Hall Hamiltonians can be simulated in an optical platform. I review the observation of topological photonic edge states using silicon-on-insulator technology, measurement of the associated topological invariants and our recent advances in studying the quantum transport of such structures. Furthermore, the addition of optical nonlinearity to this system provides a platform to implement fractional quantum Hall states of photons and anyonic states that have not yet been observed. More generally, the application of these ideas can lead to the development of optical devices with topological protection for classical and quantum information processing.
Stephen J. Lippard: Massachusetts Institute of Technology
Understanding and Improving Platinum Anticancer Drugs
Dmitri Feldman, Brown University
Particle-hole symmetry without particle-hole symmetry in the quantum Hall effect at ν = 5/2Numerical results suggest that the quantum Hall effect at the filling factor 5/2 is described by the Pfaffian or anti-Pfaffian state in the absence of disorder and Landau level mixing. Those states are incompatible with the observed transport properties of GaAs heterostructures, where disorder and Landau level mixing are strong. We show that the recent proposal of a PH-Pfaffian topological order by D. T. Son is consistent with all experiments. The absence of the particle-hole symmetry at the filling factor 5/2 is not an obstacle to the existence of the PH-Pfaffian order since the order is robust to symmetry breaking
Anthony Hyman, PhD, MPI Molecular Cell Biology and Genetics, Dresden
Biomolecular condensates: Organizers of cellular biochemistry
Danna Freedman:Northwestern University
Applying Inorganic Chemistry to Challenges in Physics
the faster you run, the less you rememberEat 12:00 noon
Joe Incandela, University of California,Santa Barbara/CERN
Zachariasen Lecture: "From the Higgs to dark matter: the search for the underlying code of our universe"
Lee Lecture: Professor Matthew Rosseinsky, University of Liverpool
Beyond the unit cell: control of function by local structure and dynamics from fuel cell electrodes to metal-organic frameworks
Luca Delacretaz, Stanford University
Transport with translational order and bad metalsI will present a hydrodynamic theory of weakly disordered electronic systems with fluctuating or static translational order, such as charge/spin density waves or Wigner crystals. This hydrodynamic approach leads to universal expressions for low frequency ac conductivities and viscosities. I will argue that similar ac conductivities are observed experimentally in a variety of bad metals, and conjecture that such materials have short range fluctuating charge order.
Jeremy England, MIT
Emergent Fine-tuning to Environment in a Complex Chemical reactionThe equilibrium steady state of an undriven mixture of reacting chemical species is uniquely determined by the free energy. Once external environmental drives are introduced, however, steady-state concentrations may deviate from these equilibrium values via sustained absorption and dissipation of work. From a physical standpoint, the living cell is a particularly intriguing example of such a nonequilibrium system, because the environmental work sources that power it are relatively difficult to access – only the proper orchestration of many distinct catalytic actors leads to a collective behavior that is competent to harvest and exploit available metabolites. Here, we study the dynamics of an in silico chemical network with random connectivity in a driven environment that only makes strong chemical forcing available to rare combinations of concentrations of different molecular species. We find that the long-time dynamics of such systems biased towards the spontaneous extremization of forcing, so that the molecular composition converges on states that exhibit exquisite fine-tuning to available work sources.
Lee Lecture: Prof. Matthew Rosseinsky, University of Liverpool
Design of Advanced Materials?
Lukasz Fidkowski, Stony Brook University
Chiral phases in Floquet quantum systems
Alex Miller: University of North Carolina at Chapel Hill
Cation-Responsive Pincer-Crown Ether Complexes for Tunable Catalysis
1st Annual UChicago MRSEC SymposiumLearn about ongoing work in the Materials Research Center!
Explore new collaborations & research directions!
GCIS 3rd Floor Atrium
11:30am -1:30pm: Lunch and Poster Session
1:30pm - 3:00pm: IRG 1 – Dynamics of Soft Interfaces
& IRG 2 – Active Materials
3:00pm - 3:15pm: Coffee Break
3:15pm-4:45pm: IRG 3 – Engineering Quantum Materials & Seed Research – “Multifunctional Interfaces of Different Dimensionality” & “Multifunctional Porous Materials”
4:45pm: Wine and Cheese
Lisa Manning, Syracuse University
Jamming in biological tissuesHost: Sid Nagel
Philip Nelson, University of Pennsylvania
Old and new news about single-photon sensitivity in human visionOne often hears that human vision is “sensitive to single photons,” when in fact the faintest flash of light that can reliably be reported by human subjects is closer to 100 photons. Nevertheless, there is a sense in which the familiar claim is true. Experiments conducted long after the seminal work of Hecht, Shlaer, and Pirenne now allow a more precise, and in some ways even more remarkable, conclusion to be drawn about our visual apparatus. A simple model that incorporates both old news (response of single rod cells) and newer news (loss at the first synapse) can account in detail for both old and new psychophysical data.
The 2nd Tuesday JFI Colloquium - Eric Borguet - Department of Chemistry, Temple UniversityInterfacial water structure, which can be probed by vibrational sum-frequency generation (vSFG) spectroscopy, is key to many processes. Time-resolved vSFG shows that in the absence of surface charge (pH 2), water at silica surfaces exhibits significantly slower OH stretch vibrational relaxation (~600 fs) compared to bulk water. However, at charged silica surfaces (e.g., pH 6), bulk-like fast dynamics (~200 fs) are observed at low ionic strength. This decelerates to ~600 fs, with the addition of NaCl. In parallel, vSFG results demonstrated that silica interfacial water structure is most sensitive to cations at pH=6-8. Consequently, it is unclear whether the observed slowing of the vibrational dynamics is due to the reduction in Debye length, or because of changes in the local hydrogen bonding environment caused by the electrolyte and how this might depend on the identity of the ions. Additional spectroscopic and time-resolved vSFG experiments on aqueous Al2O3 interfaces shed light on the ongoing debate on the role of ions in interfacial water structure and whether the observed behavior is specific to silica/water interfaces or can be generalized to other systems. Philippe Guyot-Sionnest, 2-7461 or via email at firstname.lastname@example.org. Persons with a disability who may need assistance please contact Brenda Thomas at 2-7156 or by email at email@example.com.
Snir Gazit, University of California at Berkeley
Charged fermions coupled to Ising gauge fields: Symmetry breaking, confinement, and emergent Dirac fermions.Lattice gauge theories are ubiquitous in physics, describing a wide range of phenomena from quark confinement to quantum materials. At finite fermion density, gauge theories are notoriously hard to analyze due to the fermion sign problem. Here, we investigate the Ising gauge theory in 2+1 dimensions, a problem of great interest in condensed matter, and show that it is free of the sign problem at arbitrary fermion density. At generic filling, we find that gauge fluctuations mediate pairing leading to a transition between a deconfined BCS state to a confined BEC. At half-filling, a π-flux phase is generated spontaneously with emergent Dirac fermions. The deconfined Dirac phase, with a vanishing Fermi surface volume, is a non-trivial example of violation of Luttinger's theorem due to fractionalization. At strong coupling, we find a single continuous transition between the deconfined Dirac phase and the confined BEC, in contrast to the expected split transition.
Kharasch Memorial Lecture - Sir Shankar Balasubramanian, University of Cambridge
How large is the natural DNA alphabet?
Peter Littlewood, University of Chicago
Physics of SustainabilityHost: Mel Shochet
Daniel Scolnic, University of Chicago
Measuring the size of the Universe with Standard CandleAstrophysicists use standard candles, objects which have roughly the same luminosity, to infer distances to far-away parts of the universe. Standard candles of variable stars called ‘cepheids’ were used to discover the expanding universe, and standard candles of exploding stars called ‘supernovae’ were used to discover the accelerating universe. Together, these two standard candles can be used to measure the size of the universe. Interestingly, this measurement of the size of the universe recovered conflicts with measurements of the size of the universe from extrapolations of data from the Cosmic Microwave Background. I will go over how we make our measurement, from soup to nuts, and discuss how we can be confident in the accuracy of our values. I will then discuss different ways too explain the tension we see in the different sets of measurements, and possible new physics that may be on the horizon.
The 1st Tuesday JFI Colloquium - Benjamin Lev, Department of Physics and Applied Physics - Stanford University
New Tools for Exploring Nonequilibrium Quantum Many-Body PhysicsABSTRACT: The simulation of quantum systems using ultracold atomic gases—quantum simulation—may be viewed as the creation of novel quantum systems in their own right rather than the simulation of well-known models. Often these systems possess collective properties impossible to observe in the solid state. In particular, these gaseous systems provide unique testbeds for emergent physics, especially that out of equilibrium. We present two novel avenues of inquiry into quantum nonequilibrium physics: the creation of dissipative quantum spin glasses and quantum neural networks using atoms coupled to the photonic modes of a confocal optical resonator and the study of nonequilibrium quench dynamics in highly magnetic and strongly interacting gases. Besides investigating long-unresolved issues in statistical mechanics (i.e., the order of spin glasses and thermalization in closed quantum systems), the experimental directions discussed point to novel neuromorphic computational architectures relying on driven-dissipative quantum dynamics.Host: Jonathan Simon, 2-9661 or via email at firstname.lastname@example.org. Persons with a disability who may need assistance please contact Brenda Thomas at 2-7156 or by email at email@example.com.
Kharasch Memorial Lecture - Sir Shankar Balasubramanian, University of Cambridge
Decoding human genomes on a population scale
Dominic Else, University of California, Santa Barbara
Floquet Time Crystals: How time-translation symmetry protects phases of matterA "Floquet time crystal" is a phase of matter in a periodically driven (Floquet) system which spontaneously breaks discrete time-translation symmetry. They are an entirely new "non-thermal" phase of matter which cannot exist in undriven systems. In this talk, I will discuss the recent theoretical prediction and experimental observation of Floquet time crystals. Time-translation symmetry occupies a special role in physics, since its generator is the Hamiltonian itself. Nevertheless, the theoretical formulation of time crystals turns out to be *almost* the same as for other symmetry-breaking phases of matter. I will also consider phases of matter in which the discrete time-translation symmetry is not spontaneously broken but nevertheless protects non-trivial phases, which are the analogs of "symmetry-protected topological" and "symmetry-enriched topological" phases for other symmetries.
Jingyuan Chen, Stanford University
Exact Bose-Fermi Duality on 3D Euclidean LatticeRecently a conjectured Bose-Fermi duality in 3 spacetime dimensions has drawn much interest from both high energy and condensed matter communities. We prove this duality by constructing an exact duality on lattice and showing our exact duality reduces to the conjectured duality in the continuum limit. All steps are analytic, exact, and simple.
Qiu Wang, Duke University
Leveraging Chemistry for Biology and Therapy: – New amination strategies to access biologically important molecules
Cameron Reed, Alma College
The Manhattan Project: A Look at the Physics"Host: Henry Frisch
Andrew Kruse, PhD, Harvard Medical School
New approaches to investigate G protein-coupled receptor function
Lenka Zdeborova, CNRS & CEA, Saclay, France
Statistical physics approach to compressed sensing and generalized linear regressionBayesian inference and statistical physics are formally closely related. Therefore methodology and concepts developed in statistical physics to understand disordered materials such as glasses and spin glasses can be elevated to analyze models of in statistical inference. We will present this approach in a rather general setting that covers analysis of compressed sensing, generalized linear regression, and the perceptron - a kind of a single layer neural network. At the one hand, this approach leads to the approximate message passing algorithm that is gaining its place among other widely used regression and classification algorithms. At the other hand, the related analyses leads to identification of phase transitions in the performance of Bayes-optimal estimators. We will discuss relation between these phase transitions and algorithmic hardness, and in the case of compressed sensing we will show how this understanding leads to a design of optimal measurement protocols.
Based partly on "Statistical-physics-based reconstruction in compressed sensing" PRX 2012 and reviewed in "Statistical physics of inference: Thresholds and algorithms" Advances of Physics 2016.
Andy Borovik:University of California, Irvine
Synthetic Chemistry as a Window into Biology
JFI Seminar - Prof. David Cobden, Department of Physics, Washington University
"Electronic Phases and Phase Transitions in Van der Waals Monolayers"ABSTRACT: Atomically thin materials can host many kinds of electronic phases, some unique to the 2D limit. Our observations indicate the realization of a quantum spin Hall state, an excitonic insulator, superconductivity, and ferro- and antiferromagnetism in van der Waals monolayers. Unlike 3D solids, monolayers are amenable to surface probes and can be doped by electrostatic gating. We are thus investigating ways to induce transitions between these phases electrostatically. In WTe2 monolayers at low temperatures we observe a transition between a two-dimensional topological insulator and a bulk conducting phase as a function of gate voltage, representing a gate-controlled quantum phase transition.Host: Jiwoong Park, 4-3179 or via email to firstname.lastname@example.org. Persons with a disability who may need assistance please contact Brenda Thomas at 2-7156 or by email at email@example.com.
Cenke Xu, University of California, Santa Barbar
self-dual quantum critical points in 2+1 dimensions
Jennifer M. Heemstra: University of Utah
Harnessing Nucleic Acid Molecular Recognition and Self-Assembly for Biosensing and Biomolecular Imaging
Two dynamical interfaces walk into an IRG…
a recap of tuesday's idea session12:00 Eat real food
12:15 digest bloblets
Zoran Hadzibabic, University of Cambridge
Quantum gas in a boxHost: Cheng Chin
Anette Hosoi, MIT
Hydrodynamics of Hairy SurfacesFlexible slender structures in flow are everywhere. While a great deal is known about individual flexible fibers interacting with fluids, considerably less work has been done on fiber ensembles, such as fur or hair, in flow. These hairy surfaces are abundant in nature and perform multiple functions from thermal regulation to water harvesting to sensing. Motivated by these biological systems, we consider two examples of hairy surfaces interacting with flow: (1) air entrainment in the fur of diving mammals and (2) symmetry breaking in hairy micro-channels.
In the first example, we take inspiration from semi-aquatic mammals (such as fur seals, otters, and beavers) which have specially adapted fur that serves as an effective insulator both above and below water. Many of these animals have evolved pelts that naturally entrap air when they dive. This air: (1) provides additional insulation under water, (2) provides added buoyancy, and (3) facilitates water shedding when the animals resurface. In this study we investigate diving conditions and fur properties which amplify air entrainment in fur. In the second example, we consider a fundamental component in hydraulic systems, the flow rectifier. One of the simplest ways to generate asymmetry in these devices is with a ball valve in which flow is completely obstructed in one direction and free to flow in the other. In this work we seek a variation that: (1) allows the designer to modulate the relative resistances in the rectifier and (2) can be achieved with solid state components (i.e. no moving parts).
The Tuesday JFI Seminar - Monika Schleier-Smith, Department of Physics, Stanford University
"Echoes of Entanglement: from Quantum Metrology to Scrambling"ABSTRACT: In the quest to approach the fundamental Heisenberg Limit in precision measurements, central challenges are the generation and detection of highly entangled states. I will describe how both of these challenges can be mitigated by “echo spectroscopy,” a technique inspired by the Loschmidt echo, a paradigmatic probe of chaos. A key ingredient is to effectively reverse the flow of time in an interacting many-body system by switching the sign of the Hamiltonian. I will describe progress towards engineering spin models with non-local, switchable-sign interactions using cold atoms strongly coupled to light an optical cavity. Intriguingly, similar non-local interactions feature in models for understanding fundamental bounds on chaos and information scrambling derived from the study of black holes, opening prospects for investigating these bounds in the laboratory.Host: Jonathan Simon, 2-9661 or via email at firstname.lastname@example.org. Persons with a disability who may need assistance please contact Brenda Thomas at 2-7156 or by email at email@example.com.
Viviana Gradinaru, PhD, CALTECH
Optogenetic, tissue clearing, and viral vector approaches to understand and influence whole-animal physiology and behaviorWe develop & employ optogenetics, tissue clearing and viral vectors to gain new insights on circuits underlying locomotion, reward & sleep. I will discuss how bidirectional manipulation of mesopontine cholinergic cell bodies exerted opposing effects on locomotor behavior & reinforcement learning & how these effects were separable via limiting photostimulation to PPN cholinergic terminals in the ventral substantia nigra pars compacta or to the ventral tegmental area, respectively (Xiao et al, Neuron, '16). Genetically encoded tools that can be used to visualize, monitor, and modulate mammalian neurons are revolutionizing neuroscience. However, use of genetic tools in non-transgenic animals is often hindered by the lack of vectors capable of safe, efficient & specific delivery to the desired cellular targets. To begin to address these challenges, we have developed an in vivo Cre-based selection platform (CREATE) for identifying adeno-associated viruses (AAVs) that more efficiently transduce genetically defined cell populations (Deverman et al, Nature Biotechnology, '16). As a first test of the CREATE platform, we selected for viruses that transduced the brain after intravascular delivery and found a novel vector, AAV-PHP.B, that transduces most neuronal types and glia across the brain. We also demonstrate how whole-body tissue clearing can facilitate transduction maps of systemically delivered genes (Yang et al, Cell, '14; Treweek et al, Nature Protocols, '16) and how non-invasive delivery vectors can be used to achieve dense to sparse labeling to enable morphology tracing (unpublished). Since CNS disorders are notoriously challenging due to the restrictive nature of the blood brain barrier, the recombinant vectors engineered to overcome this barrier can enable potential future use of exciting advances in gene editing via the CRISPR-Cas, RNA interference and gene replacement strategies to restore diseased CNS circuits. In addition to control of neuronal activity we need feedback on how exactly the tissue is responding to modulation. We have worked on two related topics: optical voltage sensors and imaging of single molecule RNA in cleared tissue. We used directed evolution of opsins to make them better at reporting action potentials (Flytzanis et al, Nature Communications, '14). Changes in RNA transcripts can also report on activity history of brain circuits. Preserving spatial relationships while accessing the transcriptome of selected cells is a crucial feature for advancing many biological areas, from dev bio to neuroscience. We recently reported on methods for multi-color, multi-RNA, imaging in deep tissues. By using single-molecule hybridization chain reaction (smHCR), PACT tissue hydrogel embedding and clearing and light-sheet microscopy we detected single-molecule mRNAs in ~mm-thick brain tissue samples (Shah et al, Development, '16) and by rRNA labeling we mapped the identity & growth rate of pathogens in clinical samples (DePas et al,'16).
Closs Lecture-Professor Mostafa El-Sayed, Georgia Institute of Technology
Photothermal Therapy of Cancer in Cells and in Different Animals Using Gold Nano-Rods: A Progress Report
Roger Melko, Perimeter Institute
Machine Learning the Many-Body ProblemCondensed matter physics is the study of the collective behavior of infinitely complex assemblies of electrons, nuclei, magnetic moments, atoms or qubits. This complexity is reminiscent of the “curse of dimensionality” commonly encountered in machine learning. Despite this curse, the machine learning community has developed techniques with remarkable abilities to classify, characterize and interpret complex sets of data, such as images and natural language recordings. Here, we show that modern architectures for supervised learning, such as fully-connected and convolutional neural networks, can identify phases and phase transitions in a variety of condensed matter Hamiltonians. Readily programmable through open-source software libraries, neural networks can be trained to detect multiple types of order parameter, as well as highly non-trivial states with no conventional order, directly from raw state configurations sampled with standard Monte Carlo. Further, Monte Carlo configurations can be used to train a stochastic variant of a neural network, called a Restricted Boltzmann Machine (RBM), for use in unsupervised learning applications. We show how RBMs, once trained, can be sampled much like a physical Hamiltonian to produce configurations useful for estimating physical observables. Finally, we explore the representational power of quantum and classical RBMs, their role in deep learning, and its possible relationship to the renormalization group.
John Jewett: University of Arizona
Viral muses to inspire chemistry
Bloblets in your cells: what is their mission?12:00 Eat real food
12:15 digest bloblets
Steve Kivelson, Stanford University
Intertwined Order in Highly Correlated Electron FluidsHost: Paul Wiegmann
Minjung Ryu, PhD, Purdue
Language, Culture, and Learning: Implications for Interdisciplinary Research
Jonathan Simon, University of Chicago
Exploring Landau Levels in Curved SpaceI will present recent work realizing topological phases of photons, both in curved space, and in lattices. The talk will focus on our recent exploration of Landau levels on a conical surface, generated using a non-planar (twisted) optical resonator to induce a synthetic magnetic field for optical photons, and employed to validate the famous Wen-Zee action. I will then discuss recent results demonstrating strong photon-photon interactions mediated by resonator Rydberg-electromagnetically induced transparency (EIT), and techniques we are developing to assemble topological few-body states both photon-by-photon, and through microscopic devices engineered for photon thermalization. I will conclude with our recent observation of time-resolved helical edge dynamics in Z_2 topological circuit lattices, and a T-broken extension in the microwave domain using arrays of 3D cavities and circuit quantum electrodynamics techniques. This work showcases the unique possibilities for Hamiltonian engineering and control in the photonic sector, a provides a taste of upcoming breakthroughs in engineering quantum materials from photons.
The Tuesday JFI Seminar - Elisabeth Guazzelli, Aix Marseille Univ, CNRS, IUSTI, Marseille, France
Rheology of Dense Suspensions of Non-Colloidal ParticlesABSTRACT: Dense suspensions are materials with broad applications both in industrial processes (e.g. waste disposal, concrete, drilling muds, metalworking chip transport, and food processing) and in natural phenomena (e.g. flows of slurries, debris, and lava). Despite its long research history and its practical relevance, the mechanics of dense suspensions remain poorly understood. The major difficulty is that the grains interact both by hydrodynamic interactions through the liquid and by mechanical contact. These systems thus belong to an intermediate regime between pure suspensions and granular flows. We show that we can unify suspension and granular rheology under a common framework by transferring the frictional approach of dry granular media to wet suspensions of spherical particles. We also discuss non-Newtonian behavior such as normal-stress differences and shear-induced migration. Beyond the classical problem of dense suspension of hard spheres which is far from being completely resolved, there are also entirely novel avenues of study concerning more complex mixtures of particles and fluids such as those involving other types of particles (e.g. fibers) or non-Newtonian fluids (e.g. yield-stress fluids) that we will also address. Host: Heinrich Jaeger, 2-6074 or via email at firstname.lastname@example.org. Persons with a disability who may need assistance contact Brenda Thomas at 2-7156 or by email at email@example.com.
Matthew Lapa, UIUC
Electromagnetic response and anomalies in bosonic symmetry-protected topological phasesSymmetry-protected topological (SPT) phases, gapped phases of matter protected by the symmetry of a group G and possessing interesting boundary states, have been the focus of intense investigation for the past several years. While much is known about the classification and properties of these phases, especially in low dimensions, it is still a challenge to understand the physical properties which characterize a given (interacting) SPT phase in a general dimension. In this talk I will explain how a field-theoretic description of bosonic SPT phases in terms of nonlinear sigma models (NLSMs) can be combined with the theory of gauged Wess-Zumino actions to study the electromagnetic response and anomalies of some bosonic SPT phases with U(1) symmetry in all dimensions. In particular, I will present a calculation of the topological part of the electromagnetic response of bosonic integer quantum Hall (BIQH) states in odd spacetime dimensions and bosonic topological insulator (BTI) states in even spacetime dimensions. In addition, I will argue that the boundary of the BTI state exhibits a global anomaly similar to the parity anomaly of Dirac fermions in odd spacetime dimensions. This argument can be made precise for the boundary theory of the BTI state in two spacetime dimensions. If time allows, I will explain how the connection between gauged Wess-Zumino actions and equivariant cohomology can be used to prove that these results are robust against smooth, symmetry-preserving deformations of the target space of the NLSM used to describe these states.
Gregory T. Tietjen, PhD, Yale
A biophysical approach to engineering vascular targeted nanomedicine
Ribhu Kaul, University of Kentucky
Quantum phase transitions in square lattice SU(N) and SO(N) magnetsI will discuss the phases and phase transitions in some simple SU(N) and SO(N) quantum spin models, studied both using ideas from quantum field theory and with large scale numerical simulations.
James Morken, Boston College
New Strategies in Organic Synthesis Enabled by Catalytic Reactions of Organoboron Reagents
The 1st Tuesday JFI Colloquium - Mark G. Raizen - Department of Physics, University of Texas at Austin
From Maxwell’s Demon to Einstein’s Speed DemonABSTRACT: In this talk, I will describe two historical thought experiments in statistical mechanics and their experimental realization. Maxwell’s Demon was proposed by James Clerk Maxwell in 1871 as a way to reduce the entropy of gas-phase particles by means of an “intelligent creature with deft hands.” We have realized this thought experiment with a self-acting one-way wall for atoms, as originally suggested by Maxwell. This construction has been used to cool atoms, and for efficient isotope separation which will have important medical applications. In 1907, Albert Einstein predicted that Brownian motion should be ballistic on very short time scales, rather than diffusive. Einstein concluded that this instantaneous velocity would be impossible to measure in practice, a prediction that held for over 100 years. We have realized such a ‘speed demon’ by measuring the motion of micrometer beads held in optical tweezers, and have resolved the instantaneous velocity of a Brownian particle in air and in liquid. This system can be used to study the onset of irreversibility, the “arrow of time.”Host(s):Cheng Chin, 2-7192 or via email to firstname.lastname@example.org. Persons with a disability who may need assistance please contact Brenda Thomas at 2-7156 or by email at email@example.com.
Wolfgang Ketterle, MIT
New forms of matter with ultracold atoms: synthetic gauge fields and supersolidityHosts: Cheng Chin
Yimon Aye, Cornell
Stay On Target: Deconvoluting Mixed Redox Messages through Precision Redox Targeting
The Tuesday JFI Seminar - James F. Cahoon, Department of Chemistry, University of North Carolina - Chapel Hill
From Nanowires to Nanoplatelets: Designing Semiconductor Morphology so Form Follows FunctionSemiconductors are used in a vast array of modern technologies, including solar cells that convert sunlight into electricity and microprocessors that drive computers. They can be used to direct the flow of energy in devices or to convert energy from one form to another. These functions are enabled by the specific choice of material and composition. Shape, however, is another fundamental characteristic that can be used to encode functionality. Here, I will describe my group’s efforts to usenanometer-scale morphology as a strategy to encode novel photovoltaic, electronic, and optical properties in materials created by bottom-up methods. We chemically synthesize nanostructures, such as metal oxide particles and group IV nanowires, with precise morphology and composition, and we evaluate their physical properties using nanofabrication, spectroscopic, electrochemical, and computational methods. For instance, I will describe a strategy to create silicon nanowires with lithographic-like patterns, enabling applications ranging from photonic crystals to non-volatile memory. In addition, I will outline our efforts to design wide-bandgap photocathode materials for integration in solar fuels devices. The results yield insights into the synthesis, structure-function relationships, and technological applications of designed, bottom-up semiconductor nanomaterials. Host: Bozhi Tian; Contact him at 2-8749 or via email at firstname.lastname@example.org. Persons with a disability who may need assistance please contact Brenda Thomas at 2-7156 or by email at email@example.com.
Wheland Lecture - John P. Maier: University of Basel
Electronic Spectroscopy of C60+ and its Identification in Interstellar Space
The 2nd Tuesday JFI Colloquium - Hui Zhai, Tsinghua University, Institute for Advanced Study
Closs Lecture - Christopher Chang, University of California, Berkeley
Transition Metal Signaling in the Brain and Beyond
Moh El-Naggar, PhD, Depts of Physics and Astronomy, of Biological Sciences, and of Chemistry, University of Southern California
Far, Fast, & Surprising: Extracellular Electron Transport in Microbial Redox ChainsThe stepwise movement of electrons within and between molecules dictates all biological energy conversion strategies, including respiration and photosynthesis. With such a universal role across all domains of life, the fundamentals of ET and its precise impact on bioenergetics have received considerable attention, and the broad mechanisms allowing ET over small length scales in biomolecules are now well appreciated.
In what has become an established pattern, however, our planet’s oldest and most versatile organisms are now challenging our current state of knowledge. With the discovery of bacterial nanowires and multicellular bacterial cables, the length scales of microbial ET observations have jumped by 7 orders of magnitude, from nanometers to centimeters, during the last decade alone! This talk will take stock of where we are and where we are heading as we come to grips with the basic mechanisms and immense implications of microbial long-distance electron transport. We will focus on the biophysical and structural basis of long-distance, fast, extracellular electron transport by metal-reducing bacteria. These remarkable organisms have evolved direct charge transfer mechanisms to solid surfaces outside the cells, allowing them to use abundant minerals as electron acceptors for respiration, instead of oxygen or other soluble oxidants that would normally diffuse inside cells. From an environmental perspective, these microbes are major players in global elemental cycles. From a technological perspective, microbial extracellular electron transport is heavily pursued for interfacing redox reactions to electrodes in multiple renewable energy technologies.
But how can an organism transfer electrons to a surface many cell lengths away? What molecules mediate this transport? And, from a physics standpoint, what are the relevant length, time, and energy scales? We will describe new experimental and computational approaches that revealed how bacteria organize heme networks on outer cell membranes, and along the quasi-one-dimensional filaments known as bacterial nanowires, to facilitate long-range charge transport. Using correlated electron cryo-tomography and in vivo fluorescent microscopy, we are gaining new insight into the localization patterns of multiheme cytochromes along nanowires as well as the morphology and the formation mechanism of these structures. In addition, we will examine the fundamental limits of extracellular electron transport, down to microbial energy acquisition by single cells. These findings are shedding light on one of the earliest forms of respiration on Earth while unraveling surprising biotic-abiotic interactions.