The past decade's apparent success in predicting and experimentally discovering distinct classes of topological insulators (TIs) and semimetals masks a fundamental shortcoming: out of 200,000 stoichiometric compounds extant in material databases, only several hundred of them are topologically nontrivial. Are TIs that esoteric, or does this reflect a fundamental problem with the current piecemeal approach to finding them? To address this, we propose a new and complete electronic band theory that highlights the link between topology and local chemical bonding, and combines this with the conventional band theory of electrons. We classify the possible band structures for all 230 crystal symmetry groups that arise from local atomic orbitals, and show which are topologically nontrivial. We show how our topological band theory sheds new light on known TIs, and demonstrate the power of our method to predict new TIs.
Dilute, degenerate samples of lanthanide atoms have emerged as a promising new research frontier. Their strong magnetic moment indeed allows to study the many-body consequences of long-range anisotropic dipole-dipole interactions. Experiments benefit from the control tools of ultracold atomic physics allowing to characterize few-body effects and to isolate the key many-body mechanisms. In recent years, manifestations of dipolar interactions have been observed in Bose-Einstein condensates, Mott insulators and Fermi seas. One can reach in these systems the regime where dipolar interactions dominate over usual short-range interactions of van der Waals origin. I this talk I will present our experimental results on magnetic quantum fluids made out of a Bose-Einstein condensate of dysprosium atoms. Striking effects of magnetic interactions can be observed. First we have observed and studied a modulational instability at finite wavelength that takes place in constrained geometries. Second, we have discovered a phase-transition between a gas and a liquid, characterized by the formation of self-bound droplets. The liquid owes its stability to quantum fluctuations of the fluid’s collective modes, and the same mechanism is relevant for other seemingly unrelated systems where similar liquid phases can be reached, defining a new class of ultra-dilute quantum liquids. These findings have finally revived the search for a supersolid ground-state in dipolar Bose-Einstein condensates. In a theoretical study we suggest that in strongly-confined conditions, phase-coherence and the breaking of continuous translation invariance can be simultaneously sustained, signaling supersolid order.
Binary black holes in hierarchical triples, potentially abundant in globular clusters and galactic nuclei, could show up in LIGO and future gravitational wave detectors with observably large eccentricity. Measuring the eccentricity distribution accurately could help us better understand the background and the formation of the mergers. In this talk, I describe a semi-analytical description of eccentricity distribution of mergers in galactic nuclei and other hierarchical triple systems. The result could be useful for statistically distinguishing different formation channels of observed binary mergers, and also further reduces the reliance on numerical simulations.
Control of molecules is greatly aided by cooling their external degrees of freedom. Exquisite quantum state control has already been achieved with atomic species, leading to great progress in quantum computation, simulation, searches for physics beyond the Standard Model, and novel collisions and chemical reactions. Molecules are now a current frontier in cold matter science, with diatomic molecules taking center stage at the moment. Moving to the next frontier, the creation of ultracold polyatomic molecules presents new laboratory challenges. One of our key long-term scientific goals is to achieve for polyatomic molecules the kind of single-state control now available with atoms with a very wide variety of polyatomic structures. We believe that this will open up important new scientific opportunities.
About the speaker
John Doyle's research centers on trapping neutral particles, study of fundamental collisional processes in atoms and molecules, and lab and underground-observatory-based searches for physics beyond the Standard Model. He is also currently working to realize new techniques to trap molecules and atoms and produce intense beams of the same.
The Doyle group has pioneered a general technique for cooling and loading atoms and molecules into traps. First demonstrated with atomic europium and chromium and molecular CaH, the technique uses cryogenic helium buffer gas to cool atoms to below 1 Kelvin. The cold atoms are then loaded into a magnetic trap and then evaporatively cooled. This has led to the discovery of several new findings on the physics of cold collisions as well as doubling the number of species magnetically trapped, including exotic atoms such as Dy. In addition, by developing a new technique for producing heavy, polar radical molecules in an intense beam, he has launched with collaborators a new EDM search. Heavy, highly polar molecules are ideally suited to the search for a permanent electric dipole moment (EDM) in the electron. The discovery of an EDM in these experiments would indicate new physics beyond the standard model. Work towards production of ultracold molecules aims also to build hybrid quantum devices. Finally, work is ongoing to use XUV scintillation in liquid neon and argon to search for a key Dark Matter candidate, the WIMP.
Dissipation is a pervasive problem in many areas of physics. In quantum optics, losses curb our ability to realize controlled and efficient interactions between photons and atoms, which are essential for many technologies ranging from quantum information processing to metrology. Spontaneous emission - in which photons are first absorbed by atoms and then re-scattered into undesired channels - imposes a fundamental limit in the fidelities of many quantum applications, such as quantum memories and gates. Typically, it is assumed that this process occurs at a rate given by a single isolated atom. However, this assumption can be dramatically violated: interference in photon emission and absorption generates correlations and entanglement among atoms, thus making dissipation a collective phenomenon. In this talk, I will provide a comprehensive look into the physics of subradiance, an emergent form of correlated dissipation in which interference is destructive and atomic decay is inhibited. In atomic arrays in free space, subradiant states acquire an elegant interpretation in terms of optical guided modes, which only emit due to scattering from the ends of the finite system. By interfacing atomic chains with nanophotonic structures, these states can be excited straightforwardly. Exploiting their radiative properties allows for the realization of a quantum memory with a photon retrieval fidelity that performs exponentially better with number of atoms than previously known bounds. This single example illustrates how correlated dissipation transcends the "standard model" of disordered atomic ensembles, and suggests that we should re-examine well-known concepts in quantum optics in a new light.
Brian Cole is a Columbia University Professor of Physics in the field of experimental high-energy nuclear physics. He performs research at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory and (more recently) the Large Hadron Collider at CERN studying collisions between nuclei at the highest possible energies to study “quark gluon plasma”, a unique state of matter that existed in the early universe until a few microseconds after the big bang.
Our cosmological observations today are limited to a finite volume of space, but models of the primordial universe predict a universe much larger than what we see. Those models also predict that quantum fluctuations are the origin of the structure in the universe. I will use this framework as motivation to construct the evolution equation for the density matrix of an infrared-limited set of co-moving momentum modes in two examples of nearly de Sitter universes. Including an interaction term from the gravitational action and tracing out long-wavelength modes, I will show that the nature of the resulting dissipation terms depends on how curvature fluctuations evolve on scales larger than the Hubble scale. The results are relevant for constructing effective quantum theories for early universe cosmology, aswell as for other settings where usual UV effective field theory is not applicable.
Materials with strong electronic correlations such as transition-metal oxides, rare-earth compounds or molecular conductors have focused enormous attention over the last three decades. Solid-state chemistry is constantly providing us with examples of novel materials with surprising and remarkable electronic properties. New routes for controlling the functionalities of these materials are actively being explored, such as high-quality heterostructures and selective control of structural modes with ultra-fast light pulses.
New frontiers are also opening up, which bring together condensed-matter physics and quantum optics. `Artificial materials' made of ultra-cold atoms trapped by laser beams can be engineered with a remarkable level of controllability, and allow for the study of strong-correlation physics in previously unexplored regimes.
After an overview of some aspects of this broad field, I will argue that the `standard model’ of condensed-matter physics, which views electrons in a solid as a gas of wave-like quasiparticles, must be seriously reconsidered for strongly correlated materials. I will also outline some of the theoretical and computational challenges raised by quantum matter with strong correlations.
About the speaker
Antoine Georges is a professor of physics at the Collège de France, where he holds the chair in condensed matter physics. He also has joint appointments with École Polytechnique and the University of Geneva. He received his Ph.D. from the École Normale Supérieure in 1988. His early research concerned the statistical mechanics of disordered systems, but his main focus has been on the physics of quantum materials with strong electron-electron interactions. These materials possess remarkable electronic properties and functionalities. Georges is one of the inventors of dynamical mean field theory, for which he shared the 2006 Europhysics Prize. This theory has deeply transformed our understanding of these materials and our ability to explain, calculate and predict their physical properties. In recent years, Georges has made contributions linking condensed matter physics and quantum optics and has also contributed to the field of ultra-cold atomic gases. Georges received the 2007 Silver Medal from the National Center for Scientific Research (CNRS) and was awarded a Synergy grant from the European Research Council.
Precise control over quantum systems is the foundation of quantum technology that will shape our society in revolutionary ways---from computation and simulation to sensing and communication. Alongside technological advances, better and better quantum control will enable new tests of fundamental physics. I will discuss our efforts on both fundamental physics and technological aspects.
First, I will focus on our work with cold atoms and ions in a hybrid atom--ion setup. An integrated time-of-flight mass spectrometer allows for the analysis of ion ensembles with isotopic resolution. Recent results will be highlighted such as the demonstration of non-equilibrium physics between atoms and ions as well as the discovery of a new class of molecules. Ultimately, this work aims at a quantum computation platform utilizing cold molecular ions.
Second, I will report on our search for the nuclear isomeric transition in thorium-229. This transition around 160nm eludes nuclear physics techniques but becomes accessible to lasers and is a prime candidate for future optical clocks and fundamental physics tests. In a first direct search using thorium-doped crystals and tunable VUV synchrotron light, we were able to exclude a large region of transition frequencies vs. lifetimes. Our ongoing efforts with a home-built VUV laser system will yield significantly improved sensitivity.
Lastly, future directions will be outlined using novel quantum systems with far-reaching impact on metrology, quantum sensing, quantum computation, quantum chemistry, and fundamental physics tests.
The study of black holes has revealed a deep connection between quantum information and spacetime geometry. Its origin must lie in a quantum theory of gravity, so it offers a valuable hint in our search for a unified theory. Precise formulations of this relation recently led to new insights in Quantum Field Theory, some of which have been rigorously proven. An important example is our discovery of the first universal lower bound on the local energy density. The energy near a point can be negative, but it is bounded below by a quantity related to the information flowing past the point.
I will discuss recent developments regarding new types of hadrons involving heavy quarks: hadronic molecules, doubly heavy baryons, stable tetraquarks and others. I will also explain how the discovery of the doubly heavy baryon leads to quark-level analogue of nuclear fusion, with energy release per reaction an order of magnitude greater than in ordinary fusion.
About the speaker
Marek Karliner was born in Poland in 1955 and arrived in Israel in 1969. He received his B.Sc. in physics in 1979 and his Ph.D. in 1984 (with Prof. David Horn), both from Tel Aviv University. As a graduate student he spent one year at Stanford University as Fulbright Fellow. Between 1984 and 1988 he was a Chaim Weizmann Postdoctoral Fellow and then a Research Associate at the Stanford Linear Accelerator Center. In 1988 the Higher Education Council of Israel awarded him the Alon Fellowship for Outstanding Junior Faculty and subsequently he joined TAU School of Physics and Astronomy as a senior lecturer. At TAU he has been a Professor of Physics since 1995 and also served as Chairman of Particle Physics Department in 2006-2010 and Chairman of the Raymond and Beverly Sackler Institute of Theoretical Physics in 2010-2015. Karliner's research is in the field of theoretical physics of elementary particles. He is incumbent on the Edouard and Francoise Jaupart Chair of Theoretical Physics of Particles and Fields. In 2003-2005 he was a Visiting Professor at the Cavendish Laboratory, University of Cambridge. Since 2017 he has been a Foreign Member of the Polish Academy of Arts and Sciences.
Freely falling particles are ideal test masses to study gravitational interactions. We use light pulse interferometry to study the propagation of ultra-cold atoms in free fall. So far quantum experiments have been carried out in locally flat space and can be summarized as testing the equivalence principle. Precision tests of the equivalence principle do not only test the geometrical nature of gravity but also serve as extraordinarily sensitive probes for new, ultra-weak interactions. Our current efforts focus on a test of the weak equivalence principle at the 10-13 level with two rubidium isotopes. We suppress gravity gradient systematic errors to below one part in 1013 and demonstrate a relative precision of Δg/g≈3×10−11 per shot, which improves the state of the art the best previous result for a dual-species atom interferometer by more than three orders of magnitude .
With the help of the large momentum transfer techniques  we can now create macroscopic quantum states on the order of tens of cm. The large spatial extent allows us to go beyond the equivalence principle and observe genuine gravity effects in a quantum system .
 Effective inertial frame in an atom interferometric test of the equivalence principle
C. Overstreet, P. Asenbaum, T. Kovachy, R. Notermans, J. M. Hogan, M. A. Kasevich
 Quantum superposition at the half-meter scale
T. Kovachy, P. Asenbaum, C. Overstreet, C. A. Donnelly, S. Dickerson, A. Sugarbaker, J. Hogan, M. Kasevich
Nature 528, 530–533 (2015)
 Phase shift in atom interferometry due to spacetime curvature across its wave function
P. Asenbaum, C. Overstreet, T. Kovachy, D.D. Brown, J. M. Hogan, and M. A. Kasevich
In recent decades, a large scientific effort has focused on harnessing spin transport for providing insights into novel materials and low-dissipation information processing. We introduce single spin magnetometry based on nitrogen-vacancy (NV) centers in diamond as a new and generic platform to locally probe spin chemical potentials which essentially determine the flow of spin currents. We use this platform to investigate magnons in a magnetic insulator yttrium iron garnet (YIG) on a 100 nanometer length scale. We demonstrate that the local magnon chemical potential can be systematically controlled through both ferromagnetic resonance and electrical spin excitation, which agrees well with the theoretical analysis of the underlying multi-magnon processes. Our results open up new possibilities for nanoscale imaging and manipulation of spin-related phenomena in condensed-matter systems.
Guy Sella is an associate professor in the Columbia University Department of Biological Sciences and a member of the Center for Computational Biology and Bioinformatics. His lab studies the evolutionary processes that give rise to genetic and phenotypic differences between individuals, populations, and closely related species. They use mathematical models to better understand these processes, and statistical analyses to identify their footprints in data and make inferences about them. Current work in the lab focuses primarily on the evolutionary causes of adaptation and disease, but also on a variety of other topics. Before joining Columbia, Sella was a faculty member at Hebrew University (Israel) and a visiting professor at Stanford University.
Electron Transfer (ET) is the stuff of life. The 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.
About the speaker
Moh El-Naggar is the Robert D. Beyer Early Career Chair in Natural Sciences, and Associate Professor of Physics, Biological Sciences, and Chemistry at the University of Southern California. As a biophysicist, El-Naggar investigates energy conversion and charge transmission at the interface between living cells and synthetic surfaces. His work, which has important implications for cell physiology and astrobiology, may lead to the development of new hybrid materials and renewable energy technologies that combine the exquisite biochemical control of nature with the synthetic building blocks of nanotechnology. El-Naggar was awarded the Presidential Early Career Award for Scientists and Engineers (PECASE) by President Obama in 2014. In 2010, El-Naggar received a Department of Defense Young Investigator Program (YIP) Award, from the Air Force Office of Scientific Research. In 2012, he was named one of Popular Science's ‘Brilliant 10’, the magazine's annual honor roll of the 10 most promising young scientists whose innovations will change the world. More information about El-Naggar's research can be found at http://nanobio.usc.edu