Bulletin of the American Physical Society
14th Annual Meeting of the Northwest Section of the APS
Volume 57, Number 7
Thursday–Saturday, October 18–20, 2012; Vancouver, British Columbia, Canada
Session H1: Atomic, Molecular, and Optical Physics |
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Chair: Daniel Steck, University of Oregon Room: SFU Harbour Centre 1700 Labatt Hall |
Saturday, October 20, 2012 1:30PM - 2:06PM |
H1.00001: Casting Light on Antimatter with ALPHA Project at CERN: Fundamental Physics with Trapped Antihydrogen Invited Speaker: Makoto Fujiwara Testing fundamental symmetries plays an important role in our understanding of Nature. Experiments at CERN's Antiproton Decelerator facility aim to make precision tests of matter-antimatter symmetry, in particular CPT (charge, parity, time reversal), by comparing the properties of hydrogen with those of its antimatter counterpart, antihydrogen. Demonstration of trapping of antihydrogen atoms by the ALPHA collaboration, and subsequent observation of their long-time confinement, have opened up new experimental possibilities in antimatter physics. Most recently, ALPHA has succeeded in demonstrating the first spectroscopic measurement on anti-atoms, via microwave resonance. I this talk, I will discuss how to make and trap antihydrogen atoms. I will also discuss the prospects of fundamental symmetry tests with antihydrogen, including the possibility of measuring the gravitational interaction of antimatter. [Preview Abstract] |
Saturday, October 20, 2012 2:06PM - 2:18PM |
H1.00002: Microwave Spectroscopy of Trapped Antihydrogen Mohammad Dehghani Ashkezari Theory predicts that, under CPT\footnote{Charge conjugation, Parity inversion, and Time reversal.} symmetry, the laws of physics make no distinction between matter and anti-matter. We have every reason to believe that equal amounts of both were produced in the early universe, following the Big Bang. However, our observable universe is overwhelmingly made up of matter. ALPHA is an international project located at CERN and involves $\sim30$ physicists from 15 different institutions. The primary goal of the collaboration is to investigate this gaping discrepancy between theoretical expectations and reality by precise comparison of matter and anti-matter, in particular hydrogen and antihydrogen. A critical milestone was reported in November 2010, the first-ever stable and reproducible magnetic confinement of neutral antihydrogen atoms. Shortly after, in June 2011, ALPHA announced the long-time (1000 s) trapping of antihydrogen, opening the door to precision spectroscopy. In March 2012, the first proof-of-principle spectroscopic measurement performed on trapped antihydrogen atoms using microwave radiation\footnote{C. Amole, et al., (ALPHA collaboration), Nature {\bf 483}, 439 (2012).}. Detailed aspects of this measurement is presented in this talk. [Preview Abstract] |
Saturday, October 20, 2012 2:18PM - 2:30PM |
H1.00003: Yttrium ionization scheme development for Ti:Sa laser based RILIS Andrea Teigelhoefer, Jens Lassen, Zeinab Abboud, Pierre Bricault, Henning Heggen, Peter Kunz, Ruohong Li, Thomas Quenzel, Sebastian Raeder Resonant ionization laser ion sources (RILIS) are popular ion sources if intense, radioactive ion beams (RIBs) with minimal isobaric contamination are required. The intensity of the ion beam depends strongly on the applied resonant laser ionization scheme. Based on the all solid state laser system TRIUMF's RILIS (TRILIS) is using, the off-line development towards an efficient ionization scheme for yttrium is presented. Several continuous wavelength scans have been performed to compare different nonresonant ionization schemes and to identify suitable Rydberg or autoionizing states for resonant ionization schemes. [Preview Abstract] |
Saturday, October 20, 2012 2:30PM - 2:42PM |
H1.00004: Terahertz imaging of inhomogeneous electrodynamics in single-layer graphene embedded in dielectrics Zachary Thompson, Michael Paul, Joeseph Tomaino, Joshua Kevek, Tristan DeBorde, Ethan Minot, Yun-Shik Lee We investigate electron transport properties in large-area, single-layer graphene embedded in dielectric media, using free-space terahertz (THz) imaging and time-domain spectroscopy. Sandwiched between a thin polymethyl methacrylate (PMMA) layer and a Si substrate, graphene layers of different growth recipes exhibit distinctive spatial inhomogeneity of sheet conductivity. The non-contacting, non-destructive THz probe reveals that the PMMA layer induces a small, yet noticeable reduction in conductivity. [Preview Abstract] |
Saturday, October 20, 2012 2:42PM - 2:54PM |
H1.00005: Terahertz Transmission Ellipsometry of Vertically-Aligned Multi-Walled Carbon Nanotubes Michael Paul, Nick Kuhta, Joe Tomaino, Andy Jameson, Louis Maizy, Tal Sharf, Nalin Rupesinghe, Ken Teo, Sandeep Inampudi, Victor Podolskiy, Ethan Minot, Yun-Shik Lee We demonstrate time-resolved terahertz transmission ellipsometry of vertically-aligned multi-walled carbon nanotubes. The angle-resolved transmission measurements reveal anisotropic characteristics of the terahertz electrodynamics in multi-walled carbon nanotubes. The anisotropy is, however, unexpectedly weak: the ratio of the tube-axis conductivity to the transverse conductivity, ${\sigma _z } \mathord{\left/ {\vphantom {{\sigma _z } {\sigma _{xy} =2.3}}} \right. \kern-\nulldelimiterspace} {\sigma _{xy} =2.3}$, is nearly constant over the broad spectral range of 0.4 -- 1.6 THz. The relatively weak anisotropy and the strong transverse electrical conduction indicate that THz fields readily induce electron transport between adjacent shells within multi-walled carbon nanotubes. [Preview Abstract] |
Saturday, October 20, 2012 2:54PM - 3:06PM |
H1.00006: Exploring asymmetry in the optical dispersion of dyes in solution near an absorption resonance Amelia VanEngen Spivey Dispersion is the dependence of the refractive index of a material on wavelength. Dispersion is problematic in ultrafast optics experiments, which use broad-spectrum laser pulses lasting hundreds of femtoseconds or less. Together with nonlinear effects, dispersion can cause undesirable changes (such as temporal spreading or pulse splitting) to a propagating ultrafast laser pulse. Temporal spreading of ultrafast laser pulses during propagation is primarily governed by the group velocity dispersion (GVD) coefficient. Therefore, modeling ultrafast pulse propagation in a material requires accurate knowledge of the GVD coefficient in the material. This talk presents experimental measurements of the GVD coefficient of dyes in solution using a white light Michelson interferometer. In particular, we probe the dependence of the GVD on wavelength near the absorption resonance in the dye. We find the wavelength dependence of the GVD to be asymmetric about the absorption resonance. On the low-wavelength side of the resonance, the dye contribution to the GVD is negligibly small. However, on the high-wavelength side, the dye contribution to the GVD can be significant and is highly wavelength dependent. This effect is consistent with a simple Lorentz model of dispersion and can be modeled accurately using the linear absorption spectrum of the dye. [Preview Abstract] |
Saturday, October 20, 2012 3:06PM - 3:18PM |
H1.00007: Quantum resonances in selective rotational excitation of molecules with a sequence of ultrashort laser pulses Sergey Zhdanovich, Casey Bloomquist, Johannes Floss, Ilya Averbukh, John Hepburn, Valery Milner The periodically kicked rotor is a paradigm system for studying classical and quantum chaos. In the quantum regime, the dynamics of the kicked rotor exhibit such phenomena as suppression of classical chaos, Anderson localization in angular momentum and quantum resonances in the accumulation of rotational energy. Even though these effects have been studied with ultracold atoms in optical fields and Rydberg atoms in microwave fields, they have never been observed in a real rotational system. In this work we study the effect of quantum resonance in the rotational excitation of a diatomic molecule. By using femtosecond pulse shaping and rotational state-resolved detection, we measure the rotational distribution of molecules interacting with a train of pulses. We show enhancement of population transfer from the ground to the excited rotational states at resonance, and demonstrate selective rotational excitation of two nitrogen isotopes. We utilize fractional quantum resonances for separating para- and ortho-nitrogen, paving the way to novel methods of coherent control of molecular rotation. [Preview Abstract] |
Saturday, October 20, 2012 3:18PM - 3:38PM |
H1.00008: BREAK |
Saturday, October 20, 2012 3:38PM - 4:14PM |
H1.00009: XUV Frequency Combs via Femtosecond Enhancement Cavities Invited Speaker: Arthur Mills We report on recent developments in tabletop extreme ultraviolet (XUV) sources based on high harmonic generation (HHG) in femtosecond enhancement cavities (fsEC). The XUV frequency comb is produced via HHG at the full repetition rate of the mode-locked oscillator (typically $>50$ MHz), inside a passive enhancement cavity with an enhancement of a few hundred. Several technical challenges have recently been resolved, which have led to an increase in the generated photon flux in the XUV ($10^{14}$ photons/sec), and a substantial improvement in the operating time of these sources. XUV sources based on fsECs are now able to perform direct frequency comb spectroscopy with MHz precision in atomic systems at wavelengths down to 60 nm. Ongoing research is aimed at determining the ultimate frequency stability of these new XUV frequency comb sources. XUV fsEC sources are also promising for some applications that are typically performed with XUV light at advanced light sources. These applications include electronic structure of quantum material systems, such as angle-resolved photoemission spectroscopy (ARPES), size metrology of nano-aerosol particles, and potentially velocity map imaging for studies of chemical physical problems. In this talk, we present a brief introduction to XUV frequency comb sources and the technical challenges that have been overcome to achieve the current performance levels. We will also discuss our progress on ARPES experiments with a fsEC XUV source and our efforts toward increasing the energy resolution of the produced harmonics. Finally, we describe ongoing efforts to further increase the maximum photon energy and photon flux generated, and subsequently delivered to an experiment by fsEC XUV sources. [Preview Abstract] |
Saturday, October 20, 2012 4:14PM - 4:26PM |
H1.00010: Coherent anti-Stokes Raman spectroscopy in the presence of strong resonant signal from background molecules Martin Bitter, Valery Milner Laser spectroscopy based on femtosecond coherent anti-Stokes Raman scattering (fs CARS) often involves simultaneous excitation of multiple resonances covered by the broad spectral bandwidth of ultrashort pulses. Determining the chemical composition of a mixture of molecular species with close vibrational frequencies typically requires Fourier analysis of the detected time-resolved fs CARS signal. Here we propose and demonstrate an alternative method of separating vibrational responses from two molecular species with neighboring vibrational modes (here, oxygen and carbon dioxide). We utilize ro-vibrational coupling as a mechanism of suppressing the strong vibrational response from the dominating molecular species (O$_{2}$). Coherent ro-vibrational dynamics leads to long ``silence windows'' of zero CARS signal from oxygen molecules. In these silence windows, the detected signal stems solely from the minority species (CO$_{2}$) enabling background-free detection and characterization of the O$_2$/CO$_2$ mixing ratio. In comparison to a Fourier analysis, our technique does not require femtosecond time resolution or time-delay scanning. [Preview Abstract] |
Saturday, October 20, 2012 4:26PM - 4:38PM |
H1.00011: Spin orbit coupling in a dilute gas Bose-Einstein condensate Chris Hamner, JiaJia Chang, Peter Engels The recent implementation of Raman dressing in cold atom systems opens the door for novel investigations of quantum dynamics. It provides an intriguing new tool to dynamically change the dispersion relation with unprecedented tunability. In suitable parameter regimes this scheme also allows for the generation of 1D spin orbit coupling analogous to the spin orbit coupling in complex condensed matter systems. In our experiments we have implemented spin orbit coupling for a $^{87}$Rb BEC and study its influence on hydrodynamics properties. We present results of recent and ongoing research. [Preview Abstract] |
Saturday, October 20, 2012 4:38PM - 4:50PM |
H1.00012: Dynamics of Feshbach molecules in an ultracold three-component mixture Alexander Khramov, Anders Hansen, William Dowd, Alan Jamison, Subhadeep Gupta Feshbach resonances are an integral tool in ultracold atomic physics, allowing for tunable two-body interactions and the synthesis of molecular dimers. The two lowest energy states of the $^{6}$Li atom exhibit a broad Feshbach resonance at 834 Gauss which can be used to link pairs of atoms into shallow dimers. We study ultracold mixtures of $^{6}$Li atoms near the Feshbach resonance, immersed in a bath of $^{174}$Yb. We observe dynamics of Li$_{2}$ Feshbach molecule formation and decay, as modified by a non-resonant component, and find remarkable molecule stability even in the absence of Fermi statistics. We also extract the reaction rate coefficients of the dominant chemical processes. This work opens various new possibilities for studies of strongly interacting Fermions, as interrogated by a second species. [Preview Abstract] |
Saturday, October 20, 2012 4:50PM - 5:02PM |
H1.00013: Spontaneous nucleation of topological defects in trapped Yb$^{+}$ ion-crystals Sara Ejtemaee, Paul. C. Haljan Laser-cooled arrays of trapped ions, also known as ion crystals, are currently being investigated for quantum information processing. They are also interesting as a mesoscopic ``condensed-matter'' system to study classical and quantum few-body phase transitions. Following a recent theoretical proposal, we are performing experiments to investigate the non-equilibrium dynamics of the linear-zigzag phase transition in a system of trapped $^{174}$Yb$^{+}$ ions. We use strong transverse confinement to align the trapped ions into a linear crystal. Gradually reducing the trap anisotropy induces a structural phase transition from linear to a two-dimensional zigzag configuration. Alternatively, rapidly quenching the anisotropy across the phase transition can lead to crystal structures containing spontaneously nucleated topological defects. We describe our recent experimental results on the formation and lifetime of these structural defects. [Preview Abstract] |
Saturday, October 20, 2012 5:02PM - 5:14PM |
H1.00014: Atom Interferometry with Bose-Einstein condensates to measure $\alpha$ Benjamin Plotkin-Swing, Alan Jamison, Subhadeep Gupta The most precise measurement of the fine structure constant, $\alpha$, comes from the electron $g-2$ measurement. This result relies on high orders of perturbation theory in QED. A complementary measurement of $\alpha$ with less dependence on theory would allow for extremely stringent tests of QED. Atomic recoil measurements, which measure $h/m$ for a given atomic species, are a promising direction for such a measurement. We will report on our progress toward a Bose-Einstein condensate (BEC) interferometer to measure the atomic recoil of ytterbium (Yb) with high precision. Use of a BEC allows for long interrogation times and a robust signal. Using Yb eliminates magnetic fields as a potentially damaging systematic while allowing comparison of results for different isotopes. We have established key components of the interferometer with a $^{174}$Yb BEC: diffraction with short laser pulses for momentum-state beam-splitting and with long pulses as mirrors. We are working on acceleration pulses to achieve large momenta in the different interferometer arms, necessary for a sub-ppb measurement of $\alpha$. [Preview Abstract] |
Saturday, October 20, 2012 5:14PM - 5:26PM |
H1.00015: Quantum dynamics in a trapped ultra-cold Bose gas Dorna Niroomand, Lydia Zajiczek, Jeffrey McGuirk We study spin dynamics in a trapped Rb gas near quantum degeneracy. Although the system is not degenerate, the dynamics are dominated by quantum properties of particles. We use an optical technique, based on the ac Stark effect, to imprint desired spin structures in these trapped atomic samples. These spin structures can lead to generation of instabilities, such as the Castaing instability, in which a strong longitudinal spin gradient is unstable to transverse perturbations. We report experimental results on observing the Castaing instability. [Preview Abstract] |
Saturday, October 20, 2012 5:26PM - 5:38PM |
H1.00016: Measuring geometric quantum discord using DQC1 Gina Passante, Osama Moussa, Raymond Laflamme DQC1 is a model of quantum computation that utilizes a single qubit accompanied by a register of completely mixed states. While this model is able to outperform current classical methods without substantial entanglement, it does contain non-classical correlations as measured by the quantum discord. We describe an efficient algorithm to experimentally measure a near relative of the quantum discord, the geometric quantum discord, of a DQC1-state. We provide an analytical expression that indicates the geometric quantum discord of a $(1+n)$-qubit DQC1-state decreases exponentially with $n$. This is in contrast to the quantum discord, which is independent of $n$ for the same state. In addition, we present experimental results using a four-qubit liquid-state nuclear magnetic resonance quantum information processor. [Preview Abstract] |
Saturday, October 20, 2012 5:38PM - 5:50PM |
H1.00017: The Quantum Gunslinger: A Gedanken Experiment Michael Devine Presented is the Quantum Gunslinger, a gedanken experiment that explores, in a purely classical setting, the assumptions and conclusions of John Bell's seminal paper ``On the Einstein Podolsky Rosen Paradox.'' The Quantum Gunslinger can be easily implemented as a carnival game. If a player's score violates a CHSH inequality, then the player wins a beable. If the player's score violates a Leggett Inequality, then the player wins a large ball wound from surplus string. Find out why the game operator will either quickly go out of business for giving away prizes too easily, or be forced out of business on charges of fraud. [Preview Abstract] |
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