Events List for the Academic Year

Event Time: Wednesday, March 6, 2019 | 11:00 am - 12:30 pm
Event Location:
Hennings 318
Add to Calendar 2019-03-06T11:00:00 2019-03-06T12:30:00 Signal Percolation In a Population of Bacteria Event Information: Bacterial biofilms are communities in which bacteria live in a self-produced matrix and engage in remarkable emergent behaviors. A fascinating mechanism for long-distance coordination among biofilm cells is the propagation of electrical signals within the community. These signals have a population-level benefit: they halt growth of exterior cells and provide greater nutrient access to the stressed interior. We find that signaling is heterogeneous at the single-cell level. Some cells propagate the signal (“firing cells”) and others do not. In order to understand how this signal reliably propagates over hundreds-of-cells distance despite this heterogeneity, we developed a model combining percolation theory with excitable dynamics. Our model predicts that signal transmission becomes possible when firing cells are organized near a critical phase transition between a disconnected and a fully connected conduit of signaling cells, called percolation. We confirm that the spatial distribution of firing cells is organized near the predicted phase transition by measuring signaling at the single-cell level within wild-type and mutant biofilms. Our findings suggest that near this critical point, the population-level benefit of signal transmission outweighs the single-cell-level cost. The bacterial community thus appears to be organized according to a theoretically predicted spatial heterogeneity that promotes efficient signal transmission. Event Location: Hennings 318
Event Time: Tuesday, March 5, 2019 | 2:00 pm - 2:00 pm
Event Location:
TRIUMF Auditorium
Add to Calendar 2019-03-05T14:00:00 2019-03-05T14:00:00 Superheavy element studies at LBNL Event Information: The search for new elements has netted us six additions to the periodic table this decade, bringing the total to 118 known elements. These elements must be formed one-atom-at-a-time in complete-fusion evaporation reaction. Once formed, the atoms typically exist for just seconds or less before they decay into other elements. While we have made great progress in making and studying these elements, there is much that is still unknown - including things as basic as the proton and neutron numbers of the recently discovered elements. Recently, the Berkeley Gas-filled Separator (BGS) at the Lawrence Berkeley National Laboratory (LBNL) was coupled to a new mass analyzer, FIONA. The goal of BGS+FIONA is to provide a M/DeltaM separation of ~300 and transport nuclear reaction products to a shielded detector station on the tens of milliseconds timescale. These upgrades will allow for direct A and Z identification of ii) new actinide and transactinide isotopes with ambiguous decay signatures such as electron capture or spontaneous fission decay and i) superheavy nuclei such as those produced in the 48Ca+ actinide reactions. Here we will present recent results from the FIONA commissioning and first scientific experiments. Event Location: TRIUMF Auditorium
Event Time: Monday, March 4, 2019 | 3:00 pm - 4:00 pm
Event Location:
Hennings 318
Add to Calendar 2019-03-04T15:00:00 2019-03-04T16:00:00 A Planetary Perspective of Life Event Information: Where did we come from? Are we alone? Incredibly, the answers to these questions could soon be within the reach of scientific pursuits for the first time in human history. Depending on what's out there—and on our will to find it—we might be standing on the precipice of a golden age of astrobiology. But to truly appreciate our place in the Universe, we must integrate fields that have historically stood apart—physics and biology, geology and astronomy—into a planetary perspective of life. In this talk, we'll introduce the alkaline hydrothermal vent hypothesis for the emergence of life, a hypothesis in which life emerges from specific planetary disequilibria. Once we've formed life, we'll briefly examine how it has co-evolved with Earth, transforming our atmosphere over the eons, finally producing the present oxygen-rich beacon screaming, "I'm alive!" But the detection of exobiospheres requires that we understand atmospheric oxygen in a planetary context and the potential for oxygen false positives. Time permitting, we'll then hypothesize about other forms life on exotic worlds and discuss how a planetary perspective invites us to broaden our search for life. Event Location: Hennings 318
Event Time: Monday, March 4, 2019 | 1:30 pm - 2:30 pm
Event Location:
Hennings 318
Add to Calendar 2019-03-04T13:30:00 2019-03-04T14:30:00 Computer Spectroscopy on Classical and Quantum Computers Event Information: Ideally, the cataloging of spectroscopic linelists would not demand laborious and expensive experiments. If it were possible to obtain the exact same information by running a calculation on a computer, then when this information is needed for a new molecule, new isotopologue, new charge, new electronic state, or for new vibrational levels, we would not have to set up a new experiment; we could instead change some lines in our computer program's input file.    QED (quantum electrodynamics) offers a description of electromagnetic interactions, QFD (quantum flavordynamics) also succeeds in describing weak-nuclear interactions, and QCD (quantum chromodynamics) succeeds in describing strong-nuclear interactions. Therefore a numerically converged QCD calculation (assuming available computing power) provides the fine, hyperfine, and finer than hyperfine splittings in atomic, molecular, and condensed matter spectra with only two physical approximations: neglect of gravity and neglect of "fifth" forces (a term used to describe any other missing piece which might make our calculation disagree with experiment).    We have millions of high-precision experimental spectral lines to which we can compare our QCD-level calculations. In the cases where the calculations are converged to sub-cm-1 precision, they agree with experiments every time. We are therefore be confident that a spectral database numerically generated by a computer, can fill in gaps in the NIST database, despite our ignorance of how to deal with gravity and "fifth" forces.   I will present results on the small systems where QCD-level calculations have been compared to experiments. The majority of the energy comes from the non-relativistic Schroedinger equation. A Monte Carlo implementation of FCI called FCIQMC allows for a numerically exact treatment of many electrons, and all other QED, QFD, and QCD interactions are treated with perturbation theory using the FCIQMC wavefunction. I will present FCIQMC results on up to 54 electrons, and perturbation theory corrections up to 7th order in the QED expansion for smaller active spaces.    Going beyond 54 electrons is extremely difficult on a classical computer, where simulation of quantum mechanics is un-natural and scales exponentially with the number of electrons. It would be more natural if our computer treated the quantum effects at the hardware level. A quantum computer can do the calculations with cost scaling only polynomially with respect to the number of electrons, and I will present preliminary results for small calculations that are run on D-Wave's 2048 qubit annealer and IBM's 5-qubit machine (Yorktown), their 14-qubit machine (Melbourne), and their 20-qubit machine (Austin). Event Location: Hennings 318
Event Time: Monday, March 4, 2019 | 11:00 am - 12:30 pm
Event Location:
Hennings 318
Add to Calendar 2019-03-04T11:00:00 2019-03-04T12:30:00 Gravitational wave astrophysics: a new era of discovery Event Location: Hennings 318
Event Time: Thursday, February 28, 2019 | 4:00 pm - 5:00 pm
Event Location:
Hennings 201
Add to Calendar 2019-02-28T16:00:00 2019-02-28T17:00:00 Quantum Localization in Laser-Driven Molecular Rotation Event Information: The periodically-kicked rotor is a paradigmatic system in nonlinear dynamics studies. The classical kicked rotor exhibits a truly chaotic motion with an unlimited diffusive growth of the angular momentum. In the quantum regime, the chaotic dynamics is either suppressed by a mechanism similar to Anderson localization in disordered solids, or rotational excitation is enhanced due to the so-called quantum resonance.  Although these fundamental quantum phenomena have been theoretically studied for several decades already, until recent times there has not been a single experiment demonstrating Anderson localization in a real rotating quantum system. Quantum chaotic dynamics was primarily studied by using ultra-cold atoms in pulsed optical lattices. Recently we revisited the problem of the periodically-kicked quantum rotor, and predicted that several well-known quantum localization phenomena in solid-state systems – Anderson localization, Bloch oscillations, and Tamm-Shockley surface states – may manifest themselves in the rotational dynamics of the laser-kicked molecules.  We showed that current femtosecond technology used for laser alignment of molecules offers tools for exploring these effects, and we defined conditions for their experimental observation.  In this talk, I will give an overview of the physical mechanisms behind these new molecular rotational phenomena, and will present the results of recent femtosecond experiments in which the rotational Bloch oscillations and the dynamical Anderson localizationwere observed along the lines of our proposal.  These results introduce molecular gases at ambient conditions as a new platform for studying localization phenomena in quantum transport. The observed rotational effects are important for many applications, ranging from selective excitation in the mixtures of molecular species (i.e. molecular isotopes or nuclear spin isomers) to controlling propagation of powerful laser pulses in the atmosphere. Event Location: Hennings 201
Event Time: Thursday, February 28, 2019 | 2:00 pm - 3:30 pm
Event Location:
BRIM 311
Add to Calendar 2019-02-28T14:00:00 2019-02-28T15:30:00 CM Seminar: Structure and Dynamics with Ultrafast Electron Microscopes … or how to image fundamental processes in materials Event Information: In this talk I will describe how combining ultrafast lasers and electron microscopes in novel ways makes it possible to directly ‘watch’ the time-evolving structure of condensed matter on the fastest timescales open to atomic motion.  By combining such measurements with complementary (and more conventional) spectroscopic probes one can develop structure-property relationships for materials under even very far from equilibrium conditions.   I will give several examples of the remarkable new kinds of information that can be gleaned from such studies and describe how these opportunities emerge from the unique capabilities of current generation ultrafast electron scattering and microscopy instruments.  For example, in diffraction mode it is possible to identify and separate lattice structural changes from valence charge density redistribution in materials on the ultrafast timescale and to identify novel photoinduced phases of complex and strongly correlated materials that have no equilibrium analogs [1,2].  Making use of diffuse scattering signals, it is also possible to directly probe the strength of the coupling between electrons and phonons in materials across the entire Brillouin zone and to probe nonequilibrium phonon dynamics (or relaxation) in exquisite detail [3].  In imaging mode, real space pictures of nano- to microstructural evolution in materials at unprecedented spatio-temporal resolution can be obtained.    I will assume no familiarity with ultrafast lasers or electron microscopes.   [1] Morrison et al Science 346 (2014) 445 – 448  [2] Otto et al, PNAS, 116 (2019) 450-455 [3] Stern et al, Phys. Rev. B 97 (2018) 165416     Event Location: BRIM 311
Event Time: Thursday, February 28, 2019 | 2:00 pm - 3:00 pm
Event Location:
TRIUMF Auditorium
Add to Calendar 2019-02-28T14:00:00 2019-02-28T15:00:00 Ab Initio Approaches to Correlations in Nuclei and their Applications Event Information: Correlations - intended as multiple-nucleon mechanisms that cannot be modelled by a pure mean-field potential - are the backbone of our deeper understanding of atomic nuclei. They are manifest in the fragmentation of the spectral strength which is encountered in one-nucleon addition and removal measurements. In recent years, we have advanced high-performance computational many-body techniques, such as propagator theory, that can be used to compute the spectral function but that also allow meaningful predictions of radii and binding energies up to masses of A~100. This talk will review such progress and aim at giving a broader perspective of ab initio theory, in which large scale computations are not only used to benchmark the theories of nuclear forces but they can also help to constrain our insight about nuclear phenomena. I will further discuss some cases in which the knowledge of the spectral function is important to predict, e.g., the interplay between structure and reactions and the response to neutrinos under the wide range of energies relevant to oscillation experiments. Event Location: TRIUMF Auditorium
Event Time: Thursday, February 28, 2019 | 12:45 pm - 1:45 pm
Event Location:
Hennings 318
Add to Calendar 2019-02-28T12:45:00 2019-02-28T13:45:00 Two-Stage Collaborative Group Exams - A Physics and Astronomy Education Group brown-bag teaching event Event Information: This talk is part of the Physics and Astronomy Education Group's brown-bag teaching series. Please feel free to bring your lunch. Coffee and cookies will be provided. Two-Stage Collaborative Group Exams are an easy to implement technique that leverages students’ desire to discuss challenging exam questions with each other immediately after an exam. This instructional technique adds an additional group stage immediately after a traditional solo exam. The format for this event is that we will make a brief informal presentation and then facilitate a discussion around the technique, hoping to leverage the expertise in the room in order to share implementation advice. The presentation will cover how to implement this technique, what the literature says about its effectiveness and also offer some best practices advice developed as part of an ongoing TLEF-funded project. Event Location: Hennings 318
Event Time: Tuesday, February 26, 2019 | 2:00 pm - 3:30 pm
Event Location:
HENN 318
Add to Calendar 2019-02-26T14:00:00 2019-02-26T15:30:00 CM Seminar: Theory of heat transport in the fractional quantum Hall effect Event Information: Abstract: The thermal Hall conductance is a universal and topological property which characterizes the fractional quantum Hall (FQH) state. Quantized values of the thermal Hall conductance has only recently been measured experimentally in integer quantum Hall (IQH) and FQH regimes, These finding include observation of half integer  quantized heat conductance at filling 5/2. In this talk I will briefly describe the experimental observations, a phenomenological theory of the heat transport on the edge that take into consideration the effect of heat transfer among the edge modes themselves  and between the edge modes and the bulk, and a theory of Disorder-Induced Half-Integer Thermal Hall Conductance.   Relevant papers: 1. Nature 545, 75 (2017)   Observed Quantization of Anyonic Heat Flow Authors: Mitali Banerjee, Moty Heiblum, Amir Rosenblatt, YO, Dima E. Feldman, Ady Stern, Vladimir Umansky 2. Nature 559, 205 (2018)    Observation of half-integer thermal Hall conductance Authors: Mitali Banerjee, Moty Heiblum, Vladimir Umansky, Dima E. Feldman, YO, Ady Stern 3. Phys. Rev. Lett. 121, 026801 (2018)  Theory of Disorder-Induced Half-Integer Thermal Hall Conductance  Authors: David F. Mross, YO, Ady Stern, Gilad Margalit, Moty Heiblum  4. Phys. Rev. B 99, 041302 (2019)   Phenomenological theory of heat transport in the fractional quantum Hall effect Authors: Amit Aharon, YO, Ady Stern     Event Location: HENN 318
Event Time: Monday, February 25, 2019 | 3:00 pm - 4:00 pm
Event Location:
Hennings 318
Add to Calendar 2019-02-25T15:00:00 2019-02-25T16:00:00 Studying Star Formation from the Stratosphere Event Information: Understanding how stars form out of diffuse interstellar gas is a problem that underlies much of modern astrophysics, from the formation of planets to the chemical evolution of our universe.  A key outstanding question is whether magnetic fields contribute to the observed low efficiency of the star-formation process.  In this talk, I will discuss what we have learned about the role played by magnetic fields in star formation, with a particular focus on results from the BLASTPol balloon-borne sub-mm polarimeter. BLASTPol operates 38.5 km above the Earth's surface (above 99.5% of the atmosphere), where it can produce large detailed maps of magnetic fields in nearby star-forming molecular gas clouds. By statistically comparing BLASTPol inferred magnetic-field maps of a massive molecular cloud with simulations, we find that magnetic fields play an important role in the formation of both low- and high-density cloud structures.  I will also discuss BLAST-TNG, a next-generation balloon-borne polarimeter that is scheduled for a first flight from Antarctica in December 2019. With BLAST-TNG we will apply these same analysis techniques to a larger sample of clouds with 5 times better resolution, and quantitatively determine the extent to which magnetic fields affect star-formation efficiency.  Event Location: Hennings 318
Event Time: Monday, February 25, 2019 | 11:00 am - 12:30 pm
Event Location:
Henn 318
Add to Calendar 2019-02-25T11:00:00 2019-02-25T12:30:00 Searching for light dark matter with single-phonon detectors Event Information: Searches for high energy signatures from beyond the standard model physics have advanced greatly, but a lot of ground remains to be covered for soft, low energy signals. In the context of dark matter direct detection, future single-phonon detectors will be sensitive to dark matter with a mass as low as roughly 10 keV. In this regime, the conventional nuclear recoil picture no longer applies and new theoretical tools are needed to correctly calculate the scattering rate. I will discuss the prospects for detector concepts based on superfluid helium and polar material targets, where in the latter case we find a large daily modulation of the scattering rate. Event Location: Henn 318
Event Time: Thursday, February 21, 2019 | 2:00 pm - 2:00 pm
Event Location:
TRIUMF Auditorium
Add to Calendar 2019-02-21T14:00:00 2019-02-21T14:00:00 Physics with bubble chambers Event Information: Bubble chambers have a long history of use in particle physics, starting with being used for particle discovery in the 1950s and moving through to their use in dark matter search experiments today. The many different target fluids which have been used have provided great flexibility in the use of this technology. In this talk I will start with a very brief history of these detectors and quickly move on to their use in the PICO experiment. After discussion of the stages and plans for that collaboration, a possibility of future improvements to the bubble chamber will be presented. Remote link: https://mediasite.audiovisual.ubc.ca/Mediasite/Play/3203f194c1f64086abd66af97756f23a1d Event Location: TRIUMF Auditorium
Event Time: Thursday, February 14, 2019 | 4:00 pm - 5:00 pm
Event Location:
Hennings 201
Add to Calendar 2019-02-14T16:00:00 2019-02-14T17:00:00 3-minute thesis talks Event Information: Please come and support our students as they give 3-minute presentations of their thesis projects, as part of the international "3MT" competition! Event Location: Hennings 201
Event Time: Thursday, February 14, 2019 | 2:00 pm - 3:30 pm
Event Location:
BRIM 311
Add to Calendar 2019-02-14T14:00:00 2019-02-14T15:30:00 CM Seminar: Signatures of dispersing Majorana modes in a proximitized topological material Event Information: Majorana fermions can be realized as quasiparticle excitations in a topological superconductor, whose non-Abelian statistics provide a route to developing robust qubits. In this context, there has been a recent surge of interest in the iron-based superconductor, FeSe0.5Te0.5. Theoretical calculations have shown that FeSe0.5Te0.5 may have an inverted band structure which may lead to topological surface states, which can in turn host Majorana modes under certain conditions in the superconducting phase. Furthermore, recent STM studies have demonstrated the existence of zero-bias bound states inside vortex cores which have been interpreted as signatures of Majorana modes. While most recent studies have focused on Majorana bound states, more generally, akin to elementary particles, Majorana fermions can propagate and display linear dispersion. These excitations have not yet been directly observed, and can also be used for quantum information processing. This talk is focused on our recent work in realizing dispersing Majorana modes. I will describe the conditions under which such states can be realized in condensed matter systems and what their signatures are. Finally, I will describe our scanning tunneling experiments of domain walls in the superconductor FeSe0.45Te0.55, which might potentially be first realization of dispersing Majorana states in 1D.   Event Location: BRIM 311
Event Time: Thursday, February 14, 2019 | 2:00 pm - 3:00 pm
Event Location:
TRIUMF Auditorium
Add to Calendar 2019-02-14T14:00:00 2019-02-14T15:00:00 Gamma-ray spectroscopy with GRETINA at NSCL Event Information: The gamma-ray tracking array GRETINA has completed a variety of experiments at the National Superconducting Cyclotron Laboratory at Michigan State University. An overview will be presented, showing selected results covering broad topics from nuclear structure physics to nuclear astrophysics. Event Location: TRIUMF Auditorium
Event Time: Monday, February 11, 2019 | 3:00 pm - 4:00 pm
Event Location:
Hennings 318
Add to Calendar 2019-02-11T15:00:00 2019-02-11T16:00:00 Why you should care about white dwarf stars Event Information: More than 95% of the stars in the Universe will eventually end up as white dwarf stars. Although they are currently more numerous than all the stars with 1 solar mass and above combined, they receive a relatively small share of the astronomical community attention (unless they happen to explode as a type Ia supernova). Yet, these fascinating objects have a lot to teach us about stellar evolution, planets, fundamental physics and much more. In this presentation, I will review some of most interesting topics that my group and I have recently investigated and try to convince you that they are more than just boring little dim objects. Event Location: Hennings 318
Event Time: Thursday, February 7, 2019 | 4:00 pm - 5:00 pm
Event Location:
Hennings 201
Add to Calendar 2019-02-07T16:00:00 2019-02-07T17:00:00 A Physicist's Guide to Software Engineering Jobs Event Information: I was a physics/math major at UBC and spent 7 years doing cosmology research before joining Google in 2015 to work as a software engineer. I'll try to summarize the career wisdom I picked up along the way, give advice on how to get a job as a software engineer, and paint a picture of daily life working for a large internet company with a goofy name. I'll also give an overview of the sorts of problems software engineers get to tackle, and how they compare to the problems you get to work on in P&A. Event Location: Hennings 201
Event Time: Thursday, February 7, 2019 | 2:00 pm - 3:00 pm
Event Location:
TRIUMF Auditorium
Add to Calendar 2019-02-07T14:00:00 2019-02-07T15:00:00 What is the Dark Matter? Event Information: Four fifths of the matter in the universe consist of something completely different from the "ordinary matter" we know and love. I will explain why this "dark matter" is an unavoidable ingredient to understand the universe as we observe it, and I will describe what the fundamental, particle nature of the dark matter could possibly be. I will then give an overview of strategies to search for dark matter as a particle, describe a few examples of possible hints of discovery, and outline ways forward in this exciting hunt. Event Location: TRIUMF Auditorium
Event Time: Thursday, February 7, 2019 | 2:00 pm - 3:00 pm
Event Location:
BRIM 311
Add to Calendar 2019-02-07T14:00:00 2019-02-07T15:00:00 CM Seminar: Many body entanglement, strange metals and black holes Event Information: It may well be that mankind has understood only the tip of the iceberg when it comes to the nature of matter. Densely many body entangled compressible states of matter may exist exhibiting entirely different physical behaviors compared to the "classical" short ranged entangled product state stuffs from the high energy- and condensed matter textbooks. Although not computable directly - a quantum computer is required - a remarkable confluence occurred in theoretical physics involving empirical notions from condensed matter physics merging with the holographic duality of string theory, and notions of quantum information.  This theoretical development suggests universal principles of a new kind to be at work. As a common denominator, these suggest paradoxically that observable properties may be unreasonably simple. I will highlight some very recent experimental developments both in the Netherlands and Stanford aimed at finding out whether such principles are actually the secret behind the long standing mysteries revealed by condensed matter experimentation in  especially  the cuprate superconductors.   Event Location: BRIM 311