# This Week at Physics

## Events at Physics |
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### Events During the Week of October 14th through October 21st, 2018

### Monday, October 15th, 2018

**Plasma Physics (Physics/ECE/NE 922) Seminar****Relativistic Hybrid Simulations of Cosmic Ray Generation and Transport****Time:**12:05 pm**Place:**2241 Chamberlin Hall**Speaker:**Dr. Colby Haggerty, University of Chicago**Abstract:**The generation and transport of Cosmic Rays (CR) is an inherently multiscale phenomenon. Linking the dynamics of a cold thermal background plasma with low density, relativistic CRs through the shared magnetic field requires modeling the physics of both populations. To better study these problems, we have developed a kinetic ion, fluid electron hybrid code to include relativistic ion dynamics (dHybridR). With dHybridR, we perform the first simulations of non relativistic collisionless shock, self-consistently accelerating relativistic ions. We document the effects of the transition of accelerated particles to relativistic velocities and we show that the shock develops a CR induced precursor which modifies the macroscopic shock quantities (i.e. compression ratio and shock speed). In addition to CR generation, we present simulations of CR transport and the as sociated streaming instabilities. We show that for weak CR currents, simulations initially agree with linear theory and that the thermal population is indirectly heated through landau damping.### Tuesday, October 16th, 2018

**Atomic Physics Seminar****Exploring quantum many-body dynamics and quantum information processing with reconfigurable arrays of atoms****Time:**10:00 am**Place:**5310 Chamberlin Hall**Speaker:**Prof. Hannes Bernien, University of Chicago**Abstract:**Controllable, coherent quantum many-body systems can provide insights into fundamental properties of quantum matter, enable the realization of exotic quantum phases, and ultimately offer a platform for quantum information processing that could surpass any classical approach. Recently, reconfigurable arrays of neutral atoms with programmable Rydberg interactions have become promising systems to study such quantum many-body phenomena, due to their isolation from the environment, and high degree of control. Using this approach, we demonstrate high fidelity manipulation of individual atoms and entangled atomic states. Furthermore, we realize a programmable Ising-type quantum spin model with tunable interactions and system sizes up to 51 qubits. Within this model, we observe transitions into ordered states that break various discrete symmetries. Varying the rate at which the quantum phase transition is crossed allows us to observe the power-law scaling of the correlation length, as predicted by the Kibble-Zurek mechanism. The scaling exponent observed is consistent with theoretical predictions for the Ising universality class when sweeping into a Z2-ordered phase, and with the 3-state Chiral Clock Model for transitions into the Z3-ordered phase. An alternative, hybrid approach for engineering interactions is the coupling of atoms to nanophotonic structures in which guided photons mediate interactions between atoms. I will discuss our progress towards entangling two atoms that are coupled to a photonic crystal cavity and outline the exciting prospects of scaling these systems to many qubits and to quantum networks over large distances.**Host:**Saffman**Chaos & Complex Systems Seminar****Renewable energy: A viable path forward****Time:**12:05 pm**Place:**4274 Chamberlin (Refreshments will be served)**Speaker:**Michael Winokur, UW Department of Physics**Abstract:**The rate of growth in renewable energy production has generally exceeded even the most optimistic projections. This dramatic scenario has been driven by a steady stream of technological advancements in combination with a breathtaking reduction in actual the cost of the energy production. Many traditional sources of energy are becoming economically uncompetitive. This introductory level talk will give a broad overview of the potential sources of renewable energy with an emphasis on the recent history of solar and wind energy production and likely near-term developments which will further improve device performance. Time permitting some of the issues associated with energy storage will be discussed.**Host:**Clint Sprott### Wednesday, October 17th, 2018

**No events scheduled**### Thursday, October 18th, 2018

**R. G. Herb Condensed Matter Seminar****Non-equilibrium Quasiparticles in Superconducting Quantum Circuits****Time:**10:00 am**Place:**5310 Chamberlin Hall**Speaker:**Prof. Eli Levenson-Falk, University of Southern California**Abstract:**Superconducting electrical circuits are an exciting quantum information technology platform. However, quasiparticles--electron-like single-particle excitations of the superconducting condensate--can cause loss and noise, limiting the performance of these devices. The generation mechanisms, behavior, and annihilation channels of these quasiparticles are still poorly understood, hindering efforts to eliminate them from circuits. I will review the evidence for different quasiparticle models, show measurements using Andreev bound states as quasiparticle traps, and discuss future experiments that will determine the best ways to mitigate the harmful effects of quasiparticles.**Host:**McDermott**Cosmology Journal Club****Time:**12:00 pm**Place:**5242 Chamberlin Hall**Abstract:**Please visit the following link for more details:

http://cmb.physics.wisc.edu/journal/index.html

Feel free to bring your lunch!

If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Ross Cawthon (cawthon@wisc.edu) and Santanu Das (sdas33@wisc.edu).**Astronomy Colloquium****"Pulsating White Dwarfs and Orbital Decay in Binaries"****Time:**3:30 pm**Place:**4421 Sterling Hall, Coffee and cookies 3:30 PM. Talk Begins at 3:45 PM**Speaker:**Meng Sun, UW Astronomy Department**Abstract:**Motivated by the discovery of a handful of pulsating, extremely low-mass white dwarfs in compact binaries, a formation model was developed for these systems. Evolutionary models are constructed using the MESA code. Magnetic braking torques are used to shrink the orbit and remove the envelope before the helium core can significantly grow in size. The resulting models for the stellar structure are used to understand the properties of g and p-mode oscillations.

WASP-12b is a hot Jupiter with an orbital period of only 1.1 days, making it one of the shortest-period giant planets known. Recent transit timing observations measure the orbital period to decrease on a 3.2 Myr timescale. These observations imply that a Gyr-old planet is now about to be destroyed by its star over the next few Myr. One mechanism to produce orbital decay is through tidal friction. Calculations are presented for the dynamical tide excitation of internal gravity waves by the tidal force. I show that sufficient tidal friction to explain the observations may be possible if the star is near the end of its main sequence lifetime.

Indirect evidence of orbital decay in binaries comes from the lack of binaries with close orbital separations, as they have already suffered orbital decay and merged. A broad parameter study of orbital decay due to tides is presented for a range of primary and secondary stars as well as orbital separation. The focus is on the red giant branch phase of the primary star. Both the dynamical tide, damped by nonlinear wave breaking or radiative diffusion, and the equilibrium tide, damped by the turbulent viscosity in the convective envelope, are included in the calculations of tidal friction. The calculations of orbital decay are compared to the sample of close APOGEE binaries with red giant branch primaries and substellar companions, as well as the sample of exoplanet host stars.

### Friday, October 19th, 2018

**Theory Seminar (High Energy/Cosmology)****Consistency relations in multi-field inflation****Time:**2:00 pm**Place:**5310 Chamberlin Hall**Speaker:**Jinn-Ouk Gong, KASI**Abstract:**The consequences of spatial coordinate transformation in multi-field inflation are studied. Among the spontaneously broken de Sitter isometries, only dilatation in the comoving gauge preserves the form of the metric and thus results in quantum-protected Slavnov-Taylor identities. The corresponding consistency relations between correlation functions of cosmological perturbations are derived in two different ways, by the connected and one-particle-irreducible Green's functions. The lowest-order consistency relations are explicitly given, and even in multi-field inflation the consistency relations in the soft limit are independent of the detail of the matter sector.**Physics Department Colloquium****The Physics of Divergence: Resurgence and Non-Perturbative Physics****Time:**3:30 pm**Place:**2241 Chamberlin Hall**Speaker:**Gerald Dunne, University of Connecticut**Abstract:**Solvable interesting problems in physics are very rare. Almost all nontrivial problems require approximations, the most common of which is perturbation theory. We are all familiar with the basic idea of perturbation theory, but it holds some surprising secrets, which can be understood physically. These secrets also introduce some novel concepts from a new mathematical formalism called "resurgent asymptotics". The talk is largely non-technical, concentrating on the key physical ideas and examples, illustrated with applications in quantum mechanics and quantum field theory.**Host:**Alex Levchenko