Session D6: Poster Session I

Electron Momentum Distribution in Multiply-Ionized Atoms as a Function of Atomic Number and Degree of Ionization

We present momentum-space properties of multiply-ionized atoms as a function of atomic number $Z$ and the degree of ionization of the atom. In particular, we have calculated the Compton profiles of all possible electronic configurations of He, Li, Be, B, and N atoms as they are progressively ionized with the outer-shell electrons being stripped off. The values of the Compton profiles presented here can be used to deduce doubly differential cross sections of variously ionized atoms colliding with other atoms and ions. The single-electron radial wave functions were obtained from the Hartree-Fock atomic model. Compton profiles of neutral atoms, available in the literature, are in excellent agreement with the present calculation.   

Long-range interactions between two helium atoms

The dispersion coefficients $C_n$ (with n up to 10) for the long-range interaction between two helium atoms are calculated using variation method in Hylleraas coordinates. For the any combined system He($nS$)-He($n^{'}S$) among the ground state He$(1\,^1\!S)$ and the lowest excited $S$ states He$(2\,^1\!S)$ and He$(2\,^3\!S)$, significant improvements are made upon previous calculation and our results provide definitive values for these coefficients. For the He$(1\,^1\!S)$-He$(2\,^3\!P)$ system, we also assess coefficients $C_6^{\pm}$ and $C_6^0$ using a semi-empirical method based on tabulated oscillator strengths and available photoionization cross sections. The results from the two methods agree to within 1.5\%. In addition, we have calculated dispersion coefficients $C_ {n\leq10}$ for the four systems He$(1\,^1\!S)$-He$(2\,^1\!P)$, He$(2\,^1\!S)$-He$(2\,^3\!P)$, He$(2\,^3\!S)$-He$(2\,^3\!P)$, and He$(2\,^3\!P)$-He$(2\,^3\!P)$.   

Spectroscopically Accurate Calculations of the Rovibrational Energies of Diatomic Hydrogen

The Born-Oppenheimer approximation has been used to calculate the rotational and vibrational states of diatomic hydrogen. Because it is an approximation, our group now wants to use a Born-Oppenheimer potential to calculate the electronic energy that has been corrected to match closely with spectroscopic results. We are using a code that has corrections for adiabatic, relativistic, radiative, and non-adiabatic effects. The rovibrational energies have now been calculated for both bound and quasi-bound states. We also want to compute quadrupole transition probabilities for diatomic hydrogen. These calculations aspire to investigate diatomic hydrogen in astrophysical environments.   

Measurement of Absolute Cross Sections for Excitation of the \textbf{2s$^{2} \doub ^{1}S - 2s2p ^{1}P^{o}$ Transition in O$^{4+}$}

Experimental electron excitation cross sections are reported for the 2s$^{2 1}$S - 2s2p$^{ 1}$P$^{o}$ transitions in O$^{4+}$ located at 19.689 eV. The JPL electron-cyclotron resonance ion source is utilized [1], along with the electron energy loss method, in a merged electron-ion beams geometry[2]. The center-of-mass interaction energies for the measurements are in the range 18 eV (below threshold) to 30 eV. Data are compared with results of a 26-term \textbf{\textit{R}}-matrix calculation that includes fine structure explicitly \textit{via} the Breit-Pauli Hamiltonian [3]. There is good agreement with theoretical results and with previous electron energy-loss measurements [3]. Clear resonance enhancement is observed in both experiment and theoretical results near threshold for this $^{1}$S - $^{1}$P$^{o}$ transition. J. Lozano and N. Djuric acknowledge support through the NASA-NRC program. This work was carried out at JPL/Caltech and was supported by NASA. [1] J. B. Greenwood, S. J. Smith, A.Chutjian, and E. Pollack, Phys. Rev. A \textbf{59} 1348, (1999). [2] A. Chutjian, Physica Scripta \textbf{T110}, 203 (2004). [3] M. Bannister et al., Int.J. Mass Spectrometry \textbf{192}, 39 (1999).   

Three body elastic scattering in the shape independent representation

Exact solutions of the three-body Schrödinger equation with shape independent two-body interactions are obtained in closed form. A consistency equation relating the wave equation at large distances to the wave function where the three particles coincide is derived. Our solution satisfies this relation to high order.   

$Ab~Initio~f$ values for Fe II $J=9/2 \rightarrow 9/2^o$ transitions

Relativistic configuration interaction $f$ values have been obtained for 264 transitions between the lowest 12 $J=9/2$ and the 22 $J=9/2^o$ levels. Length and velocity gauges agree to 3.8\% for in-shell transitions and 10.0\% for shell jump transitions. Two $J=9/2^o$ levels are so nearly degenerate that it was necessary to introduce a semi-empirical correction to produce the correct level ordering. The results are in overall good agreement with the semi-empirical results of Kurucz \footnote{R. L. Kurucz, http://kurucz.harvard.edu/atoms/2601/} and Raassen \footnote{A. J. J. Raasen, ftp://ftp.wins.uva.nl/pub/orth/iron/FeII.E1 (1999)}. An efficient method of including magnetic Breit effects in the energy matrix is presented.   

Two-photon, sub-Doppler hyperfine measurements of the $6\mbox{d} ^2\mbox{D}_j$ states of cesium

We measured the hyperfine structures of the $6\mbox{d} ^2\mbox{D}_j$ states of cesium using multiphoton, sub-Doppler absorption spectroscopy. In addition to improving upon the precision of previously published hyperfine coupling constants, we demonstrate a simplified approach to frequency calibration. Two narrow-band diode lasers excite cesium within a vapor cell in a two-step resonantly enhanced process. 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, and the second laser is scanned over the $6\mbox{p} ^2\mbox{P}_{3/2} (\mbox{F}') \rightarrow 6\mbox{d} ^2\mbox{D}_j (\mbox{F}'')$ hyperfine manifold. The frequency scale is directly referenced to the $^{87}$Rb ground state hyperfine transition, 5s$^2\mbox{S}_{1/2} (\mbox{F}=1) \leftrightarrow 5 \mbox{s} ^2\mbox{S}_{1/2} (\mbox{F}=2)$. We modulate the scanned laser frequency using an electro-optic modulator driven by an RF signal generator trained to a rubidium clock, and use the resulting sidebands for frequency calibration. The accuracy of this approach is demonstrated by measuring the hyperfine coupling constants of the $6\mbox{d} ^2\mbox{D}_{5/2}$ state, $\mbox{A} = -4.66 \pm 0.04 \,$MHz and $\mbox{B} = 0.9 \pm 0.6 \,$MHz, which agree with the literature\footnote{N. Georgiades, E. Polzik, and H. Kimble, Opt.\ Lett.\ {\bf 19}, 1474 (1994).}: $\mbox{A} = -4.69 \pm 0.04 \,$MHz and $\mbox{B} = 0.2 \pm 0.7 \,$MHz. We also improve upon the precision of previously reported $6\mbox{d} ^2\mbox{D}_{3/2}$ coupling constants\footnote{C. Tai, W. Happer, and R. Gupta, Phys.\ Rev.\ A {\bf 12}, 736 (1975).} ($\mbox{A} = 16.3 \pm 0.15 \,$MHz and $\mbox{B} < \pm 8 \,$MHz) by measuring $\mbox{A} = 16.34 \pm 0.05 \,$MHz and $\mbox{B} = -0.1 \pm 0.3 \,$MHz.   

Analysis of the Spectrum of Doubly-Ionized Cesium (Cs III)

We have made new observations of the spectrum of doubly-ionized cesium (Cs III) in the region 400 {\AA} to 2.3 $\mu $m using grating and Fourier transform spectrometers. The spectrum was excited in sliding spark and pulsed radio-frequency discharges. Definitive separation of ionization stages was obtained by varying the source operating conditions. More than 1000 lines were classified as transitions between 76 odd and 97 even parity levels. Of 126 expected levels in the configurations 5s$^{2}$5p$^{5}$, 5s5p$^{6}$, and 5s$^{2}$5p$^{4}$(5d, 6s, 6d, 7s, 6p, and 4f), 120 were found as well as some levels of 5s$^{2}$5p$^{4}$(7d, 8s, 7p, 5f, and 5g). The levels were theoretically interpreted using Hartree-Fock calculations and least-squares fitting of energy parameters to the observed levels. Transition probabilities were calculated using semi-empirical wave functions derived from the least-squares fits. The $^{2}$P interval in the 5s$^{2}$5p$^{5 }$ground configuration and the hyperfine structure of the $^{2}$P$_{1/2}$ and $^{2}$P$_{3/2}$ levels were determined to high accuracy by observation of the forbidden transition 5s$^{2}$5p$^{5} \quad ^{2}$P$_{1/2}$ -- $^{2}$P$_{3/2}$ at 7219 {\AA}. The hyperfine structure of this transition shows it to be pure magnetic dipole in character in agreement with theoretical calculations of the magnetic dipole and electric quadrupole transition rates.   

Matrix-element spectroscopy of the 5s $^{2}S_{1/2}$ $\rightarrow$ 5p $^{2}P_{j}$ $\rightarrow$ 5d $^{2}D_{j'}$ transitions in $^{87}$Rb

Recent advances in the quality of excited-state transition matrix elements have permitted renormalization of earlier measurements of transition amplitudes associated with the 5s $^{2}S_{1/2}$ $\rightarrow$ 5p $^{2}P_{j}$ $\rightarrow$ 5d $^{2}D_{3/2}$ two-quantum transitions in atomic $^{87}$Rb. Previous measurements were made to high precision, but further reduction of the measurements was limited by uncertainties in data describing the influence of energetically distant transitions. Availability of more reliable matrix elements, including relativistic all-order calculations of transition matrix elements in alkali atoms, has since significantly improved the situation. In the present report, we show that theoretical relative transition amplitudes for the excited state 5p $^{2}P_{j}$$\rightarrow$ 5d $^{2}D_{3/2}$ doublet (ratio= 1.089) are now in excellent agreement with experiment (ratio=1.090). This result, combined with our recent work on cesium, shows that it is possible to determine relative line strengths, for transitions connecting atomic excited states, with precision previously found only in state-of-the-art measurements of alkali resonance doublets. An overview of the experimental technique and supporting data is also presented. Supported by NSF.   

Single trapped indium and barium ion optical frequency standards and a laboratory constraint on the drift of fundamental constants

Single trappped ions cooled to the Lamb-Dicke regime are spectroscopic systems free of many external perturbations and are therefore attractive as optical frequency standards. We report continued development of single indium ion and barium ion rf Paul-Straubel traps and laser cooling systems. The forbidden ${^1}S_0 \leftrightarrow {^3}P_0$ transition in In$^+$ at 237 nm has a quality factor of $10^{15}$ and is immune to $\sim 1$ Hz quadratic Stark shifts that can limit other systems. In addition, the extraordinarily long $5D_{3/2}$ lifetime ($\tau \sim 80$~s) in a single trapped barium ion yields an electric dipole forbidden 2051 nm $6S_{1/2} \leftrightarrow 5D_{3/2}$ transition with a quality factor of $10^{16}$. Further, the odd isotope $^{137}$Ba$^+$ (I = 3/2) has an excited state with total angular momentum $F' = 0$ so an optical frequency standard based on this transition also avoids significant quadratic Stark shifts. We present our latest experimental probes of these transitions using new low linewidth diode pumped solid state laser systems (a frequency quadrupled non-planar ring oscillator Nd:YAG at 946 nm and a diode pumped Tm,Ho:YLF at 2 $\mu$m) and propose a laboratory constraint on fundamental constant drift.   

Studies of Yb $^{1}$S$_{0}$ -- $^3$P$_0$ clock transitions

We are exploring two quite different methods for observing the ultra-sharp $6s^2$ $^{1}$S$_{0}$ -- $6s6p$ $^3$P$_0$ optical interval in atomic Yb, which is considered a primary candidate for future optical frequency standards [1].In the first method, we observe the 578 nm single photon transition allowed in the odd isotopes through internal hyperfine coupling of the nuclear spin.† We shine a 578 nm laser beam on cold Yb atoms held in a magneto-optical trap (MOT), and detect a decrease in MOT fluorescence when the laser is resonant with the clock transition.† Our second approach is to use the even Yb isotopes, connecting the $^{1}$S$_{0}$ and $^3$P$_0$ states† by† a multi- photon transition [2]. Sharp electromagnetically induced transparency and absorption (EITA) resonance features appear when the photon frequencies combine to equal† the $^{1}$S$_{0}$ -- $^3$P$_0$ clock interval.† We will describe our initial studies of† 2 and 3 photon resonances in Yb, including Doppler-free 3 photon EITA. [1]S. G.† Porsev, A. Derevianko, E. N. Fortson, Phys. Rev. A {\bf 69}, 021403(R)† (2004); H. Katori, in {\it Proc. 6th Symposium Frequency Standards and Metrology}, edited by P. Gill (World Scienti.c, Singapore, 2002), pp. 323-330 [2]Tao Hong, Claire Cramer, Warren Nagourney, E. N. Fortson, physics/0409051 and to be published in Phys. Rev. Lett.; Robin Santra, Ennio Arimondo, Tetsuya Ido, Crhis H. Greene, Jun Ye, physics/0411197   

Material preparation and infrared spectroscopy of diffusion doped Cr: ZnSe and Cr: CdTe

The preparation and infrared spectroscopy of diffusion doped Cr:ZnSe and Cr:CdTe windows will be reported. Cr$^{2+}$ doped II-VI semiconductors are of significant current interest as gain media in mid-infrared (2-3 $\mu $m) solid-state lasers. Compared to Cr:ZnSe, Cr:CdTe exhibits an extended infrared emission, which is of interest for laser applications beyond 3$\mu $m. Cr doping in ZnSe and CdTe was achieved through a thermal diffusion process controlled by temperature and time. Commercial CrSe powder was used as the dopant source in the diffusion experiments. Various samples of Cr:ZnSe and Cr:CdTe were prepared with Cr$^{2+}$ peak absorption coefficients ranging from $\sim $0.8 cm$^{-1}$ to 28.7 cm$^{-1}$. The corresponding Cr$^{2+}$ concentrations ranged from $\sim $1x10$^{17}$cm$^{-3}$ to $\sim $3x10$^{19}$cm$^{-3}$ assuming absorption-cross sections of 1.1x10$^{-18}$cm$^{2}$ for Cr:ZnSe and 2.2x10$^{-18}$cm$^{2}$ for Cr:CdTe. For low Cr$^{2+}$ concentrations ($\sim $1x10$^{18}$cm$^{-3})$ the room-temperature decay time varied between 5-6 $\mu $s for Cr:ZnSe and 2-3$\mu $s for Cr:CdTe. The effect of Cr concentration quenching on the mid-infrared emission was observed for doping concentrations above $\sim $1x10$^{19}$cm$^{3}$.   

Localized Hartree-Fock density-functional calculation of atomic inner-shell excitation

We present a spin-dependent localized Hartree-Fock (LHF) density-functional theoretical (DFT) approach for the accurate calculation of the electronic energies of atomic inner-shell excited states. In this approach, electron spin-orbitals are obtained by solving Kohn-Sham (KS) equation with a spin-dependent LHF exchange potential and Lee-Yang-Parr correlation potential. A generalized pseudospectral (GPS) technique, allowing non-uniform spatial discretization, is used for high precision solution of the LHF-DFT equations. The method is applied to the study of the inner-shell excitation energies for both closed-shell (Be and Ne) and open-shell (Li, B, and O) atoms. Our calculated results are in very good agreement with available theoretical and experimental data.   

Non-Local Potentials in Density Functional Theory

There has been many unsuccessful efforts to accommodate the Hartree- Fock (HF) method into the Kohn-Sham (KS) scheme of the density functional theory. A great number of HF numerical calculations based on the KS method with local potentials demonstrated the impossibility of the accommodation but have not proven it. We have proven that the HF method cannot be reproduced within the framework of KS theory because the single-particle densities of finite systems obtained in HF calculations are not $v$-representable, i.e., do not correspond to any ground state of a non-interacting electron system in a local external potential $[1]$. As a result, while the kinetic energy of a finite electron system evaluated in the HF method is larger than that calculated in the KS scheme, the corresponding exchange energy is lower. However, the HF ground state energy is obviously the lowest. The problem with the HF method is the non-local nature of the HF potential, while the KS theory deals with local potentials and $v$-representable densities. For all other atoms, except the He atom, the HF potentials are non-local, so that the HF and the KS methods yield different results.\\ \\ $[1]$ M.Ya. Amusia, et al., Phys. Lett. A {\bf 330}, 10 (2004).   

Fast-beam laser spectroscopy of helium-like silicon and hydrogen-like nitrogen-towards improved precision

Using Doppler-tuned fast-beam laser spectroscopy and a high finesse build-up cavity excited by a 1319 nm Nd:YAG laser we previously measured the inter-combination 1$s$2$s \quad ^{1}$S$_{0}$-1$s$2$p \quad ^{3}$P$_{1}$ interval in Si$^{12+}$ to be 7230.5(2) cm$^{-1 }$[1]. The precision was limited by uncertainty in the velocity of the \textit{$\beta $ }$\sim $ 5{\%} ion beam. An order of magnitude higher precision would provide a clear test of calculations of QED contributions in two-electron ions. We aim to attain this by employing co- and counter-propagating beams and a dual wavelength high-finesse cavity. Work towards developing the necessary 1450 nm narrow-band laser will be presented. Work is also in progress on an improved measurement of the 2S$_{1/2}$-2P$_{3/2}$ fine structure - Lamb shift transition in N$^{6+}$[2]. Our aim is to test QED calculations relevant to the interpretation of high-precision spectroscopy of atomic hydrogen. Our new set-up uses two $^{13}$CO$_{2}$ lasers and a 5$^{o}$ interaction geometry. [1] M. Redshaw and E.G. Myers, PRL \textbf{88 }023002 (2002) [2] E.G. Myers and M. R. Tarbutt, in \textit{Hydrogen Atom, }edited by S.G. Karshenboim et al., Springer 2002.   

The Search for a Permanent Electric Dipole Moment of $^{199}$Hg

We will report on the search for a permanent electric dipole moment (EDM) of $^{199}$Hg. The existence of a nonzero EDM would imply a source of CP violation beyond the standard model. The present limit on the EDM of $^{199}$Hg is $|d(^{199}{\rm Hg})| < 2.1 \times 10^{-28} \,e\,{\rm cm}$.\footnote {M. V. Romalis, W. C. Griffith, J. P. Jacobs, and E. N. Fortson, Phys. Rev. Lett. {\bf 86}, 2505 (2001).} In that work, two quartz vapor cells containing polarized Hg vapor were placed in parallel magnetic and anti-parallel electric fields, and the spin precession frequencies were determined using an optical technique. An improved version of that experiment incorporates two additional Hg vapor cells that have no applied electric field. The new cells serve as magnetometers, cancelling noise due to magnetic field gradient fluctuations and providing an additional check on systematic effects. Our present efforts are focused on understanding the origin of a significant systematic effect that has led to spurious EDM-like signals. We will also discuss our measurement of a linear Stark interference effect that is a possible systematic for the EDM experiment (see other abstract, this meeting). Current results will be presented.   

High Power FBG Stabilized Precision IR Laser Source and Application to Convenient Second Harmonic Generation

A tunable high power single frequency IR laser source in the range of 965-985nm has been developed, with a focus on applications to high precision spectroscopy. A PM (polarization maintaining) single mode fiber coupled laser diode with 500mW output power is stabilized using a narrow linewidth PM-FBG. In this configuration, the laser has inherent short term stability ($<$20 kHz), while long term stability is obtained through feedback (piezo stretching), which enabled precise locking to an external interferometer. The PM fiber gives good polarization stability and the laser has reliable, mode-hop-free operation. This fiber coupled single frequency source is coupled into an single pass PPLN waveguide for frequency doubling. Measured single pass conversion efficiency of 100{\%} per Watt has been obtained, with results on a new nominal 300{\%} per Watt waveguide presented. High power ($>$100 mW input) scaling will be presented. A more efficient but less convenient alternative method using PPKTP in an enhanced build up cavity will also be discussed.   

Bound on Lorentz and CPT violations with the dual noble gas maser

We report recent measurements constraining CPT and Lorentz violation using the ${}^{129}$Xe/${}^3$He Zeeman maser and the current status of the maser. Experimental investigations of CPT and Lorentz symmetry provide important tests of the framework of the standard model of particle physics and theories of gravity. The two-species ${}^{129}$Xe/${}^3$He Zeeman maser sets stringent limit on rotation- and boost-dependent Lorentz and CPT violation involving the neutron, consistent respectively with no effect at the level of $10^{-31}$ GeV and $10^{-27}$ GeV. These results will be presented, along with a description of ongoing efforts to improve the masers' frequency stability.   

Alternative Theory for Special Relativity

It is evident to construct a new approach to the theory of special relativity by using tonsorial representation of mass and derive special relativity formulas from orthogonal symmetry of mat-quantum entities. This approach gives us the ability to understand the missing view of matter and lead us to construct fine structure of elementary particles and photons (mathematical model of electron and photon will be introduced in deferent articles.   

Bound nucleons have unique masses that govern elemental properties

It is known that measured binding energies associated with elements require equivalent energy to break the nuclear bond of a nucleus. Based upon the proposals contained in recent published works [1] [2] and with support from experimental high-energy data, it can be shown that a portion of listed binding energies are attributable to bound nucleons having a unique mass for every element. The figures show, relative to the hydrogen proton, that of the: a) 1.112 MeV binding energy per nucleon for 2H, 44{\%} or 0.486 MeV represents a change in mass ($\Delta $m) for the proton or neutron; b) of 5.629 MeV binding energy per nucleon for 7Li, 87{\%} or 4.890 MeV represents a change of mass for each nucleon; c) likewise, 56Fe has 8.811 MeV binding energy per nucleon and of this 92{\%} or 8.119 MeV represents a change in mass for each nucleon, and 232Th has 7.639 MeV binding energy per nucleon and of this, 90{\%} or 6.848 MeV represents a change in mass for each nucleon. This demonstrates that the nucleons of each element have unique masses. It has been shown that if three protons are removed from 82Pb the result is not 79Au; therefore, we conclude and predict that in addition to the Z number, elemental properties are determined by the unique proton and neutron masses for each element. megforce@physast.uga.edu [1] ``The Order of the Forces,'' [2] ``The Geatron Nuclear Model''   

Post ionization alignment effect in the fragmentation of molecules in an ultrashort intense laser feld

We studied the angular distributions of the fragmented ions of diatomic molecules in an intense linearly polarized short laser pulse. In addition to the well-known dynamic alignment of the neutral molecules before ionization, we identified a more important post ionization alignment effect of the molecular ions. The latter is modelled quantum mechanically as resulting from the breakup of a rotating linear rotor. We showed that only for very short pulses are the two alignment mechanisms not important. In this case the angular distributions of the fragmented ions mimic the shape of the electronic density of the outermost molecular orbital. Thus for the first time, it is possible to directly observe the electron cloud distribution of a molecular orbital experimentally without the complications from the final states. This work was supported in part by the US DOE.   

Empirical formula for the static field ionization rates of atoms and molecules by lasers from the tunneling to the barrier-suppression regime

We propose an empirical formula for the static field ionization rates of atoms and molecules by extending the well-known analytical tunneling ionization rates to the barrier-suppression regime. The proposed empirical formula can provide accurate ionization rates for atoms and molecules in the intense laser field under the single active electron approximation. The theory can be used to study highly nonlinear phenomena such as high harmonic generation, above threshold ionization and the dissociation dynamics of molecules by intense lasers beyond the usual tunneling ionization regime. The empirical formula retains the simplicity of the original tunneling ionization rate expression but can be used to calculate ionization rates of atoms and molecules by lasers at high intensities. This work was supported in part by the US DOE.   

Dissociation and ionization of H$_{2}^{+}$ in intense femtosecond laser fields studied by coincidence 3D momentum imaging

Dissociation and ionization of H$_{2}^{+}$ in intense laser fields have been measured simultaneously using a coincidence 3D momentum imaging method. The H$_{2}^{+}$ beam is crossed by a laser beam (45-135 fs, 790 nm, 10$^{13}$-10$^{15}$ W/cm$^{2})$, and the momentum of each fragment in H$^{+}$+H and H$^{+}$+H$^{+}$ is determined. The angular and kinetic energy release spectra are obtained. At similar intensities, the dissociation mechanisms in long and short pulses are found to be quite different, dominated by bond-softening and above threshold dissociation, respectively. The ionization of H$_{2}^{+}$ becomes measurable from about 2$\times $10$^{14}$ W/cm$^{2}$, increases rapidly with laser intensity, and aligns strongly along the laser polarization with a broad kinetic energy distribution. The overall ionization to dissociation ratio is less than previously predicted by theory.   

Optimizing Transient Laser Alignment of Diatomic Molecules

Intense, short laser pulses have been used to transiently align diatomic molecules for use as targets in subsequent strong-field experiments. The laser induces a series of Raman transitions within each molecule, forming a rotational wavepacket that exhibits periodic angular localization along the laser polarization axis [1]. We probe this alignment by exploding the molecule using a more intense, time-delayed circularly polarized 30 fsec 780 nm pulse, and measuring the momenta of the multiply charged ion fragments using a mass spectrometer equipped with a helical wire-anode detector. We have observed transient alignment in N$_{2}$, O$_{2}$, and CO and find that the use of multiple laser kicks, with appropriate relative delays, can significantly enhance the degree of alignment while reducing the level of ionization. We are now using transiently aligned targets to compare intense laser ionization rates for atoms with those for molecules aligned parallel or perpendicular to the laser polarization [2]. In addition we are exploring the use of a laser pulse-shaper and genetic feedback algorithm [3] to further enhance alignment efficiency through a closed-loop optimization of the aligning pulse shapes. This work is supported by DOE BES and the UVa FEST. [1] H. Stapelfeldt and T. Seideman, Rev. Mod. Phys. \textbf{75, }543 (2003). [2] I.V. Litvinyuk et al., Phys. Rev. Lett. \textbf{90}, 233003 (2003). [3] B.J. Pearson et al., Phys. Rev. A \textbf{63}, 063412 (2001).   

Generalized Oscillator Strengths for Multipole Transitions in $I^{-}$ and $Si^{-}$

Generalized oscillator strengths for monopole, dipole and quadrupole transitions in the negative ions $I^-$ and $Si^-$ are investigated using the one-electron Hartree-Fock approximation and with many-electron correlations taken into account through the random phase approximation with exchange. Results are obtained for values of the momentum transfer $q$ varying from 0.1 to 2 {\it a.u.} and energy transfer $\omega$ from 0 through 8~Ry. We find that correlations are particularly significant in the monopole and dipole transitions, impacting both the magnitude and shape of the characteristic maxima as well as their positions relative to those obtained in the HF approximation.   

Inner-shell Photodetachment from Li$^{-}$ and C$^{-}$

Photodetachment from the K-shell of Li$^{-}$ and C$^{-}$ has been investigated using the merged ion-photon beam technique on the Advanced Light Source Beamline 10.0.1. Photoexcitation and detachment of 1$s$ electrons leaves the neutral atoms in core-excited states that subsequently Auger decay to produce positive ions which are detected as a function of photon energy. Recent experiments yield higher resolution spectroscopy than our previous studies [1,2] and provide new measurements of the absolute cross sections for double detachment. Several resonances are investigated for Li$^{-}$ in the photon energy range 57-66 eV, while the spectrum for C$^{-}$ shows one prominent resonance near 281.8 eV. Comparisons of the cross sections, the character of observed resonances, and the effects of post-collision interactions will be discussed. [1] N. Berrah \textit{et al.}, Phys. Rev. Lett. \textbf{87}, 253002 (2001); [2] N.D. Gibson \textit{et al.}, Phys. Rev. A \textbf{67}, 030703 (2003).   

Inner Shell Studies of Negative Ions

The peculiar binding potential in negative ions leads to structure and spectra significantly different from their atomic and positive ion cousins, including for example the absence of Rydberg series. In addition, the highly correlated ground and excited states formed in negative ions offer stringent tests of the latest high-level theoretical models of electron correlation, and close interaction between these theories and basic experiments can elucidate processes of importance in may fields. A summary of recent experiments lead by our team on BL 10.0.1 IPB at the ALS will be presented. These include studies targeting the prototypical He negative ion [1], investigations of the unusual near-threshold cross section onset of negative ions, including demonstration of the Wigner threshold law angular momentum dependence, observation of multi-electron ejection leading to high charge-state products, and inner-shell studies of cluster negative ions. This work is funded by DOE, BES. We would like to thank B.S. Rude for his timely and valuable help during these experiments. [1] R. C. Bilodeau et al., Phys. Rev. Lett. 93, 193001 (2004).   

K-Shell Photodetachment of Excited C$^{-}$

Photodetachment of K-shells of negative ions have been of significant interest, both experimentally and theoretically [1-3], with a variety of new phenomenology uncovered. The phenomenology is due largely to the elastic and inelastic collisions suffered by the inner-shell photoelectron in exiting the system through the electron cloud formed by the outer-shell electrons. It is, thus, of interest to investigate how the K-shell photodetachment is changed when the outer-shell electron cloud is altered, i.e, when the negative ion is in an excited state. C$^{-}$ is one of the few negative atomic ions with a bound excited state. The ground state is 1s$^{2}$2s$^{2}$2p$^{3} \quad ^{4}$S and the excited state is the $^{2}$D multiplet of the same configuration. Calculations of the photodetachment cross section for this excited state of C$^{-}$ have been performed and compared with previous work on the ground state of C$^{-}$ [4,5]. Significant differences are found. This work was supported by DOE, NSF, NASA and IDRIS. [1] N. Berrah, \textit{et al}, Phys. Rev. Lett. \textbf{87}, 25300 (2001). [2] N. Berrah, \textit{et al}, Phys. Rev. Lett. \textbf{88}, 093001 (2002). [3] H. Kjeldsen, \textit{et al}, J. Phys. B \textbf{34} L353 (2001). [4] H.-L. Zhou, S. T. Manson, L. VoKy and A. Hibbert, Bull, Am. Phys. Soc. \textbf{48}, 97 (2003). [5] N. D. Gibson, \textit{et al}, Phys. Rev. A \textbf{67}, 030703 (2003).   

Photodetachment of Excited C$^{-}$: Angular Distributions

Calculations of the of the dipole photoelectron angular distribution parameter, $\beta $, resulting from the photodetachment of the excited 1s$^{2}$2s$^{2}$2p$^{3} \quad ^{2}$D state of C$^{-}$ have been performed using a modified R-matrix formalism [1] covering the photon energies from threshold to 11 eV, a region that includes transitions to 13 states of neutral carbon; $\beta $ has been obtained for each of them. The states investigated are: 1s$^{2}$2s$^{2}$2p$^{2} \quad ^{3}$P, 1s$^{2}$2s$^{2}$2p$^{2}$ $^{1}$D, 1s$^{2}$2s$^{2}$2p$^{2} \quad ^{1}$S, 1s$^{2}$2s$^{2}$2p3s $^{3}$P, 1s$^{2}$2s$^{2}$2p3s $^{1}$P, 1s$^{2}$2s2p$^{3} \quad ^{3}$D, 1s22s2p$^{2}$3s $^{1}$P, 1s$^{2}$2s$^{2}$2p3p $^{3}$D, 1s$^{2}$2s$^{2}$2p3p $^{3}$S, 1s$^{2}$2s$^{2}$2p3p $^{3}$P, 1s$^{2}$2s$^{2}$2p3p $^{1}$D, 1s$^{2}$2s$^{2}$2p3p $^{1}$S, and 1s$^{2}$2s2p$^{3}$P. Three of the transitions, the ones to the $^{1}$S and $^{3}$S states of carbon, are parity-unfavored [2], i.e., $\beta $ = -1, independent of energy. For the other ten channels, there are significant variations with energy reflecting both the variation of the magnitudes of the dipole matrix elements with energy, along with the variation of their phases. For the transition to 1s$^{2}$2s$^{2}$2p$^{2} \quad ^{3}$P, there exists a measurement at a single energy [3], and agreement with the calculation with the experimental point is quite good. This work was supported by DOE, NSF and IDRIS. [1] H.-L. Zhou, \textit{et al}, Phys. Rev. A \textbf{70}, 022713 (2004) and references therein. [2] S. T. Manson and A. F. Starace, Rev. Mod. Phys. \textbf{54}, 389 (1982). [3] D. J. Pegg, C. Y. Tang, J. Dellwo and G. D. Alton, J. Phys. B \textbf{26}, L789 (1993).   

Dramatic Distortion of the $4d$ Giant Resonance by the $C_{60}$ Fullerene Shell

Giant resonances are universal features of the excitation of finite many-fermion systems: nuclei, atoms, fullerenes, and clusters. They represent collective, coherent oscillations of many particles and, most prominently manifest themselves in photon absorption cross sections or in the so-called "zero" sound in Fermi-liquids. The photoionization cross section for the endohedral Xe$@C_{60} $ atom is investigated within the framework of representing the $C_{60} $ by a delta-type potential. Results demonstrate that in Xe$@C_{60}$ the $4d^{10}$ giant resonance is distorted significantly when compared with that of the isolated Xe atom. The reflection of the photoelectron waves by the $C_{60}$ causes strong oscillations in the photoionization cross section resulting in the replacement of the Xe $4d$ giant resonance by four prominent peaks. The approximation of the $C_{60}$ by an infinitely thin real potential preserves reasonably well the sum rule for the $4d$ electrons but modifies the dipole polarizability of the $4d$ shell.   

R-matrix with Intermediate Coupling Frame Transformation Calculation of the Spin-Orbit Interactions in Ar Photoionization

Motivated by the recent observation of the giant spin orbit interactions in Ar photoionization [1], we have performed a highly-correlated R-matrix multichannel quantum defect theory (MQDT) along with a term-coupled LS-JK frame transformation method to account for fine structure effects. Briefly, it was found in [1] that the cross sections for the LS forbidden $3p^4[^3P]4p$ $^4D^o_{1/2}$ and $3p^4[^3P]4p$ $^4D^o_{3/2}$ states were 16 to 30 times larger than those for the LS-allowed doublet states, indicating strong relativistic effects. A comparison of the experimental results with our LS and $LS-JK$ frame transformation R-matrix calculations will be presented and the nature of the effects responsible for the observed spectra elucidated. \begin{enumerate} \bibitem{1} D. H. Jaecks, O. Yenen, K. W. McLaughlin, S. Canton, J. D. Bozek and M. Downsbrough, Phys. Rev. A {\bf 70}, 040703(R) (2004). \end{enumerate}   

A theoretical and experimental study of the photoionization of Al$^+$.

High resolution photoionization cross section measurements have been made at ALS, corresponding to the $2p$ excitation (photon energy $>$80eV) of the Al$^+$ ground state $2p^63s$. These, with absolute measurements from ASTRID [1] for energies 20-160eV, are compared to data from R-matrix calculations. In the near threshold region ($<$25eV), theory detects two $3pns\,^3P^{\rm o} $ resonance series, a $3pns\,^1P^{\rm o}$ and a $3pnd\,^1P^{\rm o}$ series. The experiment [1] detects a single $3pns$ series and we find excellent agreement with the theoretical positions. Above the $2p$ ionization threshold, the ALS data shows much more detail and by comparing with oscillator strengths and resonance positions from the calculation we identify much of the resonant structure. [1] West et al, 2001, PRA 63, 052719   

Shape variation of the two-electron photoionization spectrum with photon energy growth

We trace the evolution of the energy spectrum of both outgoing electrons emitted after absorption of a single photon with the latter's energy growth. We use quite precise non-variation two-electron initial state wave functions, obtained by Correlation Function Hyperspherical Harmonic Method. We obtain the values of $\omega_{1}$ and $\omega _{2}$ at which the spectrum curve changes it shape. At $\omega =\omega _{1}$ the usually considered $\mathbf{U}$-shape changes to $\mathbf{W}$-shape. At $\omega =\omega _{2}$ the central $\mathbf{W}$ peak splits into two. We consider ground states of the helium atom and of helium-like ions with the nuclear charge $Z$, the negative ion of hydrogen H$^{-}$ and the excited $n^{1}S$ state of helium. The limiting laws for $Z\gg 1$ and $n\gg 1$ are obtained. The analysis is carried out without calculations of the particular energy distributions. We believe that the predicted features could be observed experimentally detecting both outgoing electrons in coincidence.   

K-Shell Photoabsorption in O, Ne, Mg, Si, and S Ions

We report on new photoabsorption calculations for neutral and ionized elements of importance for X-ray astronomy observations. Within our R-matrix calculations, spectator Auger broadening effects are taken into account by using an optical potential, and core relaxation is included by using pseudoorbitals and a pseudoresonance elimination method. The resultant photoabsorption cross sections are used in modeling of observed spectra from distant sources to predict elemental abundances in the interstellar medium.   

Study of spin-orbit resolved angular distribution components of Xe 5p.

The role of relativistic effects and interchannel coupling for spin-orbit resolved mainlines has been described successfully with the relativistic random phase approximation (RRPA) for photoemission experiments within the dipole approximation. Nondipole photoemission experiments near the Xe 4p thresholds hold a new challenge for theory especially for the Xe 5p photolines. Angular distribution parameters $\beta $ and $\xi $ = 3$\delta +\gamma $ for the xenon 5$p_{1/2}$ and 5$p_{3/2}$ photoelectrons have been measured at the Advanced Light Source in the 80--220 eV photonenergy range. The results are compared with RRPA calculations [1] and experimental data [2]. Even though both experimental data sets agree well with theory for the dipole parameter $\beta $ both sets of experimental results show a fairly large disagreement with RRPA calculations [1] for the nondipole results. More interestingly, both experimental data sets do not agree with each other. This shows that there are still open questions that need to be addressed by experimenters and theorists. [1] W.R. Johnson and K.T. Cheng, Phys. Rev. A \textbf{63}, 022504 (2001). [2] R. Sankari, S. Ricz, A. Kover, M. Jurvansuu, D. Varga, J. Nikkinen, T. Ricsoka, H. Aksela, and S. Aksela Phys. Rev. A \textbf{69}, 012707 (2004).   

First measurements of macroscopic drag currents under the action of photon flux

Until recently, it was believed that photoelectron angular distributions of atoms and molecules at photon energies below 1 keV is well described by the dipole approximation. While this is true for the angle-integrated total and partial cross sections to which only the squares of the transition matrix elements contribute, recent calculations and measurements [1] have shown that nondipole effects can strongly influence the differential cross sections. These nondipole effects lead to a forward-backward asymmetry in photoelectron emission resulting in a net flux of electrons parallel or anti-parallel to the photon propagation direction. The integrated flux can be measured as a macroscopic current called drag current [2]. With our new instrument we were able to measure these drag currents on a variety of gases such as Ne, Xe, and N$_{2}$ in the photonenergy range between 80 and 240 eV. Our results show that drag currents are non-negligible electron transport processes even at low photon energies. This may be of importance to fields such as astrophysics or physics of the upper planetary atmospheres. [1] O. Hemmers, R. Guillemin, D.W. Lindle, Rad. Phys. Chem. \textbf{70}, 123 (2004). [2] M.Ya. Amusia, A.S. Baltenkov, L.V. Chernysheva, Z. Felfli, A.Z. Msezane, and J. Nordgren, Phys. Rev. A \textbf{63}, 052512 (2001).   

Double-Excited States of Mg below the Mg$^+$(3p) Threshold

The photoionization process from the valence shell of alkaline earth atoms just above the first ionization threshold shows clear deviation from the simple one-electron picture. This is due to electron correlations between the two outer electrons, which can be simultaneously excited into states above the first ionization limit. It is well known that in the energy region between the first and second ionization threshold the spectra are dominated by two double-excitation series, one broad ($npms$ $^1$P$_1$, $m>n$) and one narrow ($npmd$ $^1$P$_1$, $m \ge n$) series. For Mg it was predicted \footnote{V.\ Radojevi\'c and W.\ R.\ Johnson, Phys.\ Rev.\ A {\bf 31}, 2991 (1985).} that a weaker autoionization series ($npms$ $^3$P$_1$, $m > n$) will be superimposed on the broad resonance series due to the onset of relativistic effects and, thus, the breakdown of the $LS$ coupling scheme for Mg. Using highly monochromatized synchrotron radiation, we have found clear evidence for this weak series and will present improved resonance parameters for the autoionizing resonances.   

Angular anisotropy parameters for photo-detachment of negative ions

Dipole and nondipole angular anisotropy parameters are investigated in photoionization of negative ions first by deriving general analytical expressions for their near-threshold behavior and then performing numerical calculations for the outer and intermediate subshells of the negative ions $I^-$ and $Si^-$. The results are compared with those of their respective isoelectronic neighbors, Xe and P. The calculations are performed within the one-electron Hartree-Fock approximation and with many-electron correlations considered using the random phase approximation with exchange. The derived analytical expressions for the parameters are used to check the accuracy of our numerical results as well as to demonstrate the range of validity of the Wigner threshold law for negative ions. Differences and similarities in the behavior of the dipole and nondipole parameters for the negative ions and neutral atoms are demonstrated and discussed.   

Observation of very long-lived entanglement

Arbitrary atomic Bell states with two trapped ions are generated in a deterministic and preprogrammed way. The resulting entanglement is quantitatively analyzed using various measures of entanglement. For this, we reconstruct the density matrix using single qubit rotations and subsequent measurements with near-unity detection efficiency. This procedure represents the basic building block for process tomography of quantum computations. As a first application, the temporal decay of entanglement is investigated in detail.We observe ultralong lifetimes for Bell states, close to the fundamental limit set by the spontaneous emission. Furthermore, if we encode the Bell states in ground state sublevels, this limit can be evaded and entanglement can be maintained for over 10 seconds.   

Entangled and disentangled evolution for a single atom in a driven cavity

For an atom in an externally driven cavity, we show that special initial states lead to near-disentangled atom-field evolution, and superpositions of these can lead to near maximally-entangled states. Somewhat counterintutively, we find that (moderate) spontaneous emission in this system actually leads to a transient increase in entanglement beyond the steady-state value. We also show that a particular field correlation function could be used, in an experimental setting, to track the time evolution of this entanglement.   

Nantennae: Far-field fluorescence decay rate modulation in pairs of oriented semiconducting polymer nanostructures

We report fluorescence lifetime measurements on pairs of uniformly z-oriented polymer nanostructures that reveal far-field coherent coupling persisting on a distance scale of several optical wavelengths. Far-field photonic coupling between pairs of oriented luminescent polymer nanostructures is manifested by an oscillatory modulation in the fluorescence decay rate as a function of interparticle distance (both enhancement and inhibition of spontaneous luminescence relative to isolated particles), that results from modification of the vacuum field at the position of the probe dipole by the presence of the second radiating dipole. These results provide the first observation of a dipole-dipole interaction in the ``inductance'' interparticle distance scale between the near-field ($\approx $ 200 nm) and far-field ($>$ 500 nm), realized in an easily scalable solid-state format at room temperature, important for the realization of efficient nanophotonic devices.   

High-Contrast Interference in a Thermal Cloud of Atoms

The coherence properties of a gas of bosonic atoms above the BEC transition temperature were studied. Bragg diffraction was used to create two spatially separated wave packets, which interfere during expansion. Given sufficient expansion time, high fringe contrast could be observed in a cloud of arbitrary temperature. Fringe visibility greater than 90{\%} was observed, which decreased with increasing temperature, in agreement with a simple model. When the sample was ``filtered'' in momentum space using long, velocity-selective Bragg pulses, the contrast was significantly enhanced in contrast to predictions.   

Improved measurement of atomic recoil frequency using atom interferometry

We have recently used a single state time domain atom interferometer to make a measurement of atomic recoil frequency in cold $^{85} Rb$ atoms precise to 2.5 ppm. The interferometer involves excitation by off-resonant standing wave pulses applied at $t=0$ and $t=T$. The pulses diffract and recombine a superposition of momentum states corresponding to the same internal state. This results in a population grating ``echo'' in the vicinity of $t=2T$. The grating was detected using an off resonant readout pulse. This pulse results in a backscattered signal detected using a heterodyne technique. Our measurement of the recoil frequency is in excellent agreement with the value of the recoil frequency obtained from previous measurements of the transition wavelength, atomic mass, and Planck's constant. We present improved measurements using PMT detection, reducing the effect of magnetic field gradients, and increasing the spatial extent of our interferometry beams. We also investigate the role of collisions between hot and cold $^{85} Rb$ atoms on the lifetime of our echo signal and discuss the precision that can be achieved using an atomic fountain.   

A precision measurement of atomic recoil frequency using grating

We have used a time domain atom interferometer to measure the atomic recoil frequency to a precision of 2.5 parts per million by manipulating trapped $^{85}$Rb atoms in the F=3 ground state. Our studies confirm that the measurement is insensitive to a range of common systematic effects such as AC Stark shifts, strength of the atom field coupling, magnetic fields, field gradients and the distribution of atoms in the magnetic sub-levels of the ground state. The measurement is in excellent agreement with the recoil frequency inferred from previous measurements of transition wavelength and the atomic mass. Our studies suggest that significant improvements can be achieved in an atomic fountain. We also discuss measurements of gravity and sensitivity to magnetic field gradients.   

Measurement of $^{85}Rb$ excited state lifetime using two-pulse photon echo

We have observed two-pulse photon echoes in a Doppler broadened rubidium vapor. The system interacts with traveling wave optical pulses that are $\sim10 ns$ in duration. The pulses are on resonance with the $F=3 \rightarrow F'=4$ transition in $^ {85}Rb$ and they are generated from a cw laser using an acousto- optic modulators. The first pulse, occurring at $t=0$, induces a macroscopic dipole moment that dephases due to atomic motion. The second pulse, occurring at $t=T$, reverses the direction of the dephasing process so that the echo is formed at $t=2T$. The echo is detected using a heterodyne tehnique and its intensity decays exponentially as a function of $2T$. Our results suggest that the excited state lifetime can be determined to a precision of $\sim1$ $\%$ from the decay time constant. We present a detailed analysis of the systematic effects that contribute to the decay.   

Magnetic media for atomic diffraction

We are investigating the use of magnetic data recording media as an atomic diffraction grating. In order to optimize the visibility of diffraction order fringes we model the scattering of a thermal MOT cloud from the grating. We treat separately the region far from the grating where gravity dominates and the region near the grating where the magnetic field dominates. Thermal spreading is reduced by a combination of focusing (using a curved grating) and gravitational acceleration (which reduces the relative momentum spread of atoms incident upon the grating). Preliminary experimental scattering results from our rubidium MOT apparatus are presented. This work was supported by the American Chemical Society.   

Guiding atoms in a hollow-core photonic bandgap fiber

We discuss the current progress of our experiment to guide rubidium atoms in hollow-core photonic bandgap fiber. The atoms are contained within the hollow region of the fiber by the dipole potential created with a strong red-detuned laser. This technique has several significant advantages over other atom guiding experiments using hollow core fiber. First, the design of the air/silica structure allows low attenuation propagation ($<$ 0.1 dB/m) at certain wavelengths down the hollow core. As a result, the optical potential is uniform over the length of the fiber. Also, the light field is almost exclusively inside the hollow core, and it is relatively easy to couple light into the fiber. Since the field inside the fiber can be relatively high, it is possible to detune the laser far from resonance while maintaining a strong dipole potential, and thereby greatly reduce the scattering rate. We acknowledge support from the Air Force Office of Scientific Research and the National Science Foundation under Grant No. 0355202.   

Design and Construction of a Ca/Sr Atom Interferometer

We are constructing a Ca/Sr dual species atom interferometer. We expect to achieve a high degree of common-mode drift cancellation by overlapping atomic and laser beams and tuning the effective velocity of each atomic beam via the Ramsey ``pulse area.'' The device will also feature the use of precision prisms for stable alignment and cancellation of and stabilization of various systematic shifts. As part of this project we have developed a new external-cavity diode laser stabilization scheme, a low-cost high-accuracy method of testing prism deflection angles, and a high temperature vapor cell. We are currently working to lock our lasers to ultra-high finesse optical cavities to achieve Hz-level short term stability.   

Atomic clocks based on adaptive phase measurements with entangled atoms

We show that the frequency stability of atomic clocks limited by local oscillator frequency fluctuations [1] can be greatly improved by using an adaptive measurement strategy with entangled atoms. Our method uses multiple atomic sub-ensembles with various degrees of spin-squeezing and sequential adaptive measurements of the Ramsey phase. With properly optimized degree of squeezing, this method reaches the Heisenberg limit for phase measurements $\delta\phi\simeq 1/N$, where $N$ is the number of atoms. In addition, we show that multiple interrogation times for these sub-ensembles can be used to improve the long-term stability of the clock. This method allows one to use a very long interrogation time, limited only by environmental fluctuations. The combination of the above two methods leads to an ultimate long-term frequency stability of the clock scaling as $\sigma_y(\tau)=\frac{\langle\delta{\bar \omega}(\tau)^2\rangle^{1/2}}{\omega_0}\propto\frac{1}{N\tau}$, where $\tau$ is the averaging time, to be compared with the usual projection-noise limited clock stability scaling as $\sigma_y(\tau)\propto \frac{1}{\sqrt{N\tau}}$. [1] A. Andr\'{e}, A. S. S\o rensen, and M. D. Lukin, Phys. Rev. Lett. {\bf 92}, 230801 (2004).   

Noise diagnostics using one-dimensional quantum cellular automata

We study propagation of correlated errors during quantum simulation due to global pulse errors. Our model system consists of a one dimensional alternating array of two distinct species (or subspaces) of atoms distributed in n lattice sites with a nearest neighbor Ising-type interaction. Time evolution is generated according to a set of quantum cellular automata (QCA) rules which can be implemented through application of global control pulses on either species. We characterize the fidelity for generating entangled states and discuss how to use the system as a sensitive detector of environmental noise. We discuss how to build an architecture suitable for ensemble QCA experiments using a two-dimensional optical lattice.   

Scalable architecture for solid state quantum computation

Solid state approaches to quantum computation offer intriguing prospects for large scale integration and long term stability. Most of the current approaches restrict the computation to nearest-neighbors interactions. This condition generally decreases thresholds for fault tolerant computation. We explore the prospects for improving the scalability of solid-state quantum computation schemes via cavity QED on chip or long range transport of electron spin, and consider analogies between solid-state computation and scalable architectures for ion-based computation. Specifically we investigate dominant sources of errors in electron spin transport and study techniques to purify and correct these errors. Finally, we discuss several approaches for long-lived storage of electronic spin qubits and investigate novel architectures that utilize these resources for scalable quantum computation.   

Magnetic Field Effects on Pure-state and Thermal Entanglement of Anisotropic Magnetic Nanodots

Anisotropic magnetic nanodots have recently been proposed as promising candidates for qubits for scalable quantum computing [1,2]. The main advantages of such magnetic qubits are their well-separated energy levels (which may allow operation at temperature of the order of a few K), nanometer size (which simplifies fabrication), and large spin values (which facilitates measurement of qubit states). The entanglement properties of eigenstates of a pair of Heisenberg-interacting nanodots have been analyzed in [2], where we have shown that ferromagnetic (FM) coupling produces two significantly entangled excited states. Here we investigate the magnetic field effects on the entanglement of these and other states. We show that entanglement of excited FM eigenstates of two non-identical nanodots can be tuned to its maximum value by applying a relatively weak non-uniform magnetic field. [1] J. Tejada, E.M. Chudnovsky, E. del Barco, J.M. Hernandez, and T.P. Spiller, Nanotechnology {\bf 12}, 181 (2001). [2] R. Skomski, A.Y. Istomin, A.F. Starace, and D.J. Sellmyer, Phys. Rev. A {\bf 70}, 062307 (2004).   

Fault-tolerant Quantum Communication Based on Solid-state Photon Emitters

We describe a novel method for long distance quantum communication in realistic, lossy photonic channels. The method uses single emitters of light as intermediate nodes in the channel. One electronic spin and one nuclear spin degree of freedom associated with each emitter provide quantum memory and enable active error correction. We show that these two degrees of freedom, coupled via the contact hyperfine interaction, suffice to correct arbitrary errors, making our protocol robust to all realistic sources of decoherence. The method is particularly well suited for implementation using recently-developed solid-state nano-photonic devices, and we discuss preliminary experimental investigations using nitrogen-vacancy centers in diamond.   

Universal quantum computing with a multi-qubit device with untunable always-on coupling

We present a method to implement universal one-bit and two-bit quantum logical gates in a two-qubit device with fixed always-on coupling. In this method the one-bit gate is decomposed into two conditional two-bit gates that are implemented by local manipulations similar to those for the two-bit gates. We demonstrate, by implementing one-bit NOT gate and creating Bell states, that this method can be realized in rf-driven inductively coupled two SQUID flux qubits with realistic device parameters. This method is simple, does not need any additional hardware resources, and can be readily extended to multi-qubit logical gates required for scalable quantum computation.   

Determining a quantum state in a subspace with a single apparatus

We suggest a protocol for determining an unknown quantum state in a subspace using a single apparatus within an enlarged Hilbert space. This constitutes a positive operator valued measurement (POVM) scheme, where the large Hilbert space comes from a direct sum of a complementary subspace and the system's subspace, rather than from the conventional direct product of the Hilbert space of an ancilla (a subsystem) with that of the system. We propose an experimental implementation using a multi-level atom interacting with laser fields.   

Quantum Simulations with Trapped Ions

A quantum simulator is necessary for solving many-body quantum problems that would be intractable using a classical computer, even with advanced numerical techniques. Quantum simulators can solve only a limited set of problems, but building one would represent an important milestone in the road to universal quantum computation. We are using an array of strontium ions confined in a linear rf trap to build a multi-body quantum simulator. In our experiment, each ion simulates a single spin system, while Coulomb and optical forces simulate spin-spin interactions and magnetic fields. This system can simulate the most basic models of condensed matter physics: the Ising model and the XYZ Heisenberg model. We are building more complex ion traps that will let us work with many more ions, and with two-dimensional arrays of ions. Ultimately, these systems will show us how to perform complex simulations in two dimensions, investigate new ordered states of matter, and further develop technology for a universal quantum computer.   

Generalization of the one-qubit Bloch Sphere for the two-qubit SU(4) dynamic group

The common definition of the Bloch Sphere is based on the isomorphism of su(2) and so(3) Lie algebras. We generalize the Bloch construction to the case of the SU(4) group using the Lie group isomorphism SU(4)$\cong $Spin(6). Since Spin(n+1)/Spin(n)=S$^{n}$, the associated chain of subgroups Spin(3) $\subset $ Spin(4) $\subset $ Spin(5) $\subset $ Spin(6), embedded in the SU(4) group, allows a natural identification of a set of spheres invariant under the adjoint SU(4) action. An alternative route, using the Lie group isomorphism so(4) $\cong $su(2)$\times $su(2) and a canonical Cartan decomposition, is also discussed.   

Progress Towards Trapped-Ion Quantum Information Processing at McMaster University.

We are constructing a trapped-ion quantum information processor to explore quantum computing technology and applications and general quantum state engineering. In particular, we will trap $^{24}$Mg$^{+}$ and $^{25}$Mg$^{+}$ ions in a linear RF (Paul) trap geometry. We will use the ground-state hyperfine levels of the $^{25}$Mg$^{+}$ ions as internal-state qubits and the ions' shared motional degree of freedom as a ``quantum data bus.'' We discuss progress in constructing the apparatus, including an all-solid-state source of 280-nm UV laser light.   

Laser Cooling of Erbium Atoms

We have identified five closed, or nearly-closed, $J\to J $+ 1 transitions in atomic erbium at wavelengths of 401 nm, 583 nm, 631 nm, 841 nm, and 1299 nm. These transitions can be reached by common tunable single-frequency laser systems, and are thus in principle suitable for laser cooling. The 401 nm and 583 nm lines have known natural lifetimes of 5.8 ns and 0.96 $\mu $s, respectively, but the lifetimes of the 631 nm, the 841 nm and the 1299 nm lines have not been investigated to date. We have performed measurements of the 631 nm and 841 nm lines and have determined their lifetimes to be (5.6 $\pm $ 1.4) $\mu $s and (20 $\pm $ 4) $\mu $s, respectively. Calculations of the 1299 nm line lifetime will also be presented. Knowing these lifetimes, we can predict that precooling on the 401 nm line together with narrowband cooling on the 841 nm line should produce temperatures approaching a recoil limit of 80 nK. Such cold temperatures, in combination with erbium's large magnetic moment and atomic mass, will allow studies of magnetic trapping deep in the quantum regime and of cold collisions with strong dipole-dipole interactions. Applications include atomic frequency standards, quantum information processing, and deterministic atom-by-atom doping of optically active materials.   

Properties of Multiple Adiabatic Rapid Passage Sequences

Multiple repetitions of adiabatic rapid passage (ARP) sweeps can enable huge optical forces on atoms with light beams of different $\vec{k}$-vectors. Alternation of the ARP-induced atomic inversion can coherently transfer momentum between the beams, thereby imparting the difference $\hbar \overrightarrow{\Delta k}$ to the atoms. When the rate of these sweeps $\omega_m \equiv 2\pi/T \gg \gamma$, $F_{ARP} \sim \hbar k \omega_m/\pi \gg \hbar k \gamma/2$, the usual radiative force that has been used for laser cooling since the early 1980's. We have expanded on our earlier studies\footnote{M. Cashen et al., J. Opt. B: Quant. Semiclass., {\bf 4}, 75 (2002).} of ARP forces. Since the process is more efficient if the start and end points of $\vec{\Omega}(t)$ are closer to the polar axis of the Bloch sphere, we consider a pulse whose frequency sweeps through atomic resonance. Each cycle consisting of two pulses changes the initial Bloch vector $\vec{R}(t)$ to $\vec{R}(t+T) \equiv \hat{U}[t,\vec{\Omega}(t)] \vec{R}(t)$ where the operator $\hat{U}$ depends on the laser sweep parameters. We show that $\hat{U}$ simply rotates the Bloch vector, and we view this as a rotation of the Bloch sphere instead. Thus a sequence of periodic pulses is just a sequence of identical rotations. Even with a small non-adiabatic transition probability during each sweep, the sequence of $\vec{R}(nT)$'s is bounded on a small circle near the South pole ($n$ = integer). Thus the force still adds coherently.   

Measurement of Excited State Fraction in a MOT versus Laser Detuning

A reliable model-independent, semi-empirical method for determining the excited state fraction in a magneto-optical trap is demonstrated. This method does not rely on fluorescence; the excited state fraction is measured directly using Magneto-Optical Trap Recoil Ion Momentum Spectroscopy (MOTRIMS). The MOTRIMS technique uses an ion beam as a probe of the internal states of the trapped atoms, and the excited-state fraction emerges directly from this ``$Q$-value'' measurement. Experimental results are compared with theoretical models.   

A Bright Metastable Helium Beam for Neutral Atom Lithography

We have used non-monochromatic light to produce large optical forces over a wide range of atomic speeds, e.g., slowing a beam of metastable helium (He*)\footnote{M. Cashen and H. Metcalf, {\it J. Opt. Soc. Am. B} \textbf{20}, 915 (2003). }. Our He* beam has now been brightened by active collimation\footnote{M. Partlow et al., {\it Phys. Rev. Lett.} \textbf{93}, 213004 (2004). } using large transverse bichromatic forces on the $2^{3}S_{1} \rightarrow 2^{3}P_{2}$ transition at $\lambda = 1083$ nm. An LN$_{2}$ cooled discharge source yielding $10^{14}$ atoms/sr-s with $\overline{v} \approx$ 1000 m/s forms the beam. We have captured atoms from a transverse velocity range of $\pm$ 87 m/s (175 mrad cone) in an interaction length of only 5 cm comprised of four interaction regions. The collimated beam has an integrated flux of $1.4\times10^{11}$ atoms/s and thus contains $\sim1/4$ of the total source output. Further collimation with a subsequent optical molasses yields an overall increase in brightness by a factor of 4100. Small improvements to the collimation will produce a flux density high enough to expose a resist for atomic nanolithography in less than one minute. The bichromatic detuning was $\delta = \pm 2\pi \times 60 \,{\rm MHz}\, (\pm 37\gamma)$. For this $\delta$, the bichromatic force is optimum for $I \sim 0.7$ W/cm$^{2}$ (4100 $\times I_{sat}$) for each of four frequencies. The light originates from a single, extended-cavity DBR diode laser and is injected into two fiber amplifiers.   

Precise measurements of atomic g factor ratios using trapped Rb

We have measured the dephasing time of a coherence grating and inferred the temperature of a cloud of trapped atoms. The grating involves a spatially periodic superposition of adjacent magnetic sublevels of the F = 3 ground state in $^{85}$Rb. The dephasing exhibits Larmor oscillations in the presence of a magnetic field. We initially measured the frequency of Larmor oscillations to a precision of $\sim$0.1$\%$ using pulsed magnetic fields. We have improved the precision by over two orders of magnitude by using steady B fields. A precise measurement of the Zeeman shift of the atomic levels would require an absolute measurement of the B field at the location of the trap. Nevertheless, we show that it is possible to measure of the g factor ratios for $^{85}$Rb and $^{87}$Rb that are precise to ~50 parts per million.   

Influence of sub-Doppler force on the Doppler trap parameters of a magneto-optical trap

We have measured the trap frequency as well as the damping coefficient of a magneto-optical trap by using a transient oscillation method. The dependence of such trap properties on the various experimental parameters such as the cooling laser intensity, detuning, and magnetic field gradient is investigated. We find that the measured trap frequency is in excellent agreement with the simple rate-equation analysis based on the Doppler cooling theory. In contrast, the damping coefficient is about twice larger than the calculated one, which is attributed to the existence of the sub-Doppler trap near the trap center. We also have shown for the multi-level atom the trap parameters are affected by the laser intensity, detuning of other directions. From the measurement of the damping coefficient, we have found that the trap parameters are affected by the sub-Doppler force. These observations are explained by the direct calculation of the force where the detuning of transverse laser is different from the considered axis.   

Comparison of Pulsed and cw Dipole Traps for Confining Ultracold Rubidium

We are planning to use the free electron laser (FEL) at Jefferson Laboratory (Jlab) to spatially confine ultracold rubidium atoms using the optical dipole force. We anticipate applications of a high power, pulsed laser source like the FEL to precision measurements in traps, studies requiring blue or UV light for trapping, and experiments requiring very deep optical traps. The Jlab FEL is a pulsed laser. To date, almost all far-off-resonance traps (FORT) for confining ultracold atoms have used cw laser light. As a precursor to the FEL experiments, we are currently investigating the loading efficiency of a pulsed Nd:YAG laser FORT in direct comparison to a cw Nd:YAG FORT of comparable average power. We will present our findings on these experiments. Supported in part by the National Science Foundation, grant no. INT-0225869, Jefferson Laboratory, and Old Dominion University.   

Experiments with mixtures of bosonic/fermionic isotopes of Rb

Mixture of $^{87}$Rb and $^{84}$Rb (predicted to have a Feshbach resonance at $\sim $100 Gauss for (5/2,5/2) and (5/2,3/2) states, t$_{1/2}$=33 days) is an interesting system for studies of fermionic quantum degeneracy, as well as of formation of ultra-cold molecules. Our high efficiency double MOT system is coupled to a mass separator, which allows us to isolate and trap short-lived isotopes of various elements. In this system we have obtained a BEC of $^{87}$Rb, and demonstrated the trapping of $^{84}$Rb in a MOT. Progress towards sympathetic cooling of $^{84}$Rb, and the creation of ultra-cold molecules will be presented.   

Two-photon photo-ionization of the Ca $4s3d \; ^1D_2$ level in an optical dipole trap

We report an optical dipole trap for calcium. The trap is created by focusing a 488 nm argon-ion laser beam into a calcium magneto-optical trap. The argon-ion laser photo-ionizes atoms in the trap because of a near-resonance with the $4s4f \; ^1F_3$ level. By measuring the dipole trap decay rate as a function of argon-ion laser intensity, we determine the $^1F_3$ photo-ionization cross section at our wavelength to be approximately 230 Mb. Our interest in the calcium optical dipole trap is in its potential application in ultracold plasmas. Due to the high aspect ratio, a plasma generated from a dipole trap would be a 2-D ultracold neutral plasma at early times. Correlation heating is reduced compared to the 3-D case [chen04], bringing the 2-D plasma closer to the strongly-coupled regime. Furthermore, the plasma expansion depends on the exact density distribution of the initial cloud. The density profile of a dipole trap is more defined than that of a MOT, meaning that these new plasmas should have better reproducibility. \newline \newline [chen04] Y. C. Chen, et al, Phys. Rev. Lett. \bf {93}, 265003 (2004)   

Towards magnetic trapping and evaporative cooling of atoms with non-zero orbital angular momentum: suppression of electronic interaction anisotropy in transition metal atoms

Angular momentum transfer is expected to occur rapidly in collisions of atoms in states with non-zero angular momenta due to the large anisotropy of atom - atom electronic interactions. We show that despite the presence of internal angular momenta, transition metal atoms Sc (D-state atom) and Ti (F-state atom) interact in collisions with helium effectively as spherical atoms. The electronic interaction anisotropy of the transition metal atoms with He is dramatically suppressed due to the presence of the outer shell spherically symmetric s-state electrons. As a result, the angular momentum transfer is slow. Thus magnetic trapping and sympathetic cooling of transition metal atoms by collisions with S- state alkali metal atoms should be readily achievable. Our results open up new avenues of research in the ultracold regime with a broad class of complex transition metal atoms.   

Interaction of a BEC with Dipole Barriers

Over the past few years cold atoms have become a remarkable and versatile test bed for many areas of physics, including condensed matter, quantum computation and atom optics. One advantage of testing theories in cold-atom systems is that it is possible to create a wide variety of potentials, to modify them in real time, and to carry out measurements of quantities which are often impossible or very difficult to measure in other systems. We will discuss several experiments involving the scattering of atoms from a Bose-Einstein condensate off of time- dependent and time-independent dipole barriers. In particular, condensates incident on barriers may be used to shed light on the still controversial question of tunneling times. A direct measurement of the B\"{u}ttiker-Landauer time\footnote{M. B\"{u}ttiker and R. Landauer, {\it Pysical Review Letters} \textbf{49} (23), 1739 (1982). }is possible, via directly modulating the barrier height; measurements of weak-measurement or Larmor times are possible by coupling to internal degrees of freedom of the atoms\footnote{A. Steinberg, {\it Journal of the Korean Physical Society} \textbf{35}(3), 122(1999). }; and studies of the effects of quantum measurement may be performed in several ways. The present status of these experiments will be presented.   

New Features in Component Separation with Rotating and Nonrotating Binary Bose-Einstein Condensates

We explore experimentally the dynamics of component separation in two-component Bose-Einstein condensates prepared coherently in the $|F=2,m_F=1\rangle$ and $|F=1,m_F=-1\rangle$ spin states of ${}^{87}$Rb. The double condensate is created out of a single condensate by driving a two-photon hyperfine transition with radiofrequency fields. The condensates are confined with nearly identical trapping potentials, and subsequent evolution of the two components is driven by differences in their scattering lengths. Images taken along two orthogonal axes after the condensates are released reveal an oscillating sequence of alternating and overlapping component distributions involving coaxial cylindrical shells. Similar experiments with rotating condensates exhibit qualitatively different separation dynamics.   

Nondestructive Imaging of Spinor-Condensate Dynamics

The ability to probe the spatial dependence of the coherences and populations of a Spin-1 Bose condensate nondestructively opens a new window on the physics of this complex quantum fluid. In particular, we report recent measurements of the spin- dependent mean-field energy of a $^{87}$Rb condensate, responsible for its ferromagnetic character. The rich dynamics produced by the interplay between the spin-dependent interaction and the quadratic Zeeman shift are experimentally elucidated.   

Few atoms in a trap: universal behavior at the Van der Waals length scale

We present results of variational Monte Carlo calculations for the universal equations of state at the Van der Waals length scale\footnote{B. Gao, J. Phys. B \textbf{37}, L227 (2004).} for a N-atom system (N = 2 to 5) in a trap. The theory provides a systematic understanding of few atoms in a trap, including, in particular, the shape-dependence of interaction energy that becomes important at large scattering lengths. The theory also shows that atoms in a trap have significant long-range correlation for large scattering lengths, with the implication that any independent particle model, such as the Hartree-Fock approximation, is likely to fail for such systems.   

Quantum phase transition of a Bose gas in a lattice with a controlled number of atoms per site

We have studied the superfluid-Mott insulator quantum phase transition [1] of a gas of $^{87}$Rb atoms in an optical lattice. We are able to prepare the gas with a controllable number of one, two, or three atoms per lattice site, as verified with photoassociation spectroscopy. We measure momentum distributions using standard time-of-flight imaging techniques. These are similar to those of ref. [1], and exhibit narrow peaks at moderate lattice strengths. We find that the width of these peaks increases for lattice heights greater than about 13 times the recoil energy [2], and we observe interesting differences in this behavior, depending on the number of atoms per site. The data suggest that the quantum phase transition occurs at higher lattice strength with larger site occupation. We acknowledge the support of this work by the R. A. Welch Foundation, The N. S. F., and the D.O.E. Quantum Optics Initiative. [1] Markus Greiner \textit{et al., }Nature \textbf{415}, 39 (2002). [2] Thilo St\"{o}ferle \textit{et al.}, Phys. Rev. Lett. \textbf{92}, 130403 (2004).   

Optimization of Evaporative cooling in an all-optical trap

All-optical approaches for creating degenerate quantum gases offer versatility, simplicity and speed[1]. We have studied the loading and evaporation processes in CO$_{2}$ laser traps of $^{87}$Rb atoms in detail. Using a high power laser, we have loaded over 20 million atoms into a single beam trap and have created condensates in excess of $10^5$ atoms with only a few seconds of evaporation. We have measured the key properties governing evaporative cooling in the trap from initial loading down through condensation. We will discuss optimization of loading and evaporation using optical techniques and will present our latest results. \\ \\ 1. M.D. Barrett, J.A. Sauer, and M.S. Chapman, Phys. Rev. Lett., \textbf{87}, 010404 (2001)   

An Optical Trap for $^{85}$Rb and $^{87}$Rb

We report on the simultaneous optical trapping of an ultra-cold mixture of $^{85}$Rb and $^{87}$Rb. Using this trap we have been able to explore the interspecies Feshbach resonance between $^{85}$Rb and $^{87}$Rb. With adiabatic magnetic field ramps a Feshbach resonance provides the opportunity to create hetronuclear molecules, as well as superpositions of atomic and molecular states. Recently at JILA, the $^{85}$Rb Feshbach resonance has demonstrated that large molecular conversion efficiency and long molecular lifetimes demand atomic gases with low densities [1]. In consideration of this we discuss our efforts in implementing an optical trap with very weak confinement. We acknowledge the funding for this work from the NSF and ONR. [1] E. Hodby\textit{, et al}. cond-mat/0411487   

Effects of 3-body resonances in ultracold bose gases

We are investigating the $3$--boson system using a model $2$--body potential capable of supporting bound states. Of particular interest is the atom--dimer scattering for large two-body scattering lengths (for example, in the vicinity of a Feshbach resonance). We study $3$--body effects in the context of a many body field theory accounting for correlations to the appropriate order. We are exploring the possibility of applying this to both homogeneous and optical lattice configurations in $^{85}$Rb. We acknowledge support for this project from the NSF.   

Superfluidity in highly-elongated Bose gases

The behaviors of Bose gases under highly-elongated confinement are investigated at finite temperature using the path integral Monte Carlo method. For varying asymmetry of the trap, we determine the superfluid density along the tight and weak confinement direction in response to an imposed rotation about different symmetry axis as a function of temperature. The decreased superfluid response to a rotation about the tight confinement direction, as compared to that to a rotation about the weak confinement direction, can be explained in terms of the moment of inertia. An experiment, which could measure these effects, is proposed.   

Mean field theory for the domain formation in a spin-1 condensate

Spin domains were recently observed in the off-equilibrium dynamics of a large condensate of $^{87}$Rb atoms confined in a cigar shaped optical trap\footnote{Private communications with M. -S. Chang and M. S. Chapman.}. For a two component condensate, the number of atoms within each component is conserved. The dynamics of domain formation has been investigated in detail using the mean field theory\footnote{K. Kasamatsu and M. Tsubota, Phys. Rev. Lett. {\bf 93}, 100402 (2004).}. For a spin-1 condensate (with $^ {87}$Rb or $^{23}$Na atoms), the number of atoms for each component varies due to spin exchange collisions $2|F=1,m_F=0\rangle \leftrightarrow |F=1,m_F=-1\rangle+|F=1,m_F=1\rangle$. In this study, we investigate the effect of such exchange interactions on the dynamics of domain formation in a spin-1 condensate. Using both analytic calculations for a homogeneous condensate and numerical simulations for a trapped condensate, we provide a detailed understanding of the stable and unstable regions of the off- equilibrium dynamics. We also address the important role of an external magnetic field.   

Microwave ionization of non-hydrogenic Rydberg atoms

We have studied ionization of Li $np$ and Sr $5snd$ Rydberg states, whose quantum defects are 0.05 and 2.3, respectively, by linearly polarized, 17.5-GHz pulsed microwave fields where scaled microwave frequencies $\Omega (= n^3 \omega$ in which $\omega$ is microwave angular frequency) are nearly equal to or larger than the classical Kepler frequencies of the Rydberg electron, $1/n^3$ (a.u.). Our measurements show that threshold fields of ionization of Li $np$ and Sr $5snd$ states coincide with each other within experimental errors in the high scaled frequency region in spite of the different sizes of the ionic cores. The ionization thresholds manifest global monotonical increases in the scaled plot, verifying quantum suppression of classical diffusive ionization of non-hydrogenic atoms in this regime. We also report the dependence of ionization thresholds of Li $np$ states on the microwave pulse width and frequency, and the existence of local structures which are observed at several sub-harmonic resonances above $\Omega = 1$, and effects of frequency chirp on MW ionization at high frequency region.   

The Kicked Rydberg Atom: Exploring the Ultra-fast Ultra-intense Regime at Nanosecond Timescales

With the development of high-intensity femto-second laser systems there is increasing interest in the response of atoms to pulsed electric fields with timescales comparable to the classical electron orbital period, T$_{n}$, and field strengths sufficient to dominate the electron motion. We show that the essential physics of such interactions can be explored under less extreme conditions using very-high-$n$ Rydberg atoms ($n\ge $350) subject to unidirectional pulsed electric fields, termed half-cycle pulses (HCPs), with durations T$_{p}<<$T$_{n}$. Particular interest centers on modeling the effect of a freely-propagating train of attosecond HCPs which it is suggested might be used to engineer atomic wavefunctions. Such a pulse train, for which the net field experienced by an atom is zero, is modeled using a train of HCPs upon which is superposed a variable offset dc field. The presence of an offset field leads to dramatic changes in the dynamics and overall survival probability, the latter peaking when the average field experienced by an atom is zero. This behavior is discussed with the aid of CTMC simulations and results from population trapping near the continuum.   

Satellites Bands of Cs and Rb

In species for which a ground-state atom exhibits an electron-atom scattering resonance, the interaction potentials between ground and excited state Cs and Rb atoms were predicted [1,2] to produce oscillations out to hundreds of a.u. It is proposed here that these oscillatory potential curve extrema are responsible for producing satellite bands observable in experimantal absorption spectra [3]. These bands could be identical with curious satellite structures found in line-braodening absorption spectra of Cs vapor and recently also in Rb. Currently we are investigating the preliminary evidence that these features may derive from long-range oscillations in the Cs-Cs and Rb-Rb Rydberg interaction potentials. If confirmed, this could provide an indirect verification of the previously proposed existence of long-range Rydberg molecule bound states. [1] M. I. Chibisov, A. A. Khuskivadze, and I. I. Fabrikant, J Phys. B35, L193 (2002) [2] E. L. Hamilton, C. H. Greene, and H. R. Sadeghpour, J Phys. B35, (2002) [3] H. Heinke, J. Lawrenz, K. Niemax, and K. H. Weber, Z. Phys. A312, 329 (1983). This work was supported in part by NSF.   

Ionization of Xenon Rydberg Atoms at Conducting Surfaces

The ionization of xenon Rydberg atoms at an atomically flat Au(111) surface is being studied to explore how atoms respond to the presence of a nearby surface and to probe electron tunneling processes. Remarkably, experiments using atoms in Stark states in which the electron probability density is initially oriented towards the surface or towards vacuum lead to ionization at similar atom/surface separations. This disagrees with the predictions of hydrogenic theory, which suggests that ionization distances should be very different. This apparent discrepancy is explained in terms of perturbations in the structure of the atomic states induced by the presence of the surface. These result in energy level shifts as the surface is approached and in the appearance of avoided crossings between states in adjacent n-manifolds. These avoided crossings result in the electron probability density oscillating between being oriented toward the surface or toward vacuum. Thus, on average, the electron probability densities associated with the extreme red and blue members of adjacent Stark manifolds are similar, leading to ionization at similar atom/surface separations.   

Atomic Engineering: Production of Very-High-n Quasi-1D Atoms

Quasi-one-dimensional (quasi-1D) atoms can be produced by photoexciting selected Stark states in the presence of a weak dc field. For $n\ge $500, such direct excitation of quasi-1D atoms becomes problematic because stray fields and effective laser linewidths lead to creation of a range of Stark states with no preferred orientation. We show here that very-high-$n$ quasi-1D atoms can be produced by a multi-step process in which lower-$n$ ($n\sim $350) quasi-1D atoms are first produced. The excited electron is then localized in phase space near the outer classical turning point at which time it is transferred to a highly-elongated very-high-$n$ orbit using a half-cycle pulse (HCP). This leads to population of a broad distribution of final $n$states centered at $n\sim $580 which it is shown can be dramatically narrowed by subsequent application of further HCPs. The factors that govern the final $n$ distribution are discussed with the aid of classical simulations. The availability of very-high-$n$ quasi-1D atoms allows the dynamics of the periodically kicked atom to be examined at high scaled frequencies, $\nu _0 \approx 15$. Novel behavior, such as local increases in survival probability with increasing number of kicks, is observed.   

Long-range interactions and many-body effects in a cold Rydberg gas

In recent years, the unique combination of properties of ultracold Rydberg atoms, such as long radiative lifetimes or strong long-range interactions, has led to proposals for using them to implement fast quantum gates. Here, we explore the behavior of macroscopic atomic samples where laser excitation of ultracold atoms to high-lying Rydberg states is locally blockaded due to the strong van der Waals interactions between Rydberg atoms. We discuss a mean-field model that defines local blockade domains and agrees well with experimental observations. In a $N$-atom mesoscopic sample under perfect blockade condition, the single excitation is described by a many-body Rabi frequency, {\it i.e.} $\sin^2 (\sqrt{N}\Omega \tau )$. Here, we generalize the result to a macroscopic sample with several ``domains" containing effectively $N_{\rm eff}$ atoms; the number of excited atoms is then $ N_{\rm exc} \sim \sum_{\rm domain}\sin^2 \left(\sqrt{N_{\rm eff}} \Omega \tau \right). $   

Molecular Resonances due to Long-Range Interactions between Ultracold Rydberg Atoms

Molecular resonances have previously been observed in the spectroscopy of cold dense Rydberg gases [1]. These are due to avoided crossings between interatomic potentials which originate at various doubly-excited asymptotes. In the vicinity of transitions to Rb \textit{np} atomic Rydberg states ($n\sim $70), we have recently seen multiple molecular resonances which correspond to various pairs of highly-excited states. Examples of these combinations include ($n$-1)$d$+\textit{ns} and ($n$-1)$p$+($n$+1)$p$. We will report on measurements of these and other resonances as well as modeling of the spectra based on the long-range interatomic potentials and the strong couplings between them. [1] S.M. Farooqi, et al., Phys. Rev. Lett. \textbf{91}, 183002 (2003).   

Keplerian-Like Systems in the Dissociation of Polyatomic Ions

In the dissociation of H$_{3}^{+}$ and D$_{3}^{+}$ measured in triple coincidence into the Coulomb interacting channels of H$^{+}$+H$^{+}$+H$^{-}$ and D$^{+}$+D$^{+}$+D$^{-}$, the results exhibit unique features when scrutinized from a center-of-mass energy partitioning perspective. Starting from the Wannier concept of the reaction zone boundary, classical and molecular simulations of the three Coulomb interacting fragments were undertaken, with the goal of modeling the measured system energy partitioning. Starting from various configurations of dissociated H$_{3}^{+}$ and D$_{3}^{+}$, the simulations show that a bound H$^{+}$-H$^{-}$ or D$^{+}$-D$^{-}$ complex may form due to post-dissociation interactions. For short times these complexes exhibit classical Keplerian-like orbits with each fragment maintaining its original physical characteristics. In order to identify and explore the properties of the time development of the three-body system's center-of-mass energy partitioning, we use a generalized form of the Dalitz plot that highlights the time dependence of the three body correlations with which we can then relate to experimental results. Comparisons will be made between the experimental and theoretical results.   

Dissociation and ionization in capture of antiprotons by the hydrogen molecular ion

Antiprotonic atoms and anti-hydrogen are hot areas of current experimental research. Cross sections for antiproton capture will soon be measured directly for the first time by the ASACUSA collaboration at the CERN antiproton decelerator and trap. In the present work [1], cross sections and initial quantum number distributions are calculated for capture of the antiproton ($\bar{p}$) and the negative muon ($\mu^-$) by the hydrogen molecular ion H$_2^+$ using the fermion molecular dynamics (FMD) method. The capture of $\bar{p}$ is found to be almost entirely adiabatic, occurring via target dissociation without ionization, but nonadiabatic effects are found to play a significant role in the capture of $\mu^-$, especially at the higher capture energies. Generally good agreement is obtained with the recent adiabatic classical-trajectory Monte Carlo (CTMC-a) calculation of Sakimoto [2]. The capture properties of H$_2^+$ are shown to be completely different from those previously calculated for both the H atom and neutral H$_2$ molecule. Proposed experiments [3] on $\bar{p}$ capture by H, H$_2$ and H$_2^+$, at the same relative collision energies, will provide a major test of our theoretical understanding [4].\\ $[1]$ J.S. Cohen, J.\ Phys.\ B (to be published).\\ $[2]$ K. Sakimoto, J.\ Phys.\ B {\bf 37}, 2255 (2004).\\ $[3]$ Y. Yamazaki {\it et al.}, Nucl.\ Instrum.\ Methods B {\bf 154}, 174 (1999); {\bf 214}, 196 (2004); Hyperfine Interact. {\bf 138}, 141 (2001).\\ $[4]$ J.S. Cohen, Rep.\ Prog.\ Phys. {\bf 67}, 1769 (2004).   

Variational calculations with complex Gaussian functions

The complex-valued exponential functions depending on the all inter-particles distances [1] first was used for variational calculations of the three-particle quantum-mechanical systems with Coulomb interaction between the particles. On calculations of three particle systems was shown that complex exponential basis function is especially efficient for molecular-like systems. It is necessary to underline, that calculation formulas of integrals are greatly complicated for four particle systems [2], and unknown for many particle systems. That creates grand problem for using complex exponential functions for many particle systems. The other way is to use complex-valued ``Gaussian'' functions, depending on squares of inter-particle distances. Calculations with these functions are simple by using complex numbers arithmetic. In this work we present results of testing new functions. We make a calculation of four particle systems: hydrogen and exotic positronium molecules in basis of 45 complex functions, and find energies and some other averages. For example, we obtain binding energy of positronium molecules equal to -0.513 a.u. It is shown that complex-valued ``Gaussian'' functions like complex-valued exponential functions can be significantly improve the accuracy of variational calculations of few--particle molecular systems \newline [1] T.K.Rebane and O.N.Yusupov, Zh. Eksp.Teor.Fiz . 98, 1870 (1990) \newline [2] V.S.Zotev and T.K.Rebane , Phys. Rev. A 65, N6 ( 2002)   

Acoustic Analogue to Slow Light

Acoustic waves provide an easy way to understand and demonstrate low group velocities. This poster provides an interesting analogy to the widely discussed slowing of light waves. We compare our slowing of light data to our new slowing of sound data. Sound waves are sent into a closed aluminum tube, and their frequencies are scanned around the resonant frequencies of the tube to obtain the dispersion curve for the system. We compare the group velocity obtained from the dispersion curve to the directly observed group velocity of a propagating pulse. In this way we show that a pulse of sound in our system travels at 3 meters per second in air.   

Narrow-linewidth operation of high power broad-area laser diodes using a passively stabilized variable external cavity design

Many applications in atomic spectroscopy require the use of lasers with a narrow linewidth and high beam quality. External cavities have long been used with low power laser diodes to achieve this and to continuously tune the wavelength. Recently, broad-area laser diodes and laser diode arrays have been fabricated to produce many watts of cw output power. These are necessary in applications requiring high powers, such as spin- exchange polarization of $^{129}Xe$, and as affordable alternatives to solid-state lasers in high-resolution spectroscopy. Coupling these lasers to external cavities becomes increasingly difficult, as the beam quality goes down with increasing power. We describe an external cavity based on the Littman-Metcalf design that can be easily aligned in a wide range of cavity lengths to adapt to different types of high power laser diodes and different applications. The cavity utilizes passive stabilization techniques to maintain a stable mode structure over long periods of time. We have narrowed the linewidth of a Coherent 2W single-stripe cw laser diode ($\sim$ 780nm) from about 550GHz to $<$ 200MHz with a coupling efficiency greater than 60$\%$. We also describe the continuous tunable range of the cavity and its applications to high- resolution spectroscopy.   

Diode Pumped Cesium Laser

We have demonstrated a Cs vapor laser with diode laser pumping and have achieved a slope efficiency of 41{\%} and overall optical efficiency better than 32{\%}. A narrowband diode laser operating at 852 nm pumps the 6$P_{3/2}$ state (D$_{2}$ line) which is then rapidly quenched to the 6$P_{1/2}$ state by an ethane buffer gas. This creates a population inversion between the 6$P_{1/2}$ and 6$S_{1/2}$ states and lasing at 894 nm. The experimental set-up consisted of an injection seeded SDL-8630 diode laser pump and a Cs vapor cell positioned inside a stable laser cavity. The laser cavity was longitudinally pumped through the input cavity mirror. This mirror had a concave radius of 20 cm with 90{\%} transmission at 852 nm and about 99{\%} reflectivity at 894 nm. A series of flat output mirrors were used with reflectivities for both 894 nm and 852 nm ranging from 20{\%} to 90{\%}. The optimal output coupler reflectivity was 30{\%} at 894 nm. The length of the laser cavity was 16.5 cm. The pump laser had a maximum output power of 500 mW at 852 nm with FWHM of less than 1 MHz. The Cs vapor cell was 2.5 cm long with Brewster windows at both ends. It was filled with metallic cesium and 100 Torr of ethane at 20 $^{o}$C and was placed inside an oven. We acknowledge support from the Air Force Office of Scientific Research and the National Science Foundation under Grant No. 0355202   

How to screw up your relative intensity measurement

Relative intensity measurements are used for high-sensitivity and high accuracy absorption determinations. They require the detector response to be directly proportional to the input light signal, or at least to be a monotonic function of the input light signal. We have found small variations in the response linearity of photomultiplier tubes that do not conform to these constraints. This nonlinearity makes it impossible to measure 1\% absorption with an accuracy better than 10\%. In this paper we will discuss methods for correcting this error in low-light-level measurements.   

Absolute soft x-ray calibration of laser produced plasmas using a focusing crystal von Hamos spectrometer

Absolute x-ray calibration of laser-produced plasmas was performed using a focusing crystal von Hamos spectrometer. The plasmas were created by a high repetition rate Nd-YAG laser (0.53 $\mu m$/200 mJ/3 ns/10 Hz) on massive solid targets (Mg, Al, Fe, Cu, Mo, Ta). Cylindrical mica crystal (radius of curvature R=20 mm) and a CCD linear array as a detector (Toshiba model TCD 1304AP) were used in the spectrometer. Both the mica crystal and CCD linear array were absolutely calibrated in a spectral range of $\lambda =7-15 \AA$. The spectrometer was used for absolute spectral measurements and the determination of the plasma parameters. High spectrometer efficiency allows for the monitoring of absolute x-ray spectra, x-ray yield and plasma parameters in each laser shot. This spectrometer is promising for absolute spectral measurements and for monitoring of laser-plasma sources intended for proximity print lithography.   

A millimeter-scale atomic magnetometer

We are developing a MEMS-fabricated chip-scale atomic magnetometer that uses all-optical excitation to interrogate the spin-precession frequency of alkali atoms. Recently we demonstrated a magnetometer physics package that had sensitivity of 50 pT / Hz$^{1/2}$ at 10 Hz, had a volume of 12 cubic millimeters, and used 195 mW of power. The physics package includes a laser, micro-optics package, rubidium vapor cell, and photo diode. The current magnetometer measures the hyperfine splitting of two magnetically sensitive states via a coherent population trapping resonance, and we are exploring methods to measure the Larmor frequency directly in our small physics package to improve the sensitivity. Operation at the lower Larmor frequency decreases the power consumption of the local oscillator as well. Through improved thermal packaging, we aim to decrease power consumption of physics package to below 20 mW.   

Detection of NMR and Radio Frequency Fields with Alkali-Metal Magnetometers

We describe several applications of ultra-sensitive high-density alkali-metal magnetometers for NMR and NQR detection. Using a spin-exchange relaxation-free (SERF) atomic magnetometer operating at low field we demonstrate first detection of NMR signals from thermally-polarized water sample. We also demonstrate detection of less than 10$^{13}$ $^{129}$Xe atoms whose NMR signal is enhanced by a factor of 540 due to Fermi-contact interaction with the alkali atoms. This technique allows detection of less than 10$^{9}$ $^{129}$Xe spins in a flowing system suitable for remote NMR applications. We also present a new tunable RF magnetometer that can detect fields in a wide range of frequencies and demonstrate sensitivity of 2 fT/Hz$^{1/2}$ at 100 kHz. A detailed analysis of fundamental sensitivity limits indicates that it can achieve sensitivity of 0.01 fT/Hz$^{1/2}$ and can rival other methods for detection of nuclear quadrupole resonance (NQR) at several MHz.   

Frontiers in Research with Highly Charged Ions

At the 85th Nobel Symposium in 1992, Joe Sucher remarked that a significant part of atomic physics was entering a new era, which he termed ``the ion age'' [1]. He gave special mention to \textit{highly charged} ions, which, at the time, were becoming a more feasible topic of investigation because of advances in methods to produce and control them. During the past decade, these, and additional advances, have spawned a host of emerging applications for highly charged ions in areas as diverse as microelectronics and biomedicine. I will present some recent examples involving the NIST Electron Beam Ion Source/Trap (EBIS/T) to illustrate present and future opportunities for both fundamental and applied research with highly charged ions. [1] J. Sucher, Phys. Scr. \textbf{T46}, 239 (1993).   

Calculations of Light Field Distributions Within and Beyond Wavelength-Scale Apertures

We describe a computationally efficient method for calculation of electromagnetic fields within and beyond a diffracting aperture using Hertz vector diffraction theory. Commonly used diffraction models (Fresnel, Kirchhoff, Rayleigh-Sommerfeld, paraxial approximations) typically diverge or fail to accurately represent physical electromagnetic fields for points of interest in or near the aperture plane. These models also neglect to include the perturbation of the light field due to the aperture itself. Calculations using Hertz vector diffraction theory include the perturbation effects of the aperture, and the resulting fields satisfy Maxwell's equations for all space for aperture size larger than approximately half the wavelength of light. Calculated light field distributions using this method agree with experimental measurements previously conducted by the microwave community. By using line integral methods around the rim of the aperture instead of a two-dimensional integration over the aperture area, the computational times can be reduced by a factor of approximately 15 to 20. We will present basic equations for calculations using this method as well as two-dimensional beam profiles for diffraction of light by circular, elliptical, rectangular, and square apertures. Results will include the dependence of the beam distribution upon the incident laser polarization.   

Time Resolved Optical Emission Spectroscopy during Pulsed DC Sputter Deposition of TiO2 Thin Films

Time resolved optical emission spectroscopy (TR-OES) is used to analyze pulsed DC magnetron plasmas during the sputter deposition of TiO$_{2}$ thin films. The studies are focused on the temporal behavior of the emission lines of atomic titanium, argon and oxygen in three chosen emission windows (386 nm to 427 nm, 747 nm to 782 nm and 824 nm to 858 nm) during the \textit{off-time} and the \textit{on-time} of the pulsed DC plasma. Single- and double-exponential fits were used to describe the various optical emissions during the \textit{off-time} of the plasma. The various decay constants are correlated with the disappearance of the fast beam-type electrons in plasma once the power is turned off as well as to the disappearance of Ar metastables and Ti and O atoms. We find a slow increase of the optical emission intensities that follow the cathode current (with or without an intensity overshoot) when the power is turned on at the beginning of the \textit{on-time}.   

Time-Resolved Imaging of a Pulsed DC Magnetron Plasma During the Sputter Deposition of TiO$_{2}$ Films

Time resolved images of the optical emissions from a pulsed DC magnetron plasma during the sputter deposition of TiO$_{2}$ films were taken with a Roper Scientific ICCD camera. The camera was exposed to the discharge for 0.05-0.2$\mu $s with 0.05-0.2$\mu $s separation between each exposure. At the beginning of the \textit{on-time} when the power is turned on, the discharge initially starts preferentially in the opposing corners of the \textit{race track}. During the rest of the \textit{on-time}, the emission from the straight sections of the \textit{race track} of the magnetron is always slightly stronger than the emission from the two rounded corners of the \textit{race track}. This pattern extends into the start of the \textit{off-time} when the power is turned off. The optical emissions persist for several microseconds into the \textit{off-time}.~Spectral filters were used in order to record the temporal behavior of the various emission lines (Ar, O, Ti).   

Electronic and Positronic Guiding Center Ions

A novel type of guiding center drift ion is described. These ions only occur in strong magnetic fields. They consist of a neutral atom to which either an electron or a positron is weakly bound, at sufficiently large radius that it may be described by ${\mathbf E} \times {\mathbf B}$ drift dynamics. The attractive electric field arises from the weak induced dipole moment of the neutral atom in the field of the outer charge. Such ions may occur naturally in astrophysical plasmas and may also have been formed in recent antihydrogen experiments, where their presence would provide proof that deeply bound $\overline{H}$ atoms are being created. Binding energies and orbital dynamics are described in two limits: (i) a ground state H atom along with an outer charge in a zero-angular-momentum orbital, and (ii) a classical guiding center drift H atom (a proton about which an electron ${\mathbf E} \times {\mathbf B}$ drifts in the Coulomb field) with an electron or positron bound at larger radius. For case (i) the affinity of a positronic H$^+$ ion is shown via a full quantum calculation to be $2.23 (B/B_0 )^2 e^2 /a$, where $B_0 = 2.35 \times 10^5$ Tesla and $a$ is the Bohr radius. This scaling with $B$ agrees with a recent estimate.\footnote{V.G.~Bezchastnov et al., Phys. Rev. A {\bf 61}, 052152 (2000).} For case (ii) much larger binding energies (of order meV) are found because the induced dipole moment of a guiding center atom is much larger than that of ground state hydrogen.   

Accuracy of gates in a quantum computer based on vibrational eigenstates

A model is developed to study the properties of a quantum computer that uses vibrational eigenstates of molecules to implement the quantum information bits and optimally shaped femto-second laser pulses to apply the quantum logic gates. Particular emphasis of this study is on understanding how the different factors, such as properties of the molecule and of the pulse, can be used to affect the accuracy of quantum gates in such a qubit. Optimal control theory and numerical time-propagation of vibrational wavepackets are employed to obtain the shaped pulses for the gates NOT and Hadamart transform. The effects of the anharmonicity parameter of the molecule, the target time of the pulse and of the penalty function are investigated. Influence of all these parameters on the accuracy of qubit transformations is observed and explained. It is shown that when all these parameters are carefully chosen the accuracy of quantum gates reaches 0.999 .   

Mode analysis of a single component fermion - BEC mixture

We analyze the collective modes of a single component fermion - BEC mixture in the ultra-low temperature regime in which the fermions behave as a normal Fermi-liquid. If the Fermi-velocity exceeds the sound velocity of the BEC and the homogeneous mixture is mechanically stable, we find two coupled collective modes. The lowest energy mode is a damped excitation that decays by virtue of Landau damping. The higher energy mode exhibits the characteristics of a zero sound excitation in the long wavelength limit. We calculate the decay rate of the damped mode and point out that this mode terminates at a well-defined wavenumber. If a critical fermion density is exceeded, the fermions become immiscible to the BEC, and the mixture undergoes phase separation. Our analysis reveals the mechanism of the related instability. We estimate the growth rate and length scale on which the phase separation sets in. We discuss the prospects for experimental observations and the implications for other cold atom quantum liquid systems such as Cooper-pairing of a spin polarized fermion system (of different spin densities).   

Doppler-effect experiments and Lorentz symmetry

Within the context of the Lorentz-violating standard-model extension, I present preliminary results of a study of precision Doppler-effect experiments. While other types of experiments, such as clock-comparison and spin-torsion experiments, already provide sensitive tests of Lorentz symmetry in atomic systems, they do not cover all possible types of Lorentz-violating interactions. Doppler-effect experiments provide tests of some sectors of the standard-model extension that are unprobed by other classes of experiments. I present analysis of already-completed Doppler experiments from the Heidelberg Storage Ring.   

Stark Slowing Asymmetric Rotors: Weak Field Seeking States and Nonadiabatic Transitions

We present calculations of Stark shift curves for several small asymmetric rotors, including a quantitative analysis of nonadiabatic transition probabilities and orientational distribution functions, applicable to typical Stark slowing conditions. Stark deceleration is one of the few methods that can be used to slow polyatomic molecules. In a Stark slower, the Stark effect is exploited to create a force that can decelerate molecules. To date, Stark slowing has focused on diatomic and symmetric top molecules. Asymmetric rotors have received relatively little attention although they are the most common type of molecule in nature. Asymmetric polyatomic molecules can be Stark slowed if they have large enough dipole moments, but can exhibit quite different orientational behavior than their symmetric counterparts. Nonadiabatic transition probabilities are key to Stark slowing applications, because the transition can convert a weak field seeking state into a strong field seeking state. Nonadiabatic transitions occur as a result of the breakdown of the adiabatic approximation in energy regions where two Stark curves approach each other. To assess effective nonadiabatic transition probabilities, a semi-classical approach is used.   

Ultracold Collisions with Frequency-Chirped Light: the Influence of Chirp Direction

We report measurements of collisions between ultracold Rb atoms induced by frequency-chirped laser light. In particular, the influence of the direction of the chirp is studied. A typical chirp sweeps 1 GHz in 100 ns. The red-to-blue (positive) chirp starts below 800 MHz the 5S$_{1/2}$-5P$_{3/2 }$cycling transition while the blue-to-red chirp (negative) chirp starts 200 MHz above. If the attractive potential of a pair of atoms is resonant 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. On the present time scales of the chirp, the two directions result in similar collision rates. * Work supported by DOE.   

Evolution of the L satellites in the X-ray emission spectra of $\beta $ region

The X-ray satellites L$\beta _{1}^{I}$, L$\beta _{1}^{II}$, L$\beta _{1}^{III}$, L$\beta _{1}^{IV}$, L$\beta _{2}^{I}$, L$\beta _{2}^{(b)}$, L$\beta _{2}^{II }$and L$\beta _{2}^{(c)}$ observed in the L-emission spectra in elements with Z = 26 to 92, have been calculated. The energies of various transitions have been calculated by available Hartree-Fock-Slater (HFS) data using the semi-empirical Auger transition energies in the doubly ionized atoms and their relative intensities have been estimated by considering cross - sections of singly ionized 2x$^{-1}$ (x $\equiv $ s, p) states and then of subsequent Coster-Kronig and shake off processes. The calculated spectra have been compared with the measured satellite energies in the L emission spectra. Their intense peaks have been identified as the observed satellite lines. The one to one correspondence between the peaks in calculated spectra and the satellites in measured spectra has been established on the basis of the agreement between the separations in the peak energies and those in the measured satellite energies. Group of transitions under the transition schemes L$_{2}$M$_{x}$-M$_{x}$M$_{4,5}$ and$_{ }$L$_{3}$M$_{x}$-M$_{x}$N$_{4,5}$ (x $\equiv $ 1-5), which give, rise to these satellites have been identified. It is observed that the satellite L$\beta _{2}^{(b)}$ in all these spectra can be assigned to the superposition of $^{3}$F$_{4}-^{3}$G$_{5}$ and $^{3}$F$_{4}-^{3}$D$_{3 }$transitions and that this must be most intense one out of all these satellites, contributing in order of decreasing intensity. Each of the remaining satellites is found to have different origin in different elements. The possible contributions of the suitable transitions to all these lines have also been discussed. \newline References:\newline 1. Y. Cauchois and C. Senemaud, X-Ray Wavelength Tables, 2$^{nd}$ ed., (Oxford: Pergamon) pp. 217-314, (1978).\newline 2. S.N.Soni, J. Phys. B: At. Mol. Opt. Phys. \textbf{23}, 1117-1128, (1990).\newline 3. S. N. Soni and M. H. Massoud, J. Phys. Chem. Solids \textbf{58(1)}, 145-151 (1997).\newline 4. S. N. Soni and S. Poonia, J. Phys. Chem. Solids \textbf{61(9)}, 1509-1518 (2000).\newline 5. S. Poonia and S. N. Soni, J. Phys. Chem. Solids \textbf{62(3)}, 503-511 (2001).   

Femtosecond Laser Cooling of Trapped Ions

We present work toward laser cooling of trapped ions with femtosecond pulse trains. Our scheme is applicable to hydrogen and other elements that are not currently laser cooled. In this proof-of-principle experiment, we confine approximately $10^5 \: {\rm Yb}^+$ ions in a linear Paul trap and probe them on the strong ${\rm S}_{1/2} - {\rm P}_{1/2}$ transition at 370 nm. A high-repetition-rate mode-locked laser drives the two-photon ${\rm S}_{1/2} - {\rm D}_{3/2}$ transition at 871 nm for laser cooling. An optical resonator enhances the mode-locked laser intensity applied to the ions, greatly increasing the two-photon transition rate.   

The X-Factor

Applications of polarized $^3$He gas, in particular neutron spin filters and targets for electron scattering, require the highest possible $^3$He polarization $P_{He}$. We recently reported that the $^3$He polarization achievable using the spin-exchange optical pumping method is often limited to 75\%, although the cells were polarized for conditions in which the traditional rate balance model would predict close to 100\% $^3$He polarization. In a more extensive study of cells with a larger range of surface to volume ratio (S/V), we have found that the achievable polarization saturates at a value of 20\% to 50\% below that of the measured alkali-metal polarization. In all respects this limit to the $^3$He relaxation behaves as if there exists an additional temperature-dependent source of $^3$He relaxation. This results in the measured $P_{He}$ to be precisely what we would expect from a standard rate balance argument if the extra relaxation is included, however the source of the extra relaxation is unknown. We have found that the $^3$He relaxation varies from 20\% - 100\% of the spin exchange rate depending on the cell tested. Here we present evidence from studies to show that the extra relaxation is dependent on S/V, but that this is not the only relevant parameter. Preliminary studies indicate that the N$_2$ and $^3$He pressure may be relevant, but further work is necessary.   

Using Hyperpolarized Xenon-129 NMR to Detect Atherosclerosis

Hyperpolarized noble gas MRI has recently emerged as a powerful diagnostic tool in medicine, as it allows researchers to obtain high-resolution lung images in real time. Yet perhaps more promising is the application of spin-polarized noble gas NMR to biological spectroscopy. Although both $^{129}$Xe and $^{3}$He benefit from the extremely high signal-to-noise ratios characteristic of polarized noble gas NMR, xenon is preferable for such studies because unlike helium it is highly lipophilic (thus readily absorbed by most tissues) and because its NMR chemical shift is much greater. Atherosclerosis is a good candidate for $^{129}$Xe NMR study because xenon dissolved in blood will be absorbed by artery walls, exactly where the symptoms of the disease are most manifest. We have previously verified that $^{129}$Xe spectroscopy can be used to detect the degree of atherosclerosis in human blood vessel samples by demonstrating that the dissolved xenon spectrum correlates with the apparent pathology and histology of the tissue. In this work we expand upon our earlier research by quantifying the features of the $^{129}$Xe NMR spectrum in order to characterize the underlying physical effects of atherosclerosis. In addition to showing high-resolution NMR spectra of xenon dissolved in healthy and diseased artery tissue, we will also compare $T_{1}$ and $T_{2}$ data and diffusion measurements for the different samples.   

Optimization of FM and AM Pumping light for CPT Resonances at High Buffer Gas Pressure

Coherent-population trapping (CPT) using modulated light is a promising method for miniature atomic clocks because the light both generates and detects the clock resonance. Traditionally, the sidebands of frequency-modulated (FM) light have been used to generate coherences in the ground state hyperfine structure of alkali-metal atoms. The first order sidebands, which are separated by a frequency equal to the ground-state hyperfine splitting of the alkali metal, adequately excite the clock resonances provided that the buffer gas pressure in the cell is not too high. High buffer gas pressures offer practical advantages for miniature frequency standards, including suppression of diffusion losses in miniature cells, smaller light shifts, and lower frequency stability standards for the pumping light. Higher gas pressures also broaden the optical absorption lines and reduce the contrast of FM CPT. We show that CPT signals using amplitude-modulated (AM) light do not degrade as severely with increasing pressure. Optimum waveforms for AM light at high and low pressures will be discussed, considering constant light polarization and alternating-circular polarization utilized by the push-pull pumping method$^{1}$. We present push-pull CPT data with both AM and FM light at varying buffer gas pressure and compare with theory. \newline [1]Y.-Y. Jau, E. Miron, A. B. Post, N. N. Kuzma, and W. Happer, Phys. Rev. Lett. {\bf 93}, 160802 (2004)   

Absolute frequency measurement of the $^{1}$S$_{0}$$\leftrightarrow$$^{3}$P$_{0}$ clock transition at 578.4 nm in ytterbium

We report the first precision absolute frequency measurements of the highly forbidden (6s$^{2})^{1}$S$_{0}\leftrightarrow $(6s6p)$^{3}$P$_{0}$ optical clock transition at 578.4 nm in two odd isotopes of ytterbium. Atoms are cooled to tens of microkelvins in two successive stages of laser cooling and magneto-optical trapping that use transitions at 398.9 nm and 555.8 nm, respectively. The resulting trapped atomic cloud is irradiated with excitation light at 578.4 nm and absorption is detected by monitoring trapped atom depletion. With the laser on resonance, we demonstrate trap depletions of more than 80 {\%} relative to the off-resonance case. Absolute frequency measurements are made for $^{171}$Yb (I=1/2) and $^{173}$Yb (I=5/2) with an uncertainty of 4.4 kHz using a femtosecond-laser frequency comb calibrated by the NIST cesium fountain clock. The natural linewidth of these J=0 to J=0 transitions is $\sim $10 mHz, making them well-suited to support a new generation of optical atomic clocks based on confinement in an optical lattice. Lattice-based optical clocks have the potential to surpass the performance of the best current atomic clocks by orders of magnitude. The accurate ytterbium frequency knowledge presented here (nearly a million-fold reduction in uncertainty) will greatly expedite Doppler- and recoil-free lattice spectroscopy.   

Side-pumped hollow-core optical fiber for atom guiding

We demonstrate a side-illumination technique for coupling light into hollow-core optical fibers for evanescent-wave atom guiding. Microprisms embedded into a multimode, double-clad hollow fiber allow light to be coupled efficiently ($>$ 90{\%}) at arbitrary locations along the length of the fiber. The technique offers significant advantages over end-pumped configurations.   

Correlated Two-Electron Capture by Ion with Emission of Photon

The correlated double electron capture into the K shell of bare ions with emission of a single photon is considered. The process is treated as a time-reversed atomic double photoionization. For ten years of experimental investigations there is no evidence of existence of the reaction. There is a theoretical prediction (Phys. Rev. A 55 (1997) 1952), that a probability of the process grows rapidly with the ion charge due to relativistic effects and that the cross section does not depend on target atoms. However the recent experiment (GSI Scien.Rep., ISSN 174 (2001) 98) failed to observe this process under the recommended conditions. The present work reveals an incorrectness of those theoretical predictions and provides an expression to determine optimal experimental conditions for observing the process. We suggest to use ion beams slower than those in the experiment (NIM B98 (1995)303), and do not recommend to use heavy ions. We show that the cross section can increase significantly for solid-state targets and decelerated ion beams. The novel technique of deceleration of multicharged ions planned at GSI can be applied to perform such experiments.