Bulletin of the American Physical Society
2013 Joint Meeting of the APS Division of Atomic, Molecular & Optical Physics and the CAP Division of Atomic, Molecular & Optical Physics, Canada
Volume 58, Number 6
Monday–Friday, June 3–7, 2013; Quebec City, Canada
Session K1: Poster Session II (4:00 - 6:00PM) |
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Room: 400A |
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K1.00001: FUNDAMENTAL SYSTEMS AND PRECISION MEASUREMENTS II |
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K1.00002: Measurement of the magnetic dipole moment of the Cs $6s^{2}S_{1/2} \to 7s^{2}S_{1/2}$ transition using two-pathway coherent control Dionysios Antypas, Daniel S. Elliott We present results of our laboratory measurements of the magnetic dipole transition moment for the $6s^{2}S_{1/2} \to 7s^{2}S_{1/2}$ transition in atomic Cesium. Our experimental scheme is based on a novel two-pathway coherent control scheme, in which two coherent laser fields, one the second harmonic of the other, are employed to excite three distinct optical interactions. Observations of the interference between these transitions allow a determination of the transition moment M$_{1}$. The use of two laser fields provides a decreased sensitivity to systematic errors, compared to other single-beam experiments on weak transition moments. Our measurement is in good agreement with, but of higher precision than, previous measurements, and serves as a benchmark of our technique and apparatus. With this system, we are working towards a new measurement on the Parity-Violation effect on the same transition. [Preview Abstract] |
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K1.00003: Progress on a higher precision measurement of the n$=$2 triplet P fine structure of atomic helium E.B. Davidson, K. Kato, H. Beica, M.C. George, A.C. Vutha, M. Weel, C.H. Storry, E.A. Hessels Precision measurement of the 2$^{\mathrm{3}}$P fine structure of atomic helium, when combined with precise theory, can be used to determine the value of the fine-structure constant. We report on progress towards an improved measurement using a new technique which reduces systematic effects, while improving the signal-to-noise ratio. An intense beam of 2$^{\mathrm{3}}$S metastable helium atoms is created in a hollow-cathode liquid-nitrogen-cooled DC-discharge source. The atoms are laser excited to the 2$^{\mathrm{3}}$P state and microwave transitions are driven between the 2$^{\mathrm{3}}$P states using the Ramsey method of separated oscillatory fields (SOF). Atoms which complete the SOF sequence are shelved into the 2$^{\mathrm{3}}$S m$=$-1 metastable state using laser transitions through the 3$^{\mathrm{3}}$S state. These m$=$-1 atoms can be detected with high efficiency. [Preview Abstract] |
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K1.00004: Towards a measurement of the proton radius using the Lamb shift in hydrogen A.C. Vutha, N. Bezginov, I. Ferchichi, V. Isaac, M.C. George, M. Weel, C.H. Storry, E.A. Hessels The discrepancy between the charge radius of the proton, measured using muon-proton interactions versus electron-proton interactions, constitutes the \textit{proton radius puzzle }[Pohl \textit{et al.}, Nature 466:213 (2010), arXiv:1301.0905 (2013), Science 339:417 (2013)]. To aid in a resolution of the proton radius puzzle, we are developing an experiment with a fast metastable hydrogen beam, to measure the n$=$2 Lamb shift using the microwave separated oscillatory fields (SOF) technique. To avoid systematic effects from the frequency-dependent response of our microwave system, the measurement will use an SOF technique [Klein \textit{et al., }Phys. Rev. A 36, 3494 (1987)], in which the frequency is fixed and the relative phase is varied. We report on the current status of the experiment, including metastable hydrogen beam production by charge exchange of protons with a molecular hydrogen target, hyperfine-state preparation using microwaves, and Lyman-alpha photon detection using a large-solid-angle high-efficiency detector. [Preview Abstract] |
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K1.00005: Current Work to Improve Precision in Measurements of Helium Fine Structure Nima Hassan Rezaeian, Davis Shiner With the recent improvement on the 2$^{3}$P Helium fine structure calculation by Pachucki and the quest for finding the most precise value for $\alpha$, spectroscopic measurement of the helium atom has a great advantage to find this primary constant. Distinctively, the 32 GHz atomic fine structure of 2$^{3}$P J2 to J0 interval with uncertainty of 100Hz leads a factor of three better than the best current value of $\alpha $ and an impulsion to the theory to evaluate the largest term of order m$\alpha^{8}$ is our ambition. This measurement not only tests the quantum electrodynamics, but also establishes the fine structure constant $\alpha$ with uncertainty of 1.6 ppb. The electron g-factor measurement of $\alpha$, even though, is by far more accurate at 0.37 ppb, our end result would be a examination to the best alternative atom recoil measurements with different approach. To reach on this level of accuracy, we implement our frequency selector with precision better than 1 to 100 along with laser cooling mechanism to enhance the signal to noise ratio by increasing the signal strength. [Preview Abstract] |
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K1.00006: Precise measurements of the $7P_{1/2}$-state hyperfine splittings and isotope shift in $^{203}$Tl and $^{205}$Tl David Kealhofer, Gambhir Ranjit, Protik Majumder We have undertaken a series of high-precision atomic structure measurement in thallium to test ongoing \emph{ab initio} atomic structure calculations of relevance to symmetry violation experiments in this element. In 2009, we completed a two-step vapor cell spectroscopy experiment in atomic indium\footnote{M. Gunawardena \emph{et al.}, Phys. Rev. A 80, 032519 (2009)}. Currently we are using a similar two-color, two-step spectroscopy scheme to measure of $7P_{1/2}$ hyperfine structure and isotope shift using a heated thallium vapor cell. One laser, locked near the thallium $6P_{1/2}\rightarrow7S_{1/2}$ 378 nm transition excites both naturally-occurring stable isotopes to an intermediate state. A second laser at 1301 nm overlaps the UV beam within the thallium vapor cell in both a co-propagating and counter-propagating configuration. Analysis of subsequent Doppler-free IR absorption spectra as we scan across the $7S_{1/2}\rightarrow7P_{1/2}$ transition allows us to extract both hyperfine and isotope shift information for this excited state. Frequency modulation of the IR beam provides convenient \emph{in situ} calibration method for the splittings. Statistical precision is currently at the 0.1 MHz level. Current results will be presented. [Preview Abstract] |
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K1.00007: Shifts due to distant neighboring resonances for laser measurements of $2^{\,3}S_1$-to-$2^{\,3}P_J$ transitions of helium A. Marsman, E.A. Hessels, M. Horbatsch Quantum-mechanical interference between transitions from the metastable $2^{\,3}S_1m_J$=0 state to $2^{\,3}P_1m_J$=$\pm1$ and to $2^{\,3}P_2m_J$=$\pm1$ is shown to cause shifts in these resonances, despite the fact that the resonances are separated by more than 1000 natural widths. The $2^{\,3}P_1$-to-$2^{\,3}P_2$ fine-structure interval can be determined from the difference of these laser transitions, and a comparison between experiment and theory for this interval allows for precise tests of the quantum-electrodynamic (QED) theory used to calculate the interval. The shifts described here are large enough to be important for this test of QED and therefore to affect the continuing program of determining the fine-structure constant from comparison between accurate experimental measurements and theoretical calculations of the helium $2^{\,3}P$ energy intervals. [Preview Abstract] |
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K1.00008: Optical pumping for nuclear beta decay J.A. Behr, S. Smale, I. Craiciu, A. Vantyghem, A. Gorelov, M. Anholm, R.S. Behling, B. Fenker, D. Melconian, G. Gwinner, D. Friesen For nuclear beta decay experiments to test the standard model, we must produce laser-cooled, polarized atoms with vector polarization of at least 99.9\%, with knowledge of the polarization from atomic observables at 0.1\% accuracy. We cycle on and off an AC MOT, and optically pump $^{37}$K atoms for 2 ms with trap off. We use circularly polarized light on the 4S$_{1/2}$ $\rightarrow$ 4P$_{1/2}$ transition, using RF sidebands on a diode laser to excite transitions from both F=1 and F=2 ground states. We test techniques with stable $^{41}$K atoms, which have very similar hyperfine splitting to $^{37}$K. Optical pumping techniques include flipping spin state with liquid crystal variable retarders, 0.25 mm thick SiC substrate mirrors in front of the beta detectors, combining 769.9 D1 and 766.5 nm D2 with an angle-tuned narrow bandpass filter, relieving stress from conflat-compatible windows to minimize birefringence, and shifting the frequency of the light with the spin flips to compensate for Zeeman shifts. We must avoid coherent population trapping effects. The polarization is measured by the time dependence of the excited state population after optical pumping light is applied, probed by measuring fluorescence and by nonresonant photoionization. [Preview Abstract] |
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K1.00009: Commissioning of the Francium Trapping Facility at TRIUMF M. Tandecki, J.A. Behr, M.R. Pearson, S. Aubin, R. Collister, G. Gwinner, E. Gomez, L. Orozco, J. Zhang The Francium Trapping Facility was constructed in 2011-2012 at TRIUMF in Vancouver. The goal of the facility is to study different aspects of weak neutral currents -- which cause parity violating effects -- in francium atoms using two different techniques. The first section of the apparatus, a magneto-optical trap to accumulate francium atoms produced by the ISAC radioactive beam facility as ions, has been commissioned in Sep 2012. $^{207,209,221}$Fr were trapped with trap lifetimes of the order of 20s. This is of the same order as their radioactive lifetimes ($t_{1/2}$ = 14.8 to 286.1s). Following the online run, $^{225}$Ac ($t_{1/2}$ = 10 days) was implanted into a tantalum foil, to have an offline source of $^{221}$Fr available; recoiling francium atoms from this source were trapped as a proof-of-principle. The commissioning run paved the way for spectroscopic measurements which will be presented in other contributions. The next phase of the experiment will see the construction of the second section of the setup; a science chamber below the current glass cell, which will house a microwave cavity and electric field plates, to study the atoms in a MOT and a dipole force trap. [Preview Abstract] |
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K1.00010: Trapping Cold Neutral Atoms with a Nanofiber for a Hybrid Quantum System J. Lee, J.A. Grover, J.E. Hoffman, S. Ravets, J. Hertzberg, K.D. Voigt, A. Choudhary, U. Chukwu, P. Kordell, M. Hafezi, J.M. Taylor, J.R. Anderson, C.J. Lobb, L.A. Orozco, S.L. Rolston, F.C. Wellstood We explore uses of atoms trapped in the evanescent optical field near a 500-nm diameter nanofiber for the creation of a hybrid quantum system by magnetically coupling to a superconducting(SC) circuit. Optically-trapped Rb atoms loaded from a grating MOT (GMOT) in a dilution refrigerator can be transported and coupled to the magnetic field of a high-Q SC resonator operating at the Rb ground state hyperfine frequency (6.8 GHz). The resonator can be coupled to a SC qubit to form a hybrid quantum system. We will present our current research progress, including fabrication of ultra-low loss nanofibers, a sub-Doppler cooled GMOT, progress toward atom trapping, design for atom/SC integration, and effects of optical power on the SC circuit. [Preview Abstract] |
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K1.00011: Experimental progress with novel surface electrode ion trap structures for quantum information processing Craig Clark, Matthew Blain, Francisco Benito, Chin-wen Chou, Mike Descour, Rob Ellis, Ray Haltli, Edwin Heller, Shanalyn Kemme, Jon Sterk, Boyan Tabakov, Chris Tigges, Peter Maunz, Daniel Stick Segmented surface electrode ion traps are one of the most mature platforms among candidates for scalable quantum information processing. In this poster, an overview of current results from four specific projects will be presented. Two projects involve increased light collection from trapped ion for state detection and/or remote entangling of distant ions. The first involves cavity integration into a linear surface trap, and the second, involves integration of diffractive optical elements into a linear surface trap for increased light collection. Another project involves a trap with a ring geometry which could be used to trap long chains of equally spaced ions. Finally, we report on initial testing of a trap structure with vastly improved in-plane optical access. In this structure in-plane beams can be focused to less than 8 microns while keeping a distance of at least 5 beam radii to the trap structure. Along with these projects other relevant progress from Sandia National Laboratory's ion trap group will be presented. This work was supported by Sandia's Laboratory Directed Research and Development (LDRD) and the Intelligence Advanced Research Projects Activity (IARPA). Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
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K1.00012: Photon blockade meets electromagnetically induced transparency Haytham Chibani, James Alves De Souza, Eden Figueroa, Celso Jorge Villas Boas, Gerhard Rempe One of the outstanding goals of quantum optics is the realization of controllable nonlinearities at the level of single quanta of matter and light. Here, we theoretically study the optical control of the quantum dynamics of a system which merges single-atom cavity quantum electrodynamics with electromagnetically induced transparency, namely a three-level atom strongly coupled to a high-finesse cavity. We explore the photon statistics of the light emitted from the cavity by calculating the equal-time second-order intensity correlation function $g^{2}(0)$. We find a rich structure in the behavior of $g^{2}(0)$ which exhibits photon statistics varying from sub-Poissonian ($g^{2}(0) \approx 0$) to super-Poissonian ($g^{2}(0) \approx 100$), and which can be optically tuned via the control field intensity. We also show that when the system is strongly driven, $g^{2}(0)$ shows two sub-Poissonian regions at different control field intensities, resulting from a single-photon and a two-photon blockade, respectively. The observed quantum control paves the way towards the implementation of a novel quantum device which allows the switching and/or the attenuation of the amplitude noise of a laser beam. [Preview Abstract] |
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K1.00013: Scalable Techniques with Trapped Ion Quantum Information Processing Ryan Bowler, John Gaebler, Ting Rei Tan, Yiheng Lin, David Hanneke, John Jost, Jonathan Home, Adam Meier, Emanuel Knill, Dietrich Leibfried, David Wineland We report progress towards combining all the building blocks required for scalable quantum information processing using trapped atomic ions. Included elements are qubits with long coherence times, a laser-induced universal gate, motional state initialization using a second ion species, and information transport. Our techniques include the use of a multiple electrode segmented trap, wherein information transport is achieved through the transport of ions between spatially distinct locations. While experiment timescales had previously been dominated by ion transport and re-initialization of motional states, we have achieved diabatic transport of ions on timescales comparable to quantum logic with low motional excitations [1]. We have also achieved rapid sympathetic ground state cooling with use of an electromagnetically-induced transparency cooling scheme [2]. In addition, we have demonstrated a method to efficiently measure gate fidelity in a scalable way involving multiple qubits and randomized benchmarking [3]. [1] R. Bowler \textit{et. al.} Phys. Rev. Lett. \textbf{109}, 080502 (2012) [2] Y. Lin \textit{et. al. }arXiv:1211.6647 [3] J. P. Gaebler \textit{et. al.} Phys. Rev. Lett. \textbf{108}, 260503 (2012) [Preview Abstract] |
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K1.00014: Qubit Manipulations Techniques for Trapped-Ion Quantum Information Processing John Gaebler, Ting Rei Tan, Yiheng Lin, Ryan Bowler, John Jost, Adam Meier, Emanuel Knill, Dietrich Leibfried, David Wineland We report recent results on qubit manipulation techniques for trapped-ions towards scalable quantum information processing (QIP). We demonstrate a platform-independent benchmarking protocol for evaluating the performance of Clifford gates, which form a basis for fault-tolerant QIP. We report a demonstration of an entangling gate scheme proposed by Bermudez {\it et~al.} [Phys. Rev. A. {\bf 85}, 040302 (2012)] and achieve a fidelity of 0.974(4). This scheme takes advantage of dynamic decoupling which protects the qubit against dephasing errors. It can be applied directly on magnetic-field-insensitive states, and provides a number of simplifications in experimental implementation compared to some other entangling gates with trapped ions. We also report preliminary results on dissipative creation of entanglement with trapped-ions. Creation of an entangled pair does not require discrete logic gates and thus could reduce the level of quantum-coherent control needed for large-scale QIP. [Preview Abstract] |
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K1.00015: Progress Towards a Quantum Memory with Telecom-Wavelength Conversion Daniel Stack, Qudsia Quraishi, Patricia Lee, Ian Grissom, Ronald Meyers, Keith Deacon, Arnold Tunick Fiber-based transmission of quantum information over long distances may be achieved using quantum memory elements and quantum repeater protocols.\footnote{Duan et al., Nature {\bf 414}, 413-418 (2001)} However, atom-based quantum memories typically involve interactions with light fields outside the telecom window needed to minimize absorption in transmission by optical fibers. We report on progress towards a quantum memory based on the generation of 780 nm spontaneously emitted single photons by a write-laser beam interacting with a cold $^{87}$Rb ensemble. The single photons are then frequency-converted into (via four-wave mixing in a cold Rb sample) and out of (via sum frequency generation in a PPLN crystal) the telecomm band. Finally, the atomic state is read out via the interaction of a read-pulse with the quantum memory. With such a system, it will be possible to realize a long-lived quantum memory that will allow transmission of quantum information over many kilometers with high fidelity, essential for a scalable, long-distance quantum network. [Preview Abstract] |
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K1.00016: Atom Number Measurements in a Strong Light-Assisted Collision Regime Matthew Ebert, Michael Gibbons, Alex Gill, Xianli Zhang, Mark Saffman, Thad Walker We present a method for measuring small numbers of cold Rb atoms trapped in a FORT, in a regime of strong light-assisted collisions. Knowing the mean number of detected photons for a single atom, the light-assisted collisional loss rate is obtained by fitting a two-body loss rate model to the camera signal measured at different exposure times. The photon number from a short camera exposure can be used to estimate, either on a shot-by-shot basis or for a collection of shots, the number of atoms in the trap. The method presented improves our ability to characterize and minimize systematic errors that can degrade the fidelity of our deterministic single atom loading using the Rydberg blockade protocol. This work is supported by the NSF and the AFOSR Quantum Memories MURI. [Preview Abstract] |
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K1.00017: Engineered spin-spin interactions on a 2D array of trapped ions Joe Britton, Brian Sawyer, John Bollinger We work with laser cooled $^9\mbox{Be}^+$ ions confined in a Penning trap to simulate quantum magnetic interactions. The valence electron of each ion behaves as an ideal spin-$1/2$ particle. We recently demonstrated a uniform anti-ferromagnetic Ising interaction on a naturally occurring two-dimensional (2D) triangular crystal of $100 < N < 350$ ions. The Ising interaction is generated by a spin-dependent optical dipole force (ODF). For spins separated by distance $d$, we show that the range can be tuned according to $(d/d0)^{-a}$, for $0 [Preview Abstract] |
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K1.00018: Secure network of entangled atomic clocks Peter Komar, Michael Bishof, Liang Jiang, Jun Ye, Mikhail Lukin We propose a scheme for entangling atomic clocks separated by large distances using the concept of quantum networks. The protocol allows the clocks at different locations to be used in a network for a ``supreme clock signal'' with a stability set by the Heisenberg limit for the total number of atoms in the network. The realization we consider consists of multiple optical clock qubits at each location, as well as entanglement links created by sharing EPR photon pairs using quantum repeaters. We analyze the effect of local oscillator phase noise, time delays, and decoherence on the overall stability using different feedback schemes. We show that, for the current-state-of-the-art laser noise spectrum, the network is able to utilize a fully entangled GHZ state for a large number of clock qubits. We show that such a network can be made completely secure by preventing outside parties and individual participants from taking unfair advantage, while at the same time, providing access to the ``supreme clock signal'' for all honest contributors. Our protocol could serve as the backbone for a future global positioning system that will greatly surpass the accuracy and stability of the current GPS network. [Preview Abstract] |
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K1.00019: QUANTUM AND/OR NON LINEAR OPTICS |
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K1.00020: Coherent Light Generation Using Four-Wave Mixing Erik Brekke, Laura Alderson Four-wave mixing can be used to generate coherent, diffraction limited output beams, with frequencies difficult to acquire in commercial lasers. Here a narrow ECDL locked to the two photon 5s-5d transition in Rubidium, combined with a tapered amplifier system, generates a high power cw beam at 778 which is used to generate coherent light at 420 nm through parametric four-wave mixing. By controlling both the intensity and frequency of the incoming beam, this process has been optimized, and the frequency dependence analyzed. The efficiency of the process is limited when on resonance, and further investigations are underway to increase efficiency and characterize the frequency of the generated beam. [Preview Abstract] |
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K1.00021: Optical Pattern Formation in Cold Atoms: Explaining the Red-Blue Asymmetry Bonnie L. Schmittberger, Daniel J. Gauthier The study of pattern formation in atomic systems has provided new insight into fundamental many-body physics and low-light-level nonlinear optics. Pattern formation in cold atoms in particular is of great interest in condensed matter physics and quantum information science because atoms undergo self-organization at ultralow input powers. We recently reported the first observation of pattern formation in cold atoms but found that our results were not accurately described by any existing theoretical model of pattern formation. Previous models describing pattern formation in cold atoms predict that pattern formation should occur using both red and blue-detuned pump beams, favoring a lower threshold for blue detunings. This disagrees with our recent work, in which we only observed pattern formation with red-detuned pump beams. Previous models also assume a two-level atom, which cannot account for the cooling processes that arise when beams counterpropagate through a cold atomic vapor. We describe a new model for pattern formation that accounts for Sisyphus cooling in multi-level atoms, which gives rise to a new nonlinearity via spatial organization of the atoms. This spatial organization causes a sharp red-blue detuning asymmetry, which agrees well with our experimental observations. [Preview Abstract] |
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K1.00022: Using Rydberg Atom Electromagnetically Induced Transparency for Microwave Electrometry Applications Jonathon Sedlacek, Haoquan Fan, Renate Daschner, Charles Ewel, Harald K\"{u}bler, James Shaffer We present a method to probe microwave fields and atom surface interactions using Rydberg atom electromagnetically induced transparency (EIT). The basic mechanism is to couple an external microwave field or surface polariton modes to a ladder-type Rydberg atom EIT system. Our technique is sensitive to both the amplitude and the polarization of the microwave field. In addition to developing this method for a microwave electric field standard, we are applying it to study Rydberg atoms interacting with surface polaritons and near-field effects with sub-wavelength resolution. We also investigate improvements in our sensitivity based on using dispersive, rather than absorptive effects, induced in the atoms. [Preview Abstract] |
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K1.00023: ABSTRACT WITHDRAWN |
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K1.00024: Resonant two-photon absorption and electromagnetically induced transparency in open ladder-type atomic system Han Seb Moon, Heung-Ryoul Noh We have experimentally and theoretically studied resonant two-photon absorption (TPA) and electromagnetically induced transparency (EIT) in the open ladder-type atomic system of the 5S$_{1/2}$(F $=$ 1)-5P$_{3/2}$(F' $=$ 0, 1, 2)-5D$_{5/2}$(F'' $=$ 1, 2, 3) transitions in $^{87}$Rb atoms. As the coupling laser intensity was increased, the resonant TPA was transformed to EIT for the 5S$_{1/2}$(F $=$ 1)-5P$_{3/2}$(F' $=$ 2)-5D$_{5/2}$(F'' $=$ 3) transition. We demonstrate the influence of the atomic system openness and the multi-photon interaction on the resonant TPA and EIT in the three-level ladder-type atomic system. From the numerical results, considering all the degenerate magnetic sublevels of the 5S$_{1/2}$-5P$_{3/2}$-5D$_{5/2}$ transition, both the competing EIT and TPA phenomenon could be understood by the decomposition of the spectrum into an EIT component owing to the pure two-photon coherence and a TPA component caused by the mixed term [Preview Abstract] |
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K1.00025: Post-selection effect of polarization in intensity correlation of electromagnetically induced transparency HeeJung Lee, HanSeb Moon We have studied intensity fluctuations of a laser field propagating through a resonant Rb medium in a situation of electromagnetically induced transparency (EIT). We observed that the intensity fluctuations are depended on selecting polarization of the field after a Rb cell. These results are confirmed by placing a half-wave plate which induced the fluctuations between linearly polarized optical fields and a quarter-wave plate which induced the fluctuations between opposite circular polarized optical fields at the same condition. The magnitude of the correlations depends on the applied magnetic field. We also performed the incident power and temperature dependence of second-order correlation function g$^{(2)}$(0) at zero delay time in the condition of using quarter wave plate. [Preview Abstract] |
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K1.00026: Single Photon Nonlinear Optics in Graphene Michael Gullans, Darrick Chang, Frank Koppens, F. Javier Garc\'Ia de Abajo, Mikhail Lukin Achieving strong interactions between photons is a central goal in quantum information science and classical nonlinear optics. We show that one can realize significant nonlinear interactions at the few photon level in bulk graphene by taking advantage of the electric field enhancement associated with the strong confinement of graphene plasmons. We also show that one can achieve significantly out-coupling to free space by using a nonlinear grating. We discuss applications of this system that emerge due to the unique fabrication opportunities and electrical control of graphene. [Preview Abstract] |
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K1.00027: Blue light generation using periodically poled nonlinear crystals Ali Khademian, David Shiner We have studied blue light generation using SHG of IR light. We have used single pass waveguides and bulk crystals with buildup cavities. The nonlinear crystals used were periodically poled Lithium Niobate (LN) [1] and Potassium Titanyl Phosphate (KTP) [2]. Each of these approaches had limitations with regards to the maximum power handling and the stability of operation. Currently we are working on a different crystal in a new buildup cavity to circumvent some of the previous difficulties resulting from photorefractive damage and excessive heating due to blue absorption. Our initial measurements show that Lithium Tantalite (LT) has higher photorefractive threshold and much lower blue absorption (2{\%} vs 15{\%} for 20 mm crystal length). The new buildup cavity incorporates a more convenient commercial piezo mirror translator for feedback control. The buildup cavity can be operated with a minimum of 6 V as opposed to the 1000 V previously. We are exploring the use of a single DSP (digital signal processor) to perform all the locking and electronic control functions of the cavity. We are studying the coupling and propagation properties of the IR beams more carefully to minimize cavity and coupling losses, particularly due to front wave distortion caused by mirrors and lenses used in the setup. To optimize our cavity and to make the best and simplest choice of optical elements possible, different commercial (off the shelf) lenses and mirrors have been evaluated experimentally in our setup. [1] Koustrubh Danekar, Ali Khademian, and David Shiner, Opt. Lett. 36, 2940 (2011), [2] Ali Khademian and David Shiner, JWA33, CLEO (2007) [Preview Abstract] |
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K1.00028: Blue (420 nm) and Infrared (1324 nm) Coherent Beams Generated by Multiple Wave Mixing in Rb Vapor R.J. Knize, J.F. Sell, M.A. Gearba Utilizing nonlinear optical processes in Rb vapor we describe the generation of coherent optical fields at 420 nm and 1324 nm. Input laser beams at 780 nm and 776 nm enter a heated Rb vapor cell collinear and circularly polarized. Rubidium atoms are excited to the $5D_{5/2}$ state, with cascading decays through the $6P_{3/2} \rightarrow 5S_{1/2}$ and $6S_{1/2} \rightarrow 5P_{1/2}$ states producing blue (420 nm) and IR (1324 nm) beams, respectively. Scaling the input 780 nm and 776 nm laser powers to $\geq$ 200mW we obtain a coherent blue beam of 9 mW power, almost an order of magnitude larger than previously achieved. An IR beam of $\leq$ 3 mW is also produced and we describe the dependencies of both beams in relation to the Rb density, the frequency detuning between Rb ground state hyperfine levels, and the input laser intensities. [Preview Abstract] |
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K1.00029: Effects of four-wave mixing on light propagating in an EIT medium Nikolai Lauk, Christopher O'Brien, Michael Fleischhauer The typical EIT media consist of $\Lambda$ type atoms where a propagating signal field is resonant with an optical transition which is coupled by a strong resonant laser to an adjacent transition. Quantum interference makes the medium transparent to the signal. In many EIT experiments, the driving laser also acts as a far-detuned field on the signal transition, which for high optical depth causes a four-wave mixing (FWM) process. The far-detuned field generates a new co-propagating idler field which gives rise to gain for the signal field. The presence of gain introduces noise on the signal field, due to both spontaneous emission as well as a vacuum contributions of the idler. Using the Heisenberg-Langevin approach and solving the corresponding Maxwell-Bloch equations for the propagating field operators in a EIT FWM medium, we find analytic expressions for the noise and discuss the effect of FWM on EIT experiments, such as those done for EIT based quantum memories. [Preview Abstract] |
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K1.00030: Optical Coherence of the Fluorescence of a Driven Single-Atom with Slow and Fast Light Media Tony Abi-Salloum, Jon Davis, Frank Narducci In this talk we examine the first- and second-order two-time correlation functions of the fluorescent field of a driven single-atom in the presence of a slow light medium. We suggest experimental arrangements of the Young's double slit type (g(1) measurements) or of the Hanbury Brown and Twiss type (g(2) measurements in which one arm contains a positively or negatively dispersive atomic medium. The slow propagation of the corresponding field through the added medium has a dramatic effect on the resulting correlation functions. In this talk, We present a systematic study of these systems and their impact on the first- and second-order coherence functions with varying group velocity delay. Different cases of negatively (slow light) and positively (fast light) dispersive media are studied leading to a variety of alterations in the correlation functions. [Preview Abstract] |
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K1.00031: Atomic Localization Beyond the Diffraction Limit Using EIT Zach Simmons, Jared Miles, Deniz Yavuz The diffraction limit sets a minimum size for regions that can be resolved or addressed using light. We demonstrate an experiment where excitation of atoms to a specific hyperfine level is confined to $\sim$100nm wide bands, about 8 times smaller than the excitation wavelength. The technique uses the nonlinear power dependence of EIT to coherently transfer atoms only near the nodes of a standing wave. Increasing the standing wave intensity can produce vanishingly small low-intensity areas about the nodes and as a result atomic transfer occurs only in very narrow bands. Since regions smaller than the diffraction limit cannot be directly imaged, confirmation of narrowing is provided by an autocorrelation measurement technique. The experiment is performed using $^{87}$Rb atoms trapped in an optical dipole trap and utilizes $\sim$100ns EIT pulses. [Preview Abstract] |
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K1.00032: Optical Pumping Wavefront Propagation Zachary DeLand, Brian Lancor, Thad Walker We present a method of tracking the propagation of a slow-moving optical pumping wavefront in an optically thick rubidium cell. An unpolarized gas of rubidium atoms initially presents an opaque medium for a resonant D1 circularly polarized pump laser. However, absorption of the pump beam optically pumps atoms into a state of near transparency. This allows beam propagation through the cell with a velocity proportional to the absorption rate. The progress of the beam propagation can be tracked by measuring the line average polarization of the cell as a function of time, using the Faraday rotation of a probe beam. We will present simulations and results demonstrating the progress of this optical pumping wavefront as it pumps the entire cell to transparency. This is an important diagnostic for testing models of spin-exchange optical pumping of $^3$He. This work is funded by the DOE. [Preview Abstract] |
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K1.00033: ABSTRACT WITHDRAWN |
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K1.00034: COLD ATOMS, MOLECULES AND PLASMAS II |
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K1.00035: Progress toward creation of a Rb-87 MOT to be loaded directly into a wide-range accordion lattice John Huckans We report on our progress toward creation of a Rb-87 three-dimensional magneto-optical trap (3D MOT) to be loaded directly into an optical lattice. Preliminary calculations suggest the feasibility of achieving an approximate 10$^{2}$ increase in phase space density by combining standard optical molasses techniques with spatial density compression of a 3D MOT with an accordion lattice.\footnote{J.H. Huckans, Univ. of Maryland doctoral dissertation (2006).}$^,$\footnote{L. Fallani et al., Opt. Express 13, 4303-4313 (2005).}$^,$\footnote{T.C. Li et al., Opt. Express 16, 5465-5470 (2008).}$^,$\footnote{R.A. Williams et al., Opt. Express 16, 16977-16983 (2008).} [Preview Abstract] |
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K1.00036: Sympathetic cooling and reactions in an ion-neutral hybrid trap. Winthrop Smith, James Wells, Douglas Goodman, Ilamaran Sivarajah, Frank Narducci We investigated the sympathetic cooling of $Na^{+}$ ions by collisions with cold Na atoms in a hybrid trap consisting of a MOT and a linear Paul trap. Since $Na^{+}$ is a closed shell ion and lacks optically accessible transitions from the ground state, we applied four general non-optical techniques for thermometry in a hybrid trap. Simulations using SIMION 7.0 and also our experimental results suggest that there is a cooling effect, but this effect is modest for large numbers of ions $(\sim 10^{4})$. When we attempted to use the Na MOT to cool $Ca^{+}$ ions, there was evidence of a surprisingly large charge exchange rate, to be discussed. [Preview Abstract] |
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K1.00037: Progress towards state detection of molecular ions using quantum logic techniques Shiqian Ding, Meng Gao, Roland Hablutzel, Dzmitry Matsukevich The manipulation and detection of the internal (rovibrational) states of a single molecular ion via quantum logic techniques can be utilized for precision measurements, spectroscopy and studies of quantum mechanical aspects of chemical reactions. In our proposed scheme, we transfer the internal state of the single molecular ion to the state of the co-trapped single atomic ion via the excitation of the common modes of motion such that from the detected state of the atomic ion we can infer the internal state of our molecular ion. We report on the production of a sympathetically cooled SiO$^{+}$ molecular ion (co-trapped with a Yb$^+$ atomic ion) as verified by the measurement of the trap frequency. To decrease the Zeeman shifts of the molecular ion enegry levels, we minimize bias magnetic field and destabilize the resulting $^{171}$Yb$^+$ dark states via polarization modulation of the laser beams. We also present our work towards the coupling of the internal state of the molecular ion to the motional state of the ions and preparation of a molecular state using broadband optical pumping. [Preview Abstract] |
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K1.00038: Fermion Pairing Across a Dipolar Interaction Induced Resonance Zhe-Yu Shi It is known from the solution of the two-body problem that an anisotropic dipolar interaction can give rise to s-wave scattering resonances, which are named dipolar interaction induced resonances (DIIR). We study the zero-temperature many-body physics of a two-component Fermi gas across a DIIR. In the low-density regime, it is very striking that the resulting pairing order parameter is a nearly isotropic singlet pairing and the physics can be well described by an s-wave resonant interaction potential with finite range conditions, despite the anisotropic nature of the dipolar interaction. The pairing energy is as strong as a unitary Fermi gas near a magnetic Feshbach resonance. In the high-density regime, the anisotropic effect plays an important role. We find phase transitions from singlet pairing to a state with mixed singlet and triplet pairing and then from mixed pairing to pure triplet pairing. The state with mixed pairing spontaneously breaks the time-reversal symmetry. [Preview Abstract] |
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K1.00039: Electromagnetic induced transparency in strongly correlated quantum gases Hsiang-Hua Jen, Daw-Wei Wang We develop a very general theory for the electromagnetic induced transparency (EIT) in ultracold quantum gases, applicable for both Bose and Fermi gases with arbitrary inter-particle interaction strength. Different from the standard theory for a frozen atom without inter-atom interaction, we consider the full kinetics and interaction of atoms, and derive the exact probe field electric susceptibility (i.e. the EIT spectrum) within the linear response theory at zero temperature. We find that the EIT spectrum is directly related to the dynamical Green's function of the ground state, and therefore can be a direct measurement of the many-body physics. We apply our theory to analytically and numerically several strongly interacting cases: 1D Luttinger liquid, Mott insulator state in optical lattice, and the superfluid case of two-component Fermi gases. We discuss how the Luttinger exponent, single particle gap, and pairing mechanism can be observed from the EIT spectrum. [Preview Abstract] |
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K1.00040: Computing the Polaron to Bubble Crossover of an Impurity in a Bose-Einstein Condensate Alina Blinova, Malcolm Boshier, Eddy Timmermans Cold trapped atoms provide an ideal laboratory for exploring many-body quantum phenomena. We study the case of a distinguishable neutral atom - an impurity - immersed in a dilute Bose-Einstein condensate (BEC). When strongly coupled to the BEC, the impurity self-localizes, resembling an electron in a dielectric crystal in the polaron system described by Landau. When the BEC-impurity interaction is increased further, we discover that the system gradually changes to a state resembling the ``bubble'' formed by an electron in superfluid helium. Because the BEC-impurity interaction can be Feshbach-tuned over a wide range, this system offers a unique way to study the cross- over between the polaron and bubble regimes. We obtain the ground state wavefunctions of the impurity and of the BEC by numerically minimizing the Gross-Pitaevskii energy functional for the system using an iterative conjugate gradient scheme implemented in spherical polar coordinates. The results allow us to study the cross-over from polaron to bubble regimes. This poster will discuss our numerical method, describe the behavior of the system in the polaron, cross-over, and bubble regimes, and also present a phase diagram for the BEC-impurity system which can serve as a roadmap for future experiments. [Preview Abstract] |
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K1.00041: Extracting Equation of State of a Trapped Gas from the Frequency of its Collective Excitations Maxim Olshanii, H\'{e}l\`{e}ne Perrin We address the question of a relationship between frequency of small collective excitations of an unknown trapped cold gas and its Equation of State (EoS). In particular, we compare the frequency-EoS relationship obtained using a nonlinear double amplitude-coordinate perturbative expansion [M.\ Olshanii, H.\ Perrin, V.\ Lorent, PRL 105, 095302 (2010)] with the formula resulting from a scaling variational anzats [G.E. Astrakharchik, R. Combescot, X. Leyronas, S. Stringari, PRL 95, 030404 (2005)] and show that for power-law EoS's, the two agree exactly. We further compare predictions of both methods with {\it ab initio} numerical results. We argue that the frequencies of collective excitations represent a new reliable second thermodynamical axis, to complement the existing one, based on density profiles [N.\ Navon, S.\ Nascimb\`{e}ne, F.\ Chevy, C.\ Salomon, Science 328, 729 (2010)] . [Preview Abstract] |
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K1.00042: Observation of thermally activated vortex pairs in a quasi-2D Bose gas Sang Won Seo, Jae-yoon Choi, Woo Jin Kwon, Seji Kang, Jeong Ho Han, Yong-il Shin The Berezinskii-Kosterlitz-Thouless (BKT) theory provides a microscopic mechanism for the 2D phase transition, where vortices with opposite circulation are paired below a critical temperature. The BKT mechanism has been experimentally tested in many 2D systems, but there has been no direct observation of the vortex pairing in a 2D superfluid. Here we report on the observation of thermally excited vortex pairs in a trapped quasi-2D Bose gas. We measure the in-plane distribution of thermally activated vortices in a trapped quasi-2D Bose gase, where the visibility of density-depleted vortex cores is enhanced by radially compressing the sample before releasing the trap. The pairing of vortices is revealed by the two-vortex spatial correlation function obtained from the vortex distribution. The vortex density decreases gradually as temperature is lowered, and below a certain temperature, a vortex-free region emerges in the center of the sample. This represents a crossover from a Berezinskii-Kosterlitz-Thouless phase with vortex-pair excitations to a vortex-free Bose-Einstein condensate in a finite-size 2D system.\\[4pt] [1] J. Choi, S. W. Seo, and Y. Shin, arXiv:1211.5649 (2012). [Preview Abstract] |
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K1.00043: Experiments with Superfluid Atom Circuits Avinash Kumar, Jeffery Lee, Stephen Eckel, Fred Jendrzejewski, Christopher Lobb, William Phillips, Gretchen Campbell We trap a neutral $^{23}$Na BEC in an all optical toroidal potential, and mechanically impart angular momentum to the BEC to obtain superfluid currents. The experiments done in our group have demonstrated the existence of persistent quantized currents and studied the behavior of the currents in the presence of ``a weak link barrier.'' Just as RF SQUIDS are used to detect magnetic fields, our setup could be used to detect small changes in rotation in an analogous way. We will report on our recent results, including the demonstration of hysteretic behavior and attempts to measure the current-phase relationship of the ``weak link barrier.'' [Preview Abstract] |
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K1.00044: Towards a Quantum Gas Microscope for Fermionic Atoms Lawrence Cheuk, Vinay Ramasesh, Melih Okan, Matthew Nichols, Waseem Bakr, Martin Zwierlein Experiments with ultracold fermionic atoms in optical lattices represent uniquely controllable realizations of many body physics. We present progress toward the construction of such an experiment, the Fermi gas microscope, which will allow for fluorescence detection of fermions in optical lattices with single-site resolution. Our experiments employ fermionic potassium and lithium atoms, with bosonic sodium used as a sympathetic coolant. Once the fermionic species are cooled to quantum degeneracy, they will be loaded into a single layer of an optical lattice and imaged with single-site resolution. Such local probing should reveal microscopic density or spin correlations difficult to distinguish in traditional bulk measurements. High-resolution probing will also allow detecting sharply localized quantum states such as edge states at the boundary of topological states of matter. Finally, microscopy will enable local manipulation and engineering of many-fermion states, e.g. for entropy redistribution in a quantum gas or for designing quantum circuits. [Preview Abstract] |
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K1.00045: Screening of the interaction between fermionic polarons Shimpei Endo, Masahito Ueda We study the induced interaction between heavy atoms immersed in a light Fermi sea. We show that when the density of the light fermions is large enough, the induced interaction between $N$ heavy atoms is screened and the heavy atoms behave as independent quasi-particles. We also show that the $N$-body Efimov effect is suppressed for any $N$ in the dense Fermi sea limit. [Preview Abstract] |
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K1.00046: Energy spectra of small two-component Fermi gases in a cubic box with periodic boundary conditions X.Y. Yin, D. Blume The properties of two-component Fermi gases become universal if the interspecies $s$-wave scattering length and the average interparticle spacing are much larger than the range of the underlying two-body potential. Using an explicitly correlated Gaussian basis set expansion approach, we determine the eigenenergies of two-component Fermi gases in a cubic box with periodic boundary conditions as functions of the interspecies $s$-wave scattering length and the effective range of the two-body potential. The universal properties of systems consisting of up to five particles are determined by extrapolating the finite-range energies to the zero-range limit. We determine the eigenenergies of states with vanishing and finite momentum. For the infinitely large scattering length case, we compare our results with those presented in the literature. [Preview Abstract] |
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K1.00047: Breathing mode of a harmonically trapped two-dimensional Fermi gas Chao Gao, Zhenhua Yu For two-dimensional (2D) atomic Fermi gases in harmonic traps, the $SO(2,1)$ symmetry is broken by the inter-atomic interaction explicitly via the contact correlation operator. Consequently, the frequency of the breathing mode $\omega_B$ of a 2D Fermi gases in a harmonic trap with frequency $\omega_0$ can be different from $2\omega_0$, which is implied by symmetry. At zero temperature, we use the sum rules of density correlation functions to yield upper bounds for $\omega_B$.We further calculate $\omega_B$ through the Euler equations in the hydrodynamic regime. The obtained value of $\omega_B$ satisfies the upper bounds and shows deviation from $2\omega_0$. [Preview Abstract] |
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K1.00048: Probing one-dimensional strongly correlated systems with a Bosonic Quantum Gas Microscope Philipp M. Preiss, M. Eric Tai, Ruichao Ma, Kazi Rajiubl Islam, Markus Greiner One-dimensional quantum systems often exhibit strongly correlated many-body physics. These strong correlations can be quantified by the entanglement entropy of a sub-system, which diverges logarithmically with system size in the gapless phase (such as the superfluid phase), violating the area law of entanglement generally followed in the ground state of the gapped phases. We study a one-dimensional system of Rb-87 in an optical lattice under a Quantum Gas Microscope to probe strong correlations with single-site resolution. While it is experimentally difficult to measure the entanglement entropy for a large system, the particle number fluctuations of a sub-system contain the signature of entanglement and are expected to show the same logarithmic divergence. With our Bosonic quantum simulator, it is also possible to study non-trivial emergent properties, such as the fractionalization of a fundamental excitation into multiple collective excitations in the system, analogous to the spin-charge separation in one-dimensional electronic systems. [Preview Abstract] |
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K1.00049: Damping Rates for Bloch Oscillations of Cold Atoms in Optical Lattices T. Bergeman Reeves {\it et al} [1] have obtained experimental results on cold atoms in incommensurate optical lattices showing that the damping processes for Bloch oscillations from mean field effects and from disorder may counteract each other. Screening effects of disorder by mean field effects had been discussed also theoretically [2,3]. Ref. [2] posits a general mechanism based on certain approximations, but it is not always clear over what range these approximations are valid and how they might be extended. By numerical calculations based on the time-dependent Gross-Pitaevskii equation, I survey such damping effects as a function of the amplitudes of the mean field and of a ``disorder'' potential from a second noncommensurate lattice, as in [1]. One question of interest is the following: for a given arbitrary value of the disorder potential, as a function of atom density or atom-atom interaction, where is the mimimum in the damping of the Bloch oscillations?\\[4pt] [1] J. Reeves, M. Vogt, B. Gadway, D. Pertot and D. Schneble, BAPS {\bf 57}, 76 (2012). \\[0pt] [2] T. Schulte et al., Phys, Rev, A {\bf 77}, 923619 (2008). \\[0pt] [3] S. Walter et al., Phys. Rev. A {\bf 81}, 033623 (2010). \\ [Preview Abstract] |
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K1.00050: Investigating the laser angle dependence of movable pinhole traps for neutral atom quantum computing Travis Frazer, David Roberts, Jason Schray, Glen Gillen, Katharina Gillen-Christandl Neutral atom approaches meet all DiVincenzo quantum computing criteria but scalability. Our proposed solution is a two-dimensional array of dipole traps formed in the diffraction pattern immediately behind an array of pinholes [1]. For two-qubit gates, trapped atoms can be brought together and apart by changing the trap laser angle and exploiting the polarization dependence of the trapping potential [2]. We are investigating the diffraction pattern for a large range of angles of incidence through direct measurement and computations. We will present these results and our experimental progress with our in-house system for transferring atoms from our MOT to the pinhole traps.\\[4pt] [1] G. D. Gillen, et al., Phys. Rev. A 73, 013409 (2006).\\[0pt] [2] K. Gillen-Christandl and B. D. Copsey, Phys. Rev. A 83, 023408 (2011) [Preview Abstract] |
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K1.00051: Long range magnetic ordering of ultracold fermions in an optical lattice P.M. Duarte, R.A. Hart, T.-L. Yang, R.G. Hulet We present progress towards the observation of long range antiferromagnetic (AFM) ordering of fermionic $^{6}$Li atoms in an optical lattice. We prepare a two spin state mixture of $10^{6}$ atoms at $T/T_{F}=0.1$ by evaporatively cooling in an optical dipole trap. The sample is then transferred to a dimple trap formed by three retroreflected laser beams at 1064~nm that propagate in orthogonal directions. The polarization of the retroreflected light is controlled using liquid crystal retarders, which allow us to adiabatically transform the dimple trap into a 3D lattice. Overlapped with each of the three dimple/lattice beams is a beam at 532~nm, which can cancel the harmonic confinement and flatten the band structure in the lattice. This setup offers the possibility of implementing proposed schemes\footnote{C. J. M. Mathy et al., Phys. Rev. A \textbf{86}, 023606 (2011)} which enlarge the size of the AFM phase in the trap. As a probe for AFM we use Bragg scattering of light\footnote{T. A. Corcovilos et al., Phys. Rev. A \textbf{81}, 013415 (2010)}. We have observed Bragg scattering off of the (100) lattice planes, and using an off-angle probe we can see the diffuse scattering from the sample which serves as background for the small signals expected before the onset of AFM ordering. [Preview Abstract] |
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K1.00052: Direct Measurement of the Zak phase in Topological Bloch Bands Monika Aidelsburger, Marcos Atala, Julio T. Barreiro, Dmitry Abanin, Takuya Kitagawa, Eugene Demler, Immanuel Bloch Geometric phases that characterize the topological properties of Bloch bands play a fundamental role in the modern band theory of solids. We report on the direct measurement of the geometric phase acquired by cold atoms moving in one-dimensional optical lattices. Using a combination of Bloch oscillations and Ramsey interferometry, we extract the Zak phase---the Berry phase acquired during an adiabatic motion of a particle across the Brillouin zone---which can be viewed as an invariant characterizing the topological properties of the band. For a dimerized optical lattice, which models polyacetylene, we measure a difference of the Zak phase equal to 0.97(2)$\pi$ for the two possible polyacetylene phases with different dimerization. This indicates that the two dimerized phases belong to different topological classes, such that for a filled band, domain walls have fractional quantum numbers. Our work establishes a new general approach for probing the topological structure of Bloch bands in optical lattices. [Preview Abstract] |
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K1.00053: A hybrid-trap BEC for radiofrequency-dressed optical lattice experiments Nathan Lundblad, Joanna Moody Recent work in lattice-based ultracold atomic physics has focused on the development of increasingly precise and complex apparatus to push the boundaries of what can be measured with such systems. Historically such experiments have generally been confined to simple-cubic lattices with recent forays into systems both more fertile and more challenging, such as the honeycomb lattice or even the kagome net. We report progress towards nonstandard-geometry optical-lattice experiments using a recently-constructed BEC apparatus at Bates College. We summarize laser system construction, document the design and construction of a spin-flip Zeeman slower, present characterization of the laser cooling process, and present the results of magnetic trapping and evaporative cooling, including recent results showing transfer to a 1064nm fiber-laser dipole trap and the resulting path to BEC. We also report on progress toward observation of adiabatic eigenstates in radiofrequency-dressed spin-dependent lattices loaded from said BEC, and present plans for observations of toroidal Wannier-function lattices. We also present a discussion of other possible nonstandard-geometry lattices that will be explored with this new apparatus. [Preview Abstract] |
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K1.00054: Spin interactions in ultra-cold many-body systems Sebastian Hild, Peter Schauss, Johannes Zeiher, Takeshi Fukuhara, Marc Cheneau, Manuel Endres, Christian Gross, Stefan Kuhr, Immanuel Bloch Spin Hamiltonians are used to explain a variety of different phenomena in solid state physics. Quantum simulation of such systems with ultracold gases promises deeper insight in the emerging physics. Here we report on the realization of two kinds of effective spin Hamiltonians with ultracold Rubidium atoms in optical lattices. Single site resolved detection enabled the direct measurement of a single spin impurity immersed into a bath of opposite spins. The measurement revealed coherent superexchange dynamics in the Heisenberg regime as well as evidence for polaronic behavior in the superfluid regime. In a second experiment we used Rydberg atoms to realize long-range interacting effective spin systems. By high resolution optical detection we observed the emergence of spatially ordered patterns upon laser excitation of a dense 2D gas. The results pave the way towards quantum simulation of novel long-range interacting quantum systems with ultracold atoms. [Preview Abstract] |
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K1.00055: Amplitude Effects in Lattice Modulation Spectroscopy Andreas Dirks, Karlis Mikelsons, Jim Freericks, H.R. Krishnamurthy Linear-response calculations for a periodically modulated optical lattice depth within the Mott-insulating phase of the Hubbard model clearly predict a resonance in the doublon production rate at the Hubbard repulsion U. Using a recently developed strong-coupling approach, we examine the effect of an increasingly high amplitude of the modulation. We find that multi-quanta excitations are likely to occur beyond a certain threshold. [Preview Abstract] |
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K1.00056: Precise measurement of phase transitions in spinor Bose-Einstein condensates Anshuman Vinit, Carlo Samson, Chandra Raman We investigate out-of-equilibrium phenomena in sodium spinor Bose-Einstein condensates by studying the evolution of system following a dynamical instability. Sodium condensates are initially prepared in $|F=1,m_F=0 \rangle $ state and are rapidly quenched across a quantum phase transition. It leads to pair formation of $ |F=1,m_F= +1 \rangle $ and $|F=1,m_F=-1 \rangle $ atoms and results in their rapid amplification through spin-mixing instability. We reveal strong tunability of this amplification using magnetic field gradients. We observe a suppression of up to a factor of 10 in instability rates in the neighborhood of the phase transition. These observations show good agreement with predictions based upon numerical solutions to the Bogoliubov de-Gennes equations. We also observe a dramatic sharpening of the quantum phase transition point as magnetic field inhomogenieties are reduced, resulting in a resolution of the phase transition at the 1 Hz level. [Preview Abstract] |
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K1.00057: Non-equilibrium dynamics of arbitrary-range Ising models with decoherence: an exact solution Michael Foss-Feig, Kaden Hazzard, John Bollinger, Ana Maria Rey Understanding the interplay between dissipation and interaction driven many-body correlations is crucial to the fields of quantum simulation, quantum metrology, and quantum information. Dissipation can degrade the delicate correlations that are often sought in isolated many-body quantum systems, but it can also give rise to rich non-equilibrium dynamics and steady-state behaviors not otherwise possible. Motivated by experiments with trapped ions and Rydberg atoms, we have obtained an exact solution for the dynamics of arbitrary-range Ising models in the presence of generic Markovian decoherence [1]. Our solution enables us to exactly quantify the spin-squeezing achievable in present day trapped ion experiments [2]. We find that the interplay between interactions and decoherence causes many-body correlations to decay much faster than predicted by simple mean-field or single-particle arguments. In addition to revealing the precise mechanism of this enhanced decoherence, our exact solution points to a possible avenue toward mitigating it. \\[4pt] [1] M. Foss-Feig, K. R. A. Hazzard, J. J. Bollinger, and A. M. Rey, arXiv:1209.5795 [quant-ph] (2012)\\[0pt] [2] J. W. Britton et al., Nature 484, 489-492 (2012) [Preview Abstract] |
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K1.00058: The Multi-Layer Multi-Configuration Time-Dependent Hartree Method for Bosons: Theory and Applications Lushuai Cao, Sven Kr\"onke, Oriol Vendrell, Peter Schmelcher We introduce the multi-layer multi-configuration time-dependent Hartree method for bosons (ML-MCTDHB), which represents a unique tool for investigating the nonequilibrium dynamics of multi-species bosonic systems in arbitrary dimensions. Being an ab initio method for solving the time-dependent Schr\"odinger equation, ML-MCTDHB takes all correlations into account. The multi-layer feature of ML-MCTDHB allows for tailoring the wave function ansatz in order to describe intra- and inter-species correlations accurately and efficiently. Examples are shown here to demonstrate the beneficial scaling and the efficiency of the method, especially in the study of nonequilibrium dynamics. [Preview Abstract] |
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K1.00059: Progress towards using Feshbach Resonance Optimized Photoassociation spectroscopy to map excited electronic states of Rb dimers Sean Krzyzewski, Thomas Akin, James Dizikes, Gregory Parker, Michael Morrison, Eric Abraham We present progress towards measuring the complete vibrational spectrum of singly-excited molecular electronic potential curves of Rubidium using Feshbach optimized photoassociation. In this process, Feshbach resonances are used to enhance the photoassociation signal by altering the initial scattering wave function, increasing the overlap with the final excited-state bound wave function. We focus on the purely triplet $0^-_g$ state of Rb$_2$ that connects asymptotically to the $5^2S_{1/2} + 5^2P_{1/2}$ separated-atoms limit, due to its simple electronic structure. We present calculated absolute PA rates into vibrational states of excited electronic states that are inaccessible with conventional PA spectroscopy. These rates are found from a close-coupled scattering calculation. [Preview Abstract] |
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K1.00060: Ultra-cold three-body interactions of multi-level atoms Victor Colussi, J.P. D'Incao, Chris H. Greene We investigate the problem of three bodies interacting via a multichannel generalization of the Fermi pseudo-potential. This work specifically considers the case where each body has access to multiple internal states and thresholds. In this regime of ultra-cold few-body interactions, we analytically explore the unitarity limit for multi-level atoms, looking ultimately for novel instances of Efimov physics. We also model, using this machinery, few-body interactions in spinor Bose-Einstein condensates for a variety of atomic compositions. [Preview Abstract] |
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K1.00061: Collision induced losses in a dual-species magneto-optical trap of Lithium and Rubidium Sourav Dutta, Adeel Altaf, John Lorenz, D.S. Elliott, Yong P. Chen We have constructed a new apparatus for simultaneous trapping and cooling of $^{\mathrm{7}}$Li and $^{\mathrm{85}}$Rb atoms in a dual species magneto-optical trap (MOT), aimed at creating ultracold polar LiRb molecules for potential applications in quantum computing. The key improvements over our previous apparatus include a time of flight mass spectrometer for imaging ions and a compact Zeeman slower for $^{\mathrm{7}}$Li. Our dual species MOT allows us to trap $\ge $ 5x10$^{\mathrm{8}} \quad^{\mathrm{7}}$Li atoms loaded from the Zeeman slower and $\ge $ 10$^{\mathrm{8}}$ $^{\mathrm{85}}$Rb atoms loaded from a dispenser. We have observed interspecies collision induced losses from the MOTs, measured the trap loss rate coefficients $\beta_{\mathrm{Li,Rb\thinspace }}$and $\beta _{\mathrm{Rb,Li\thinspace }}$and studied their dependence on the MOT parameters. We will also present results on photo-association (PA) of Rb$_{\mathrm{2}}$ molecules and report our progress towards creating ultracold LiRb molecules by PA. [Preview Abstract] |
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K1.00062: Ion-neutral chemistry at ultralow energies:Dynamics of reactive collisions between laser-cooled Ca$^+$ or Ba$^+$ ions and Rb atoms in an ion-atom hybrid trap O. Dulieu, F.H.J. Hall, P. Eberle, G. Hegi, M. Raoult, M. Aymar, S. Willitsch Cold chemical reactions between laser-cooled Ca$^+$ or Ba$^+$ ions and Rb atoms were studied in an ion-atom hybrid trap [1]. Reaction rate constants were determined in the collision energy range $E_{coll}/k_B =$ 20~mK-20~K. Product branching ratios were studied using resonant-excitation mass spectrometry. The dynamics of the reactive processes including the radiative formation of CaRb$^+$ and BaRb$^+$ molecular ions has been analyzed using accurate potential energy curves and quantum-scattering calculations for the radiative channels. It is shown that the energy dependence of the reaction rates is governed by long-range interactions, while its magnitude is determined by short-range non-adiabatic and radiative couplings. The quantum character of the collisions is predicted to manifest itself in the occurrence of narrow shape resonances at well-defined collision energies. The present results highlight both universal and system-specific phenomena in cold ion-neutral collisions.\\[4pt] [1] F.H.J. Hall et al., Phys. Rev. Lett. 107, 243202 (2011).\\[0pt] [2] F.H.J. Hall et al. accepted by Mol. Phys. (arXiv:1301.0724). [Preview Abstract] |
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K1.00063: The effect of Vibrational excitation of molecular hydrogen on the dynamics of reaction between O$(^{1}D)$ and H$_{2}$ at ultracold temperatures G.B. Pradhan, N. Balakrishnan, B.K. Kendrick The effect of vibrational excitation of H$_2$ molecule on the reactivity of O$(^{1}D)$+H$_{2}$ reaction is explored. A time-independent quantum mechanical approach based on hyperspherical coordinates combined with the potential energy surfaces of Dobbyn and Knowles has been used for the calculation. Energy dependent cross section, probability, and rate coefficients are computed for elastic, inelastic, and reactive channels over collision energies ranging from the ultracold to thermal regimes. Our calculations show that total reaction probabilities, cross sections, and rate coefficients are almost independent of the initial vibrational quantum number of the H$_2$ molecule. The collision outcome is strongly influenced by the intermediate H$_2$O complex formed in the reaction than the initial vibrational quantum number. However, the OH vibrational distribution is found to be sensitive to the initial vibrational level of the H$_2$ molecule. For all three vibrational levels of H$_2$ the reaction is found to populate high rotational levels of OH. [Preview Abstract] |
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K1.00064: An Atom Chip-Based BEC System Having High Resolution In-Trap Imaging and Dynamic Optical Projection Capability Cameron J.E. Straatsma, Seth C. Caliga, Evan A. Salim, Dana Z. Anderson We present an Rb87 BEC system based on a glass and silicon atom chip that enables high-resolution (NA $=$ 0.6) in-trap imaging of a hybrid magnetic and optical trap. Atoms can be condensed and tightly confined in a magnetic trap established with on-chip wires, while an optical projection system is used to impose optical potentials. The optical potentials are produced using blue-detuned light modulated by a two-dimensional acousto-optic deflector. The Fourier transform of the RF signals applied to the deflectors determines the projected optical pattern, and therefore the atoms can be subjected to a practically arbitrary two dimensional potential that has a separable Fourier transform. We have used both fluorescence and absorption techniques to image atoms. The system allows for in-trap dynamical studies, for example, observing trapped-gas behavior in response to thermal gradients and changing optical potentials. We have used this system to perform studies, described elsewhere, of an atomtronic battery and a matterwave transistor oscillator. [Preview Abstract] |
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K1.00065: High Spatial Resolution Imaging and Addressing of 2D Quantum Gases Li-Chung Ha, Eric L. Hazlett, Logan W. Clark, Ulrich Eismann, Cheng Chin We report on our method of both imaging 2D Bose gases and imprinting arbitrary potentials onto 2D quantum gas of cesium atoms. By carefully characterizing our imaging systems we are able to attain imaging and addressing resolutions of $\sim$1 $\mu$m. With this versatile system we are exploring exotic trapping geometries that are otherwise very difficult to prepare. Our system can allow for the investigation of novel quantum phenomena, such as quantum critical dynamics and quantum gases in fractional dimensions. [Preview Abstract] |
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K1.00066: Magic wavelengths for optical cooling and trapping of potassium M.S. Safronova, Ulyana Safronova, Charles W. Clark We carry out a systematic study of the static and dynamic polarizabilities of the potassium atom using a first-principles high-precision relativistic all-order method in which all single, double, and partial triple excitations of the Dirac-Fock wave functions are included to all orders of perturbation theory. Recommended values are provided for a large number of electric-dipole matrix elements. Static polarizabilities of the $4s$, $4p_j$, $5s$, $5p_j$, and $3d_j$ states are compared with other theory and experiment where available. We use the results of the polarizability calculations to identify magic wavelengths for the $4s-np$ transitions for $n = 4, 5$, {\em i.e.} those wavelengths for which the two levels have the same ac Stark shifts. These facilitate state-insensitive optical cooling and trapping. The magic wavelengths for the $4s-5p$ transitions are of particular interest for attaining a quantum gas of potassium at high phase-space density. We find 20 such wavelengths in the technically interest region of $1050-1130$~nm. Uncertainties of all recommended values are estimated. [Preview Abstract] |
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K1.00067: Production of 10.4 W of single frequency coherent light at 780 nm by second harmonic generation Martin Lichtman, Michal Piotrowicz, Mark Saffman We have developed a high power, 10.4 W single frequency source at 780 nm, using second harmonic generation in a double-pass arrangement through a 50 mm long PPLN crystal. The source power is from a 20 W erbium-doped fiber amplifier at 1560 nm, giving a conversion efficiency of 52\%. Comparison of the conversion efficiency with calculations based on a modified Boyd-Kleinman theory and numerical solution of the non-linear Schr\"odinger equation will be presented. The 780 nm light is used to create an array of blue-detuned traps for quantum computing experiments with Cs atoms. [Preview Abstract] |
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K1.00068: Multiple Isotope Magneto Optical Trap from a single diode laser Eduardo Gomez, Victor Valenzuela, Saeed Hamzeloui, Monica Gutierrez We present a simple design for a Dual Isotope Magneto Optical Trap. The system requires a single diode laser, a fiber modulator and a tapered amplifier to trap and completely control both $^{85}$Rb and $^{87}$Rb. We generate all the frequencies needed for trapping both species using the fiber intensity modulator. All the frequencies are amplified simultaneously with the tapered amplifier. The position and power of each frequency is now controlled independently on the RF rather than on the optical side. This introduces an enormous simplification for laser cooling that often requires an acousto-optic modulator for each frequency. The range of frequency changes is much bigger than what is available with acousto-optic modulators since in our case is determined by the modulator bandwidth (10 GHz). Additional isotopes can be simply added by including additional RF frequencies to the modulator and extra beams for other uses can be produced the same way. [Preview Abstract] |
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K1.00069: Sensitivity of STIRAP to Optical Detuning Yuan Sun, Harold Metcalf We study the effect of optical detunings on the efficiency of STIRAP excitation of He atoms from the metastable $2^3S_1$ state to the Rydberg states in the range of $n=20$. The intermediate state of the 3 level system is $3^3P_{2,1,0}$, connected to $2^3S_1$ by $\lambda = 389$ nm light (blue) and the Rydberg states by $\lambda \sim 800$ nm light (red). The copropagating laser beams cross the atomic beam perpendicularly and are arranged for the encounter to be in the STIRAP order (red before blue) to excite Rydberg atoms efficiently. The transverse velocity spread of the atomic beam induces detunings of both red and blue light. We have implemented a transverse Doppler molasses to reduce this velocity spread. Also, we provide an alternative view of STIRAP to explain the role of detuning based on a Feynman path integral approach. It shows how the tiny population in the intermediate level is vital to the STIRAP process. [Preview Abstract] |
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K1.00070: Double-loop Microtrap for Ultracold Atoms Bin Jian, William A. van Wijngaarden A microtrap consisting of two concentric circular loops having radii of 300 and 660 $\mu$m, respectively, is demonstrated. The microtrap is formed using the magnetic field generated by the current passing through the double-loop wire pattern superposing a small external bias magnetic field perpendicular to the wire pattern plane. The double-loop wire pattern is fabricated on an atom chip device. The maximum three dimensional trap depth exceeds 1 mK when using an atom chip current of 2.6 Amps. The trap position below the atom chip surface can be adjusted over a distance of 100 microns by varying the bias field. Experimentally, more than $10^5$ $^{87}$Rb atoms were loaded into the microtrap from a quadrupole magnetic trap and remained trapped for several hundred milliseconds which was limited by the background pressure. The loading of a linear array of three microtraps is also demonstrated. The trap dimensions are readily scaled to micrometer size, which is of interest for creating a one and two dimensional array of neutral atom traps on a single atom chip. [Preview Abstract] |
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K1.00071: A spin dependent hexagonal optical lattice with complex valued tunneling Malte Weinberg, Julian Struck, Christoph Oelschlaeger, Juliette Simonet, Patrick Windpassinger, Klaus Sengstock The realization of ultracold quantum gases in hexagonal optical lattices allows for the investigation of unique topological properties especially in connection to Dirac cones. Here we report on prospects of engineering artificial gauge potentials for bosons in a tunable hexagonal optical lattice. An intrinsic spin-dependency offers a versatile method to lift the degeneracy of this bipartite lattice via the orientation of the quantization axis. It is thus possible to tailor gaps at the Dirac points in the dispersion relation. Moreover, complex tunneling parameters can be experimentally realized by applying an external periodic force which breaks time reversal symmetry. As the resulting Peierls phases range from 0 to 2$\pi $ it is possible to emulate artificial gauge potentials in such a system. With these tools at hand, we discuss the feasibility of the emulation of strong field physics with ultracold quantum gases in the honeycomb lattice as a step towards the realization of complex quantum systems, i.e. quantum Hall states and topological insulators. [Preview Abstract] |
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K1.00072: Bound States of the Spin-Orbit Coupled Ultra-Cold Atoms Rytis Jursenas, Julius Ruseckas, Gediminas Juzeliunas, Ian Spielman Motivated by recent theoretical [1, 2] and experimental [3, 4] research, we consider the Hamiltonian for the one-dimensional atomic center of mass motion with the spin-orbit and Raman coupling included. The Hamiltonian is perturbed by a short-range potential describing the impurity scattering. We concentrate on the bound state problem, though the continuous spectrum of the Hamiltonian is of interest as well. We model the potential in terms of the Dirac delta function. By taking into account a correct treatment of the Dirac deltas [5, 6], we construct the associated self-adjoint operators and show that the number of bound states of the Hamiltonian under consideration is highly dependent on the treatment of the eigenfunctions at a zero point. Additionally, we establish all possible bound states and present their behavior in various regimes of both the spin-orbit and the Raman coupling. [1] J. Br\"{u}ning et al, Phys. A: Math. Gen. 40 (2007), F113. [2] S. Takei et al, Phys. Rev. A 85 (2012), 023626. [3] Y.-J. Lin et al, Nature 471 (2011), 83. [4] L. W. Cheuk et al, Phys. Rev. Lett. 109 (2012), 095302. [5] F. A. B. Countinho et al. Rev. Bras. Ens. de Fis. 31 (2009), 4302. [6] D. Griffiths and S. Walborn, Am. J. Phys. 67 (1999), 446. [Preview Abstract] |
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K1.00073: Experimental studies of transport and dynamics of BEC in synthetic gauge fields and spin-orbit coupling Yong P. Chen, Robert Niffenegger, Abraham Olson, Chuan-Hsun Li, David Blasing We have set up a $^{87}$Rb BEC experiment focusing on the transport and dynamical phenomena of BECs in synthetic gauge fields and spin orbit interactions. The synthetic gauge and spin-orbit fields are created optically using a pair of counter propagating Raman beams, detuned $\sim$400-1000 GHz from the D2 line (780 nm), coupling different hyperfine spin (in the F=1 ground manifold) and momentum states. We have characterized the loading of our BEC into synthetic dressed state energy bands, in both the spin-orbit (weak Raman coupling) and vector gauge potential (strong coupling) regimes. We have developed techniques to probe the dressed band structure through driven inter-band transitions. We have also studied various dynamical and transport phenomena of the BECs in the dressed bands, and developed schemes to generate spin dependent electromagnetic fields that may be used to study spin dependent transport physics previously explored in solid state systems. [Preview Abstract] |
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K1.00074: PHOTON INTERACTIONS WITH ATOMS, IONS AND MOLECULES II |
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K1.00075: Comparison of laser-induced fragmentation channels of CS$^{+}$ and CO$^{+}$: a study in chemically similar molecules K.J. Betsch, T. Severt, U. Ablikim, M. Zohrabi, B. Jochim, K.D. Carnes, I. Ben-Itzhak In an effort to address how well the idea of chemically similar molecules extends into strong field phenomena, we explore similarities and differences in ultrafast laser-induced fragmentation channels from CS$^{+}$ and CO$^{+}$ molecular ion beams. We find similar fragmentation channels and features of interest, such as a laser-intensity-dependent high kinetic-energy-release (KER) peak in the dissociation channels of both molecules. However, molecule-specific features, such as the relative abundances and KERs of individual channels, are also observed. For example, we observe that, in the asymmetric-charge breakup channel \mbox{CS$^{+} \rightarrow$ CS$^{2+} \rightarrow $C + S$^{2+}$}, the carbon atom is neutral. This is opposite to the asymmetric-charge breakup from CO$^{+}$, where the carbon fragment carries the charge. Based upon their chemical similarity, we would expect similar asymmetric breakup for the two molecules. We will discuss why the actual behavior differs from our expectations. [Preview Abstract] |
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K1.00076: The Short-Pulse X-ray Facility at the Advanced Photon Source Linda Young, Paul Evans The Short-Pulse X-ray (SPX) Facility will extend time-resolved x-ray scattering and spectroscopy to the picosecond time scale while retaining the powerful characteristics of synchrotron radiation, i.e., user-controlled continuous tunability of energy, polarization, and bandwidth combined with exquisite x-ray energy and pulse-length stability over a wide energy range. Experiments at the SPX facility will produce 1-ps stroboscopic snapshots of molecular rotations, molecular excited-state transient structures, stress/strain wave propagation, magnetic domain wall dynamics, phase transitions, and the coupling between electronic, vibrational, and magnetic degrees of freedom in condensed matter systems. Time-resolved studies of transient dynamics will be possible with simultaneous picosecond time resolution and picometer structural precision for a variety of atomic, molecular, supramolecular, nanoscale, and bulk material systems. Pump-probe experiments using high-average-power, sub-picosecond, high-repetition-rate laser systems will make efficient use of the MHz x-ray rates of the SPX. Five end stations for x-ray scattering, diffraction, spectroscopy, imaging, and microscopy can be developed as part of the Advanced Photon Source Upgrade project. [Preview Abstract] |
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K1.00077: Polarization bremsstrahlung of fast ions on a multi-atomic chain Miron Ya. Amusia, Victor I. Matveev We have considered the Polarization or Atomic Bremsstrahlung (AB) [1] generated in the process of scattering of a fast charge particle on a linear chain of isolated atoms. The specific feature of AB is that the radiation is generated by the varying in direction and size dipole moment induced in the target atom by the incoming projectile. In case of multi-atomic targets, one must take into account that the projectile interacts with several atoms simultaneously, inducing a common time-dependent dipole moment. As a concrete target, we choose a linear chain of equally spaced atom with interatomic distance $d$. Using the approach developed in [2] for ion-chain scattering, we obtained intensity and angular distribution of the polarization bremsstrahlung spectrum for arbitrary number $N $of atoms in the chain. We demonstrate that the interference of photon radiation amplitudes leads to impressive alteration of the spectral angular distributions of AB on the target atomic chain as compared to that on an isolated atom. The result allows generalization for the cases when the target is a plane formed of chains. Of special interest is the case when chains form a tube. Essential difference is expected when the projectile goes inside and outside this tube.\\[4pt] [1] M. Ya. Amusia, Radiation Physics and Chemistry, 75, 1232, 2006.\\[0pt] [2] V. I. Matveev and D. U. Matrasulov, JETP Letters, \textbf{96}, 700, 2012 [Preview Abstract] |
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K1.00078: Strong-field dissociation dynamics of NO$^{2+}$: A multiphoton electronic or vibrational excitation? Bethany Jochim, M. Zohrabi, U. Ablikim, B. Gaire, F. Anis, K.D. Carnes, B.D. Esry, I. Ben-Itzhak, E. Wells, T. Uhl\'{I}kov\'{a} We utilize a 3-D momentum imaging technique to study laser-induced dissociation of a metastable NO$^{2+}$ beam into N$^{+}$+ O$^{+}$. Using an estimated initial vibrational population, measured kinetic energy release and angular distribution spectra, and time-dependent Schr\"{o}dinger equation calculations, we identify the most likely dissociation pathways. While lower intensity pulses ($<$10$^{15}$ W/cm$^{2}$) drive perpendicular transitions between the lowest two electronic states, for higher intensity pulses ($\sim $10$^{16}$ W/cm$^{2}$), dissociation parallel to the laser polarization becomes prominent. Contrary to commonly-held intuition that electronic transitions always prevail, we find that the dominant process underlying this highly-aligned feature is a multiphoton permanent dipole transition solely within the electronic ground state, leading to its continuum. [Preview Abstract] |
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K1.00079: Zero photon dissociation of CS$^{2+}$ in intense ultrashort laser pulses Travis Severt, K.J. Betsch, M. Zohrabi, U. Ablikim, Bethany Jochim, K.D. Carnes, B.D. Esry, I. Ben-Itzhak We measured the dissociation of a CS$^{2+}$ molecular ion beam in intense laser pulses ($<$50 fs, $<$$10^{15}$ W/cm$^2$), focusing on the zero photon dissociation (ZPD) and above threshold dissociation (ATD) mechanisms. The ZPD mechanism leads to dissociation with the net absorption of zero photons in a strong field. The present work extends the idea of ZPD to more complex molecules than the H$_2^+$ discussed in literature. Preliminary data suggests that ZPD is larger than ATD for CS$^{2+}\rightarrow$ C$^+ +$ S$^+$. We speculate that a pump-dump process occurs whereby the vibrational wavepacket in the electronic ground state of CS$^{2+}$ is pumped into the electronic first excited state's continuum by a single photon during the laser pulse. Once this continuum vibrational wavepacket passes the potential barrier in the ground electronic potential, the emission of a second photon is stimulated by the same laser pulse, most likely when the wavepacket moves through the internuclear distance where the two electronic states are in resonance with the driving field. A comparison is made to ZPD and ATD in the isovalent CO$^{2+}$ species. Curiously, ATD is the favored mechanism in CO$^{2+}$. The underlying molecular structure and dynamics determining this preference will be discussed. [Preview Abstract] |
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K1.00080: Photoionization of Endohedral Atoms Using R-matrix Methods: Application to Xe@C$_{60}$ Thomas Gorczyca, Muhammet Fatih Hasoglu, Steven Manson, Connor Ballance It is demonstrated that the effect of a static cage potential on the photoionization of endohedrally-enclosed atoms can be incorporated into standard R-matrix calculations using one of two independent methods. For photoionization processes occurring entirely within the fullerene, the outer-region solutions can be modified by the additional cage potential to yield phase-shifted Coulomb functions that are matched to the inner-region R-matrix. Alternatively, if the cage potential is contained within the R-matrix ``box,'' it can be directly incorporated into the formalism via simple one-electron integral contributions to the Hamiltonian, yielding a modified R-matrix itself. Both methods are applied to the photoionization of Xe@C$_{60}$ in the vicinity of the giant $4d\rightarrow \epsilon f$ resonance, and are found to be in excellent agreement with each other. Furthermore, good agreement with recent experimental results is obtained, validating the present approach and demonstrating that the full power of the many-electron, multi-channel, open-shell capabilities of the R-matrix method can be brought to bear on the photoionization of confined-atom systems in general. [Preview Abstract] |
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K1.00081: Dissociation of CO$^{+}$ molecular ions by strong laser fields U. Ablikim, M. Zohrabi, B. Gaire, Nora G. Kling, K.J. Betsch, Bethany Jochim, K.D. Carnes, I. Ben-Itzhak We study the strong-field laser-induced dissociation of a CO$^{+}$ ion beam employing a coincidence 3D momentum imaging technique. Kinetic energy release(KER) features, fragment angular distributions, and available potential energy curves help us determine the possible fragmentation pathways. At low laser intensity (30fs FWHM pulses centered near 800 nm), the CO$^{+}$ dissociates into C$^{+}$+O, meanwhile the C+O$^{+}$ channel appears at higher intensities. The fact that C$^{+}$+O channel is observed at laser intensities as low as 5 $\times$ 10$^{12}$ W/cm$^{2} $ indicates that the initial target is in the metastable a$^{4} \Sigma^{+}$ quartet state, rather than the vibrationally ``cold'' doublet ground state X$^{2}\Sigma ^{+}$, as the latter requires at least six photons to dissociate. The angular distribution of the low KER dissociation suggests that a combination of parallel and perpendicular transitions play a role and that their relative importance varies with increasing intensity. Moreover, multiphoton dissociation of the CO$^{+}$ electronic ground state also contributes to the signal as the laser intensity increases. We will discuss other pathways and their dependence on the laser pulse parameters. [Preview Abstract] |
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K1.00082: Double Photoionization of atoms using screening potential Hari P. Saha We will report the results of our investigation on double photoionization of atoms using our recently extended MCHF method [1]. As a test case, triple differential cross sections for double photoionization of helium atom will be calculated for 20 eV excess photon energy. The initial state will be calculated using the sophisticated multi-configuration Hartree-Fock method. The angle dependent screening potential approximation [2,3] which accounts for electron correlation between the two final state continuum electrons, will be used to calculate the final state wave function, The results will be compared with the experimental [4] and accurate theoretical calculations [5].\\[4pt] [1] Hari P. Saha, (unpublished).\\[0pt] [2] M.R.H. Rudge, Rev. Mod. Phys. 40, 564 (1968).\\[0pt] [3] C.Pan and A.F Starace, Phys. Rev. Lett. 67, 185 (1991); Phys. Rev. A45, 4588 (1992).\\[0pt] [4] Brouning et al., J. Phys. B 31, 5149 (1998).\\[0pt] [5] Colgan et al., J.Phys. B 34, L457 (2001). [Preview Abstract] |
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K1.00083: Resonant inter-Coulombic decay processes from atom to fullerene and backward in the photoionization of Ar@C$_{60}$ Mohammad Javani, Mohamed Madjet, Himadri Chakraborty, Steve Manson In a theoretical study of the photoionization of Ar@C$_{60}$ we find the evidence of strong decay probability of Ar single-core-electron excited states through degenerate ionization continua of the encapsulating fullerene \textit{via} a mechanism known as the resonant inter-Coulombic decay (RICD) [1]. The resulting resonance structures in C$_{60}$ subshell cross sections are found to assume significantly different shapes from those of the pure autoionizing resonances of Ar. We further predict an abundance of ``backward RICD'' processes. These are the decay of C$_{60}$ inner-shell excitations through Ar continua. Several of such resonances are also obtained in 3$p$ and 3$s$ cross sections of the confined Ar. Mutual hybridizations between some of Ar and C$_{60}$ orbitals influence the properties of these resonances. Calculations are carried out on a framework of time-dependent local density approximation where the fullerene ion-core of sixty C$^{4+}$ ions is smudged into a continuous jellium distribution [2].\\[4pt] [1] V. Averbukh and L.S. Cederbaum, \textit{Phys. Rev. Lett.} \textbf{96}, 053401 (2006);\\[0pt] [2] M.E. Madjet, T. Renger, D.E. Hopper, M.A. McCune, H.S. Chakraborty, J.-M. Rost, and S.T. Manson, \textit{Phys. Rev. }A \textbf{81}, 013202 (2010). [Preview Abstract] |
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K1.00084: Evolution of plasmonic and hybrid photoionization properties of alkaline earth metallofullerenes with the increasing fullerene size Aakash Patel, Himadri Chakraborty A theoretical study of the photoionization of endohedral fullerenes with a selection of fullerene molecules of increasing size and with confined alkaline earth atoms like Be and Mg is carried out. The fullerene ion cores, comprised of C$^{4+}$ ions, are smudged into a continuous jellium charge distribution, while the delocalized cloud of carbon valence electrons plus the electrons of the encaged atom are treated in the Kohn-Sham local density approximation (LDA) [1]. Only the spherical geometry is considered. The photoionization spectra are calculated by the time-dependent LDA that includes essential electron correlations [1]. A systematic evolution of the mixing of valence atomic levels with states of fullerene single-electron bands is found along the sequence. This hybridization as a function of the fullerene size is seen to primarily define the properties of the subshell-differential ionization spectra both in the low energy plasmonic as well as the high energy oscillatory regions.\\[4pt] [1] M.E. Madjet, T. Renger, D.E. Hopper, M.A. McCune, H.S. Chakraborty, J.-M. Rost, and S.T. Manson, \textit{Phys. Rev. }A \textbf{81}, 013202 (2010). [Preview Abstract] |
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K1.00085: Control of photodetachment spectra through laser dressing Nathan Morrison, Chris H. Greene Photodetachment and photoionization spectra often display rich resonance structures. The properties of these spectra can be modified through dressing with intense laser fields, providing control over photon absorption and the emitted electron. We present a Floquet $R$-matrix method for calculating photodetachment cross sections in the presence of a dressing laser. The full wave functions in the Floquet formalism for bound and escaping electrons are found by solving the Schr\"odinger equation near the atomic core and applying analytic boundary conditions outside of the interaction region. These calculations are used to investigate the modification of existing resonances, such as modifying the shape, or $q$ parameter, of Feshbach resonances. We also investigate the creation of new resonances in cases where high-lying bound states become autoionizing through the absorption of dressing laser photons. [Preview Abstract] |
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K1.00086: Observations of Multiple Bound-Bound Transitions in the Negative Ion of Lanthanum La$^{-}$ C.W. Walter, N.D. Gibson, D.J. Matyas, C.T. Crocker, K.A. Dungan, B.R. Matola, M.T. Scharpf, J. Rohl\'{e}n The negative ion of lanthanum has been investigated with tunable infrared laser photodetachment spectroscopy. The relative signal of neutral atom production was measured with a crossed laser-ion beam apparatus over the photon energy range 0.29 -- 0.77 eV. The spectrum reveals a number of sharp peaks due to bound-bound electric-dipole transitions in La$^{-}$, observed here through a two-step process of excitation followed by photodetachment of the upper state. The observed photodetachment spectrum is compared to theoretical calculations of energy levels and transition strengths by O'Malley and Beck [1]. The richness of the observed bound state spectrum is unprecedented for atomic negative ions, and it highlights the unique properties of La$^{-}$ for applications such as laser cooling.\\[4pt] [1] S.M. O'Malley and D.R. Beck, \textit{Phys. Rev. A} \textbf{79}, 012511 (2009); \textit{Phys. Rev. A} \textbf{81}, 032503 (2010). [Preview Abstract] |
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K1.00087: Attosecond timing of asymmetric chemical bond breaking M. Magrakvelidze, J. Wu, L. Ph. H. Schmidt, M. Kunitski, T. Pfeifer, M. Schoeffler, M. Pitzer, M. Richter, S. Voss, H. Sann, H. Kim, T. Jahnke, A. Czasch, U. Thumm, R. Doerner Making use of a two-particle-coincidence technique which achieves attosecond time resolution in a long circularly polarized multicycle femtosecond laser pulse, we resolve at an attosecond time scale time the laserdriven ionization and fragmentation of H$_{2}$ by relating the instant of ionization of H$_{2}$ to the ejected electron direction and by subsequently breaking the H$_{2}^{+}$ bond in the same pulse. We find that the proton with which the bonding electron remains is determined by the ejection time of the first electron. This show that electron localization and asymmetrical breaking of molecular bonds is ubiquitous even in symmetric laser pulses. Our approach provides an ultrafast stopwatch using the jointly measured directions of two emitted particles as hands. This technique uses a single circularly polarized IR laser pulses and allows the measurement of time intervals based on momentum differences which can be detected with extremely high precision, even for long pulses, thereby providing a powerful tool for ultrafast science. [Preview Abstract] |
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K1.00088: Image-based adaptive femtosecond control of molecules A. Voznyuk, T. Burwitz, D. Schmitz, E. Wells, B. Jochim, M. Zohrabi, K. Betsch, U. Ablikim, M.F. Kling, K.D. Carnes, I. Ben-Itzhak, R. Siemering, R. de Vivie-Riedle Incorporating three-dimensional momentum images as feedback into an adaptive control loop allows for identification and manipulation of precise control objectives. For laser control of molecular dynamics, this is accomplished by rapidly inverting velocity map images and deriving a fitness function from the angle-resolved kinetic energy release of the photofragments. We have applied this technique to acetylene, ethylene, and diatomic molecules to explore isomerization and angle-resolved dissociation, among other objectives. Beyond the experiments themselves, the resulting images can also be utilized to unravel the control processes and inform subsequent theoretical efforts. Here we present progress toward understanding the dissociation dynamics in these systems controlled by complex ultrafast laser pulses. [Preview Abstract] |
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K1.00089: Substitution effects in strong and ultrastrong field photoionization of chloromethane and dichloromethane Patrick Grugan, Nagitha Ekanayake, Bruce Wen, Samantha White, Lauren Howard, Sara Lemar, Zach Condon, Panpan Ruan, Zachary Bond, Rosie Scalzi, Caitlin McCowan, Anthony Tramontozzi, Ivette Planell-Mendez, Alejandro Londono, Alex Daniels, Matthew DeCamp, Barry Walker We investigate the intensity dependence of carbon ion fragments from chlorinated species of methane in strong and ultrastrong laser fields up to $5$x$10^{18}$ $W/cm^2$. $C^{n+}$, $1\le n\le 5$, yields are all reduced in chlorinated species when compared to the production from methane [1]. Larger molecular ions ex. $CH_2^{2+}$, which are common to both gas species ionized at $10^{15}$ $W/cm^2$, show a marked difference between all species indicating the pathways of molecular ionization [2] are different. At ultrahigh intensities ionization is expected to be free from molecular effects; however we observe the substitution suppression effect extends to highly charged $C^{5+}$ ions at intensities above $10^{18}$ $W/cm^2$. This work is supported by the Army Research Office under Award No. W911NF-09-1-0390 and National Science Foundation under Award No. 0757953. MFD acknowledges support from the DOE-EPSCoR grant DE-FG02-11ER46816.\\[4pt] [1] S. Planiyappan et.al. PRL 100, 183001(2008)\\[0pt] [2] Z. Wu et. al. J. Chem. Phys. 126, 07431(2007) [Preview Abstract] |
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K1.00090: IR-laser assisted XUV double ionization of helium Aihua Liu We studied the few-XUV photon and multi (XUV$+$IR)-photon double ionization of helium by solving the time-dependent Schr\"{o}dinger equation within a finite element discrete variable representation scheme. For the equal energy sharing, we discuss the joint angular distributions of the two emitted electrons for n-XUV photon double ionization with (for n$=$1) and without (for n$=$1,2,3) the presence of a short IR pulse. We find that the assisting IR pulse promotes side-by-side emission (both electrons are emitted along the linear laser polarization axis in the same directions) and enables the back-to-back emission (electrons are emitted in opposite directions along the laser polarization). [Preview Abstract] |
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K1.00091: Fragmentation dynamics of noble gas dimers in two-color intense laser fields M. Magrakvelidze, J. Wu, R. Doerner, U. Thumm We studied the dissociation dynamics of noble gas dimer ions in two-color infrared intense laser fields by analyzing their fragment-kinetic-energy-release spectra as a function of the pump-probe delay. Our calculations predict a striking ``delay gap'' in the kinetic-energy-spectra for all noble gas dimers that was so far only measured for the Ar$_{2}$ dimer [1]. We identify this phenomenon as a frustrated dissociation mechanism. This mechanism requests different pump- and probe-pulse wavelengths and involves the pump pulse to both, singly ionize the neutral dimers and dipole-couple adiabatic states in the dimer ion. \\[4pt] [1] J. Wu, M. Magrakvelidze, A. Vredenborg, L. Ph. H. Schmidt, T. Jahnke, A. Czasch, R. D\"{o}rner, and U. Thumm, Phys. Rev. Lett. \textbf{110}, 033004 (2013). [Preview Abstract] |
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K1.00092: Adiabatic hyperspherical study of one-dimensional H$_2$ Youliang Yu We present a calculation of the adiabatic hyperspherical potentials for one-dimensional H$_2$. Although the adiabatic hyperspherical representation has proven very useful in understanding atomic systems, especially highly correlated states like doubly excited states, it has not yet been applied to the electronic and nuclear degrees of freedom for a molecule more complicated than H$_2^+$. We thus present the first such calculation, albeit for a one-dimensional model of H$_2$. Our model, however, is chosen to exactly reproduce the three-dimensional H$_2$ and H$_2^+$ ground Born-Oppenheimer potentials. One of our goals is to identify and understand the role of doubly excited states --- which are rigorously defined in the adiabatic hyperspherical representation, unlike standard quantum chemistry. We are especially interested in understanding their role in strong-field and attosecond processes. We also want to take advantage of the fact that the adiabatic hyperspherical representation produces rigorously defined and discrete effective potentials for all ionization channels to help understand processes like strong-field dissociative ionization. These topics, and others, will be discussed. [Preview Abstract] |
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K1.00093: Ultrafast photoionization of toluene and the di- and trimethylbenzene isomers: the effects of orbital symmetry on intense-field stability Collin McAcy, Joshua Beck, Timothy Scarborough, Cornelis Uiterwaal Our recently published work on the femtosecond intense-field photoionization of azabenzene and the diazabenzene isomers (J. Chem. Phys. 136, 054309 (2012)) presents the four molecules as a systematic series of perturbations to the ring structure of benzene. In these molecules, we have observed correlations between molecular orbital symmetry and stability against intense-field ionization and fragmentation. We further our exploration of this phenomenon with preliminary results on the ultrafast photoionization of seven similarly-structured substituted benzenes -- toluene [$C_{6}H_{5}CH_{3}$], and the di- and trimethylbenzene isomers [$C_{6}H_{4}(CH_{3})_{2}$ and $C_{6}H_{3}(CH_{3})_{3}$] -- divided into four molecular series related through various degrees of symmetry. Ions are created with 50 fs, 800 nm pulses under single-molecule conditions. Ion yields are collected with a time-of-flight ion mass spectrometer, and recorded as a function of laser intensity without the focal volume effect (Phys. Rev. Lett. 100, 023002 (2008)). [Preview Abstract] |
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K1.00094: Characterization of Focused Ultrashort Pulses as a Function of Wavelength Joshua Beck, Collin McAcy, Skyler Marsh, Ryan Karnemaat, Tim Scarborough, Cornelis Uiterwaal In previous experiments, we have studied the photoionization and photofragmentation of substituted benzenes using intense fields from an 800 nm, femtosecond laser source and an experimental method that eliminates the focal volume effect without the need for data deconvolution [Phys. Rev. Lett. 100, 023002 (2008)]. Using this approach, we have found that in many substituted benzenes REMPI dominates the ionization process at around 800 nm [Phys. Chem. Chem. Phys., 2011, 13, 13783-13790]. We have now started to expand our studies using an optical parametric amplifier (Spectra-Physics TOPAS-C) which is tunable between 475 nm and 2800 nm. For reliable wavelength-dependent experiments, proper characterization of the position of the focus, including focal pulse duration and pulse intensity for the various wavelengths, is of crucial importance. We present preliminary characterization of post-OPA foci imaged at the interaction volume using reflective optics. Initial results will employ a spherical mirror, though the final experiment will require an off-axis parabolic mirror. Diagnosis of the focus will allow us to align this mirror and record its focal intensity distribution in real time, making accurate wavelength-dependent photoionization experiments feasible. [Preview Abstract] |
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K1.00095: Control over the Dissociation of Highly Excited Oxygen in Attosecond XUV Pump- IR Probe experiments Henry Timmers, Niranjan Shivaram, Arvinder Sandhu We present results on the phase and amplitude control over the photodissociation yield of O$_{\mathrm{2}}^{\mathrm{+}}$ in a pump-probe experiment. Using an attosecond pulse train, we create excited state wavepackets along both the B and c state pathways of O$_{\mathrm{2}}^{\mathrm{+}}$. We use a two-IR pulse probe to steer the wavepacket. By tuning the excitation spectrum and phase between the two IR pulses, we find we can modulate the dissociated O$^{\mathrm{+}}$ yield with the frequency of IR intensity modulation and control the phase difference between the two dissociation pathways. [Preview Abstract] |
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K1.00096: SPECTROSCAPY, LIFETIMES, OSCILLATOR STRENGTHS |
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K1.00097: Relativistic configuration interaction calculations of transition energies and hyperfine quenching rates for Ne-like ions M.H. Chen, K.T. Cheng Relativistic configuration interaction (RCI) calculations of Ne-like $2p^5 3s - 2p^6$ transition energies and hyperfine quenching rates have been performed. Large-scale CI expansions exceeding 600,000 configurations are realized with a new, parallel version of our RCI code. Since initial and final states are not in the same complex, we use $2p^5 3s$ potentials for the initial excited state and $2p^6$ potential for the final ground state to generate B-spline basis functions. Relaxation effects on transition energies thus calculated range from $-$0.5371 eV in Na$^{+}$ to $-$0.0077 eV in Xe$^{44+}$. Our results are compared with electron beam ion trap measurements of Ne-like W$^{64+}$ [P.\ Beiersdorfer et al.,\ Phys.\ Rev.\ A {\bf 86}, 012509 (2012)], with NIST database, and with other theoretical predictions. [Preview Abstract] |
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K1.00098: Calculation of Bethe Logarithm by Drake-Goldman Method to Hydrogen Molecular Ions Zhen-Xiang Zhong, Ting-Yun Shi, Zong-Chao Yan Precision spectroscopy of hydrogen molecular ions can be used to determinate proton to electron mass ratio $m_p/m_e$. Several experiments are carrying out to measure rovibrational transition of HD$^+$ to a precision of $10^{-9}$, and two photon transition of H$_2^+$ to $10^{-10}$ level. Current theoretical calculations are as precision as $10^{-10}$, which are done by calculate relativistic and radiative corrections up to $R_{\infty}\alpha^5$ order. Uncertainty of $R_{\infty}\alpha^2$ order corrections have been reduced to sub kHz for H$_2^+$ states $(v,L): (0,0), (0,1),(1,0)$ and HD$^+$ rovibrational states $(v=0-4, L=0-4)$. Bethe Logarithm appeared in $R_{\infty}\alpha^3$ order corrections has been calculated to more than 8 digits for H$_2^+$ and HD$^+$ rovibrational states $(v=0-4, L=0-4)$. In this poster, we will report our recent work on Bethe Logarithm, which is calculated by Drake-Goldman method. The work was supported by the NSFC under Grants No. 11004221 and No. 10974224, by the National Basic Research Program of China (973 Program) under Grant No. 2010CB832803, and by the NSERC of Canada. The work was carried out at the computing facilities of SHARCnet of Canada and Wuhan University of China. [Preview Abstract] |
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K1.00099: Relativistic many-body calculations of excitation energies, oscillator strengths, transition rates, and lifetimes in samarium like ions Ulyana Safronova, Alla Safronova, Peter Beiersdorfer Excitation energies, oscillator strengths, transition probabilities, and lifetimes are calculated for $(5s^2+5p^2+5d^2+5s5d+5s5g+5p5f)$--$(5s5p+5s5f+5p5d+5p5g)$ electric dipole transitions in Sm-like ions with nuclear charge $Z$ ranging from 74 to 100. Relativistic many-body perturbation theory (RMBPT), including the Breit interaction, is used to evaluate retarded E1 matrix elements in length and velocity forms. The calculations start from a $1s^22s^22p^63s^23p^63d^{10}4s^24p^64d^{10}4f^{14}$ Dirac-Fock potential. First-order perturbation theory is used to obtain intermediate coupling coefficients, and the second-order RMBPT is used to determine the matrix elements. The contributions from negative-energy states are included in the second-order E1 matrix elements to achieve agreement between length-form and velocity-form amplitudes. The resulting transition energies and transition probabilities, and lifetimes for Sm-like W$^{12+}$ are compared with results obtained by the relativistic Hartree-Fock approximation (COWAN code) to estimate contribution of the $4f$-core-excited states. Trends of excitation energies and oscillator strengths as function of nuclear charge $Z$ are shown graphically for selected states and transitions. This work provides a number of yet unmeasured properti [Preview Abstract] |
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K1.00100: S-matrix calculations of energy levels of alkalilike ions Jonathan Sapirstein, K.T. Cheng A recent S-matrix based QED calculation of energy levels of the lithium isoelectronic sequence is extended to the general case of a valence electron outside an arbitrary filled core. Formulas are presented that allow calculation of the energy levels of valence $ns,np_{1/2}$, $np_{3/2}$, $nd_{3/2}$, and $nd_{5/2}$ states. Emphasis is placed on modifications of the lithiumlike formulas required because more than one core state is present, and a discussion of an unusual feature of the two-photon exchange contribution involving autoiononizing states is given. The method is illustrated with a calculation of energy levels of the sodium isoelectronic sequence, with results for $3s_{1/2}$, $3p_{1/2}$, and $3p_{3/2}$ energies tabulated for the range $Z=20-100$. A detailed breakdown of the calculation is given for $Z=74$. Comparison with experiment and other calculations is given, and prospects for extension of the method to ions with more complex electronic structure discussed. [Preview Abstract] |
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K1.00101: Production of very-high-$n$ strontium Rydberg atoms Shuzhen Ye, Xinyue Zhang, Thomas Killian, F. Barry Dunning, Moritz Hiller, Shuhei Yoshida, Joachim Burgdoerfer The production of very-high-$n$, $n \sim $ 300, strontium Rydberg atoms is explored using a crossed laser-atom beam geometry. $n^{1}$S$_{0}$ and $n^{1}$D$_{2}$ states are created by two-photon excitation via the 5s5p $^{1}$P$_{1}$ intermediate state using radiation at 461 and 413 nm. Rydberg series in the different strontium isotopes present in the beam can be selectively excited by tuning the 461 nm light allowing measurements of the isotope shifts in the series limits, that for $^{88}$Sr-$^{86}$Sr being $\sim +$210MHz, and that for $^{88}$Sr-$^{84}$Sr being $\sim +$440 MHz. Well-resolved Rydberg series can be seen for values of $n$ approaching $\sim $ 500. Photoexcitation spectra calculated using a two-active-electron model reproduce the relative strengths of the measured $^{1}$S$_{0}$ and $^{1}$D$_{2}$ lines. The surprisingly large photoexcitation rates provide new opportunities to study quasi-stable two-electron excited states and to explore the behavior of strongly coupled Rydberg systems at high $n$. [Preview Abstract] |
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K1.00102: Spectroscopy of excited triplet states of ultracold $^{39}$K$^{85}$Rb molecules relevant to populating $a\,^3\Sigma^+, v'' =0$ Edward Eyler, Jayita Banerjee, Ryan Carollo, Michael Bellos, Phillip Gould, William Stwalley We report the observation and analysis of the $3\,^3\Pi$ and $3\,^3\Sigma^+$ states of ultracold $^{39}$K$^{85}$Rb molecules. The observations are based on resonance-enhanced multiphoton ionization (REMPI) of ultracold KRb molecules. These ultracold molecules are formed by photoassociation of ultracold $^{39}$K and $^{85}$Rb atoms in a magneto-optical trap, followed by spontaneous emission. We also propose schemes for utilizing these excited triplet states for the formation of ultracold KRb molecules in the $v''=0$ level of the metastable $a\,^3\Sigma^+$ state. [Preview Abstract] |
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K1.00103: Application of Laser Induced Breakdown Spectroscopy to Monitor Rare Earth Ions in Glass Matrix Prakash Sharma, Michael Carter, Akshaya Kumar The Laser Induced breakdown spectroscopy (LIBS) is a real time online technique that can be used to monitor the concentration of rare earth ions in amorphous glass matrix. This study has significant application in the glass industry where the composition of the glass can be monitored in real time using LIBS technology for quality control. The Eu3$+$ ions doped silicate glasses were developed via sol gel method. The glasses of varying molar percentages of Eu3$+$ (0.02, 0.05 and 0.08 mole percent), were prepared to study the effect of variation in concentration of Eu3$+$ ions on the LIBS signal and to calculate its limit of detection (LOD). The spectral assignment of the observed LIBS spectrum has been made. In order to find the maximum signal to noise ratio, we also recorded the intensity of LIBS signal for various integration start delay (ISD) time at a constant power of (pulsed Nd: YAG) laser. The ocean optics LIBS 2500plus spectrometer along with a Q switched Nd:YAG laser (Quantel, Big Sky) were used to record the LIBS spectrum. [Preview Abstract] |
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K1.00104: Optical Frequency Comb Spectroscopy of Rare Earth Atoms Jerlyn Swiatlowski, Christopher Palm, Trinity Joshi, Caitlin Montcrieffe, Derek Jackson Kimball We discuss progress in our experimental program to employ optical-frequency-comb-based spectroscopy to understand the complex spectra of rare-earth atoms. We plan to carry out systematic measurements of atomic transitions in rare-earth atoms to elucidate the energy level structure and term assignment and determine presently unknown atomic state parameters. This spectroscopic information is important in view of the increasing interest in rare-earth atoms for atomic frequency standards, in astrophysical investigations of chemically peculiar stars, and in tests of fundamental physics (tests of parity and time-reversal invariance, searches for time variation of fundamental constants, etc.). We are presently studying the use of hollow cathode lamps as atomic sources for two-photon frequency comb spectroscopy. [Preview Abstract] |
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K1.00105: Oscillator strengths for spin-changing S - P transitions in He Donald C. Morton, Qixue Wu, G.W.F. Drake Following earlier work [1], we have calculated electric dipole (E1) and magnetic quadrupole (M2) oscillator strengths and spontaneous decay rates for 24 spin-changing transitions in atomic helium. The transitions are $n\;^1{\rm S}_{0} - n'\;^3{\rm P}_{1,2}$ and $n\;^3{\rm S}_{1} -n'\;^1{\rm P}_{1}$ with $n,n'\leq3$ or $n\leq10$ for $n' = n$. The E1 calculations include the relativistic corrections obtained with the Breit operators summed over intermediate states for both infinite nuclear mass and the finite nuclear mass of $^4$He, along with the anomalous magnetic moment of the electron. We obtained both length and velocity forms of the interaction Hamiltonian for comparison. The corrections for the nuclear mass and the electron anomaly almost cancel showing that the omission of both is a good approximation.\newline [1] D.C. Morton and G.W.F. Drake, Phys.\ Rev.\ A {\bf 83}, 042503 (2011). [Preview Abstract] |
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K1.00106: Magnetic dipole decay rates and $1/Z$ expansions for the $1s2s\;^3S_1$ state of helium and heliumlike ions Lauren Moffatt, G.W.F. Drake The lifetime of the metastable $1s2s\;^3S_1$ state of helium is determined by relativistic magnetic dipole (M1) transitions to the ground state, giving an extraordinarily long lifetime of 7859 s. The M1 transition rates are evaluated numerically using large basis set variational calculations in Hylleraas coordinates for all the He-like ions up to Ar$^{+16}$. The coefficients of a $1/Z$ expansion, based on the results from the variational calculation, are evaluated up to ninth order, with the zeroth and first order coefficients being determined analytically. This $1/Z$ expansion is used to evaluate the lowest-order M1 transition rates for heliumlike ions along the isoelectronic sequence from K$^{+17}$ to Fm$^{+98}$. The results for helium are compared with other theory [1], and experimental measurements by Moos and Woodsworth [2] and Hodgman [3], and the ionic results are compared with electron beam ion trap measurements by Trabert [4].\\[4pt] [1] G. Lach and K. Pachucki, Phys.\ Rev.\ A {\bf 64}, 042510 (2001).\newline [2] H. W. Moos and J. R. Woodsworth, Phys.\ Rev.\ A {\bf 12}, 6 (1975).\newline [3] S.S. Hodgman {\it et al.}, Phys.\ Rev.\ Lett.\ {\bf 103} 053002 (2009).\newline [4] E. Trabert, Can.\ J. Phys.\ {\bf 86}, 73 (2010). [Preview Abstract] |
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K1.00107: Hyperfine-induced radiative decay rates of heliumlike $^8$B and $^{11}$B Qixue Wu, G.W.F. Drake Hyperfine mixing of $LS$-coupled atomic states can open new radiative decay channels for processes that would normally be strongly suppressed. For example, spin-forbidden processes may become enhanced. We study the lifetimes of the hyperfine levels of the two-electron isotopes $^8$B $(I=2)$ and $^{11}$B $(I=3/2)$ in connection with nuclear charge radius measurements by the isotope shift method [1]. We find that the effects of hyperfine structure are relatively small for both $^8$B and $^{11}$B. For the $1s2p\;^1P$ hyperfine states, the decay rates are dominated by transitions to the $1s^2\;^1S$ ground state with $A = 3.72\times10^{11}$ s$^{-1}$. For the $1s2p\;^3P$ states, hyperfine structure alters the decay rates by less than 1\%. The dominant decay channel is the spin-allowed transition to the $1s2s\;^3S$ manifold of states. The decay rate for $^8$B summed over final state hyperfine structure is in the range $A = 4.535\times10^7$ to $4.555\times10^7$ s$^{-1}$. The decay rate to the ground state for the $1s2p\;^3P_1$ state is $4.169\times10^6$ to $4.283\times10^6$ s${-1}$. The effects of hyperfine structure are smaller still for $^{11}$B.\newline [1] W. Noertershaeuser {\it et al.} Phys.\ Rev.\ A {\bf 83}, 012516 (2011); Phys.\ Rev.\ Lett.\ {\bf 102}, 062503 (2009). [Preview Abstract] |
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K1.00108: Enantiospecific Chemical Mixture Analysis via Microwave Spectroscopy of Buffer Gas Cooled Samples David Patterson, Melanie Schnell, John Doyle We present experimental results demonstrating a sensitive, highly specific chemical analyzer via Fourier transform microwave (FTMW) spectroscopy of molecular samples cooled via buffer gas cooling to about 7 K. Room temperature spectroscopic methods are routinely used to identify and quantify small and medium sized molecules. These methods fail for larger molecules, which at room temperature occupy hundreds of thousands of ro-vibrational states, leading to broad spectral features composed of a large number of weak, unresolved lines. In contrast, samples cooled to a few degrees K exhibit qualitatively simpler spectra, composed of many fewer and much stronger resolvable, narrow lines. Here we show that a continuous, cold buffer gas cooled source provides an attractive source for a spectroscopy based chemical mixture analyzer. In addition, we will present novel extensions to FTMW which render it sensitive to the chirality of the analyte. In this work, opposite enantiomers are distinguished via a change in the phase of the emitted microwave radiation. This technique provides a robust, general, chirally sensitive chemical analyzer, and is the first demonstration of microwave spectroscopy applied to chiral analysis. [Preview Abstract] |
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K1.00109: Improved measurement of the Land\'{e} g factor of the 5D$_{5/2}$ state of Ba II with a single trapped ion Thomas Noel, Carolyn Auchter, Matt Hoffman, Boris Blinov We report an improved measurement of the Land\'e g factor of the 5D$_{5/2}$ level of singly ionized barium. The measurement was performed by interrogation of Doppler-cooled $^{138}$Ba$^{+}$ ions in a linear Paul trap. The 5D$_{5/2}$ g factor is extracted from radiofrequency spectroscopy of both the ground level and the metastable 5D$_{5/2}$ level. We measure the ground and 5D$_{5/2}$ Zeeman splittings at multiple trap rf voltages and magnetic field strengths in order to ensure that ac Zeeman shifts from trap currents do not contaminate the measurement. Other systematics including effects from the power line phase, magnetic field gradients, and magnetic field drifts are addressed. The g factor is found to be 1.20040(4), an increase in precision of an order of magnitude over our previous measurement. This increased precision will enable a new measurement of the octupole moment of the $^{137}$Ba nucleus, reducing the dependence on atomic theory calculations to below experimental error. [Preview Abstract] |
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K1.00110: Final state electron distributions of $^6$Li$^+$ following $\beta$-decay of $^6$He Eva Schulhoff, G.W.F. Drake When the isotope $^6$He undergoes $\beta$--decay into $^6$Li$^+$ ($^6{\rm He} \rightarrow {^6{\rm Li}^+} + e^- + \bar{\nu}_e$), there is a sudden change in the Coulomb potential binding the atomic electrons. In response, a given initial electronic state of $^6$He relaxes into all possible final electronic states of $^6$Li$^+$. In this work we calculate the redistribution function. The method of calculation involves expanding the initial state of $^6$He in terms of a complete set of final states of $^6$Li$^+$. A Hylleraas-type basis set was used to create a pseudospectrum (up to 797 states) which spans both the bound and continuum states of Li$^+$. Starting from both the $1\;^1S_0$ and $2\;^3S_1$ initial states $^6$He, the excitation probabilities to the final $^6$Li$^+$ states, as well as the total ionization probabilities, were calculated in the sudden approximation with neglect of nuclear recoil. The transition probabilities from the $1\;^1S_0$ initial state are compared with those of Wauters and Vaeck [Phys.\ Rev.\ C {\bf 53}, 497 (1996)] and Frolov and Ruiz [Phys.\ Rev.\ A {\bf 82}, 042511 (2010)]. Finally, the transition probabilities show resonant behavior near the energies corresponding to doubly-excited states. [Preview Abstract] |
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K1.00111: Miniaturized Sources and Traps for Spectroscopy of Multicharged Ions Joseph N. Tan, Nicholas D. Guise Penning traps made extremely compact (\textless 150 cc) with rare-earth (NdFeB) magnets\footnote{J.N. Tan, S.M. Brewer, and N.D. Guise, Rev. Sci. Instrum. \textbf{83}, 023103 (2012).} have been used recently to isolate highly charged ions (HCI) for spectroscopy. For example, radiative lifetimes of metastable states are measured by observing the visible fluorescence emitted by isolated Ar XIV (441 nm, 2p $^{2}$P$_{3/2} \to $ 2p $^{2}$P$_{1/2})$ and Kr XVIII (637 nm, 3d $^{2}$D$_{3/2} \to $ 3d $^{2}$D$_{1/2})$. These measurements use HCIs extracted from an electron beam ion trap (EBIT) at NIST. For planned experiments, a new apparatus is being developed which will incorporate a ``mini-EBIT'' source using similar permanent-magnet structures. It combines a mini-EBIT and a compact Penning trap to facilitate production of multicharged ions including bare nuclei with nuclear charge in the range Z$=$1 to Z$=$10, in a cryogen-free setup with multiple ports for laser and atomic beam access to the isolated HCI. One goal is to produce one-electron ions in Rydberg states with transitions accessible to an optical frequency comb. Such engineered atomic systems are sought to enable tests of theory\footnote{U.D. Jentschura, et al., Phys. Rev. Lett. \textbf{100}, 160404 (2008).} that could illuminate the proton radius puzzle.\footnote{R. Pohl et al., arXiv:1301.0905 [physics.atom-ph].} [Preview Abstract] |
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K1.00112: Lifetimes for Rydberg States of Cs with $n < 45$ in a Black-Body Radiation Field James Truxon, Constantine Theodosiou Natural and effective lifetimes have been calculated semi-empirically for high Rydberg states of neutral Cesium, using wave functions obtained through direct inward numerical integration of the Schr\"{o}dinger equation with a central potential that includes relativistic and core-polarization corrections. A majority of experimental studies of Cesium lifetimes has been carried out at higher temperatures which allow thermal radiation to significantly deplete the lifetime of states with principal quantum number greater than $n 16$. Therefore we have also explicitly included blackbody-induced transitions in our calculations, in order to evaluate the lifetimes at temperatures of 0K, 350K, and 600K. States with principal quantum numbers $n = 6 - 40$ and orbital angular momentum quantum numbers $l = 0 - 4$ were considered. We find good agreement between our calculations and experimental results across a range of energies, angular momenta, and temperatures, but identify specific areas for continued research. We present a table of select numerical results from this calculation, along with a comprehensive list of experimental data acquired from the literature between 1959 and 2011, and theoretical data acquired from the literature from 1981 through 2011. [Preview Abstract] |
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K1.00113: ATOMIC, MOLECULAR AND CHARGED PARTICLE COLLISIONS II |
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K1.00114: Angular dependence of collision-induced dissociation of H$_2^+$ on internuclear distance Ben Berry, Nora G. Kling, A. Max Sayler, Dag Hathiramani, Jack W. Maseberg, K.D. Carnes, I. Ben-Itzhak In slow (keV) collisions between molecular ions and atoms, the dominant processes are collision-induced dissociation (CID: H$_2^+$ + Ar $\rightarrow$ H$^+$ + H + Ar) and dissociative capture (DC: H$_2^+$ + Ar $\rightarrow$ H + H + Ar$^+$). Using a coincidence 3D momentum imaging technique, CID and DC are experimentally separated. Furthermore, CID by electronic excitation to a repulsive state is distinguished from that caused by ro-vibrational excitation. In electronic excitation CID the measured angular distribution varies with the kinetic energy release (KER) of the molecule. By converting KER to internuclear distance using the reflection method, the results are found to be in agreement with theory based on the $1^{st}$ Born approximation $\left[1\right]$. We have also upgraded the experimental setup, improving the detection of low energy fragments which allows for better measurement of the ro-vibrational CID mechanism.\\[4pt] [1] T.A. Green and J.M. Peek, Phys Rev. \textbf{183}, 166 (1969) [Preview Abstract] |
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K1.00115: Coupled $\ell$-wave confinement-induced resonances in cylindrically symmetric waveguides Panagiotis Giannakeas, Fotios Diakonos, Peter Schmelcher A semi-analytical approach to atomic waveguide scattering for harmonic confinement is developed taking into account all partial waves. As a consequence $\ell$-wave confinement-induced resonances are formed being coupled to each other due to the confinement. The corresponding resonance condition is obtained analytically using the $K$-matrix formalism. Atomic scattering is described by transition diagrams which depict all relevant processes the atoms undergo during the collision. Our analytical results are compared to corresponding numerical data and show very good agreement. [Preview Abstract] |
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K1.00116: Formation of heavy-Rydberg ion pairs in collisions between Rydberg atoms and attaching targets Changhao Wang, Michael Kelley, F. Barry Dunning Electron attachment in collisions between K(np) Rydberg atoms and electron attaching molecules can lead to the creation of heavy-Rydberg ion pair states comprising a weakly-bound positive-negative ion pair orbiting at large internuclear separations. The lifetimes of such states are being examined together with the factors that influence them. These include their binding energies and the available decay channels which can be controlled by varying n, the Rydberg atom velocity, and the target species. The ion pair states are formed in a small collision cell and allowed to exit into an analysis region where their number and binding energy distribution is determined by electric field induced dissociation. Ion pair production is analyzed with the aid of a Monte Carlo collision code that models both the initial Rydberg electron capture and the subsequent evolution of the product ion pair. Research supported by the Robert A. Welch Foundation. [Preview Abstract] |
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K1.00117: Interaction between single neutral atoms and an ultracold atomic gas Michael Bauer, Farina Kindermann, Philipp Franzreb, Benjamin G\"anger, Jan Phieler, Shrabana Chakrabarti, Nicolas Spethmann, Dieter Meschede, Artur Widera Recently hybrid systems immersing single atoms in a many body system have been a subject of intense interest. Here we present an example of controlled doping of an ultracold Rubidium cloud with single neutral Cesium impurity atoms. We observe thermalization of ``hot'' Cs atoms by elastic interaction with an ultracold Rb gas, employing different schemes of measuring the impurities' energy distribution. In addition we present a concept and review the current status of a new setup, which will be capable of breeding an all optical BEC in a few seconds. Our setup will feature mechanisms for independently manipulating and imaging both single atoms and the BEC, thereby providing an unrivaled level of control over impurities in a quantum gas. Possible research directions include the investigation of coherent impurity physics and the creation and characterization of polarons in a BEC. [Preview Abstract] |
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K1.00118: Travelling-Wave Deceleration of Buffer-Gas Beams of CH Maya Fabrikant, Noah Fitch, Nicholas Farrow, Tian Li, Jonathan Weinstein, Heather Lewandowski Buffer-gas beams are a promising method for the production of bright sources of cold molecules. We have created ground state CH radicals in a buffer-gas cell to produce a cold molecular beam of 10$^{11}$ mol./pulse. However, slowing and trapping molecules created in these sources presents challenges because of large pulse lengths and velocity spreads compared to more familiar supersonic beams. Traveling-wave decelerators are uniquely suited to meet these challenges because of their ability to confine molecules in three dimensions during deceleration and their versatility afforded by analog control of the last electrodes. We present a protocol for Stark deceleration of beams with a large velocity spread for use with a travelling-wave decelerator. Our method involves confining molecules transversely with a hexapole for an optimized distance before deceleration which precisely rotates the phase-space distribution of the molecules so that the portion of the packet that enters the decelerator always matches the phase-space acceptance. We demonstrate with simulations that using this method, we can effectively decelerate a significant portion of the molecules in many successive wells which may then be combined and trapped. [Preview Abstract] |
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K1.00119: Collisions of co-trapped cold OH molecules with ultracold rubidium Yomay Shyur, Travis Briles, Heather Lewandowski Controlling interactions between cold molecules using external fields can elucidate the role of quantum mechanics in molecular collisions. We report progress on collisions between ultracold rubidium atoms and cold OH molecules. The OH molecules are slowed in a stark decelerator and trapped using static electric fields. Once the molecules are trapped, they are overlapped with a magnetic trap of ultracold rubidium atoms to study collisions. The post-collision OH molecules are detected using a state selective ionization scheme by first resonantly exciting the molecule on the A$^{\mathrm{2}}\Sigma^{\mathrm{+}}$-X$^{\mathrm{2}}\Pi $ (1,0) band near 282nm and then ionizing the molecule with a 118.2nm (10.49 eV) photon. This detection method greatly increases the signal to noise ratio of OH density measurements over traditional laser-induced fluorescence methods and allows for greater precision in determining collision dynamics. [Preview Abstract] |
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K1.00120: Studies of rotationally inelastic collisions of NaK and NaCs with Ar and He perturbers J. Jones, C. Faust, K. Richter, C.M. Wolfe, S. Ashman, R.F. Malenda, P. Weiser, S. Carlus, A. Fragale, A.P. Hickman, J. Huennekens We report studies of rotationally inelastic collisions of Ar and He atoms with the molecules NaK and NaCs prepared in various ro-vibrational levels of the $A\,^1\Sigma^+$ electronic state. We use laser induced fluorescence (LIF) and polarization labeling (PL) spectroscopy in a pump-probe, two step excitation process. The pump excites the molecule to a ro-vibrational level $(v,J)$ in the $A$ state. The probe laser is scanned over transitions to the $3\,^1\Pi$ state in NaK or the $5\,^3\Pi$ state in NaCs. In addition to strong direct lines, we observe weak satellite lines that arise from collision-induced transitions of the $A$ state level $(v,J)$ to $(v,J+\Delta J)$. The ratio of intensities of the satellite line to the direct line in LIF and PL yields information about population and orientation transfer. Preliminary results show a strong propensity for collisions with $\Delta J$=even for NaK; the propensity is larger for He than for Ar. Collisions of NaCs with He show a similar propensity, but collisions of NaCs with Ar do not. Theoretical calculations are also underway. For He-NaK, we have completed potential surface calculations using GAMESS and coupled channel scattering calculations of rotational energy transfer and transfer of orientation. [Preview Abstract] |
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K1.00121: ABSTRACT WITHDRAWN |
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K1.00122: Electron Impact Excitation Collision Strengths for EUV Lines of Fe VII Swaraj Tayal, Oleg Zatsarinny New extensive calculations are performed for electron collision strengths, rate coefficients and transitions probabilities for the astrophysically important lines in Fe VII. The collision strengths were calculated in the close-coupling approximation using the B-spline Breit-Pauli R-matrix method. The multiconfiguration Hartree-Fock method with term-dependent non-orthogonal orbitals is employed for an accurate representation of the target wave functions. The close-coupling expansion includes 189 fine-structure levels of Fe VIII covering all possible terms of the ground $3p^63d^2$ and one-electron excited configurations $3p^53d^3$, $3p^63d4l$, $3p^53d5s$, and $3p^63d5p$. The effective collision strengths are obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities at electron temperatures in the range from $10^4$ to $10^7$ K. There is an overall good agreement with the previous R-matrix frame-transformation calculations, but significant differences are also noted for some transitions. The corrections to the previous results come mainly due to more extensive expansions for the Fe VII target states. [Preview Abstract] |
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K1.00123: Energy dependence of the ($e,2e$) recoil/binary peak ratio across He autoionizing levels N.L.S. Martin, B.A. de Harak, K. Bartschat In previous work we reported out-of-plane $(e,2e)$ measurements and calculations for helium auto\-ionizing levels. The results were presented as $(e,2e)$ angular distributions\footnote{B.A. deHarak, K. Bartschat, and N.L.S. Martin, Phys. Rev. Lett. {\bf 100}, 063201 (2008)} and $(e,2e)$ energy spectra\footnote{B. A. deHarak, K. Bartschat, and N. L. S. Martin, Phys. Rev. A {\bf 82}, (2010) 06270} of ejected electrons. The angular distributions, which were energy integrated across an energy window of 0.3~eV for each resonance, showed a pronounced recoil peak for both $(2p^2)^1\negthinspace D$ and $(2s2p)^1\negthinspace P$, whereas that for direct ionization was negligible. We are currently measuring the energy dependence (in 30meV steps) of the recoil/binary peak ratio across these two resonances; theory predicts a rapid variation of this ratio. We will present our results and compare them with first and second order theoretical calculations. [Preview Abstract] |
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K1.00124: Electron impact K-shell ionization cross sections at various projectile energies Bidhan C. Saha, Arun K. Basak, M. Alfaz Uddin, A.K.F. Haque Recently Cengiz [1] has reported the inelastic interactions of electrons in a medium with approximate expressions for evaluating the differential scattering due to distance and close interactions. For inner-shell ionization it is shown that the two interactions produce almost identical results and thus the total effect can be taken approximately twice the contribution from the distance interactions. This simple empirical formula of Ref. [1] (see Eq. 41) is modified by incorporating both the ionic and relativistic corrections for the electron impact ionization cross section (EIICS) and applied to evaluate the K-shell ionization cross sections of both neutral and ionic targets over wide ranges of incident energies. \\[4pt] [1] A. Cengiz, Rad. Phys. Chem. 65 (2002) 33. [Preview Abstract] |
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K1.00125: Low-energy electron elastic scattering from Os atom: New electron affinity Z. Felfli, F. Kiros, A.Z. Msezane Bilodeau and Haugan [1] measured the binding energies (BEs) of the ground state and the excited state of the Os$^{-}$ ion to be 1.07780(12) eV and 0.553(3) eV, respectively. These values are consistent with those calculated in [2]. Here our investigation, using the recent complex angular momentum methodology wherein is embedded the crucial electron-electron correlations and the vital core polarization interaction, has found that the near threshold electron-Os elastic scattering total cross section (TCS) is characterized by three stable bound states of the Os$^{-}$ ion formed as resonances during the slow electron collision, with BEs of 1.910 eV, 1.230 eV and 0.224 eV. The new extracted electron affinity (EA) value from the TCS of 1.910 eV for the Os atom is significantly different from that measured in [1]. Our calculated elastic differential cross sections (DCSs) also yield the relevant BEs for the ground and the two excited states of the Os$^{-}$ ion. The complex characteristic resonance structure in the TCS for the Os atom is ideal for catalysis [3], but makes it difficult to execute the Wigner threshold law in describing the threshold detachment behavior of complex atoms and extracting the reliable attendant EAs. \\[4pt] [1] R. C. Bilodeau and H. K. Haugen, Phys. Rev. Lett. \textbf{85}, 534 (2000); [2] P. L. Norquist and D. R. Beck, Phys. Rev. A\textbf{61}, 014501 (2000); [3] A. Tesfamichael et al, J. Phys. Chem. C \textbf{116}, 18698 (2012) [Preview Abstract] |
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K1.00126: Angular distributions for electron-impact ionization of Mg Gregory Armstrong, James Colgan, Kate Nixon, Andrew Murray We present angular distributions for electron-impact single ionization of the ground and excited states of magnesium. The time-dependent close-coupling method is used to solve the two-electron time-dependent Schr\"{o}dinger equation in full dimensionality. The ionization process is treated as a two-active-electron process, where the two outgoing electrons move in the field of the frozen Mg$^{+}$ ground state. Recent experiments have provided the first measurements resulting from ionization of an excited target, via excitation from the ground state using a dye laser. The measured angular distributions for ionization of the first excited state of Mg showed interesting differences compared to the corresponding distributions for the ground state. Morever, the target may be aligned by varying the polarization of the exciting laser. In this work, we analyse the angular distributions of the outgoing electrons as the target alignment is varied, and make comparison with the case of the spherically symmetric ground state. \\ \\ The Los Alamos National Laboratory is operated by Los Alamos National Security, LLC for the National Nuclear Security Administration of the U. S. Department of Energy under Contract No. DE-AC5206NA25396. [Preview Abstract] |
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K1.00127: Progress towards an optically pumped electron spin filter Munir Pirbhai, Jonah Knepper, Nick Ryan, Dale Tupa, Timothy Gay Polarized electron beams are an indispensable probe of spin-dependent phenomena in fields of atomic and molecular physics, magnetic materials and biophysics. While their uses have become widespread, the sources producing them remain technically complex. The standard gallium arsenide (GaAs) polarized electron emitters require stringent conditions such as ultrahigh vacuum systems, and challenging activation procedures to operate. Therefore, we are actively seeking alternatives to the GaAs photocathodes. One option involves the production of polarized electron beams by spin exchange collisions with oriented rubidium vapor [1, 2, 3]. We have built a new prototype using this principle. At present, it supplies about 1$\mu $A of electron current with 13{\%} polarization. We will report on how the rubidium density and different quenching gases, used in the optical pumping process to orient the alkali vapor, affect the electron beam polarization. \\[4pt] [1] P. S. Farago and H. C. Siegmann, Phys. Lett. 20, 279 (1966).\\[0pt] [2] R. Krisciokaitis-Krisst, W.K. Peterson, Nuclear Instruments and Methods 118, 157 (1974).\\[0pt] [3] H. Batelaan, A. S. Green, B. A. Hitt, and T. J. Gay, Phys. Rev. Lett. 82, 4216 (1999). [Preview Abstract] |
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K1.00128: Imaging of energy transfer in a frozen Rydberg gas Donald P. Fahey, Thomas J. Carroll, Michael W. Noel The dipole-dipole interaction is the dominant mechanism for energy exchange among atoms in a frozen Rydberg gas on microsecond time scales. By way of selective field ionization and a spatially sensitive ion detector, we image the transfer of energy among Rydberg atoms. We explore the effect of different spatial arrangements of Rydberg atoms on the energy transfer. [Preview Abstract] |
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K1.00129: Body vs. 4-Body Treatment of Single Ionization of Helium A.L. Harris, K. Morrison In the process of single ionization of helium, a projectile collides with a helium atom and one of the atomic electrons is ionized. After the collision, the residual He$^{+}$ ion is left in the ground state. Single ionization of helium is a 4-body process because there are 4 particles involved in the collision. However, this collision is often approximated as a 3-body process, where the non-ionized helium electron is considered inactive. Essentially, this second electron is neglected in the calculations. Recently, calculations have been performed using a full 4-body model, and some discrepancies are observed between the 3-body and 4-body models. To understand the causes of these discrepancies, we have undertaken a comprehensive study of 3-body and 4-body models for single ionization of helium. Results are presented for a wide range of incident projectile energies, ionized electron energies, and scattering angles. [Preview Abstract] |
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K1.00130: Electron impact exctation of Al X Kanti Aggarwal, Francis Keenan Emission lines of Al ions, including Al X, are important for the modeling and diagnostics of lasing, fusion and astrophysical plasmas, for which atomic data are required for a variety of parameters, such as energy levels, radiative rates (A- values), and excitation rates or equivalently the effective collision strengths ($\Upsilon$), which are obtained from the electron impact collision strengths ($\Omega$). Experimentally, energy levels are available for Al X on the NIST website, but there is paucity for accurate collisional atomic data. Therefore, here we report a complete set of results (namely energy levels, radiative rates, and effective collision strengths) for all transitions among the lowest 98 levels of Al X. These levels belong to the (1s$^2$) 2s$^2$, 2s2p, 2p$^2$, 2s3$\ell$, 2p3$\ell$, 2s4$\ell$, and 2p4$\ell$ configurations. Finally, we also report the A- values for four types of transitions, namely electric dipole (E1), electric quadrupole (E2), magnetic dipole (M1), and magnetic quadrupole (M2), because these are also required for plasma modeling. For our calculations of wavefunctions, we have adopted the fully relativistic GRASP code, and for the calculations of $\Omega$, the Dirac atomic R-matrix code (DARC) of PH Norrington and IP Grant. Additionally, parallel ca [Preview Abstract] |
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K1.00131: Electron scattering from excited states of H: derivation of the ionization threshold law Aaron Temkin, Janine Shertzer The titled elastic scattering wave function is the final state in the matrix element for excitation of that ($N)$ state. In the T-P model [1] wherein only radial correlations are included, the potential is dominated by the Hartree potential for the $N$th state. The solution and the matrix element are derived as a function of $N$ and the total energy ($E)$. Because the analytic continuation is complex, $N\to 1/i\sqrt \varepsilon $, where $\varepsilon $ is the energy of the ionized electron, the ionization threshold law acquires an exponential factor \textbraceleft $Q(E) \propto E^{3/2}\exp [-\pi \sqrt {8/3} /\sqrt E ]$\textbraceright . That factor completely overwhelms $E^{3/2}$ in the limit$E\to 0$. This result is qualitatively similar to that of Ref. [2], $Q_{MI} (E)\propto \exp [-6.87/(E/2)^{1/6}]$. That comparison and other implications of the law will be discussed.\\[4pt] [1] A. Temkin, Phys. Rev. \textbf{126}, 130 (1962), R. Poet, J. Phys. B \textbf{11}, 3081 (1978).\\[0pt] [2] J. H. Macek and W. Ihra, Phys. Rev. A\textbf{55}, 2024 (1997). [Preview Abstract] |
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