Bulletin of the American Physical Society
2019 Annual Meeting of the APS Far West Section
Volume 64, Number 17
Friday–Saturday, November 1–2, 2019; Stanford, California
Session E01: AMO, Plasma Physics and Education |
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Chair: Alla Safronova, University of Nevada Reno Room: Science Teaching and Learning Center STLC 105 |
Saturday, November 2, 2019 8:30AM - 8:42AM |
E01.00001: Distinguishing State-of-the-Art Atomic Structure Calculations with a Measurement of the $3p_{1/2} \rightarrow 2s_{1/2}$ X-Ray Transition in Neonlike Germanium Wyatt Joyce, Peter Beiersdorfer We measured the $(2s_{1/2}2p^63p_{1/2})_{J=1} \to (2s^22p^6)_{J=0}$ line of neonlike germanium, which has been measured in multiple experiments with widely disparate results. Our measurement was performed at an electron beam ion trap using a very high resolution flat-crystal spectrometer. Our experimental setup attained the highest spectral resolving power ($E/\Delta E \approx 5800$) of any such measurement. This resulted in a relative measurement accuracy of $1\times10^{-5}$. Our new value not only enables us to distinguish among the past measurements, but our value also serves as a benchmark for evaluating two implementations of the many-body perturbation theory (MBPT) used for performing highly accurate theoretical calculations. Earlier work that focused on $n=2 \rightarrow n=2$ transitions of neonlike germanium found that the two implementations of MBPT gave divergent results. However, our measurement of the $n=3 \rightarrow n=2$ transition is reproduced by both calculations within $10^{-4}$, and one calculation even matches the spectroscopic accuracy of $10^{-5}$. [Preview Abstract] |
Saturday, November 2, 2019 8:42AM - 8:54AM |
E01.00002: The Superfluid Pairing Gap of a Unitary Fermi Gas Annette Lopez, Patrick Kelly, Ettore Vitali We address the problem of computing the superfluid pairing gap of a fermionic cold gas from first principles. Cold atomic Fermi systems are unique laboratories to explore many-body systems, due to the unprecedented experimental control that can be currently achieved. These systems find applications in condensed matter physics, nuclear physics, and nuclear astrophysics; the ability to provide robust theoretical predictions for cold atoms can have a significant impact in several fields in physics. In particular, cold gases can shed light into some of the most mysterious objects in the universe, like neutron stars. In this work we use unbiased Quantum Monte Carlo techniques interfaced with state of art analytic continuation technique to compute the spectral function of a unitary Fermi gas and the superfluid gap. [Preview Abstract] |
Saturday, November 2, 2019 8:54AM - 9:06AM |
E01.00003: The Dynamical Structure Factor of a Fermionic Supersolid on an Optical Lattice Patrick Kelly, Ettore Vitali, Annette Lopez, Gianluca Bertaina, Davide Galli We perform a Quantum Monte Carlo study of a cold Fermi gas on a 2D optical lattice, realized with laser standing waves. The system is modeled with a Hubbard hamiltonian with on-site attractive interaction. At half-filling, when on average one fermion occupies each lattice site, the system displays an intriguing supersolid phase: a superfluid with a checkerboard density modulation. Interfacing unbiased Auxiliary-Field Monte Carlo simulations with state-of-art analytic continuation techniques, we compute the density dynamical structure factor $S({\bf{q}},\omega)$ of the system and the density response function $\chi({\bf{q}})$, in order to characterize this supersolid phase. These results shed light into this interesting physical regime, where $s$-wave pairing superfluidity coexists with a non-uniform local density. [Preview Abstract] |
Saturday, November 2, 2019 9:06AM - 9:18AM |
E01.00004: Simulating Radiative and Non-Radiative Decay Pathways of Photoexcited Ruthenium Polypyridyl Complexes Thomas Cheshire, Paul Giokas, David Zigler, M. Kyle Brennaman, Andrew Moran, John Papanikolas, Gerald Meyer, Thomas Meyer, Frances Houle Bottlenecks in the generation of photoinduced currents in dye-sensitized solar cells are not fundamentally understood due to the lack of detailed information on initial ultrafast processes in photoexcited dyes that compete with charge injection. The ultrafast photophysics that drive solar energy conversion are typically reported in terms of phenomenological lifetimes, yet competing transitions occurring on comparable timescales obscures the relationship between such time constants and fundamental rate coefficients. Knowledge of primary kinetics will reveal dye design strategies that may improve sensitivity and efficiency. We employ stochastic simulations, which are a form of kinetic Monte Carlo that produce an absolute time base, to model explicit photoexcitation and the subsequent relaxation pathways of a series of ruthenium polypyridyl chromophores. The initial work focuses on isolated dyes in solution, producing a scheme that can be extended to dyes adsorbed on metal oxide surfaces. We predict transient absorption signals for comparison to spectroscopic data from multiple studies, and find that common assumptions about the sub-picosecond photophysics such as singlet-triplet energy transfer efficiency do not correctly reproduce experimental observations. [Preview Abstract] |
Saturday, November 2, 2019 9:18AM - 9:30AM |
E01.00005: The influence of future durations on past photon counts in an optical system Julia Mossbridge I conducted a series of double-slit experiments with extended time scales in order to test the hypothesis that photons emitted seconds in the future could influence the detection of photons emitted in the recent past, reasoning that photons being in two times at once is at least as weird as photons being in two places at once. Positive results supported the hypothesis. In each experimental run using a single-photon double-slit optical system, after a period (33 seconds) of normal functioning, a quantum-based random number generator was used to select the future on-time duration of the light source out of four possible options (0, 220, 330 and 660 seconds). After the selected duration, the system shut down. This procedure was followed for 50 runs per day for 30 days. At both a central peak and a central trough of the interference pattern, photon counts differed significantly between durations both prior to and following the decision about the duration of the light source, revealing an oscillating retrocausality on the scale of minutes. The results support the growing trend of examining the influence of future boundary conditions on event probability, but they also suggest the horizon for those conditions may be farther out in time than previously imagined. [Preview Abstract] |
Saturday, November 2, 2019 9:30AM - 9:42AM |
E01.00006: Spectroscopic Features of Highly Ionized Xenon Plasma A.K. Gill, V.V. Shlyaptseva, A.S. Safronova, K. Takasugi, V.L. Kantsyrev, A. Stafford, R. Childers The field of high-energy-density (HED) plasma physics has important applications, such as inertial confinement fusion and development of intense radiation sources. X-ray spectroscopy is a vital tool for understanding HED plasmas. Previous work on K-shell Argon and L-shell Krypton plasmas from reverse polarity experiments on SHOTGUN-III Z-pinch device at Nihon University (Japan), that used X-ray spectroscopy to estimate plasma parameters and to observe electron beam effects, is extended here to study M-shell Xenon spectra. M-shell line radiation from HED plasmas is more complex to analyze than K- or L-shell radiation due to the substantial increase in number of ionization stages and their overlap, as such needs non-local thermodynamic equilibrium (non-LTE) modeling and experimental benchmarking. M-shell X-ray spectra in the spectral range of 9-15 {\AA} from Xenon gas-puff plasma reverse polarity experiments are analyzed in detail using a newly created non-LTE model with ionization stages from Zn-like to Ti-like Xenon. Future work is discussed. [Preview Abstract] |
Saturday, November 2, 2019 9:42AM - 9:54AM |
E01.00007: Characterization of laser-based broadband x-ray spectrum for high areal density objects Lei Chen, Hiroshi Sawada, Tyler Daykin, Trevor Hutchinson, Bruno Bauer, Vladimir Ivanov, Farhat Beg, Hui Chen, Gerald Williams, Harry McLean X-ray radiography is essential to probe high areal density objects in high energy density and inertial confinement fusion experiments. To characterize laser-produced broadband x-ray spectrum, x-ray radiography experiments were carried out by using a 50-TW Leopard laser at the Nevada Terawatt Facility. In these experiments, bremsstrahlung and electrons spectra were measured to determine characteristics of fast electrons, while radiographic images of three Al wires with different diameters were recorded using the laser-produced broadband x rays. The measured bremsstrahlung is modeled with a hybrid Particle-in-cell code to infer fast electron spectrum and divergence angle. Calculated x-ray spectra are used in the Monte Carlo code to simulate transmission profiles of the Al wires. The measurements agree with calculations when a simulated x-ray spectrum composed of line emissions and bremsstrahlung is used. Simulations with only 22 keV Ag K$\alpha $ or exponential x-ray spectrum cannot reproduce the measurement, suggesting that the proper x-ray source spectrum and photon sensitivity of detector are critical in the transmission calculations to infer the density of an object. [Preview Abstract] |
Saturday, November 2, 2019 9:54AM - 10:06AM |
E01.00008: Superhard Tantalum Borides Via Microwave Plasma Chemical Vapor Deposition . Kallol Chakrabarty, Aaditya Rau, Paul A. Baker, Shane A. Catledge Tantalum borides have become a subject of interest due to their excellent properties: high hardness, wear resistance, chemical inertness. Different techniques have been used to synthesize tantalum borides, including high temperature/pressure compression in diamond anvil cells$^{\mathrm{\thinspace }}$and traditional powder or pack boriding and chemical vapor deposition. These methods have some limitation such as small volumes of deposition and contamination issue. In this research work, we have used novel Microwave Plasma Chemical Vapor Deposition method to synthesize tantalum boride. H$_{\mathrm{2}}$ and B$_{\mathrm{2}}$H$_{\mathrm{6\thinspace }}$was used as a feed gas and boron was diffused into tantalum substrate. The sample was analyzed using X Ray Diffraction and Nanoindentation. The Structure of the produced sample was mixture of TaB and TaB$_{\mathrm{2\thinspace }}$Phase. XRD patterns show a clear increase in the relative intensity of the TaB$_{\mathrm{2}}$ phase with temperature, accompanied by an increase in hardness measured via nanoindentation. The hardness value of the produced sample was in superhard regime and mean hardness was 40\textpm 10 GPa. [Preview Abstract] |
Saturday, November 2, 2019 10:06AM - 10:18AM |
E01.00009: University of Nevada, Reno's Learning Assistant Program: Lasting Supports for Physics Undergraduates Donald Fisher, Noelle Daigle The University of Nevada, Reno's learning assistant program is designed to encourage professors to incorporate collaborative learning into their lecture times with assistance from undergraduate learning assistants. This type of learning breaks the cold environment associated with traditional undergraduate physics programs. Learning Assistants provide more support than what a Professor alone can provide both in lecture and outside of the classroom. Our Learning Assistants run a help center where students in beginning or advanced physics courses can come to work on homework, labs, or review with assistance on hand. Our goal is to see how the long-lasting support in physics affects the learning environment of undergraduate physics students and the attrition rates. Additionally, our program has shown to be beneficially for the faculty, students, and Learning Assistants. [Preview Abstract] |
Saturday, November 2, 2019 10:18AM - 10:30AM |
E01.00010: Bridging the pathways to PhD programs for Cal-State and Underrepresented Students Wing To Cal-Bridge is an NSF funded scholarship program to close the gap between Under-Represented Minority (URM) and Women in Physics and Astronomy during the critical transition phase between undergraduate to graduate school. As of 2017, URM earns 13\% of Bachelors in Physics which is already a gap to URM’s population of 30\% in USA. The representation worsens at the PhD level where it drops to 6\% in Physics. The program supports Cal-State University students from their junior year to their 1st year in a graduate program through strong academic, social, financial support and mentorship. From 2013-2019 Cal-Bridge has awarded 59 scholarships, of the 33 students who have graduated with Bachelors, 27 students enter into PhD programs. Cal-Bridge Scholars are presentative of CSU students population with 70\% from URM and 42\% women. We will highlight how Cal-Bridge has already made a substantial dent in the URM and Women in Physics and Astronomy gap as seen in the October 2019 issue of Physics Today. The program also note an increased visibility and improved the attitude towards physics and astronomy courses at Cal-State campuses. [Preview Abstract] |
Saturday, November 2, 2019 10:30AM - 10:42AM |
E01.00011: A Time-Symmetric Analysis of Two-Particle Quantum Entanglement Michael Heaney Two-particle quantum entanglement is numerically simulated using a time-symmetric formulation of nonrelativistic quantum mechanics that has no collapse postulate. The experimental predictions are identical to the conventional formulation predictions. Several of the mysterious properties displayed by entangled particles become transparent in the time-symmetric analysis. [Preview Abstract] |
Saturday, November 2, 2019 10:42AM - 10:54AM |
E01.00012: Development and Parameterization of a Bidirectional Comb Laser Kelly Fradet, Ricky Arnold, Bachana Lomsadze A frequency comb is a laser source whose spectrum is made up of discrete, equally spaced frequency lines, similar in shape to the teeth on a comb. Frequency combs are typically created using mode-locked lasers. Since the development of frequency comb technology, a method known as dual-comb spectroscopy (DCS) has attracted attention as a revolutionary approach to optical detection. DCS contains two frequency combs and its working principle is similar to Fourier transform Infrared spectroscopy (FTIR). But DCS doesn’t require moving mechanical parts and hence enables the measurement of high-resolution absorption spectra rapidly. In DCS, one frequency comb interrogates the sample and the linear response is sampled in time with another comb that has a slightly different repetition rate. The resulting interferogram is captured by a single photodetector. Because of these qualities DCS is used both in the laboratory and outside for field applications such as atmospheric monitoring. However, DCS setups are expensive as they require two separate mode locked lasers. To overcome this limitation, we built two mode-locked lasers (with different repetition rates) from a single resonator. We successfully produced a dual-comb signal and set up an experiment using a Fabry-Perot interferometer to monitor and remove phase fluctuations. This improvement to DCS makes the technique even more powerful for practical applications outside the laboratory. [Preview Abstract] |
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