Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session G1: Poster Session I |
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Room: Knoxville Convention Center Ballroom AB, 4:00pm - 6:00pm |
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G1.00001: ATOMIC AND MOLECULAR STRUCTURE AND PROPERTIES |
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G1.00002: New and Updated Atomic Databases at NIST Yuri Ralchenko, Joseph Reader, Alexander Kramida We present a number of updated and newly developed databases at NIST. New spectral lines compilations for all ionization stages of Na and Mg and other data sets were recently added to the Atomic Spectra Database (currently version 3.0.3) which now contains data on 75,000 energy levels and about 130,000 spectral lines for all elements up to Z=99. A new database (SAHA) containing benchmark data for plasma populationkinetics modeling has been released in its beta version. SAHA database presents various selection and graphical tools for comparison of results calculated with the most advanced collisional-radiative computer codes. Finally, we report on a new comprehensive bibliographic database covering references on energy levels, spectral linesm and line shapes and broadening. [Preview Abstract] |
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G1.00003: Resonance and intersystem lines of astrophysical importance in neutral Sulphur Narayan C. Deb, Alan Hibbert We report extensive configuration interaction calculations of S I, for fine structure levels belonging to the configurations $3s^23p^4$, $3s3p^5$, $3s^23p^3(^4S^o,^2D^o,^2P^o) n\ell$, with $n\ell$=$4s,5s,6s,4p,5p,6p,3d,4d,4f,5f,5g$. Correlation effects are added using additional $s,p,d$ orbitals. For most levels, there is good agreement between our {\em ab initio} energies and the tablulations of NIST. Oscillator strengths have been calculated for all possible transitions between these levels, after refinements to both energy levels and CI mixing coefficients introduced by means of our `fine-tuning' process. Our results show significant improvement over previous calculations. [Preview Abstract] |
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G1.00004: High-precision atomic calculations using the relativistic all-order method: including triple excitations Eugeniya Iskrenova-Tchoukova, Marianna S. Safronova High-precision atomic calculations combined with experiments of matching accuracy provide an excellent opportunity to improve our understanding of atomic structure as well as to test atomic theory. One very appealing and challenging application of such calculations is the study of parity nonconservation (PNC) in atoms and ions. It requires a systematic study and accuracy estimates of the PNC amplitude and other atomic parity conserving quantities. While the implementation of the relativistic all-order method that completely includes single and double excitations yielded very accurate data for some atomic properties, the results for a number of atomic properties where the correlation was very large were much less accurate. The partial inclusion of the triple excitations, where only energy and single excitation coefficient equations were modified, provided improved accuracy for certain cases where specific contributions were dominant but produced inconsistent results in other cases. This work is aimed at the consistent inclusion of the triple excitations. We evaluate computational challenges involved in the efficient implementation of the all-order method with triple excitations balancing the need for accurate calculation and computational difficulties associated with an extremely large number of the corresponding triple excitation coefficients. [Preview Abstract] |
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G1.00005: Relativistic all-order calculations of Stark-induced $6P_{1/2}-7P{1/2}$ amplitudes in thallium W.R. Johnson, M.S. Safronova, U.I. Safronova, T.E. Cowan Stark-induced amplitudes $\alpha$ and $\beta$ of the $6P_{1/2}-7P_{1/2}$ transition in Tl I are calculated in the relativistic single-double (SD) approximation, where single and double excitations of the Pb-like core are summed to all-orders in perturbation theory. Dipole matrix elements and energies for transitions from $6P_{1/2}$ and $7P_{1/2}$ states to $nS_{1/2}$ ($n$=7-10) and $nD_{3/2}$ ($n$=6-9) states are evaluated in the SD approximation and summed to give the dominant contributions to the polarizabilities. Remainders are evaluated using Dirac Fock wave functions. We obtain $\alpha=364\, a_0^3$ and $\beta= -297\, a_0^3$ compared with measured values$^1$ $\alpha=377\pm 8\, a_0^3$ and $|\beta|=313\pm 8\, a_0^3$. A calculation of the Stark shift within the $6P_{1/2}-7S_{1/2}$ transition is also carried out using SD wave functions and differs from precise measurements$^{1,\, 2}$ by about 5\%. \newline \newline $^1$ D. DeMille, D. Budker, and E. D. Commins, Phys.\ Rev.\ A {\bf 50}, 4657 (1994). \newline $^2$ S. C. Doret, P. D. Frieberg, A. J. Speck, D. S. Richardson, and P. K. Majumder, Phys.\ Rev.\ A {\bf 66}, 52504 (2002). [Preview Abstract] |
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G1.00006: Relativistic configuration-interaction calculations for the \boldmath{$4s - 4p$} transition energies of zinclike heavy ions M. H. Chen, K. T. Cheng The $4s^2\,^1S_0 - 4s4p\,^{1,3}P_1$ transition energies for zinclike ions with $Z=70$, 76, 83, 90 and 92 are calculated using the relativistic configuration-interaction (RCI) method. These calculations are based on the {\it no-pair} Hamiltonian which includes both Coulomb and frequency-dependent retarded Breit interactions and use one-electron B-spline orbitals as basis functions. Our RCI configuration expansions include not only single and double excitations but also dominant triple and quadruple excitations for highly accurate correlation results, and Davidson's method is used to solve these large eigenvalue problems for the first few eigenstates. Quantum electrodynamic and mass polarization corrections are also calculated. Our transition energy results are in very good agreement with recent high precision EBIT measurements by Tr\"{a}bert {\it et~al}.[Phys.\ Rev.\ A {\bf70}, 032506 (2004)]. [Preview Abstract] |
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G1.00007: Relativistic Configuration Interaction Calculations for the J=3/2, 5/2 States of Mo VI Lin Pan, Donald R. Beck Relativistic configuration interaction calculations have been done for the 4p$^5$ 4d$^2$, $n$f ($n$=4-6) $J$=5/2 levels of Mo VI. The careful treatment of correlation is crucial to obtain accurate energy values. Besides, second-order effects and the magnetic Breit effects are also important, especially to the upper levels. There are only two measurements [1,2] for the 4p$^5$ 4d$^2$ levels to date. Our results are in good agreement with the most recent measurement [1] for the lower 9 levels of 4p$^5$ 4d$^2$. For the remaining 2 levels, the discrepancies are large ($>$ 3000 cm$^{-1}$). We have also calculated the oscillator strengths in both gauges for transitions $n$d $\rightarrow$ $n$f, 4p$^5$ 4d$^2$ $J$=5/2. The average gauge agreement of those big transitions ($f > 0.01$ ) is 6.6\% for $^2$D$_{3/2} \rightarrow J$=5/2, 5.0\% for $^2$D$_{5/2} \rightarrow J$=5/2. [1] A. Kancerevicius, A. Ramonas, A. Riabcevas and S. Ciurilovas {\em Lithuanian Journal of Physics} {\bf 31}, 251 (1991) [2] A. Tauheed, K. Rahimullah and M. S. Z. Chaghtai {\em Phys. Rev. A} {\bf 32}, 237 (1985) [Preview Abstract] |
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G1.00008: Energies, Auger width and branching ratios of some core-excited states for a beryllium-like system BingCong Gou, Meng Zhang The saddle-point variational method with multiconfiguration interaction wave function is used to obtain the energies of the core-excited triplet 1$s$2$p^{3} \quad ^{3}P^{o}$ and $^{3}D^{o}$ states for the beryllium isoelectronic sequence ($Z$=4-10), including the mass polarization and relativistic corrections. Restricted variational method is carried out to extrapolate a better energy. The saddle-point complex-rotation method is used to study the Auger width and branching ratios in the Auger decay of the beryllium-like core-excited 1$s$2$p^{3} \quad ^{3}P^{o}$ and $^{3}D^{o}$ states and double core-excited 2$s$2$p^{3} \quad ^{1}D^{o}$, $^{3}S^{o}$, $^{3}P^{o}$, $^{3}D^{o}$ and $^{5}S^{o}$ resonances. The relative branching ratios of the main decay channels of these resonance states are explained satisfactorily using the spin-alignment-dependent theory. The oscillator strengths and transition rates are also calculated. Our results are compared with the available experimental and other theoretical results in the literature. [Preview Abstract] |
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G1.00009: Relativistic Configuration Interaction Energy Differences Between
Gd {\sc iv} $4f^7$ $J=7/2$ Levels Donald R. Beck This is an ion of tremendous complexity for the $ab~initio$ computationalist, because a large energy matrix is required (well above 20\,000) and a large number of basis functions (over 100\,000 determinants in some cases) is needed to create its elements. Furthermore, $4f$ pair correlation converges rather slowly in angular space \footnote{K. Jankowski $et~al$, Int. J. Quant. Chem. XXVII, 665 (1985)} in contrast, say, to that of $d$ shell electrons. The ion is of potential interest for determination of the electron electric dipole moment and in PbF$_2$:Gd scintillators. We report energy differences between the 50 $4f^7$ $J=7/2$ levels whose average error \footnote{W. C. Martin $et~al$, Atomic Energy Levels - The Rare Earth Elements, NBS, USGPO, Washington, DC (1978)} for the bottom five levels is 1309 cm$^{-1}$, comparable to the best semi-empirical results \footnote{V. A. Dzuba $et~al$, Phys. Rev. A {\bf 66}, 032105 (2002)}. Our values, however, are obtained by dividing the energy matrix up into about 50 pieces. Future work will focus on assembly (and diagonalization) of the full energy matrix. [Preview Abstract] |
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G1.00010: Stability of the helium-antiproton system Richard Drachman In the course of their Born-Oppenheimer calculations of this system Todd and Armour\footnote{A. C. Todd and E. A. G. Armour, J. Phys. B {\bf 38}, 3367 (2005)} noted that the lowest-lying state closely resembles the hydrogen negative ion, since the antiproton lies very close to the helium nucleus and shields one unit of nuclear charge. In the present paper this observation will be taken seriously to produce a variationally correct estimate of the total energy of this system, along with a similar estimate of the energy of the once-ionized system. The nonadiabatic effect of exactly treating the reduced masses improves the results. [Preview Abstract] |
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G1.00011: Polarized orbitals obtained from scattering calculations used as pseudo states Hari Saha The polarized orbitals are obtained from an ab-initio calculation of elastic scattering of electrons from atoms at zero kinetic energy using the single channel MCHF $method^1$. These orbitals are deterimined by optimizing both the excited bound orbitals responsible for the polarization of the target atom and the scattering electron orbital at zero kinetic energy of the scattered electron. As reported earlier, these orbitals give very accurate dipole polarizability of $atoms^{2,3}$. It is shown that these polarized orbitals can be used as pseudo states in the scattering of electrons from atoms. As a test case, we will show the contribution of these pseudo states to the elastic and inelastic scattering of electrons from hydrogen atoms using the recently extended MCHF method for multiopen $channels^4$. Comparison will be made with other similar calculations. \\ \\ \noindent $^1$H.P. Saha, Phys. Rev. Lett. \underline {65}, 2003 (1990). \\ \noindent $^2$H.P. Saha and C.D. Caldwell, Phys. Rev. A \underline {44}, 5642 (1991). \\ \noindent $^3$H.P. Saha, Phys. Rev. A \underline {47}, 2865 (1993). \\ \noindent $^4$H.P. Saha and D.J. Murray, J.Phys.B \underline {38},3015 (2005). [Preview Abstract] |
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G1.00012: Compton Profiles of Atoms and Ions Khondkar Karim We present momentum-space properties of several atoms and ions including He, Be, B, C, N, O, and Ne atoms, and the respective ions in many possible ionization stages. The calculations have been done using Hartree-Fock atomic model. The Compton profile data presented here could be used to obtain doubly differential cross section of electron production in ion-atom collision from electron-ion cross sections. The plots of electron distribution in momentum space reveal interesting featuures that are not apparent in electron's radial probability distribution in coordinate space. [Preview Abstract] |
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G1.00013: A time-dependent density functional calculation of dispersion coefficients Xi Chu, Gerrit Groenenboom, Alex Dalgarno Dispersion interactions determine the long-range potentials of approaching atoms. Long-range interactions play a critical role in elastic and inelastic scattering cross sections at low temperatures. In a buffer gas cooling experiment paramagnetic atoms are cooled to about 1 K by elastic collisions with cryogenically cooled helium-3 and trapped in a magnetic field. Anisotropic interactions can result in inelastic spin alignment changing collisions which lead to trap loss. The trapped paramagnetic atoms can be cooled further to the ultracold regime by evaporation. The efficiency of this process depends on the ratio of the rates for elastic and inelastic collisions of the paramagnetic molecules. Therefore calculating the anisotropy of the dispersion interactions is vital for predicting the success of both buffer gas cooling and evaporative cooling experiments. A time-dependent density functional approach is developed for accurate and fast determination of the scalar and tensor dynamic polarizabilites of a wide range of open shell atoms. These polarizabilites are then used to calculate the dispersion interactions between an open shell atom and a helium atom or between two open shell atoms. The results are significant in estimating the likelihood that these atoms can be trapped in a helium buffer gas and cooled by evaporation. [Preview Abstract] |
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G1.00014: The structure and dynamics of the $B"\overline B { }^1\Sigma _u^+ $ \textit{ungerade} double-well state in H$_{2}$. A. Marks, R. C. Ekey Jr., E. F. McCormack Due to their symmetry and average internuclear separation, the \textit{ungerade} double-well states in H$_{2}$ have been difficult to observe. In the work presented here, double resonance spectroscopy via the$EF{ }^1\Sigma _g^+ ,v'_{EF} =6$ state has been used to probe highly excited rovibrational levels of the double-well $B"\overline B { }^1\Sigma _u^+ $state of H$_{2}$. Many transitions to levels located above the double-well barrier have been observed for the first time by detecting both molecular and atomic ion production as a function of energy by using a time-of-flight mass spectrometer. While significant perturbations are observed in the energy region at and above the barrier, assignments to levels with either dominant outer-well or inner-well characteristics can still be made according to the relative vibrational spacing and the observed rotational structures. Of note, is the observation of a subset of transitions with remarkably large linewidths corresponding to extremely rapid decay. The variation of linewidth observed as a function of well character and total angular momentum suggests autoionization as the primary decay mode for these levels. The results of our investigation of the transition energies and widths along with their possible assignments will be presented. [Preview Abstract] |
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G1.00015: Electronic and Vibrational Properties of Ultra-Low Ionization Potential Molecules. Nasrin Mirsaleh Kohan, Wesley Robertson, Jeff Steill, John Turner, Charles Feigerle, Richard Pagni, Robert Compton The ionization potentials (IPs) of the tetrakis(dimethylamino)ethylene(C$_{10}$H$_{24}$N$_{4}$, TDAE) molecule and the recently synthesized 1,2,3,4,5,6,7,8-octahydro-2a,4a,6a,8a-tetraaza-cyclopenta[fg]acenaphthylene (C$_{10}$H$_{16}$N$_{4}$,OTCA) molecules are comparable to that of some alkali atoms making them useful in a number of applications. High resolution electron impact ionization of TDAE was studied using a trochoidal electron monochromator mated to a linear time-of-flight mass spectrometer. The energy threshold for the formation of the parent ion was found to be 5.3 $\pm $ 0.2 eV, in close agreement with an earlier low resolution photoionization result, $<$ 5.36$\pm $ 0.2 eV, (Chem.Phys. Lett., 1971, 9, 615). Energy onsets for some of the fragment ions, i.e. loss of CH$_{3 }$, N(CH$_{3})_{2}$, (C$_{5}$H$_{12}$N$_{2})$ etc. from the parent ion will also be presented. Fragment ions were observed to be more dominate than that of the parent ion for electron energies above $\sim $40eV. We will report further information (REMPI, Raman, and FTIR) as well as supporting theoretical studies on these fascinating molecules. For example, the Raman spectrum for OTCA at 780 nm is simplified by the high symmetry and calculations provide an accurate description of the vibrational modes. [Preview Abstract] |
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G1.00016: Radiative vacancies decay of endohedral atoms Miron Amusia, Arkadiy Baltenkov It is demonstrated that the fulleren shell affects dramatically the radiative vacancy decay of an endohedral atom A@C60. It also adds new possibilities to radiative and non-radiative decay by opening a number of new interchannel decays similar to that in ordinary atoms where initial and final state vacancies almost always belong to different subshells. We demonstrate that the radiative width of a vacancy decay due to electron transition in the atom A in A@C60 acquire an additional factor that can be expressed via the polarizability of the C60 at transition energy. In general, it can not only enhance but also totally lock the radiative decay channel. For vacancies in subvalent shells of noble gas atoms N the non-radiative decay is forbidden. For N@C60 this decay is allowed since can proceed due to transition of fulleren shell electron to the vacancy in N. Corresponding width is expressed via the C60 total photoabsorption cross-section at the transition energy. [Preview Abstract] |
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G1.00017: Adiabaticity in a Nonlinear Atom-Molecule Condensate System H. Ling, H. Pu, P. Maenner We consider the two-color Raman photo-association model, and study the adiabatic condition under which a free atomic condensate can be converted into a ground molecular condensate by the method of stimulated Raman adiabatic passage (STIRAP), founded on the nonlinear atom-molecule dark state. We attribute nonadiabaticity to the population growth in the collective excitations of the dark state, and derive an adiabatic theorem by comparing the rate change of the Hamiltonian to the level spacing in the Bogoliubov excitation spectrum of the dark state. We apply this theorem to study the powers and durations of the laser pulses that are required for an efficient STIRAP operation with different system parameters including two-body collision coefficients. [Preview Abstract] |
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G1.00018: Long-range interactions between two excited helium atoms J.-Y. Zhang, Z.-C. Yan, D. Vrinceanu, J.F. Babb, H.R. Sadeghpour Using variational wave functions in correlated Hylleraas coordinates, we have precisely calculated the dispersion coefficients $C_n$ (with n up to 10) for the long-range interaction between two excited helium atoms including the effect of finite nuclear mass. In this work, the long-range interaction coefficients reported are $C_3$, $C_6$, $C_8$, $C_9$, and $C_{10}$ for He$(2\,^1\!S)$--He$(2\,^1\!P)$; $C_6$, $C_8$, and $C_{10}$ for He$(2\,^3\!S)$--He$(2\,^1\!P)$; and $C_5$, $C_6$, $C_8$, and $C_ {10}$ for He$(2\,^1\!P)$--He$(2\,^1\!P)$ and He$(2\,^1\!P)$--He$(2\,^3\!P) $ for the $\Delta$, $\Pi$, and $\Sigma$ molecular states. [Preview Abstract] |
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G1.00019: SPECTROSCOPY, LIFETIMES, OSCILLATOR STRENGTHS |
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G1.00020: Measurements of Lifetimes and f-Values In Highly-Charged Ions Steven Smith, Ara Chutjian, Sabbir Hossain Measurements have been made of lifetimes of metastable levels of highly-charged ions (HCI). These contribute to the optical absorption, emission and energy balance in the ISM, stellar and solar atmospheres, etc. The experimental lifetime measurements are carried out using the 14.0 GHz electron cyclotron ion source at the JPL facility.[l] Ions are injected into a Kingdon ion trap and stored for times longer than the metastable lifetimes. Decay channels include inter-combination, E2, M1 and 2E transitions. The UV photons are filtered by an interference filter and detected by a UV grade photomultiplier tube using a UV grade optical system. The Kingdon trap was constructed in collaboration with Texas A and M University [2]. We previously have reported lifetimes for transitions of $C^{+}$ [1]and $0^{2+}$ [4]. Additional metastable lifetimes have been measured for $M^{6+}$, \textit{Fe}$^{9+}$\textit{, Fe}$^{10+}$ and \textit{Fe}$^{13+}$ metastable states [5]. New results for \textit{Fe}$^{11+}$ will be presented. Sabbir Hossain acknowledges support through NASA-NRC program. This work was carried out at the Jet Propulsion Laboratory/Caltech and was supported by the NASA [1] Steven J. Smith, A. Chutjian, J.B. Greenwood, Phys. Rev. A \textbf{60, }3569 (1999). [2] L.Yang and D.A$. $Church, Phys. Rev. Lett. \textbf{70, }3860 (1993).[3] S.J. Smith, I. Cadez, A. Chutjian, and M. Niimura, \textit{Ap. J.} \textbf{602}, 1075 (2004).[5] S.J. Smith , A. Chutjian, J. Lozano, \textit{Phys Rev. A}\textbf{ 72, } 062504 (2005)\underline {.} [Preview Abstract] |
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G1.00021: Classical calculation of radiative lifetimes and branching ratios for hydrogenic Stark states. Michael W. Horbatsch, Eric A. Hessels, Marko Horbatsch Recently we obtained accurate lifetime expressions for hydrogenic states on the basis of a classical Larmor radiation calculation [1]. Branching ratios (BRs) were obtained in good agreement with quantum mechanics when the Fourier components were collected to correspond to allowed final states. Accurate lifetimes were subsequently obtained for diamagnetic states [2]. Here we turn to the problem of lifetimes and BRs for Stark states of hydrogen. Classical expressions for these BRs were obtained in 1917 by H.A. Kramers. In order to go beyond that, we transform from the space of two Fourier indeces that characterize the motion in parabolic coordinates to (Dn, Dmu), which represent changes in the principal and electric quantum numbers. Using this method, we find a good correspondence between the classical predictions and quantum mechanical results even for large Dn/n. A lifetime formula and comparisons of partially summed BRs with quantum mechanical results will also be presented. [1] Phys. Rev. A 71, 020501(R) (2005); [2] Phys. Rev. A 72, 033405 (2005). [Preview Abstract] |
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G1.00022: Molecular Dications and the Auroral Mystery Feature: Measurements on Nitrogen A.N. Daw, S.M. Brewer, C.C. Estes, J.A. Kanoy, B.W. Myer, A.G. Calamai Experiments in progress at the ASU ion trapping facility will provide atomic and molecular data for N$^{+}$, N$_{2}^{++}$, and N$_{2}$, specifically, measurements of: the radiative lifetime of the $^{5}$S metastable level of N$^{+}$, the dissociation rate of N$_{2}^{++}$, electron capture rates from molecular nitrogen for both these ions, and the cross section for dissociative electron impact ionization of molecular nitrogen into metastable $^{5}$S N$^{+}$. Ions are created in a radiofrequency ion trap by electron bombardment on nitrogen gas, and both the number of stored ions and the UV radiation emitted by the stored ion population (from decaying metastable N$^{+}(^{5}$S) ions and N$_{2}^{++}$+N$_{2}$ reactions) are measured as a function of time. Preliminary data and results will be presented [Preview Abstract] |
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G1.00023: Relativistic many-body calculations of electric-dipole lifetimes, transition rates, and oscillator strengths for $2l^{-1}3l'$ states in Ne-like ions U.I. Safronova, T.E. Cowan, M.S. Safronova Transition rates, oscillator strengths, and line strengths are calculated for electric-dipole (E1) transitions between odd- parity $2s^22p^53s$, $2s^22p^53d$, and $2s2p^63p$ states and even- parity $2s^22p^53p$, $2s2p^63s$, and $2s2p^63d$ states in Ne-like ions With the nuclear charges ranging from $Z$ = 14 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 $1s^22s^22p^6$ Dirac-Fock potential. First-order RMBPT is used to obtain intermediate coupling coefficients and second-order RMBPT is used to calculate transition matrix elements. Contributions from negative-energy states are included in the second-order E1 matrix elements to ensure the gauge independence of transition amplitudes. Transition energies used in the calculation of oscillator strengths and transition rates are from second-order RMBPT. Lifetimes of the 16 even-parity and 18 odd-parity levels are given for $Z$ = 14--100. These atomic data are important in modeling of L-shell radiation spectra of heavy ions generated in electron beam ion trap experiments and in L-shell diagnostics of plasmas. [Preview Abstract] |
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G1.00024: Atomic properties of Ca$^+$, Sr$^+$, Cd$^+$, Hg$^+$, and Ra$^+$ Dansha Jiang, M.S. Safronova, U.I. Safronova We conducted a systematic study of the transition properties of Ca$^+$, Sr$^+$, Cd$^+$, Hg$^+$, and Ra$^+$ ions using a relativistic all-order method. Reduced electric-dipole matrix elements and transition rates are determined for the $ns-np_j$ and $np_j-n^{\prime}d_{j}$ transitions, where $ns$ is a ground state. The electric-quadrupole matrix elements are evaluated for the $ns-(n-1)d_j$ transitions in Sr$^+$ and Ra$^+$. The theoretical lifetimes for the $np_j$ and $nd_j$ states are compared with latest available experimental measurements. The energy levels and hyperfine constants are also calculated and compared with experiment. This work is motivated by recent lifetime measurements in Ca$^+$, Sr$^+$, and Cd$^+$. [Preview Abstract] |
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G1.00025: The Iron Project and the Rmax Project: X-ray Spectroscopy of Highly Charged Ions Justin Oelgoetz, Anil Pradhan, Sultana Nahar, Maximiliano Montenegro, Werner Eissner We will describe recent work on (1) the modeling of spectra arising from highly charged ions, and (2) the data that goes into such models. Emission from the K$\alpha$, and in some cases, K$\beta$ lines of the Li, He, and H-like states of ions is of great interest in X-ray astronomy and high-temperature laboratory sources such as fusion devices. Current results at modeling these lines including all relevant atomic processes for the elements Fe, Ni and Ca will be presented, along with a discussion of the computational methods employed and the possible implications of the work. An extensive set of oscillator strengths, line strengths and radiative decay rates for the allowed and forbidden transitions in Fe~XVIII have been obtained in the relativistic Briet-Pauli R-Matrix approximation. The results include 1174 fine structure levels of total angular momenta J= $\frac{1}{2}$ - $\frac{17}{2}$ and n $le$ 10 and about 171,500 transitions among them. Sample results will be presented. Parts of this work were supported under grants from the NSF and the NASA Astrophysical Theory Program as well as by Los Alamos National Laboratory which is operated under Department of Energy contract W-7405-ENG-36 by the University of California. Many of the calculations were carried out at the Ohio Supercomputer Center. [Preview Abstract] |
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G1.00026: Ionization energies of W~I-LXXIV and critical compilation of spectra and energy levels of Ga I-XXX Alexander Kramida, Joseph Reader Both tungsten and gallium are important materials for fusion energy research. In this work, a semi-empirical method is used to determine ionization energies (IE) of multiply charged W ions [A.E. Kramida, J. Reader, \textit{Ionization Energies of Tungsten Ions: W}$^{2+}$\textit{ through W}$^{71+}$, At. Data Nucl. Data Tables, 2006, in press]. The method is based on Hartree-Fock calculations of electron binding energies with empirical scale factors. Relative uncertainties vary from 1.7~{\%} for W III$^{ }$to 0.015~{\%} for W LXXII. Combined with previously known experimental or theoretical IE values for W I-II and LXXIII-LXXIV, these new semiempirical results allow us to build a complete table of IEs of tungsten in all stages of ionization. For gallium, all available experimental data on wavelengths and energy levels are critically compiled and evaluated [T. Shirai, J. Reader, A.E. Kramida, J. Sugar, \textit{Spectral Data for Gallium: Ga I through Ga XXXI}, J. Phys. Chem. Ref. Data, 2006, in press]. Such data exist for spectra Ga~I-VII, XIII-XXVI, and XXX. For Li-like Ga~XXIX through H-like Ga~XXXI, theoretical data on energy levels and line wavelengths are compiled. For Ga~I-III, XV-XX, XXIII-XXVI, and XXX, radiative transition probabilities are included where available. The ground state configuration and term and a value of IE are included for each ion. This work was supported in part by the Office of Fusion Energy Sciences of the U. S. Department of Energy. [Preview Abstract] |
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G1.00027: Analyzing L-Shell Multiplet Dynamics in Moderate Atomic Number Z-pinch Plasmas Arati Dasgupta, Ward Thornhill, Jack Davis, Kenneth Whitney To produce significant K-shell emissions from moderate atomic number plasmas such as iron, a plasma must be rapidly ionized through its L-shell ionization stages. In iron, emissions from the Li-like and Be-like ionization stages lie above a kilovolt and are, therefore, relatively easy to measure. They are therefore of potential importance for diagnosing under what experimental conditions and to what extent a Z-pinch plasma has reached temperatures and densities near those required for significant K-shell x-ray production. However, diagnostics based on the spectral shape of L-shell emissions are inherently more difficult than those based on K-shell emissions because of the more complex multiplet structures in the L- as opposed to the K-shell. These structures, in turn, produce line overlaps and a modified ionization dynamics due to a non-LTE distribution of populations in the substates of the multiplets. In this work, we will analyze this behavior in the Li- and Be-like ionization stages of iron using the temperature and density conditions that are predicted in 2-D MHD calculations to be generated in ZR-generator implosions at the Sandia National Laboratories.. [Preview Abstract] |
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G1.00028: Spectra of W$^{39+}$-W$^{46+}$ in the 12-14 nm region observed with an EBIT light source Joseph Reader, Yuri Ralchenko, Joshua Pomeroy, John D. Gillaspy We observed spectra of highly-ionized W in the EUV region with the EBIT light source and a grazing incidence spectrograph at NIST. Stages of ionization could be distinguished unambiguously by varying the electron beam energy in small steps between 2.1 and 4.3 keV. The spectra were calibrated by separate spectra of highly ionized iron. We also carried out collisional-radiative modeling of the EBIT plasma emission and found good qualitative agreement between theoretical spectra and our observations. Our results complement recent line identifications for W$^{40+}$-W$^{45+}$ observed in a tokamak [1]. For most lines we agree with their ionization stage assignments. New identifications include lines of W$^{39+}$, W$^{46+}$, and a strong magnetic-dipole transition of the Zn-like ion W$^{44+}$ at 13.48 nm. [1] T. Puterich et al., J. Phys. B. 38, 3071 (2005). [Preview Abstract] |
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G1.00029: Convergence of Theory and Experiments for the 3C/3D Line Ratio in Ni XIX G.X. Chen, K. Kirby, E. Silver, N.S. Brickhouse, J.D. Gillaspy, J.N. Tan, J. Pomeroy, J.M. Laming We report the results of a new Dirac {\sl R}-matrix calculation for the 3C/3D X-ray line ratio in Ni\ {\small XIX}, together with the results of new experimental measurements performed on an EBIT. The results and uncertainties were obtained independently at the Harvard-Smithsonian Center for Astrophysics and NIST, respectively, and agree well with each other. The theoretical results are converged to an uncertainty of $\sim$5\%. [Preview Abstract] |
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G1.00030: Importance of Configuration Interaction for Accurate Atomic Data: Fluorescence Yields of K-Shell Vacancy Lithium-Like Ions M.F. Hasoglu, I. Dumitriu, T.W. Gorczyca, D.W. Savin, S.T. Manson, N.R. Badnell We demonstrate that the inclusion of configuration interaction (CI) results in significant values for the K-shell fluorescence yields of Li-like ions, which are zero in a single-configuration approach. Modeling codes for simulating supernova remnants under nonequilibrium ionization conditions or photoionized plasmas such as active galactic nuclei or X-ray binaries need to be updated accordingly. A two-parameter fitting formula for the fluorescence yields has been developed. The generality of important CI effects on atomic calculations is pointed out. [Preview Abstract] |
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G1.00031: Measurement of isotope shifts in Fe II Marco Ascoli, David Kawall, Edward Eyler, David DeMille We describe absorption spectra of singly ionized iron (Fe II) obtained with a compact ion source and a high-resolution UV laser. Using a Nd:YAG laser ablation source and buffer gas cooling with room-temperature argon, Fe II ions are produced in a cold plasma. Grating spectroscopy is used to determine conditions favorable parameters providing good cooling and ion yield. This novel technique allows us to study the Fe II transition $a ^6D_9 \rightarrow z^6D^o_9$ with Doppler widths about 3 GHz, by measuring the absorption of a frequency-tripled pulse-amplified cw Ti:Sapphire laser. The isotope shift of this transition is important to the analysis of astronomical data on the cosmological evolution of the fine-structure constant $\alpha$ [1]. We will discus the design of the ion source and laser system, and present preliminary results. This study was funded by the National Science Foundation. \par \vspace{12 pt} \noindent [1] J.K Webb,M.T. Murphy, V.V. Flambaum, V.A. Dzuba, J.D. Barrow, C.W. Churchill, J.X. Prochaska, and A.M. Wolfe, Phys. Rev. Lett. \textbf{87}, 091301 (2001). [Preview Abstract] |
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G1.00032: Role of Atomic Symmetries in Radiative Cascades. Uskov Dmitry, R.H. Pratt We examine the effects of degeneracy for the problem of electron radiative cascade. A weak external field approximation in the Lindblad formalism is used to study a gradual transformation of cascade dynamics between degenerate and non-degenerate forms in the presence of external perturbations. Illustrative calculations are made for Coulomb system with SO(4) dynamic symmetry. [Preview Abstract] |
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G1.00033: Precision Measurement of the 6$P_{3/2}$ State of Cesium B.M. Patterson, T. Ehrenreich, R.J. Knize We have refined our atomic lifetime measurement technique$^{1}$ and report a precision value for the 6$P_{3/2}$ state of cesium. A single pulse ($\sim $nJ) from a mode-locked Ti:Sapphire laser excites atoms in counter-propagating thermal beams to the 6$P_{3/2}$ state. A subsequent laser pulse is amplified using a regenerative amplifier to a few $\mu $J and is frequency-doubled, and ionizes atoms in the excited state. The ions are collected using a channel electron multiplier and counted. The measurement is repeated using excitation and detection pulses that are increasingly separated in time, allowing the decay from the excited state to be determined. Our preliminary results indicate a lifetime of 30.44~ns with a statistical uncertainty of 0.02~ns. The dominant systematic effects will be addressed. These include (1) the effects of imperfect extinction ratios of the electro-optic modulators used for laser pulse selection; (2) the effects of atoms moving through spatially non-uniform laser beams; and (3) the effects of misalignment of the excitation and ionization laser beams. $^{1}$B.M. Patterson, C.D. Lindstrom, T. Takekoshi, J.R. Lowell, C. Villarreal, and R.J. Knize, Opt. Lett. \textbf{28} (19), 1814 (2003). [Preview Abstract] |
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G1.00034: Atomic beam measurements of the $^{133}$Cs $7\mbox{d} ^2\mbox{D}_j$ hyperfine structure Andrew Kortyna, Nicholas Masluk, Jonathan Farrar The hyperfine structures of the $7\mbox{d} ^2\mbox{D}_{3/2}$ and $7\mbox{d} ^2\mbox{D}_{5/2}$ states of cesium are studied using two-color, fluorescence spectroscopy in an atomic beam. Two single-mode external-cavity diode lasers probe the $7\mbox{d} ^2\mbox{D}_j$ states through two-color resonant excitation. One laser is locked to the $6\mbox{s} ^2\mbox{S}_{1/2} (\mbox{F}) \rightarrow 6\mbox{p} ^2\mbox{P}_{3/2} (\mbox{F}')$ transition using a servo-feedback circuit; optical pumping of the ground state is minimized through electro-optic modulation of this laser. The second laser is scanned over the $6\mbox{p} ^2\mbox{P}_{3/2} (\mbox{F}') \rightarrow 7\mbox{d} ^2\mbox{D}_j (\mbox{F}'')$ hyperfine manifolds. High resolution is achieved by referencing the frequency scale of the second laser directly to the $^{87}$Rb ground state hyperfine transition using a radio-frequency modulation technique. [Preview Abstract] |
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G1.00035: The Long-Range Model of High-L Rydberg Fine Structure: A Critical Comparison with Experimental Data.. Erica L. Snow, Laura E. Wright, Stephen R. Lundeen A simple view of the fine structure of non-penetrating Rydberg levels, suggested over 70 years ago [1], was refined to treat the fine structure of helium, lithium [2], and other atoms with S-state ion cores [3]. In this view the ion polarizabilities determine the fine structure pattern. Current experimental techniques provide access to highly excited high-L states in He [4], Li [5], Mg, SiIII [6], and Ba[7], and a test of the long-range model is possible with the availability of independent theoretical calculations. A critical comparison of the data treated with the long-range model will be made to the a-priori calculations of the ionic polarizabilities. [1] Joseph E. Mayer and Maria Goeppert Mayer, Phys. Rev. \textbf{43} 605 (1933). [2] Richard J. Drachman and A. K. Bhatia, Phys. Rev. A \textbf{51} 2926 (1995). [3] C. Laughlin, J. Phys. B: At. Mol. Opt. Phys. \textbf{28} 2787 (1995). [4] G. D. Stevens and S. R. Lundeen, \textit{Comments on At. and Mol. Phys., Comments on Mod. Phys.} \textbf{1,D} 207 (2000). [5] C. H. Storry, N. E. Rothery, and E. A. Hessels, Phys. Rev. A \textbf{55} 128 (1997). [6] R. A. Komara et. al., J. Phys. B: At. Mol. Opt. Phys. \textbf{38} S87 (2005). [7] E.L. Snow, et. al. Phys. Rev. A 71, 022510 (2005) [Preview Abstract] |
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G1.00036: Towards a Laser Spectroscopic Determination of the $^8$He Nuclear Charge Radius P. Mueller, K. Bailey, R.J. Holt, R.V.F. Janssens, Z.-T. Lu, T.P. O'Connor, I. Sulai, M.-G. Saint Laurent, J.-Ch. Thomas, A.C.C. Villari, O. Naviliat-Cuncic, X. Flechard, S.-M. Hu, G.W.F. Drake, M. Paul We will report on the progress towards a laser spectroscopic determination of the $^8$He nuclear charge radius. $^8$He (t$_{1/2}$ = 119 ms) has the highest neutron to proton ratio of all known isotopes. Precision measurements of its nuclear structure shed light on nuclear forces in neutron rich matter, e.g. neutron stars. The experiment is based on our previous work on high-resolution laser spectroscopy of individual helium atoms captured in a magneto-optical trap. This technique enabled us to accurately measure the atomic isotope shift between $^6$He and $^4$He and thereby to determine the $^6$He rms charge radius to be 2.054(14) fm. We are currently well on the way to improve the overall trapping efficiency of our system to compensate for the shorter lifetime and lower production rates of $^8$He as compared to $^6$He. The $^8$He measurement will be performed on-line at the GANIL cyclotron facility in Caen, France and is planned for late 2006. [Preview Abstract] |
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G1.00037: Polarization Spectroscopy of Na$_{2}$ $A-X$ Transitions Peng Qi, Jianmei Bai, Omer Salihoglu, A. M. Lyyra, T. H. Bergeman We have measured or remeasured thousands of lines in the Na$_{2}$ $A \leftarrow X$ system, using a heat-pipe oven, with sub-Doppler resolution. The line widths are typically 250 MHz with $>$10 signal:noise ratio, yeilding line centers to an accuracy of 90 MHz including calibration uncertainties. In certain cases, the rotational quantum number assignments are determined by measuring dispersed fluorescence. These data points are being added to thousands of other measured term values from about 20 sources for the NA$_{2}$ $A ^{1}\Sigma_{u}^{+}$ and $b ^{3}\Pi_{u}$ states in a comprehensive compilation and analysis [1]. The present status of this analysis is adequate to assign most of the lines observed in the present study, with iterative refinement. Accurate potential curves and spin-orbit coupling functions are obtained, and can be used, for example, to identify mixed singlet-triplet ``window'' states through which to excite higher triplet levels. \\ 1. T. Bergeman, A. M. Lyyra, Li Li, A. Ross and others: work in progress. [Preview Abstract] |
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G1.00038: Experimental and theoretical studies of pressure broadened alkali-metal lines for astrophysical applications F. Shindo, C. Zhu, J. Babb, K. Yoshino, A. Dalgarno, K. Kirby We are undertaking a program of experimental and theoretical studies of the pressure broadening of Na and K by He and H$_{2}$. This work is motivated by the need for accurate absorption coefficients to validate models of atmospheric opacities which can be used to characterize properties such as gravity and effective temperature of brown dwarfs or predict spectra of irradiated extrasolar giant planets. Due to the collisions with gaseous H$_{2}$ and He at high concentration in these objects with temperatures of around 1000 K, the profiles of Na and K lines (respectively at 590 nm and 770 nm) are strongly broadened by at least 100 nm. The design of our spectroscopic experiment allows us to collect absorption spectra of alkali vapors at temperatures around 900 K in the presence of buffer gas at pressures of several hundred torr. The atomic densities are measured precisely using the anomalous dispersion (``hook'') method.~Investigating the spectral range 380-920 nm, we observed the broadening of the K 770 nm lines and we find the K 404 nm doublet exhibits a putative satellite feature on its blue wing. The theoretical calculations utilize accurate molecular potential energies and transition dipole moments and fully quantum-mechanical methods.~Supported in part by NASA grant NAG5-12751 [Preview Abstract] |
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G1.00039: Visible to near infrared emission spectra of electron-excited H$_2$ A. Aguilar, G.K. James, J.M. Ajello, H. Abgrall, E. Roueff H$_2$ is the most abundant molecule in the universe and is an active component of star formation. Intense H$_2$ transitions in the visible optical near Infrared (VOIR) spectral region from various vibrational levels have been observed in highly-collimated jets of matter from young stellar objects~[1]. In recent work, we have demonstrated [2] that the gerade series (EF, GK, H$^1\Sigma^{+}_{g}$, I$^1\Pi_{g}$, J$^1\Delta_{g}$...) makes a significant contribution to the UV spectrum of H$_2$ via its cascade spectrum in the VOIR to the $n$~=~$2p\sigma$B and $2p\pi$C states, the upper states of the Lyman and Werner bands, respectively. We present the measured electron-impact-induced emission spectrum of H$_2$ in the VOIR region 700~nm to 950~nm at a spectral resolution of 2~nm (FWHM). A model spectrum of H$_2$ including rovibrational coupling for the strongest band systems is in excellent agreement with observed intensities. \newline [1] Nisini \textit{et al.},A\&A,\textbf{441},159-170,(2005) \newline [2] Liu \textit{et al.},Astrophys.J.Suppl.,\textbf{138},229(2002) and J.Phys.B, \textbf{36},173(2003). [Preview Abstract] |
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G1.00040: Improvements on a laser spectroscopy experiment to measure helium fine structure Marc Smiciklas, Ali Khademian, David Shiner Our group is conducting an ongoing high precision laser spectroscopy experiment to measure the fine structure splittings in the helium atom. Discussed is the work done to improve and refine our newly designed and built apparatus over our previously used experimental setup. Improvements in the detector have been implemented that greatly reduce background counts for much improved signal to noise. Also, custom designed and built 1083nm ytterbium doped fiber lasers for pumping both He-4 and He-3 atoms are being implemented for initial state preparation. This will allow consistency checks in intervals between He-3, He-4 and the most recent results from theory [D.C. Morton, Q. Wu, G.W.F. Drake, Can. J. Phys. (in press)]. Initial tests show these fiber lasers to have better than 40 percent slope efficiency with a 5 mW laser threshold. The laser uses PM and single mode fiber gratings for the cavity and should be applicable to Yb lasers in the 1000-1100nm range. These and other improvements are discussed along with the current status of the experiment itself. [Preview Abstract] |
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G1.00041: DEGENERATE FERMI GASES |
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G1.00042: Stability of fermionic molecules in a Bose-Fermi mixture Daniele Bortolotti, Alexander Avdeenkov, John Bohn In the wake of successful experiments in Fermi condensates, experimental attention is broadening to include resonant interactions in degenerate Bose-Fermi mixtures. We consider the properties and stability of the fermionic molecules that can be created in such a mixture near a Feshbach resonance. To do this, we consider the two-body scattering problem in the many-body environment, and assess its complex poles. The stability properties of the resulting molecules are non-trivial, and depend strongly on their center-of-mass motion in the gas. We also study the effects of this physics on the equilibrium properties of the gas, and in particular on the molecular population and momentum distribution. [Preview Abstract] |
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G1.00043: Investigating the BCS-BEC crossover region using ultra-cold fermionic atoms John Stewart, John Gaebler, Cindy Regal, Deborah Jin Progress towards the experimental realization of the BCS-BEC crossover has opened a rich area of physics. Starting with a two-component gas of $^{40}$K atoms cooled to quantum degeneracy we can create strong, tunable interactions through the use of a magnetic Feshbach resonance. We report on recent experiments including current thermodynamics measurements. [Preview Abstract] |
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G1.00044: Heteronuclear Feshbach Resonances in a Bose-Fermi Mixture of $^{40}$K and $^{87}$Rb M. L. Olsen, T. D. Cumby, D. S. Jin Feshbach resonances have proven to be a valuable tool in the study of atomic gases. These resonances allow control over both the sign and magnitude of the interaction between two atoms. We have observed four magnetically tunable heteronuclear Feshbach resonances between fermionic $^{40}$K and bosonic $^{87}$Rb. We report on studies of interactions in the mixture of the two species near a Feshbach resonance. [Preview Abstract] |
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G1.00045: Diffusion Monte Carlo Calculations for Trapped Fermi Gases Javier von Stecher, Seth T. Rittenhouse, Chris H. Greene Monte Carlo methods are particularly useful to test the validity of the effective theories. Blume and Greene have used diffusion Monte Carlo to study the corrections to the Gross-Pitaevskii equation for bosons [1]. We study the ground state energy of a trapped degenerate Fermi gas using Monte Carlo methods. We compare mean field results and higher order corrections with our calculations. As in the case of bosons, effective theories predict a collapse of a Fermi gas at negative $a_{0}$ [2]. We analyze the possibility of collapse considering finite range interactions. [1] D. Blume and Chris H. Greene, Phys. Rev. A 63, 063601 (2001). [2] S. T. Rittenhouse et al, arXiv:cond-mat/0510454. [Preview Abstract] |
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G1.00046: Correlations in an ultracold gas of 1D spin-polarized fermions Scott Bender, Brian Granger We use a mapping between systems of 1D bosons and fermions to investigate correlations in systems of strongly interacting 1D fermions. At zero temperature we consider a fermionic version of the Tonks-Girardeau gas that is dual to a system of noninteracting bosons. We derive exact expressions for the K- particle correlation functions and find that they exhibit an exponential decay. We then extend our focus to finite temperatures where we examine local two-particle correlations over a spectrum of interaction regimes. In each regime we calculate the short-distance one-particle correlations which yield information about the large momentum tail of the momentum distribution. [Preview Abstract] |
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G1.00047: Cooling Bose-Fermi mixtures to quantum degeneracy on a chip L. J. LeBlanc, S. Aubin, S. Myrskog, M. H. T. Extavour, D. McKay, A. Stummer, J. H. Thywissen We have demonstrated for the first time the cooling of both bosons and fermions to quantum degeneracy in a microelectromagnetic chip trap. The tight confinement of this magnetic trap allows for evaporative cooling of $^{87}$Rb towards Bose-Einstein condensation with efficiencies of up to four orders of magnitude increase in phase space density for each order of magnitude decrease in atom number. Such efficiencies are among the highest reported in a magnetic trap [1]. We compare our evaporation data to a model based on [2]. We have also trapped fermionic $^{40}$K simultaneously with the bosons. By evaporatively cooling the bosons, the fermions are sympathetically cooled to quantum degeneracy through rethermalizing collisions with the bosons. We find that the thermalization between species is weak for temperatures around 300$\mu$K and attribute this to a reduction in the cross-species collisional scattering cross-section. We have measured this reduction in cross-section as a function of temperature over the course of the sympathetic cooling. [1] A log-slope efficiency of 4.5 was reported in K.L. Moore, {\it et al.} arXiv:cond-mat/0504010. [2] O.J. Luiten, M.W. Reynolds, and J.T.M. Walraven, {\it Phys. Rev. A} {\bf 53}, 381 (1996). [Preview Abstract] |
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G1.00048: COLD ATOM, MOLECULES, AND PLASMAS |
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G1.00049: Coherent control of weak light localization in ultracold atomic $^{87}$Rb R.G. Olave, M.D. Havey, V.M. Datsyuk, D.V. Kupriyanov, I.M. Sokolov We have an ongoing program of experimental and theoretical study of creation and manipulation of coherent photonic excitations in mesoscopic ultracold atomic ensembles. In one area, we are considering coherent control of weak localization of light. By exploiting the phenomenon of electromagnetically-induced transparency (EIT), the scattering and transmission properties of an atomic gas are modified, resulting for example in very small group velocity for light. In this paper, we describe similar effects which are used to manipulate mesoscopic coherences associated with weak localization of light in ultracold $^{87}$Rb. Weak localization is an interferometric breakdown of classical radiative transport in atomic vapors, and may be studied through the coherent backscattering (CBS) effect in an ultracold atomic gas. We present results of Monte-Carlo simulations of wave propagation in realistic ultracold samples, based on elaboration of our earlier successful description of CBS in atomic gases. The results illustrate some of the basic effects and their connection with slow-light measurements in forward scattering. The basic measurement scheme and progress towards observing EIT-based control of diffuse electromagnetic waves in an ultracold atomic gas of $^{87}$Rb is also described. [Preview Abstract] |
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G1.00050: Millimeter Wave Spectroscopy of cold Rb Rydberg atoms Jianing Han, Yasir Jamil, Paul Tanner, Don Norum, T.F. Gallagher By using the cold $^{85}$Rb Rydberg atoms in a magneto optical trap, we have measured the single photon $^{85}$Rb \textit{nd}-($n$-2)$f$ millimeter wave transitions for 32$\le n\le $39. The measurements were carried out at densities of 10$^{9}$ atoms/cm$^{-3}$, roughly five orders of magnitude lower than those used in optical measurements. Since the 10 G/cm gradient of the trap magnetic field would result in 5 MHz wide resonances, we switched off the field during the measurements. The observed narrow resonances will be used to improve the accuracy of the $f$ quantum defect of $^{85}$Rb. [Preview Abstract] |
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G1.00051: Study of Ultracold Strontium Plasma Sampad Laha, Priya Gupta, Clayton Simien, Sarah Nagel, Natali Martinez, Pascal Mickelson, Thomas Killian Ultracold plasma opens up a new regime in the study of plasma physics. The interest in ultracold plasma stems from the fact that the fundamental processes of thermalization, correlation, reionization and recombination in a plasma are very different at the millikelvin temperatures. We laser cool and trap neutral Strontium atoms and then photoionize them to make ultracold plasma. The electron temperature is determined by the photoionizing laser while the ions are at the same temperature as the laser-cooled atoms. At this ultracold temperature, the ions are in the strong coupling regime. Using absorption imaging with 422nm light, we are able to study the various processes in ultracold plasma with excellent spatial, temporal and spectral resolution. This poster will include a description of the apparatus and technique used to create, study and trap ultracold plasma. We will also present results from recent experiments showing plasma oscillations and expansion. [Preview Abstract] |
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G1.00052: BOSE-EINSTEIN CONDENSATES |
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G1.00053: Multiconfigurational Time-Dependent Hartree-Fock Theory for Identical Bosons in a Double Well David Masiello, William Reinhardt Building upon the time-independent study [D. Masiello, {\it et. al.}, Phys. Rev. A {\bf 72}, 063624 (2005)], we have formulated a multiconfigurational time-dependent Hartree-Fock theory for identical bosons to explore the combined effects of the condensate's mean field and atomic correlation on the fragmentation dynamics of a double-well BEC from first principles. Our explicitly time-dependent approach includes the Hartree-Fock orbitals as well as all possible configuration amplitudes allowed within a certain model space as dynamical variables, and applies the time-dependent variational principle to derive balanced and well-defined equations of motion that include the full coupling between these variables. Due to its general formulation and rich mathematical structure, this treatment clarifies many of the principles and approximations that are found in other relevant approaches from the literature and proves to be a powerful theoretical tool in the understanding of recent double-well BEC interference experiments performed at MIT. [Preview Abstract] |
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G1.00054: Damped Oscillations of a BEC in a Double-Well Potential T. H. Bergeman, D. Ananikian We numerically study the evolution of a one-dimensional Bose gas trapped in a double-well potential below critical temperature. Following ZNG theory$^1$, the coupled dynamics of the condensate and non-condensate is described by the generalized Gross-Pitaevskii equation and the Bolzmann equation respectively. In one dimension the collision integral $C_{22}$ vanishes and only collisions between the condensate and non-condensate ($C_{12}$) are included. The excitations are treated in local density approximation. Initially the non-condensate distribution function is approximated by the local equilibrium Bose distribution. For nonzero temperature the thermodynamical chemical potential is not the same as the eigenvalue of the stationary Gross-Ptaevskii equation. The collision integral $C_{12}$ produces a source term which plays an important role in equilibration processes. \\ 1. E. Zaremba, T. Nikini and A. Griffin. J. Low Temp. Phys. {\bf 116}, 277 (1999). [Preview Abstract] |
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G1.00055: Perturbative calculation of BEC energies and wave functions in an anisotropic trap with tunable interaction: beyond the mean field and beyond zeroth order W. Blake Laing, Martin Dunn, Deborah K. Watson In this poster we report progress in pushing our beyond-mean-field perturbative calculation of Bose-Einstein condensate (BEC) ground state energies and wave functions to the first order in the wave function series and the second order in the energy series. We use dimensional scaling, group theory and graph theory to include the effect of every two-body interaction with little computation. This approach is mostly analytic and well-suited for the study of a BEC with tunable interactions, requiring no assumptions concerning the strength or the form of atomic interactions or concerning the number of atoms. [Preview Abstract] |
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G1.00056: Analytic Beyond-Mean-Field BEC Wave Functions Martin Dunn, W. Blake Laing, Deborah K. Watson, John G. Loeser We present analytic $N$-body beyond-mean-field wave functions for Bose-Einstein condensates. This extends our previous beyond-mean-field energy calculations to the substantially more difficult problem of determining correlated $N$-body wave functions for a confined system. The tools used to achieve this have been carefully chosen to maximize the use of symmetry and minimize the dependence on numerical computation. We handle the huge number of interactions when $N$ is large ($\sim N^2/2$ two-body interactions) by bringing together three theoretical methods. These are dimensional perturbation theory, the $FG$ method of Wilson et al, and the group theory of the symmetric group. The wave function is then used to derive the density profile of a condensate in a cylindrical trap.This method makes no assumptions regarding the form or strength of the interactions and is applicable to both small-$N$ and large-$N$ systems. [Preview Abstract] |
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G1.00057: Dynamics of a Dipolar Spin-1 BEC. Konstantinos Tsekouras, Su Yi, Han Pu Recent experimental data on chromium condensates has emphasized the role of dipolar interactions in BEC dynamics. We employ the SMA (single mode approximation) method to study the dynamics of a dipolar spin-1 Bose-Einstein condensate both in the absence and in the presence of a magnetic field. Particular attention is given to the interplay of the dipolar interactions with the magnetic field, and numerical simulation is used to illustrate the feasibility of observing the effects of dipolar interactions in the case of an $^{87}$Rb BEC. [Preview Abstract] |
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G1.00058: Investigation of a single boson species in a Feschbach resonance Andrew Carmichael, Juha Javanainen We investigate the Hamiltonian for a single boson species in the presence of a Feshbach resonance which permits the creation of molecules. To simplify the model we consider the resulting bosonic molecules to be a classical field and investigate the resulting Heisenberg equations of motion for occupancies and correlation functions. Similarities with and differences to some previous work involving fermions are discussed. [Preview Abstract] |
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G1.00059: Heavy impurity in a two-component Bose-Einstein condensate near phase separation Ryan Kalas, D. Blume, Eddy Timmermans We propose the use of a neutral impurity atom to probe the phase separation transition in a two-component Bose-Einstein condensate. Utilizing a Feshbach resonance, a two-component BEC mixture can be brought near phase separation. The long range fluctuations associated with this quantum phase transition can significantly alter the properties of a neutral impurity, i.e., a distinguishable third type of particle, inserted into the two-component mixture. We show, for instance, that near the phase separation the effective mass of the impurity becomes large. We discuss experiments that use the heavy impurity to probe the underlying quantum phase transition physics. [Preview Abstract] |
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G1.00060: Dependence of scattering length on dipole moment in condensates of polar molecules: Gross-Pitaevskii vs diffusion Monte Carlo simulations Shai Ronen, Daniele Bortolotti, John Bohn, Doerte Blume We consider a a Bose-Einstein condensate of polar molecules in a harmonic trap, where the effective dipole may be tuned by an external field. We demonstrate that taking into account the dependence of the scattering length on the dipole moment is essential in order to reproduce the correct ground state energy and to predict the stability diagram of the condensate. We compare Gross-Pitaevskii with diffusion Monte Carlo calculations, and show that the Gross-Pitaevskii theory with the renormalized dipole-dependent scattering length reproduces very well the Monte Carlo results. The behavior of the condensate in non-isotropic traps is also examined. [Preview Abstract] |
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G1.00061: DMRG simulations of a trapped one-dimensional Bose gas Michael Fleischhauer, Bernd Schmidt We present numerical simulations of a one-dimensional Bose gas in a harmonic trap for different interaction strength ranging from the Bogoliubov to the Tonks-Girardeau regime using the density matrix renormalization group (DMRG). Local properties such as single-particle density, density fluctuations and g$_3$ are calculated and compared to theoretical predictions from the Lieb-Liniger model within the local density approximation. Also first-order correlations are calculated for different (low) temperatures and interaction strength. The transition from a temperature-dominated regime with exponentially decaying correlations to a quantum regime with a power-law decay of correlations is demonstrated. The long-range correlations are shown to be identical to those of a homogeous Luttinger liquid with an interaction parameter (Tonks parameter) corresponding to the center of the trap. [Preview Abstract] |
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G1.00062: The angular momentum of a magnetically trapped atomic condensate Hsiang-Hua Jen, Peng Zhang, Li You The angular momentum of a magnetically trapped atom includes both an orbital and an internal part. The sum of the two, or the axial component of total angular momentum, is conserved in a cylindrically symmetric trap. For an Ioffe- Pritchard trap, whose magnetic field is not axially symmetric, we find that the difference of the orbital and internal angular momentum component becomes conserved. With an atomic condensate, the above constraints remain valid provided atomic interactions are isotropic, i.e. involving only s-waves as often assumed for low energy collisions. We have investigated the precise values of the sum/difference angular momentums $(s)$ of the ground state of a spinor condensate inside a magnetic trap and proved that the values of $s$ is limited to $[-F,F]$. We confirm and illustrate our analytical analysis with numerical simulations and our results imply that a magnetically trapped spinor condensate will necessarily possess persistent currents of different winding numbers when its spinor components are observed in the lab frame. [Preview Abstract] |
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G1.00063: Spatio-Temporial Dynamics of Ferromagnetic, Spin-1, Bose Condensates in All-Optical Traps M.-S. Chang, Q. Qin, E.M. Bookjans, W. Zhang, P.F. Griffin, L. You, M.S. Chapman We investigate spin domain formation in spin-1 condensates with ferromagnetic interactions. We show that domains generally form when all three Zeeman components co-exist, except when the system is close to the spinor ground state or the condensate is smaller than the minimum allowed domain size. We also observe spin waves created from coherent spin mixing that show good agreement with the coupled spinor Gross-Pitaevskii equations. Finally, we investigate the miscibility of different spin states and find results consistent with our previous determinations of the ferromagnetic nature of the spin dependent interactions in the $^{87}$Rb $F=1$ spinor [1]. \newline \newline [1] M.-S. Chang, {\it et al.}, Phys. Rev. Lett. {\bf 92}, 140403 (2004) [Preview Abstract] |
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G1.00064: Towards a Dual Species BEC in NaRb M. Bhattacharya, S. Muniz, D. Naik, C. Raman Multi-species mixtures of ultracold atoms are currently being studied intensively. The areas of focus include, but are not limited to condensed matter and quantum statistical effects, interaction-tuning by photo- and magneto-association, production of (degenerate) ultracold molecules, and so on. In the specific case of NaRb, predictions exist regarding Feshbach resonances [1], miscibility [2] and macroscopic quantum transitions [3]. We describe progress towards integrating Rb into our existing Na BEC set-up, including the design and implementation of a dual species oven. \newline 1. M. Bhattacharya \textit{et al.,} Eur.Phys.J.D. \textbf{31}, 301(2004). \newline 2. S.B.Weiss \textit{et al}, Phys.Rev. A,\textbf{68},042708(2003). \newline 3. H.Pu \textit{et al}, Phys.Rev.Lett \textbf{80},1134 (1998). [Preview Abstract] |
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G1.00065: Measuring Two Body Inelastic Losses in a Rb-87 Condensate J. W. Merrill, K. M. Mertes, D. S. Hall Bose-Einstein condensates (BECs) in the $|F=1,m_F=-1\rangle$ and $|F=2,m_F=1\rangle$ in ${}^{87}$Rb form a unique and controllable interpenetrating superfluid system. It is important to understand and take into account the inelastic loss processes in the binary condensate in order to create an accurate numerical model of its dynamics. Loss rates due to three-body recombination have been reported previously for the $|1,-1\rangle$ state. We describe here a measurement of the $|2,1\rangle$ inelastic loss rate in both condensates and thermal atoms, observing that losses are dominated by two-body processes, and that the condensates show the loss rate suppression expected of a coherent system of identical bosons. [Preview Abstract] |
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G1.00066: Using Computer-Generated Holograms and Optical Fields to Study Phase Dynamics and Phase Manipulation of Bose-Einstein Condensates David Scherer, Chad Weiler, Tyler Neely, Brian Anderson Maskless lithographic patterning of computer-generated holograms (CGHs) and diffractive optical elements enables the use of arbitrary-profile optical fields to manipulate Bose-Einstein condensates. This inexpensive and flexible method of tailoring potential wells and potential barriers for trapped condensates permits studies of condensate physics and dynamics in rarely explored regimes. We will describe the CGH creation technique used at the College of Optical Sciences and report on the progress of experiments aimed at studying phase manipulation of Rb-87 Bose-Einstein condensates using this promising tool in the atom optics toolkit. [Preview Abstract] |
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G1.00067: Twin optical dipole traps for loading cold atoms Ghazal Behinaein, Peyman Ahmadi, Gil Summy Achieving high atom populations in optical traps (FORTs) is essential for various experiments especially for an all optical realization of a Bose-Einstein condensate. However an efficient loading of these traps still remains a challenge. In this poster we present results of the experimental study on the loading mechanism of these traps. We show that the FORT population (N$_{FORT})$ is a sensitive function of the FORT volume. However the FORT size can't be chosen arbitrarily large since it reduces the evaporative cooling efficiency. To satisfy both of these conditions we propose a new geometry for optical traps, twin traps, in which the atoms are loaded into a FORT with large volume and then transported to a much tighter FORT which was overlapped with the first one. A detailed study of this method will be presented. [Preview Abstract] |
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G1.00068: Atom chip for studying the 1D Bose gas A.H. van Amerongen, J.J.P. van Es, N.J. van Druten We have developed an ``atom chip'' for the study of ultracold atoms. The lithographically patterned current carrying wires appear particularly suited to realize atom waveguides and other (quasi-)one-dimensional (1D) structures. For the study of repulsive bosons we constructed a wire layout to reach tight radial confinement and low axial density: a 1D box for atoms. We also plan to study the quantum gas in the crossover from the 3D to the 1D regime. Once in the 1D, regime counterintuitively the atoms become more strongly interacting as the axial density is decreased. At present we optically cool and magnetically trap 10$^{7}$ atoms with a phase space density of 10$^{-6}$ at a distance of 1 mm from the chip surface. This stage is reached using two layers of macroscopic copper wires under the microchip. We then transfer the cold sample to the chip-wire trap $\sim $100 $\mu $m from the surface. In our contribution we will discuss our trap design and our progress with the loading of the box potential and evaporative cooling towards quantum degeneracy. [Preview Abstract] |
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G1.00069: Creation and Characterization of a BEC of $^{7}$Li D. Dries, M. Junker, Y. P. Chen, C. Welford, J. Hitchcock, R. G. Hulet We have designed and built an apparatus for trapping and cooling the isotopes of Li to quantum degeneracy. Presently, $^{7}$Li atoms are first Zeeman slowed and loaded into a magneto-optical trap. The trapped cloud is cooled and compressed, magnetically polarized via optical pumping, and loaded into an electromagnetic trap. A 45 s RF evaporation is then performed, cooling the gas to 5 $\mu$K. The electromagnetic trap is switched off while a single beam optical-dipole trap is ramped on. An adiabatic RF sweep is used to transfer the population of atoms from the \textit{F}=2, m$_{F}$=2 hyperfine state to the \textit{F}=1, m$_F$=1 state, where the scattering length may be controlled by a Feshbach resonance. By tuning the scattering length to a large and positive value, evaporation proceeds efficiently below the Bose-Einstein condensation transition temperature. Quantitative information on the BEC is obtained via absorption or phase-contrast imaging of either the trapped atoms or the freely expanding cloud. [Preview Abstract] |
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G1.00070: ATOMS IN OPTICAL LATTICES |
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G1.00071: Interaction induced destruction of resonant tunneling in the nonlinear Wannier-Stark problem Sandro Wimberger, Riccardo Mannella, Ennio Arimondo Bose-Einstein condensates loaded into periodic optical lattices can be subjected to a controlled dynamical evolution, determined by the shape and time-dependence of the potentials. We propose a scheme to measure the temporal decay rates arising from {\em many} successive Landau-Zener events. We show that from a measurement of the atomic densities or from a combined density and phase measurement, we can compute the time-dependent survival or recurrence probability of the condensate, respectively. The tunneling of the condensate in a tilted optical lattice is resonantly enhanced for a suitable choice of the static Stark field (or the relative acceleration of two counter-propagating standing waves). Resonantly enhanced tunneling by more than an order of magnitude is predicted for essentially non-interacting atoms. Small mean-field interactions, as readily realized in state-of-the-art experiments, systematically tend to wash out the resonant tunneling peaks. Hence, even in a parameter regime far away from any dynamical instability in the condensate, i.e., where the kinetic and the potential energy usually dominate the dynamics, the atom-atom interactions eventually lead to a destruction of the very sensitive resonant tunneling. This example of the {\em dynamical} interplay between coherent single-particle tunneling and nonlinear mean-field interactions opens new perspectives for the study of complex quantum transport with ultracold atoms. [Preview Abstract] |
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G1.00072: Phonons in an optical lattice Tun Wang, Susanne Yelin The role of phonons for high-temperature superconductors has been an issue of considerable controversy [1], although some recent experiments using isotopes find phonons are important for such material [2]. In expectation of experimentally easily controllable parameters in an optical lattice, we study the phonon-fermion interaction in the optical lattice, which is the counterpart of the phonon-electron interaction in a crystal lattice. In our case, the phonons are the Bogoliubov excitations of the bosonic atoms. We show how these phonons are coupled with the fermionic atoms in the optical lattice and arrive at the desired Hamiltonian. We then study the phase transition properties of such a system. [1] Phys. Stat. Sol. 242, 11-29 (2005); [2] Nature, 430, 187-190 (2004); [Preview Abstract] |
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G1.00073: Fractional Quantum Hall Effect in Optical Lattices Mohammad Hafezi, Anders S{\o}rensen, Eugene Demler, Mikhail Lukin We investigate the methods to create fractional quantum Hall states of atoms confined in optical lattices. Specifically, the dynamics of ultra-cold atoms on a lattice with an effective magnetic field is investigated for different values of field and on-site interaction. An appropriate characterization of such quantum states can be achieved by using Chern numbers which can indicate a topological order and describe the state of the system in different regimes. Numerical calculation supports the existence of fractional statistics. We also discuss the practical realization of such states and techniques for their detection. [Preview Abstract] |
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G1.00074: Quantum Phase Transitions in Rotating Lattices Brandon Peden, Rajiv Bhat, Lincoln Carr, Murray Holland Two of the most important themes in the developing area of quantum fluids and ultracold gases include the role of strong interactions and highly correlated effects. We study a novel and interesting problem combining these two key areas by looking at the experimentally relevant area of ultracold atoms in rotating optical lattices. This merges the effects of strong interactions generated by the lattice with the intriguing quantum effects present in the analogy of the quantum Hall effect at high rotation rate. Hardcore bosons in a 2D rotating square lattice are investigated via a modified Bose-Hubbard Hamiltonian. Our results show quantum phase transitions between circulation values in which the symmetry of the ground state changes structure abruptly as a function of rotation. [Preview Abstract] |
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G1.00075: Atomtronics: An Ultracold Analog of Semiconductor Devices Brian Seaman, Meret Kraemer, Dana Anderson, Murray Holland An atom transistor, atom diode and the atomic analogs of solid state electronic components such as the p-type and n-type materials are devised in ultracold boson lattices. An atomic p-type material is based on a lattice with slightly less than integer filling, a small number of holes, which is a superfluid system. The n-type material is created from a bosonic lattice that has just above integer filling, which is also superfluid. An atomic diode is created by attaching a p-type and an n-type material and imposing an external step potential which places each side of the diode at the edge of the Mott insulator and superfluid boundary. Biasing of the diode will either move the system into a completely insulating state or a superfluid state depending on the direction of the bias. When two atom diodes are connected in reverse direction, an atomic transistor is created. These materials provide the building blocks for more advanced atomtronic devices as well as extremely sensitive sensors and controllers. [Preview Abstract] |
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G1.00076: Experiments with Strontium in an Optical Lattice: Optical Clocks and Ultracold Collisions$^{1}$ Martin Boyd, Tanya Zelevinsky, Andrew Ludlow, Seth Foreman, Sebastian Blatt, Mark Notcutt, Thomas Zanon, Tetsuya Ido, Jun Ye We present atomic and molecular spectroscopy of ultracold strontium in an optical lattice. In one dimension, the atoms are confined in the Lamb-Dicke regime, allowing spectroscopy free of recoil and Doppler effects. In the case of Sr, the lattice can be tuned to a magic wavelength where the ac Stark shifts of the excited and ground states of interest are equal, thus allowing extremely precise and accurate spectroscopy. This has motivated experiments toward building an optical atomic clock based on the extremely narrow ($<$10 mHz) $^{1}$S$_{0}-^{3}$P$_{0}$ clock transition in $^{87}$Sr. With $\mu $K strontium atoms we have performed high resolution frequency measurements of the clock transition including a detailed investigation of potential systematic errors such as shifts due to the lattice parameters, atom density, and magnetic fields. Confinement in the lattice has also enabled the first narrow-line photoassociation spectroscopy near the $\sim $7kHz $^{1}$S$_{0}-^{3}$P$_{1}$ transition in $^{88}$Sr, allowing accurate measurements of the nine least bound molecular states. Analysis of the photoassociation lineshapes suggests that optical tuning of the ground state scattering length should be possible without significant atom losses. $^{1}$ONR NASA NIST NSF [Preview Abstract] |
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G1.00077: Characterization and Stabilization of an Infrared CW Laser and Applications in Trapping Ultracold Atoms J. Hitchcock, Y. P. Chen, M. Junker, D. Dries, C. Welford, R. G. Hulet We are currently implementing a 25 W, single-mode ELS Versidisk laser operating at 1.03 $\mu$m, for creating an optical lattice of bosonic and fermionic isotopes of lithium. We have characterized both the intensity noise and the pointing noise from DC to 100 KHz. Some spurious noise was initially detected, but the manufacturer has since corrected these problems with a redesign of the laser power supply and the water-cooling system for the laser head. Despite these changes, single mode operation continues to be unstable. To remedy this, we have actively stabilized the laser cavity to an external Fabry-Perot cavity. We will present the results of this effort, as well as our progress in implementing an optical lattice for lithium. [Preview Abstract] |
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G1.00078: Experimental Progress Toward Trapping Atoms in Novel Geometries Hong Gao, Matthew Pasienski, Matthew R. White, Brian DeMarco We present experimental progress toward loading a Bose-Einstein condensate into an optical lattice and using a spatial light modulator (SLM) to manipulate atoms. We generate the optical lattice in such way that controlled collisions between atoms can be achieved in any direction. An SLM is used create arbitrary light intensity patterns to manipulate optically trapped atoms. We will also discuss recent results on RF-dressed condensates. [Preview Abstract] |
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G1.00079: Progress Toward Realization of the 2D Hubbard Model J. R. Williams, T. M. Essinger-Hileman, R. Stites, K. M. O'Hara A two-dimensional (2D) Hubbard model which considers spin-1/2 fermions on a 2D lattice with repulsive interparticle interactions is known to describe magnetic ordering in the cuprates and may describe a mechanism for high-temperature superconductivity as well. To experimentally realize the 2D Hubbard model, we will confine a degenerate gas of $^6$Li atoms in a three-dimensional cubic lattice in which atoms are restricted, by a proper choice of laser intensities, to move within 2D planes. A repulsive molecular interaction between the atoms mimics Coulomb repulsion and, in combination with Fermi statistics, can lead to an exchange interaction which prefers anti-ferromagnetic ordering. An anti-ferromagnetically ordered state on a two dimensional square lattice is expected for unit occupancy while a superfluid phase with {\it d}-wave pairing may occur at reduced filling fraction [1]. Also of interest are 2D lattices with geometries that frustrate anti-ferromagnetic ordering, possibly resulting in a spin-liquid phase. We will report on our progress toward realizing the Fermi-Hubbard model with a $^6$Li gas and the prospects for observing anti-ferromagnetic ordering, {\it d}-wave superfluidity and a spin-liquid phase in this system. We will also describe our development of a tunable, high-power, solid-state laser source for spectroscopy near 671 nm which provides light for both the $^6$Li magneto-optical trap and the optical lattice beams. \\ $[1]$ Phys. Rev. Lett. {\bf 89}, 220407 (2002). [Preview Abstract] |
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G1.00080: Progress Toward the Development of Neutral Atom Quantum Computing Architecture Based on 2D Optical Lattices on a Chip Rajani Ayachitula, Katharina Christandl, Michael Chmutov, Gregory Lafyatis We have shown, theoretically, that optical lattices can be created above an optical waveguide by destructively interfering two different, co-propagating waveguide modes of laser light that is blue-detuned from an atomic resonance [1]. Single atoms can be tightly trapped at the nodes of the lattice and can serve as individually addressable qubits in a quantum memory. We have studied the polarization of light about these nodes for possible Zeeman substate-dependent trapping. We have also examined the prospects for moving the atoms within the lattice and entangling atom pairs to eventually realize one- and two-qubit gates. We present experimental progress in realizing the optical lattice architecture. 1. Phys. Rev. A 70 032302 (2004) [Preview Abstract] |
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G1.00081: Vector diffraction theory calculations of light field distributions for trapping and manipulation of atoms using microlenses Glen Gillen, Shekhar Guha We have applied Kirchhoff vector diffraction theory to a curved interface between media of two different refractive indices. A microlens array (used by Dumke, et. al, in Phys. Rev. Lett. 89, 097903 (2002) to experimentally trap 85Rb atoms) can be modeled using this approach. Using the Kirchhoff vector diffraction theory, the full vector solutions for the electric and magnetic fields beyond the microlens are obtainable. Detailed calculations show the electromagnetic fields and intensity distributions for the optical dipole traps in the focal region. Following the method of, Demke et. al, we can simulate the control and splitting of a single atom trap into two separate traps, and the merging of two adjacent traps into a single atom trap using two coherent beams of perpendicular polarization and a variable orientation angle between the laser beams. We will present the vector diffraction theory and detailed calculations of beam profiles, trap depths, trap splitting, and trap merging. [Preview Abstract] |
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G1.00082: Diffraction patterns of laser light for use as optical dipole traps for cold atoms Katharina Christandl, Glen Gillen, Shekhar Guha Using Kirchhoff and Hertz vector diffraction theory we calculate detailed light distributions beyond a circular aperture. Within the diffraction pattern, localized bright and dark spots exist. If the trap laser is red-detuned atoms will be trapped in the localized light field maxima, while blue-detuned light results in atoms being trapped in light field minima. The primary advantages of using diffracted light fields to trap cold neutral atoms resides in the experimental simplicity of a single loosely focused laser beam incident upon a diffracting aperture and the ability to use either blue- or red-detuned laser light. Extension of this method to multi-dimensional arrays of apertures in a mask will result in multi-dimensional arrays of dipole atom traps. Calculations of the trap potential wells and experimental verification of the existence of the light field distributions will be presented. [Preview Abstract] |
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G1.00083: A Tonks Giradeau Gas in the Presence of a Local Potential Hao Fu, Alberto Rojo The physics of a Tonks-Giradeau Gas in the presence of a local potential is studied. In order to evaluate the single particle density matrix (SPDM) of the many-body ground state, the Wiger-Jordan transformation is used. The eigenvector with the largest eigenvalue of the SPDM corresponds to the ``Bose-Einstein Condensate''(BEC) State. We find that the ``BEC'' state density at the positon of the local potential decreases, as expected, in the case of a repulsive potential. For an attractive potential, it decreases or increases depending on the strength of the potential. The superfluidity of this system is investigated both numerically and perturbatively. An experimental method for detecting the effect of an impurity in a Tonks-Giradueau gas is discussed. [Preview Abstract] |
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G1.00084: ULTRACOLD COLLISIONS AND PHOTOASSOCIATION PROCESSES |
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G1.00085: Photoassociation spectroscopy of long range molecular states $\ ^{87}$Rb. Lu-Fano analysis and improved Le Roy-Bernstein Haikel Jelassi, Bruno Viaris De Lasegno, Laurence Pruvost In the poster, we present experimental results of the photoassociation (PA) of $\ ^{87}$Rb cold atoms in the asymptotic range of -12 cm$^{-1} $ below the 5S$_{1/2}$+5P$_{1/2}$ dissociation limit. The PA spectrum, obtained by trap loss spectroscopy, exhibits vibrational progressions corresponding to the 1$% _{g}$, 0$_{u}^{+}$ and 0$_{g}^{-}$ molecular states. We are interested first in the 0$_{g}^{-}$states. Using a Lu-Fano approach and the LeRoy- Bernstein formula we deduce from data, the quantum defect associated to each level. To explain its linear variation versus the energy, we show that an improved LeRoy-Bernstein model has to be applied. This approach lets us to determine the phaseshift of the wavefunction at the dissociation limit and the slope of the linear variation. These parameters, coupled to simple proposed analytic models, allow to deduce short range potential characteristics, as the location of the barrier and the minimum. With the same approach, we analyze 0$_{u}^{+}$ levels. The Lu-Fano graph allows to exhibit the coupling of the (5S$_{1/2}$+5P$_{1/2}$)0$_{u}^{+}$ series\ to the (5S$_ {1/2}$+5P$% _{3/2}$)0$_{u}^{+}$ ones due to spin-orbit interaction. We value the coupling, identify two (5S$_{1/2}$+5P$_{3/2}$)0$_{u}^{+}$ levels and predict the energy and the width of the first predissociated level of (5S$_{1/2}$+5P$% _{3/2}$)0$_{u}^{+}$ series. Experimental investigations confirm these predissociation predictions\medskip .\newline [Preview Abstract] |
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G1.00086: Measurement of Intensity-Dependent Trap Loss in a Rb-Ar* MOT M.K. Shaffer, E.M. Ahmed, H.C. Busch, C.I. Sukenik We have measured the intensity dependence of the inter-species trap loss rate coefficients in collisions between ultracold rubidium (Rb) and ultracold metastable argon (Ar*) simultaneously confined in a dual species magneto-optical trap (MOT). Using a modified residual gas analyzer as a quadrupole mass spectrometer, we identify both heteronuclear Penning ionization and heteronuclear associative ionization as trap loss mechanisms. We have also made trap loss measurements in the Ar* MOT alone, where both Penning and associative ionization are observed as well. We will present our findings and discuss plans for future studies of the interaction between Rb and Ar* at ultracold temperatures. Support provided by the National Science Foundation and the Office of Naval Research. [Preview Abstract] |
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G1.00087: Photo-associo-dissociative Ionization in a Rb MOT Marc Trachy, Mudessar Shah, Richard Bredy, How Camp, Giorgi Veshapidze, Ming-Tie Huang, Brett DePaola A process, called photo-associo-dissociative ionization (PADI), that is related to both photo-association and Penning ionization is presented. As in photo-association, two colliding atoms are excited together as a quasi-molecule. Unlike photo-association, the final photon in the process then excites the molecule to a dissociative curve above the ionization threshold. Experimental measurements of PADI reaction rates, relative to other cold collision rates, are given and dissociation energy distributions are shown. [Preview Abstract] |
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G1.00088: Further Control of Ultracold Collisions with Frequency-Chirped Light M. J. Wright, J. A. Pechkis, J. L. Carini, P. L. Gould We report measurements of collisions between ultracold Rb atoms induced by frequency-chirped laser light. The dependence of the collision rate on the chirp direction, the center detuning, and the delay between successive chirps has been investigated with a chirp that sweeps 1 GHz in 100 ns. If the laser light is resonant with the attractive potential of a pair of atoms at some point during the chirp, the pair is efficiently and adiabatically transferred to the excited state, resulting in collisional loss from the trap. Simulations show that our measurements are consistent with total adiabatic transfer. Through recent experiments, we have demonstrated that the collision rate for the negative chirp differs from that of the positive chirp at particular center detunings. Finally, by varying the delay between successive positive chirps, we have observed evidence of depletion for short delay times and incoherent flux enhancement for intermediate delay times. This work is supported by DOE. [Preview Abstract] |
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G1.00089: Singlet-Triplet Mixing and Ground-State Molecule Formation in Ultracold Rb$_{2}$ Ye Huang, Dajun Wang, Hyewon Pechkis, Jianbing Qi, Court Ashbaugh, Edward Eyler, Phillip Gould, William Stwalley We have observed two manifestations of singlet-triplet mixing in ultracold Rb$_{2}$. In the first, we start with high-$v$ levels of the $X{ }^1\Sigma _g^+ $ state which are produced by photoassociation and detected by REMPI. Scanning the detection laser reveals transitions to the 2${ }^3\Pi _u $ state. In the second case, we start with $a{ }^3\Sigma _u^+ $ molecules and observe transitions to 3${ }^1\Sigma _g^+ $. We propose a scheme for producing $X{ }^1\Sigma _g^+ (v$=0), starting with $a{ }^3\Sigma _u^+ $ molecules in high-$v$: $a{ }^3\Sigma _u^+ \to 3{ }^1\Sigma _g^+ \to A{ }^1\Sigma _u^+ \to X{ }^1\Sigma _g^+ $. The first step is made possible by the admixture of triplet character in the 3${ }^1\Sigma _g^+ $ state. [Preview Abstract] |
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G1.00090: Experimental progress toward making ground-state ultracold KRb molecules Dajun Wang, Court Ashbaugh, E.E. Eyler, P.L. Gould, W.C. Stwalley We propose a promising route for transferring ultracold $X\,\,^1\Sigma^+$ KRb molecules in high vibrational levels (formed via photoassociation) to the true ground state ($X\,\,^1\Sigma^+$, $v$=0, $J$=0) with two cw lasers. Using pulsed two-color two-photon ionization, we have identified transitions from high-$v$ levels of the $X$ state to the $3 \,\,^1\Sigma^+$ state. Our calculations show that several of the observed $3 \,\,^1\Sigma^+$ vibrational levels have good Franck-Condon factors for emission to $v$=0 of the $X$ state. This makes the $3\,\,^1\Sigma^+$ state a good candidate for the intermediate state in Raman population transfer. Furthermore, using a combination of pulsed resonance-enhanced one-color two-photon ionization and cw laser depletion, we have achieved rotational resolution of these transitions. With the addition of another cw laser to connect the $X$ state $v$=0, $J$=0 level to an intermediate rovibrational level, we expect to selectively produce translationally, vibrationally and rotationally ultracold KRb molecules. This work was supported by NSF. [Preview Abstract] |
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G1.00091: Formation of Alkali Hydrides via Two-photon Excitation Elizabeth Juarros, Kate Kirby, Robin C\^{o}t\'{e} Alkali hydride molecules are very polar, exhibiting large ground-state dipole moments. Ultracold sources of alkali atoms and hydrogen have been created in the laboratory. We explore theoretically the feasibility of forming such molecules from a mixture of the ultracold atomic gases, employing a two-photon stimulated radiative association process -- Raman excitation. The triplet ground state for lithium hydride is of particular interest since it supports only one bound ro-vibrational level. Using accurate molecular potential energy curves and dipole transition moments, we have calculated the rate coefficients for populating the bound ro-vibrational level of the a$^3\Sigma^+$ state of LiH via the excited b$^3\Pi$ state. We have found that significant molecule formation rates can be realized with laser intensities and atomic densities that are attainable experimentally. Also, we have calculated the rate coefficients for populating all the vibrational levels of the X$^1\Sigma^+$ state of LiH via the excited B$^1\Pi$ state. In this case, we have found that significant formation rates into the upper vibrational levels can be realized. We examine the spontaneous emission cascade which takes place from these upper vibrational levels on a timescale of milliseconds, and calculate the resulting rotational populations in $v=0$. We show that photon emission in the cascade process does not contribute to trap loss. [Preview Abstract] |
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G1.00092: Stimulated formation of ultracold ground (NaCa)$^+$ molecular ions Philippe Pellegrini, Harvey Michels, Winthrop Smith, Robin C\^ot\'e Ultracold atomic systems in which electric charges play an important role are of particular interest. Futhermore, the recently proposed possibility of sympathetic cooling of ions by cold neutral atoms in the same trap has opened the way to new fundamental collision process studies [1]. We theoretically study the possibility of forming ultracold ground (NaCa)$^+$ molecular ions starting with a Ca$^+$ ion colliding with a neutral Na atom via the excited $A^1\Sigma^+$ potential. Stimulated radiative association rates to the ground $X^1\Sigma^+$ potential are calculated. We calculated as well, the lifetime for radiative cascade from high (v,J) levels to the first ro-vibrational levels (v=0,J) of the ground electronic state, due to the large permanent dipole moment. We also present new accurate \emph{ab initio} calculations of adiabatic potentials and dipole moments for the (NaCa)$^+$ system. [1] W. W. Smith, E. Babenko, R. C\^ot\'e, and H. H. Michels in \emph{Coherence and Quantum Optics VIII}, N.P. Bigelow et al., eds., Kluwer Academic/Plenum Publishers, NY 2003, pp. 623-624. [Preview Abstract] |
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G1.00093: Reactive scattering calculations for D + H$_2$ in vibrationally excited states at ultralow temperature Ion Simbotin, Robin C\^ot\'e We calculate total cross sections for the D + H$_2(v,j\!=\!0)$ collision, and investigate their dependence on the vibrational quantum number $v$ of the initial state of H$_2$. The cross sections increase quasi-exponentially with the excitation energy of the initial vibrational state. This is similar to the exponential dependence observed in the vibrational predissociation of van der Waals complexes. We attempt to explain this simple relationship in terms of the short range details of the single channel atom--molecule wavefunctions and the couplings between the initial and final channels. [Preview Abstract] |
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G1.00094: Cold collisions in Cr-Cr and Cr-Rb mixtures Zoran Pavlovi\'c, R. C\^ot\'e, H. R. Sadeghpour We report calculations of the elastic and inelastic cross sections for collisions between two maximally spin-polarized chromium and rubidium atoms in the ultracold regime. Using available data on transition frequencies, discrete dipole matrix elements, and photoionization oscillator strengths in Cr and Rb, we obtain a value for the static polarizability of Cr-Rb and the dispersion coefficient $C_{6}$ for the van der Waals interaction. The effect of shape resonances on elastic and inelastic rate coefficients in collision of Cr-Rb mixtures is studied. We also calculate Cr-Cr differential cross sections in order to examine the anisotropic character of the magnetic dipolar interaction in the presence of a magnetic field. [Preview Abstract] |
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G1.00095: Factorization in Break-up and Recombination Processes for Atoms with a Large Scattering Length Eric Braaten, Dongqing Zhang Break-up and recombination processes for loosely-bound molecules composed of atoms with a large scattering length $a$ necessarily involve interactions that are nonperturbative in the exact 2-body interaction. If these processes involve atoms with relative momenta much larger than $\hbar/|a|$, the leading contributions to their rates can be separated into short-distance factors that are insensitive to $a$ and long-distance factors that are insensitive to the range of the interaction. In the case of inclusive break-up cross sections for atom-molecule scattering, the short-distance factors are atom-atom cross sections at a lower collision energy and the long-distance factors simply count the number of atoms in the molecule. [Preview Abstract] |
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G1.00096: The Thomas and Effimov Effects for General Partial Waves James Sternberg, Joseph Macek Description of the two-body interactions between particles is a fundamental step in modeling many-body systems. Because s-wave scattering dominates at ultra-cold temperatures, zero-range potentials (ZRPs) have been a popular way to describe the two-body interactions. Recent experiments enhance higher partial waves and this has led to interest in extending the zero-range model beyond $l=0$\cite{Stock:2005}. In this work we use a ZRP model to examine three body systems. Of particular importance in these systems is the Thomas effect, which is the divergence of the wave function when all three particles are close together. The Thomas effect is known for spin zero particles when $l=0$. In addition there is the Effimov effect, in which there are an infinite number of three body bound states if the zero-range potential boundary conditions separate in hyperspherical coordinates as the scattering length $a_l \rightarrow \infty$. We show that the Effimov effect occurs for not only the well-known $l=0$ case, but for spin $1/2$ fermions via the $l=1$ pseudopotential of ref. [1] This research is supported by Department of Energy Grant DE-FG02-02ER15283 \newline \newline [1] Ren\'{e} Stock, Andrew Silberfarb, Eric. L. Bolda, and Ivan H. Deutsch, Phys Rev. Lett. {\bf 94} 023202 (2005) [Preview Abstract] |
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G1.00097: Ultracold three-body collisions near overlapping Feshbach resonances J. P. D'Incao, B. D. Esry We adapt the framework we previously developed [1] for a single resonant interaction to the case of overlapping Feshbach resonances. As a result, ultracold three-body collision rates now depend on two different scattering lengths and have a much richer structure. We have determined the scattering length and energy dependence for all relevant ultracold three-body collision rates and will discuss the effect of the overlap on ultracold gas mixtures. These results will apply so long as the system is in the threshold regime, i.e., when the collision energy is the smallest energy in the system. [1] J. P. D'Incao and B. D. Esry, Phys. Rev. Lett. {\bf 94}, 213201 (2005). Supported by the National Science Foundation. [Preview Abstract] |
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G1.00098: Ultracold three-body collisions of H with alkali atoms Yujun Wang, J. J. Hua, J. P. D'Incao, B. D. Esry We have calculated the ultracold three-body collision rates involving some commonly used alkali atoms. In particular, we have calculated the collision rates for spin-polarized H+H+Cs, H+H+Rb, H+H+K, H+H+Na, and H+H+Li by solving the Schrodinger equation in the adiabatic hyperspherical representation. We used realistic two-body potentials to build the three-body interactions. The calculations cover energies up to roughly 1~$\mu$K and include all three-body processes possible for these systems: three-body recombination, collision induced dissociation, and elastic atom-molecule collisions. Supported by the National Science Foundation. [Preview Abstract] |
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G1.00099: Coupled-channel pseudo-potential description of Feshbach resonance in two dimensions Krittika Kanjilal, Doerte Blume We derive pseudo-potentials that describe the scattering between two particles in two spatial dimensions for any partial wave $m$, whose scattering strength is parameterized in terms of the phase shift $\delta_{m}$. Using our $m=0$ pseudo-potential, we develop a coupled channel model with 2D zero-range interactions, which describes the two-body physics across a Feshbach resonance. Our model predicts the scattering length, the binding energy and the ``closed channel molecular fraction'' of two particles; these observables can be measured in experiments on ultracold quasi-2D atomic Bose and Fermi gases with present-day technology. [Preview Abstract] |
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G1.00100: Theory of Radiative-Stark Mixing Gouthaman Balaraman, Raymond Flannery The theory of Stark mixing $n\ell-n\ell'$ transitions in atomic hydrogen $H(n\ell)$ induced by ion impact has been exactly solved analytically [1] by considering the full array of $\ell$-changing transitions only within the $n$-shell. We now incorporate the effect of radiative transitions $n\ell-n'\ell\pm1$. By considering the rates of radiative decay and Stark mixing, the region where radiative decay becomes competitive with Stark mixing can be identified. The Stark frequency $(s^{-1})$ is $\nu_S \sim v\sigma_{\ell\ell'}N^+\sim n^3/\tilde{v}$ where $N^+$ is the concentration of ions and $\tilde{v}$ is ratio of ion velocity and average orbital electron velocity. The radiative frequency $(s^{-1})$ is $A_{n\ell}=1.071\times10^{11} n^{-3}(\ell+1/2)^{-2}$. For typical laboratory conditions $N^+\sim 10^8 cm^{-3}$ and $\tilde{v}\sim 1$ the two frequencies become comparable for $n\approx 17$. In this paper, we present a phenomenological approach to the theory of Stark mixing with the radiative coupling incorporated. We call this coupled process Radiative-Stark mixing to differentiate from pure Stark mixing. \begin{thebibliography}{99} \bibitem{1} D.~Vrinceanu and M.~R.~Flannery, Phys. Rev. A, {\bf 63}, 032701 (2001) \end{thebibliography} [Preview Abstract] |
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G1.00101: Evaporative Cooling of an Imbalanced Fermi Gas Yean-an Liao, Guthrie B. Partridge, Wenhui Li, Ramsey I. Kamar, Duong Nguyen, Randall G. Hulet We investigate the evaporative cooling of a two-component mixture of an optically trapped atomic Fermi gas to degeneracy using the semiclassical Boltzmann equation and Fermi statistics. The initial numbers of the two Fermi species are chosen to be unequal to simulate our recent experiment on pairing and phase separation of a gas of polarized $^6$Li atoms.\footnote{G. B. Partridge \emph{et al.}, \emph{Science} \textbf{311}, 503 (2006).} We find that the cooling efficiency is reduced at high number polarization due to the lack of efficient collisions, in agreement with our experimental observations. We also explore the quantum effect of Pauli blocking near Fermi degeneracy which might affect the evaporative cooling process and the final number polarization. [Preview Abstract] |
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G1.00102: Atom-diatom reaction dynamics at cold and ultracold temperatures Philippe F. Weck, Naduvalath Balakrishnan Quantum-mechanical scattering calculations are reported for the $\mbox{O}(^3P)+\mbox{H}_2$ collision at cold and ultracold temperatures. We investigate the sensitivity of the reaction dynamics to long-range forces by using different analytic representations of the lowest $\mbox{H}_2\mbox{O}(^3 A'')$ electronic state which vary essentially by their descriptions of the van der Waals region. We also discuss how zero-energy resonances and Feshbach resonances, arising from the decay of quasibound states associated with the formation of van der Waals complexes in the entrance channel, affect the reactivity at low temperatures. [Preview Abstract] |
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G1.00103: Li + Na collisions at ultracold temperatures Marko Gacesa, Zoran Pavlovic, Philippe Pellegrini, Robin C\^ot\'e We are studying ultracold scattering properties of Li isotopes and Na in the presence of a magnetic field. Our main interest is to predict the widths and positions of Feshbach resonances using coupled-channels calculations and compare them to the recent experimental observations. Additional information about these resonances could be used to produce ultracold heteronuclear molecules. Depending on the Li isotope considered such molecules would allow the study of degenerate Bose-Fermi mixtures with adjustable interactions or Bose-Einstein condensation of polar molecules. [Preview Abstract] |
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G1.00104: LASER COOLING AND TRAPPING |
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G1.00105: ATTA-3: The Next-Generation Instrument for $^{81}$Kr-Dating Y. Ding, Z.-T. Lu, K. Bailey, P. Mueller, T.P. O'Connor, R.W. Dunford, L. Young, A.M. Davis, N.C. Sturchio, S.-M. Hu Atom Trap Trace Analysis (ATTA) has been used to analyze two rare isotopes: $^{81}$Kr (isotopic abundance $\sim $ 10$^{-12})$ and $^{85}$Kr ($\sim $10$^{-11})$, in environmental samples. Radiokrypton dating enabled by the ATTA method can now be used to determine the ages of old groundwater in the range of 50,000--1,000,000 years. The present apparatus (ATTA-2) has an overall counting efficiency of 0.01{\%} and, for $^{81}$Kr dating, requires a water sample of at least 1,000 liters. We are developing a new apparatus (ATTA-3) to trap and count $^{81}$Kr atoms with the goal of reaching a counting efficiency of 1{\%}. If successful, the required sample size would be reduced down to 10 liters of water or ice, and a wider range of applications in the earth sciences can be realized. This work is supported by DOE, Nuclear Phys Div, under contract W-31-109-ENG-38, and by a UofC-ANL collaborative seed grant. [Preview Abstract] |
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G1.00106: Cold Atom Manipulation with Off-Axis Rotating Trap Eun Oh, Jinwei Wu, Frank Moscatelli, Shengwang Du We have investigated the theory governing the behavior of atoms in various off-axis rotating traps in the presence of damping forces. When the radius of rotation of the trap is within the trap volume, the atoms are attracted towards the rotating origin if the damping rate $\Gamma $ is larger than the trap frequency $\omega $ (i.e., $\Gamma \quad > \quad \omega )$. This is as opposed to being repelled by the centrifugal force in the rotating accelerated reference frame. On the other hand, when the trap's rotation radius is larger than the trap size, the drag velocity of the atoms decrease with increasing rotational frequency. These anomalous properties can be used to realize high speed rotating sensors and static effective ring trap potentials for manipulating cold atoms. [Preview Abstract] |
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G1.00107: An Off-Axis Rotating Magneto-Optical Atom Trap Jinwei Wu, Eun Oh, Frank Moscatelli, Charmaine Gilbreath, Yeonju Han-Oh, Shengwang Du We present a simple configuration of a magneto-optical trap for cold atoms. The trap is very simple in design, employing only a small permanent magnet and an external Helmholtz bias coil. The trap's principal advantage is that the entire volume of the overlapping laser beams can be used for atom guiding and manipulation. An especially interesting effect is the rotation of the trapped atoms in circular motion as the permanent magnet is rotated. Clouds containing on the order of 2*10$^{6}$ atoms are rotated up to 60Hz forming a 5 mm diameter ring. This rotation can potentially be used in studying the behavior of cold atoms in 2-dimensional potential as well as applications for rotational sensors. [Preview Abstract] |
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G1.00108: Design of a Permanent-Magnet Zeeman Slower Charles Adler, Frank Narducci, Charles Sukenik, Jonathan Mulholland, Sarah Goodale During the past decade, low cost, flexible, and highly-polarized magnetic field sheet material has become available with field strengths useful for applications in modern atomic physics experiments. One advantage of using such material is that it can easily be cut to almost any desired shape without appreciable loss of field strength making it more versatile than ceramic magnets. We present the design of a Zeeman slower, made from such material, for cooling an atomic beam of neutral rubidium atoms and discuss results from an atomic beam trajectory simulation which indicates that the slower should perform well. We will also report on progress of a prototype permanent magnet Zeeman slower presently under construction in the laboratory. [Preview Abstract] |
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G1.00109: Behavior of Pulsed and Continuous-Wave Optical Dipole Traps M. Shiddiq, C.E. Lucas, E.M. Ahmed, M.D. Havey, C.I. Sukenik, R.R. Jones, D. Cho To date, almost all far-off-resonance traps (FORT) for confining ultracold atoms have used continuous-wave (cw) laser light. Recently, in addition to studies of a cw FORT, we have been investigating the behavior of a pulsed FORT constructed using a mode-locked Nd:YAG laser with 100 picosecond pulses. Both FORTs are loaded from a rubidium magneto-optical trap (MOT). For cw and pulsed traps of equal average power, we will present a quantitative side-by-side comparison of the trap loading and holding dependence on such quantities as MOT intensity and detuning, MOT hyperfine repumper laser intensity, loading time, and FORT power. We have found that although the pulsed and cw traps behave similarly in most respects, there is a notable difference in dependence on MOT laser detuning during FORT loading. Finally, we will discuss progress on implementing the free electron laser (FEL) at Jefferson Lab to make an optical trap for atomic physics and cold chemistry applications with a well depth several orders of magnitude greater than achievable with a typical table-top laser. Supported in part by the National Science Foundation, Jefferson Laboratory, and Old Dominion University. [Preview Abstract] |
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G1.00110: Experimental Progress Toward Multiple Adiabatic Rapid Passage Sequences X. Miao, E. Wertz, M. G. Cohen, H. Metcalf Multiple repetitions of adiabatic rapid passage (ARP) sweeps with counterpropagating light beams can enable huge optical forces on atoms\footnote{T. Lu, X. Miao, and H. Metcalf, Phys., Rev. {\bf A 71} 061405(R) (2005)}. The repetition rate of the ARP sweeps $\omega_s \gg \gamma$ results in a force $\hbar k \omega_s/\pi \gg \hbar k \gamma/2 \equiv F_{rad}$ where $1/\gamma \equiv \tau$ is the excited state lifetime and $F_{rad}$ is the ordinary radiative force. This is because each pair of ARP-induced inversions can coherently transfer momentum $\pm 2 \hbar k$ between the light beams, and thus $\mp 2 \hbar k$ to the atoms. In developing instruments for such experiments on the 2$^3$S$_1 \rightarrow$ 2$^3$P$_2$ transition at $\lambda$ = 1083 nm in He, we exploit recent developments in the optical communications industry. We use commercial phase and intensity modulators of the LiNbO$_3$ waveguide type having $V_{\pi}$ as low as 6 V and thus requiring relatively low rf power for the modulation. Synchronized driving of the two modulators can produce the necessary multiple ARP sequences of 10 ns chirped pulses that span several GHz, as needed for the experiment$^3$. We are also developing optical methods for characterizing these pulses. [Preview Abstract] |
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G1.00111: Nonadiabatic Transitions in Adiabatic Rapid Passage T. Lu, X. Miao, H. Metcalf Optical forces much larger than the ordinary radiative force can be achieved on a two-level atom by multiple repetitions of adiabatic rapid passage sweeps with counterpropagating light beams\footnote{T. Lu, X. Miao, and H. Metcalf, Phys., Rev. {\bf A 71} 061405(R) (2005)}. Chirped light pulses drive the atom-laser system up a ladder of dressed state energy sheets on sequential trajectories, thereby decreasing the atomic kinetic energy. Nonadiabatic transitions between the energy sheets must be avoided for this process to be effective. We have calculated the nonadiabatic transition probability for various chirped light pulses numerically. These results were compared to the first Demkov-Kunike model\footnote{Yu. Demkov and M. Kunike, Vestn. Leningr. Univ. Fis. Khim., {\bf 16}, 39 (1969); K.-A. Suominen and B. Garraway, Phys. Rev. {\bf A45}, 374 (1992)} and the well-known Landau-Zener model. In addition, an analytical form of the nonadiabatic transition probability has been found for linearly chirped pulses and an approximate form for generic symmetric finite-time pulses has been found for the entire parameter space using the technique of unitary integration. From this, the asymptotic transition probability in the adiabatic limit was derived. [Preview Abstract] |
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G1.00112: Towards fermionic superfluidity in ultracold Li-Rb mixtures Michael Brown-Hayes, Qun Wei, Woo-Joong Kim, Roberto Onofrio Ultracold dilute atomic gases are providing a new window into quantum physics, with particular regard to the first-principle study of superfluid phenomena . We will report on the development of an apparatus for simultaneous trapping and cooling of 6Li and 87Rb.Ultracold mixtures should be obtainable by using a light-assisted magnetic trap to optimize the heat capacity matching [1]. This combination of species is also expected to be more immune to Fermi-hole heating losses which could limit the minimum reachable temperature in Fermi-Bose mixtures [2]. [1] M. Brown-Hayes and R. Onofrio, Phys. Rev. A 70, 063614 (2004). [2] R. C\^{o}t\'{e}, R. Onofrio, E. Timmermans, Phys. Rev. A 72, 041605(R) (2005). [Preview Abstract] |
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G1.00113: An Optically Excited Metastable Krypton Atomic Beam Source Michael Mastroianni, Chad Orzel We report the construction of an optically excited metastable krypton atomic beam source. Ground-state Kr atoms are excited to the $5s[3/2]_1$ state by a 123 nm photon from a krypton resonance line lamp, then to the $5p[5/2]_2$ state by an 819 nm photon from a diode laser. From the $5p[3/2]_2$ state, they spontaneously decay into the $5s[3/2]_2$ ($^3P_2$) metastable state with $77\% $ probability. We characterize the source using both resonant fluorescence at 811 nm and a surface ionization detector. The source will be used to load a Kr* magneto-optical trap for Kr background evaluation by Atom Trap Trace Analysis. [Preview Abstract] |
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G1.00114: Temperature measurements using Rydberg tagging Jonathan Tallant, K. Richard Overstreet, Arne Schwettmann, Jeff Crawford, James P. Shaffer We present a new non-destructive temperature measurement technique using Rydberg tagging of ultra-cold atom traps (T$<$1mK). The time-of-flight velocity distributions of the Rydberg tagged atoms are used to deduce the temperature. We show that the initial temperature of the Rydberg atoms is identical to the trap temperature. We compare the technique to others. [Preview Abstract] |
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G1.00115: Abel inversion for study of multiple scattering in a Cs magneto-optical trap K. Richard Overstreet, Patrick Zabawa, Jonathan Tallant, Arne Schwettmann, Jeff Crawford, James P. Shaffer We present a study of multiple scattering within a Cs magneto- optical trap (MOT). We employed two Abel inversion algorithms to recover the density distribution of the MOT from fluorescent images. The method is non-destructive and provides accurate measurement of MOT density. We observe deviations of the density distribution from a Gaussian that are attributed to the multiple scattering of photons. [Preview Abstract] |
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G1.00116: Observation of novel sub-Doppler trap structures in a magneto optical trap Dahyun Yum, Yonghee Kim, Myoung-Sun Heo, Soyong Shin, Kihwan Kim, Heung-Ryoul Noh, Wonho Jhe Last decades of accomplishments in atomic physics are triggered by the invention of laser cooling and trapping technique of magneto optical trap. The studies on this trap revealed that there exist two kinds of forces therein so-called, Doppler and sub-Doppler force. We have found that with different detuning of trap laser between z axis and transverse axes, the normal sub-Doppler trap located at the center fades out while a pair of new sub-Doppler traps appear symmetrically with respect to the center. Varying the experimental conditions such as the trap frequency and the difference of detuning, the depth and the separation of this new structure are measured and compared with theoretical calculation. [Preview Abstract] |
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G1.00117: Direct Measurement of Excited State Fractions in a MOT M.H. Shah, M.L. Trachy, G. Veshapidze, H.A. Camp, M.A. Gearba, H. Nguyenc, B.D DePaola Accurate measurement of excited state fraction is critical in measurements of photo-ionization and electron impact cross sections, and the rapidly growing field of cold and ultra-cold collision cross section measurements. Many groups have reported that a large source of uncertainty in their results comes from the fluorescence-based measurement of the MOT excited state fraction. In this work we report the results of directly measured in-MOT excited state fractions as a function of trapping laser intensity and detuning. The experimental approach is based on the MOTRIMS methodology. Here instead of looking at the fluorescence, charge transfer to a beam of 7 keV Na$^{+}$ is used as a probe. The results are compared with theoretical models. [Preview Abstract] |
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G1.00118: Fabrication of an Atom Chip for Studying Atom-Surface Interactions. Owen Cherry, Jeff Carter, Czang-Ho Lee, Reena Al-Dahleh, James D. D. Martin Using photolithography processes, we have fabricated a chip-based magnetic microtrap (atom chip) suitable for trapping Rb atoms close to a gold surface in order to study atom-surface interactions. The surface, separated from the trapping wires by a polyimide dielectric, also acts as a shield to block out stray electric fields from the wires. The polyimide layer is highly planarizing to minimize surface corrugations, but $<$ 5 $\mu $m thick to attain the high magnetic field gradients required to bring the trapped atoms within 2 $\mu $m of the surface. A lift-off process has been developed to fabricate evaporated gold wires with edge roughness $\sim $100 nm, limited by the grain size of the gold. Results of atom chip performance and trap loading are presented. [Preview Abstract] |
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G1.00119: All-optical experiments with ultracold strontium Yenny Natali Martinez, Pascal G. Mickelson, Sarah B. Nagel, Thomas C. Killian We describe ongoing studies of ultracold atomic strontium using standard laser cooling and trapping techniques. An improved ultra-high vacuum system has been constructed, and magneto-optical trapping on both the dipole-allowed transition at 461 nm (blue) and the intercombination line at 689 nm (red) is performed. The transfer efficiency from the blue to the red MOT is over 50{\%}, resulting in a sample with a temperature less than 2 $\mu $K. We have designed a far-off-resonance optical dipole trap (FORT) such that the Stark shift of the upper and lower states of the narrow $^{1}$S$_{0}-^{3}$P$_{1}$ transition are comparable, allowing simultaneous Doppler cooling in the FORT. Planned experiments in the FORT include cold collision studies as well as evaporative cooling to quantum degeneracy. We present models and preliminary results. [Preview Abstract] |
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G1.00120: Controlling a single atom trapped in a ring-shaped potential Lu Zhao, Tun Wang, Susanne Yelin One alkali atom is trapped tightly in a ring-shaped potential formed by two strong far detuned evanescent waves close to a dielectric surface. Two copropagating Laguerre-Gaussian Raman beams are applied to control the rotational quantum states of the atom in the ring. We show that the orbital angular momentum of photons can be transferred to the atom to produce a coherent coupling between different rotational quantum states. This system can be applied, for example, in quantum information processing. [Preview Abstract] |
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G1.00121: Effects of Electromagnetically Induced Transparency on Laser Cooling of Three-Level Atoms Josh W. Dunn, Flavio C. Cruz, J. W. Thomsen, Chris H. Greene We present a theoretical investigation of laser-cooling schemes involving three internal atomic levels and two lasers. Such configurations can occur for a variety of atomic systems, in the form of either ladder- ($\Xi$), lambda- ($\Lambda$), or V-type three-level systems, and are common in alkaline-earth-metal atoms. Experimental evidence for sub-Doppler temperatures in these configurations exists [1], although previous theoretical and experimental work is limited in extent. We utilize novel sparse-matrix numerical techniques to find exact solutions to the atom-laser master equation, including quantized center-of-mass atomic motion. Use of such fully quantum calculations allows quantitative estimates of expected experimental temperatures. We discuss the results of a thorough exploration of parameter space, including the various regimes of intensities for each of the lasers, and their detunings, independently. The effectiveness of cooling for different atomic species is also explored. Our analysis leads to an intuitive physical picture of how these cooling schemes work, and in particular we explain the important role played by electromagnetically induced transparency (EIT) effects. [1] N. Malossi et al., Phys. Rev. A \textbf{72}, 051403 (2005). [Preview Abstract] |
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G1.00122: LOW TEMPERATURE PLASMA |
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G1.00123: Two-body Coulomb resonances in magnetic field D. Vrinceanu, L. A. Collins Unlike Coulomb scattering in a zero magnetic field, temporary bound states can form at positive energy in electron-proton collisions in a magnetic field. Classical trajectory simulations are used to explore the phase space for typical parameters used in anti-hydrogen experiments. These resonances can increase the interaction time substantially and have important consequences on three-body recombination in cold magnetized plasma. Standard scattering theory has to be modified to take into account that the free particle states are not plane waves in a magnetic field. [Preview Abstract] |
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G1.00124: QUANTUM INFORMATION |
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G1.00125: Progress toward making spin squeezed states with ions in a Penning-Malmberg trap. N. Shiga, W.M. Itano, J.J. Bollinger We describe plans and summarize initial progress towards making spin squeezed states with a few tens to $\sim$1000 $^{9}$Be$^{+} $ ions in a Penning-Malmberg trap. We use the ground-state electron spin-flip transition, which in the 4.5 T magnetic field of the trap has a transition frequency of 124 GHz, as the ion qubit. With a 30 mW Gunn diode oscillator we have observed Rabi flopping rates as high as $\sim$1 kHz. We will summarize experimental progress on realizing projection noise limited spectroscopy on this transition, which is a prerequisite for demonstrating spin squeezing. For entangling the ions we plan to use a generalization of the few ion qubit phase gate developed at NIST \footnote{D. Leibfried, et al., Nature {\bf 438}, 639 (2005).} to generate an $\exp{(i\chi {J_{z}}^2 t)}$ interaction between all of the ion qubits. This interaction can be implemented on a single plane of ions \footnote{T.B. Mitchell, et al., Science {\bf 282}, 1290 (1998).} with a motional sideband, stimulated Raman transition. [Preview Abstract] |
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G1.00126: Neutral Atoms for Quantum Registers M.J. Gibbons, S.Y. Kim, K.M. Fortier, M.S. Chapman Individually trapped neutral atoms are one of the most promising candidates for long-term storage of quantum information. We are realizing a neutral atom register using a 1-dimensional optical lattice to confine ultracold $^{87}$Rb atoms. A high gradient MOT can collect a small number of atoms, which we transfer to an optical lattice. The atoms are imaged and individually counted by a high resolution CCD camera. We will discuss our experiments, as well as our strategies for generating atom-atom and atom-photon entanglements using high finesse cavities. [Preview Abstract] |
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G1.00127: Correlated-photon experiments for teaching undergraduate quantum mechanics. Brad Melius, Enrique Galvez, Charles Holbrow We have developed a set of undergraduate laboratory experiments with correlated photons that illustrate fundamental quantum mechanical concepts, such as quantum superposition, state projection and entanglement [1]. The experiments use photon pairs produced by parametric down conversion in conjunction with coincidence detection. We report here our work on a new experiment on the Hong-Ou-Mandel dip with entangled states. The goal of the experiment is to demonstrate the bosonic symmetry of the wave function of identical photons [2]. [1] E.J. Galvez et al., Am. J. Phys. 73, 127 (2005). [2] C.H. Holbrow et al., Am. J. Phys. 70, 260 (2002). [Preview Abstract] |
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G1.00128: Entanglement between two interacting atoms in a one-dimensional harmonic trap Bo Sun, Duan Lu Zhou, Li You We investigate quantum entanglement properties between two interacting atoms in a one-dimensional harmonic trap modeled by by a contact pseudo-potential. We provide detailed results for the dependencies of atom-atom entanglement on the statistical nature of atoms being bosonic or fermionic, the scattering length, and temperature. Our results shines new light on quantum information and computation applications of cold atomic systems. [Preview Abstract] |
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G1.00129: Optimizing Quantum Repeater Protocols Liang Jiang, Jacob Taylor, Navin Khaneja, Mikhail Lukin By using dynamical programming, we systematically investigation methods for optimizing quantum repeaters protocols. We focus on balancing error-correction stages, such as purification, with connection stages which extend the distance of the generated entanglement. Given parameters describing apparatus imperfections, we can find the most time-efficient arrangement of entanglement connection and purification to achieve a targeted fidelity for the final entangled pair. Application of the method to various practical protocols yields substantial improvements compared to the existing schemes. [Preview Abstract] |
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G1.00130: Entanglement of multiple atoms via collective spontaneous emission James Clemens We have carried out a theoretical and numerical investigation of the entanglement generated by multiple atoms located at arbitrary locations in free space undergoing collective spontaneous emission starting from the fully excited state. We use a quantum trajectory unraveling of the superradiance master equation derived by Lehmberg [Phys. Rev. A {\bf 2} 883 (1970)] based on direct photodetection of the emitted field. The amount of entanglement is quantified by calculating the von Neumann entropy for different groupings of the $N$ atoms into two subsystems. Quantum trajectory theory holds an advantage for this investigation because the fundamental object is a state vector, conditioned on a sequence of photodetections, allowing us to use the unique measure of entanglement for pure states. We find that the entanglement develops during the course of the collective emission pulse starting from zero entanglement for the initial fully excited state. [Preview Abstract] |
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G1.00131: Performance of a quantum teleportation protocol based on spontaneous emission from a pair of atoms James Clemens Recently a quantum teleportation protocol has been proposed by Chen, et al. in {\it New Journal of Physics} {\bf 7}, 172 (2005) which is based on the collective spontaneous emission of a photon from a pair of atoms. If one can successfully distinguish between the superradiant and subradiant emission channels then one can teleport the state of the second atom onto a cavity field mode with which the first atom has previously interacted. One can employ temporal resolution, spatial resolution, or both in combination, of the emitted photon in order to distinguish superradiant from subradiant emission on the basis of a single detected photon. Using a quantum trajectory unraveling of the superradiance master equation developed previously [{\it Phys. Rev. A} {\bf 68}, 023809 (2003)] we calculate the overall success probability and the fidelity of the teleportation protocol under all three detection strategies. We investigate the performance of the protocol, optimizing with respect to the spacing of the two atoms. [Preview Abstract] |
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G1.00132: Precision measurements with strongly correlated atoms: beating the decoherence limit Liang Yiang, Ana Maria Rey, M. Fleischhauer, Mikhail Lukin It is well-known that~entangled~atomic states (e.g. so-called spin squeezed states) potentially allow to significantly improve~resolution in Ramsey spectroscopy. However,~entangled states are more~fragile to phase decoherence than uncorrelated states and when decoherence~~ is taken into account~~ both~of them yield the similar limit to~resolution. We propose a method to improve the limit associated with decoherence~~ by using strongly correlated atoms with~dynamics~governed by~ a spherically symmetric and gapped Hamiltonian. We show that under certain conditions the gapped~evolution of the atoms,~can~provide an~~ increase in~the signal-to-noise ratio even in decoherence-limited measurements. Finally, we discuss possible physical systems that can be used to implement this technique in real experiments. [Preview Abstract] |
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G1.00133: Error in trapped-ion quantum gates due to spontaneous photon scattering R. Ozeri, C. Langer, J.D. Jost, R.B. Blakestad, J. Britton, J. Chiaverini, D. Hume, W.M. Itano, E. Knill, D. Leibfried, R. Reichle, S. Seidelin, J.H. Wesenberg, D.J. Wineland Quantum bits that are encoded into hyperfine states of trapped ions are a promising system for Quantum Information Processing (QIP). Quantum gates performed on trapped ions use laser induced stimulated Raman transitions. The spontaneous scattering of photons therefore sets a fundamental limit to the gate fidelity. Here we present a calculation that explores these limits. Errors are shown to arise from two sources. The first is due to spin relaxation (spontaneous Raman photon-scattering events) and the second due to the momentum-recoil that is imparted to the trapped ions in the scattering process. It is shown that the gate error due to spontaneous photon scattering can be reduced to very small values with the use of high laser power. It is further shown that error levels required for fault-tolerant QIP are within reach of experimentally realistic laser parameters. [Preview Abstract] |
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G1.00134: Dynamic theory of driven multilevel dissipative quantum systems Zhongyuan Zhou, Shih-I Chu, Siyuan Han We develop a dynamic theory for a driven multilevel quantum system interacting with a fluctuating environment. In this theory, the driving field is an arbitrary external field, the environment is characterized by a spectral density function, and the density operator of system is governed by master equation. The leakage due to the coupling of both the driving field and environment is included. This theory has been used to analyze dissipation processes of a driven quantum system in a thermal bath. Analytical spontaneous decay rate is derived, which is in good agreement with that obtained by others using different methods. For two-level systems, the master equation is replaced by Bloch equations. For resonantly driven dissipative two-level systems, analytical expressions of energy relaxation time, decoherence time, as well as dephasing time are obtained, from which an approach to measure the dephasing time is proposed. [Preview Abstract] |
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G1.00135: Secure Quantum Communications using Two-Mode Squeezed States Alberto M. Marino, C.R. Stroud, Jr. The field of secure quantum communications has gained a lot of interest in recent years. The main protocols that have been proposed to date for quantum key distribution (QKD) rely on single-photon sources and detectors. In practice weak coherent pulses are used instead of single photons, making the system vulnerable to attacks. The major difficulties with these schemes are the lack of good single-photon sources and the low quantum efficiency of single-photon detectors. We propose a scheme that uses the squeezing phase of a two-mode squeezed state (TMSS) to securely transmit information between two parties. The basic principle behind this scheme is that the reduced density matrix of each of the modes of a TMSS does not contain any information about the squeezing phase $\theta$, only regarding the degree of squeezing $r$. The squeezing phase can only be obtained through a combined measurement of the two modes. The fact that it is possible to perform remote squeezing measurements allows for the implementation of a secure quantum communication protocol in which information can be transmitted directly between two parties while the encryption is done automatically by the quantum correlations present in the TMSS. In general, the main advantage gained by using squeezed light for QKD is that both sources of squeezed light, such as optical parametric oscillators, and high quantum efficiency detectors are readily available. [Preview Abstract] |
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G1.00136: Quantum telecommunication based on atomic cascade transitions Shau-Yu Lan, Thierry Chaneliere, Dzmitry Matsukevich, Stewart Jenkins, Michael Chapman, Brian Kennedy, Alex Kuzmich We report generation of an entangled pair of 1530 nm and 780 nm photons via atomic cascade emission in a cold ensemble of rubidium atoms. The former photon is ideal for long-distance quantum communication, and the latter is naturally suited for mapping to a long-lived atomic memory. Together with our demonstration of photonic-to-atomic qubit conversion, the essential elements for a telecommunication quantum repeater have been realized. [Preview Abstract] |
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G1.00137: Effect of inter-mode anharmonicities on accuracy of gates in a two-qubit system of vibrational eigenstates. Meiyu Zhao, Dmitri Babikov We propose a quantum computer in which the qubits are implemented using the vibrational modes of a polyatomic molecule and the gates are applied using the optimally shaped femto-second infrared laser pulses. In order to study this system theoretically we developed a two-qubit model based on the normal vibration modes approximation afforded by the very low vibrational excitation regime. Optimal control theory and numerical time-propagation of the vibrational wavepackets are employed. One focus of this work is on understanding how the intra- and inter-mode anharmonicities affect the accuracy of quantum gates in such a system. Another emphasis is on achieving a proper control over the relative phase between the vibrational qubit states. [Preview Abstract] |
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G1.00138: A microfabricated surface-electrode ion trap for scalable quantum information processing Signe Seidelin, John Chiaverini, Rainer Reichle, John Bollinger, Didi Leibfried, Joe Britton, Janus Wesenberg, Brad Blakestad, Ryan Epstein, David Hume, John Jost, Chris Langer, Roee Ozeri, Nobu Shiga, David Wineland We demonstrate confinement of individual atomic ions in a radio-frequency Paul trap with a novel geometry where the electrodes are located in a single plane and the ions confined above this plane. This device is realized with a relatively simple fabrication procedure and has important implications for quantum state manipulation and quantum information processing using large numbers of ions. We confine laser-cooled Mg-24 ions approximately 40 micrometer above planar gold electrodes. We measure the ions' motional frequencies and compare them to simulations. From measurements of the escape time of ions from the trap, we also determine a heating rate of approximately five motional quanta per millisecond for a trap frequency of 5.3 MHz. [Preview Abstract] |
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G1.00139: Quantum Simulators, Spin Systems, and Trapped Ions W. Lybarger, D. Berkeland, M. Boshier, J. Chiaverini, D. Dalvit, D. Lizon, W.R. Scarlett, R. Somma, K. Vant, M. Blain, B. Jokiel, C. Tigges Many quantum spin systems cannot be efficiently simulated on classical computers as they require exponentially large resources. Yet many such systems can be simulated efficiently with quantum simulators (QS) that do not require universal control like quantum computers. Following the work of Porras and Cirac [Phys. Rev. Lett. 92, 207901-1 (2004)] we discuss current theoretical and experimental efforts at Los Alamos to implement a QS for Ising-like and Heisenberg-like models with trapped ion qubit ``spins''. The states of the QS systems follow nearly the same equations of motion as the systems of interest and, unlike with real materials, the experimenter has the advantage of direct access to and control over the spins. We will discuss proof-of-principle investigations of two ion simulations in a single-well trap, in which we use state-selective optical forces to induce ion-ion interactions. Also we will describe collaborative work with Sandia NL on microfabricated multizone traps, suitable for quantum computation, that we will use for more advanced simulations. [Preview Abstract] |
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G1.00140: Reducing the sensitivity of the M{\o}lmer-S{\o}rensen gate for ion-trap quantum computing to unbalanced laser intensities J.H. Wesenberg, R.B. Blakestad, J. Britton, J.D. Jost, E. Knill, C. Langer, D. Leibfried, R. Ozeri, R. Reichle, S. Seidelin, D.J. Wineland Geometric gates for ion-trap quantum computing have been experimentally demonstrated (fidelity $\approx 0.97$), using a single pair of laser beams driving a Raman transition between motional states\footnote{D. Leibfried et al., Nature 422, 412 (2003).}. This class of gate operations only works for qubits encoded in states with field-sensitive transitions. Since qubits encoded in states with field-insensitive transitions are less susceptible to decoherence, there is presently a renewed interest in the M{\o}lmer-S{\o}rensen (MS) gate, a geometric gate compatible with field-insensitive states\footnote{P. J. Lee et al., quant-ph/0505203}. A fundamental weakness of the MS gate is that it requires two Raman transitions to be driven simultaneously, introducing a new error source in the form of potentially unbalanced strengths of the two pairs of Raman beams. We show that although the MS gate in the originally proposed form is highly sensitive to such an imbalance, a minimal modification allows it to operate at high fidelity, even with poorly balanced laser intensities. [Preview Abstract] |
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G1.00141: Semiconductor-based quantum computing: from physical gates to architectures Jacob Taylor, J. R. Petta, H.-A. Engel, W. D\"ur, A. C. Johnson, A. Yacoby, C. M. Marcus, P. Zoller, M. D. Lukin Solid state approaches to quantum computation offer intriguing prospects for large scale integration and long term stability. However, achieving fault tolerant quantum computation entails significant mitigation of environmental couplings, which is particularly challenging in the solid-state. We will discuss the theoretical and experimental development of a scalable architecture for solid-state quantum computation based on actively protected two electron spin states in quantum dots. Specifically, we find a universal set of gates for two-spin states that can be implemented using only local electrical control, with explicit suppression of hyperfine interactions, the dominant source of error. The architecture allows for a modular, hierarchical design, and includes autonomous control and non-local coupling using controlled electron transport. Fault tolerance properties of the architecture will be considered. [Preview Abstract] |
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G1.00142: Study of Rydberg-Rydberg interactions for quantum gates with neutral atoms Bindiya Arora, M.S. Safronova, Charles W. Clark The fast phase gate scheme, in which the qubits are atoms confined in sites of an optical lattice, and gate operations are mediated by excitation of Rydberg states, was proposed in [1]. The logic gate is implemented using a blockade of the simultaneous excitation of atoms into a Rydberg state. Strong coupling between atoms is required for the experimental realization of such proposal. In this work, we study Rydberg-Rydberg interactions that are resonantly enhanced by the F$\ddot{\mbox{o}}$ster processes [2]. Such resonances may provide sufficiently strong Rydberg-Rydberg interactions in low electric fields to realize a blockade necessary for the gate operations. Comparative calculations are done for alkali atoms to determine if this entanglement scheme may be better suited for a specific system.\\ \noindent [1] D.\ Jaksch, J.I.\ Cirac, P.\ Zoller, S.L.Rolston, R.\ C\^{o}t\'{e}, and M.D.\ Lukin, Phys.\ Rev.\ Lett.\ {\bf 85}, 2208 (2000).\\ \noindent [2] Thad G. Walker and Mark Saffman, J. of Phys. B {\bf 38}, S309 (2005). [Preview Abstract] |
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G1.00143: Quantum computing with polar molecules Susanne Yelin, Robin Cote, Tommaso Calarco The permanent dipoles of polar molecules allow for stable interactions of single-molecular and ensemble qubits. We show how this mechanism can be used for stable quantum information processing, using different setups and estimating their merits as compared to the present state-of-the-art. [Preview Abstract] |
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