Bulletin of the American Physical Society
2016 Annual Meeting of the Far West Section
Volume 61, Number 17
Friday–Saturday, October 28–29, 2016; Davis, California
Session F2: Atomic, Molecular and Optical Physics |
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Chair: Rajiv Singh, University of California, Davis Room: Conference Room A |
Friday, October 28, 2016 2:00PM - 2:12PM |
F2.00001: Hysteresis of Current in Noninteracting Atomic Fermi Gases in Optical Ring Potentials Mekena Metcalf, Chih-Chun Chien, Chen-Yen Lai Hysteresis is a ubiquitous phenomenon, which can be found in magnets, superfluids, and other many-body systems. Although interactions are present in most systems exhibiting hysteresis, here we show the current of a non-interacting Fermi gas in an optical ring potential produces hysteresis behavior when driven by a time-dependent artificial gauge field and subject to dissipation. Fermions in a ring potential threaded with flux can exhibit a persistent current when the system is in thermal equilibrium, but cold-atoms are clean and dissipation for reaching thermal equilibrium may be introduced by an external, thermal bath. We use the standard relaxation approximation to model the dynamics of cold-atoms driven periodically by an artificial gauge field. A competition of the driven time and the relaxation time leads to hysteresis of the mass current, and work done on the system, as a function of the relaxation time, exhibits similar behavior as Kramers transition rate in chemical reaction and one-dimensional thermal transport. [Preview Abstract] |
Friday, October 28, 2016 2:12PM - 2:24PM |
F2.00002: Cold atoms coupled to nano-mechanical systems Cris Montoya, Apryl Witherspoon, Gambhir Ranjit, Andrew Geraci, John Kitching Cold atoms coupled to nano-mechanical oscillators may have applications in precision sensing or quantum information science. We report resonant magnetic coupling of a micro-cantilever to a sample of cold Rb atoms. In our setup, the cantilever produces Zeeman state transitions in the atoms which result in a loss of population in a magnetic trap [1]. Similar cantilevers could provide single-spin sensitivity and sub-micron spatial resolution enabling new techniques in quantum simulation. Optical fields can also be used to couple cold atoms to mechanical devices. In particular, optically trapped dielectric nanospheres could reach the quantum ground state by sympathetically cooling the spheres via cold atoms [2]. Such cooled spheres can be used in quantum limited sensing and matter-wave interferometry. We describe experimental efforts to couple, via a one-dimensional optical lattice, a levitated dielectric nanosphere to a gas of cold Rubidium atoms as a first step towards sympathetically cooling the sphere. [1] C. Montoya, J. Valencia, A. A. Geraci, M. Eardley, J. Moreland, L. Hollberg, and J. Kitching, \textit{Phys. Rev. A~91, 063835 (2015)} [2] G. Ranjit, C. Montoya, A. A. Geraci, \textit{Phys Rev. A 91, 013416 (2015). } [Preview Abstract] |
Friday, October 28, 2016 2:24PM - 2:36PM |
F2.00003: Ultracold collisions of molecular radicals with alkali-metal atoms in a magnetic field Masato Morita, Jacek Klos, Piotr S. Zuchowski, Timur V. Tscherbul Collisional properties of ultracold molecular gases play a key role in sympathetic and evaporative cooling of molecular ensembles to ultralow temperatures. We use state-of-the-art ab initio and quantum scattering calculations to calculate the ratio between the elastic and spin-relaxation cross sections for molecular radicals SrOH and SrF colliding with ultracold alkali-metal atoms in the presence of an external magnetic field. We will discuss (1) the prospects of sympathetic cooling of these molecules in a magnetic trap and (2) the effect of the uncertainty of the atom-molecule interaction potential on the theoretical predictions. [Preview Abstract] |
Friday, October 28, 2016 2:36PM - 2:48PM |
F2.00004: Progress towards cavity-cooling of an optically trapped nanosensor Gambhir Ranjit, Mark Cunningham, Kirsten Casey, Andrew A. Geraci We have successfully developed a highly sensitive force sensor consisting of an optically levitated dielectric nanoparticle in high vacuum with sensitivity down to the zeptonewton scale [1]. Optically levitated sensors, due to their potential to achieve an excellent mechanical quality factor Q, are especially promising for such small force sensing even at room temperature. Such sensors will be used for the study of measurements of tiny forces like deviations of Newtonian gravity and Casmir forces at short range [2]. Currently, we are working on improving the sensitivity of our nanosensor by using cavity assisted trapping and cooling. [Preview Abstract] |
Friday, October 28, 2016 2:48PM - 3:00PM |
F2.00005: Cold atom quantum emulation of ultrafast processes Shankari Rajagopal, Ruwan Senaratne, Zachary Geiger, Kurt Fujiwara, Kevin Singh, David Weld Pulsed lasers are an invaluable probe of fast electron dynamics in condensed matter systems. However, despite tremendous progress, physical limitations on lasers and a lack of exact theoretical models still limit the exploration~of ultrafast processes in solids.~ We discuss a possible complementary approach, in which lattice-trapped cold neutral atoms driven far from equilibrium are used as a quantum emulator of ultrafast physics at sub-cycle timescales. As suggested by recent theoretical~proposals, the cold atom context is in many ways a natural choice for such experiments: equilibration timescales are more than ten orders of magnitude slower than those in solids, and strong driving forces are easily produced and manipulated. Our experimental approach uses ultracold strontium in optical traps.~ Multiple stable isotopes and a~long-lived metastable state provide control over interaction strengths, while a narrow-linewidth transition expands the typical cold-atom toolbox of readout techniques. We discuss initial efforts in quantum emulation of tunnel ionization and simulation and development of a platform for more complicated endeavors, including the study of multiple-pulse sequences and recollision processes. [Preview Abstract] |
Friday, October 28, 2016 3:00PM - 3:12PM |
F2.00006: Calculating the Ionization Energies of Acidic and Basic Amino Acids Through the Analysis of Potential Energy Surfaces C. P. De Guzman, M. Andrianarijaona, Y. Yoshida, V. M. Andrianarijaona Strain on the molecular geometry of amino acids can have varying effects on the amino acid's structure, function, and overall binding capabilities. A better understand of how strain affect the potential energy can also lead to more insight to a molecule's vertical ionization energy. For this study, acidic and basic amino acids were chosen because of their ionizable side chains are very influential on the molecule's preferred conformation (J Phys Chem A. 2011 April 7; 115(13): 2900--2912). Each atom within the amino acid was considered as potential departing sites to better understand the dynamic coupling between the vibrational modes. ORCA was used to calculate single point energies after manipulating the location of each atom along the x, y, and z coordinates. The collected data was then used to create potential energy surfaces to better understand the quantum dynamic properties of the amino acids (preliminary data was presented in http://meetings.aps.org/Meeting/MAR16/Session/M1.273). [Preview Abstract] |
Friday, October 28, 2016 3:12PM - 3:24PM |
F2.00007: Optimal geometry of x-ray fluorescence arsenic detection in skin phantoms using an x-ray optics system Benjamin Avila, Mihai Gherase Arsenic (As) is a well-known toxic element. While the toxicity of acute As poisoning was known for centuries, the adverse effects of long-term As exposure were the focus of more recent studies. The As exposure occurs via human consumption of contaminated well water -- a naturally occurring problem in many parts of the world. The excess of As intake leads to its accumulation in keratin-rich tissues such as skin, nails, and hair. Skin is less prone to external As contamination, hence, a better biomarker than nails or hair. X-ray fluorescence (XRF) uses characteristic x-ray emissions to detect elements in trace concentrations of a few $\mu $g/g or lower. Low radiation dose studies with portable spectrometers demonstrated the method's potential for the assessment of As exposure, particularly in remote parts of the world. However, the method was not optimized for superficially distributed As within the skin. In this study the sensitivity of As detection was found to reach a maximum for a 5-degree angle between the skin phantoms and the incident x-ray beam. An x-ray optics system, x-ray detector, and a positional stage assembly were used to measure the As K$\alpha $ and K$\beta $ peak amplitudes in skin phantoms with 0, 4, 6, 8, and 12 $\mu $g/g As concentrations. [Preview Abstract] |
Friday, October 28, 2016 3:24PM - 3:36PM |
F2.00008: Molecular Modeling Study of Aryl and Arylalkyl Di-n-Butyl Phosphates as Effective Butyrylcholinesterase Inhibitors Walter Alvarado, Kensaku Nakayama, Jason Schwans, Eric Sorin, Sean McCoy Alzheimer's Disease (AD) is a neurodegenerative disease characterized by plaque buildup in the brain and decreased levels of the neurotransmitter acetylcholine. Decreased levels of acetylcholine lead to decreased cell communication, which is thought to result in the manifestation of dementia. While acetylcholinesterase (AChE) is the primary enzyme responsible for the breakdown of ACh to regulate intercellular communication, butyrylcholinesterase (BChE), an AChE-like scavenger enzyme, also breaks down both ACh and larger choline derivatives. This makes BChE a primary target for treating Alzheimer's symptoms and greatly increases the demand for non-toxic BChE-specific inhibitors. Dialkyl phenyl phosphate (DAPP) derivatives are expected to interact with BChE in a manner similar to that of natural physiological substrates. This study employs massive flexible-inhibitor docking calculations to predict the relative binding affinity between the enzyme and a number of DAPP derivatives, as well as the optimal binding orientation of each DAPP derivative within the BChE active site. Our docking calculations reproduce experimentally observed inhibition trends, with the m-methylphenyl analog binding favored over o-methyl. Structural analysis shows that the o-methylphenyl substituent takes on a rear-facing orientation, located in a vacant region of the pocket relatively void of potential interaction partners. This lack of significant participation during binding results in this species having relatively weak inhibitory power. [Preview Abstract] |
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