Session P1 - Poster Session III.
POSTER session, Friday afternoon, May 28
Grand Ballroom, Student Union Memorial Center

[P1.001] Quantum Information and Cavity QED

This abstract not available.

[P1.002] ^\primeSuperluminal^\prime Tunnelling as a Quantum Measurement Effect^

We exploit the analogy between tunnelling across a potential barrier and Aharonov's weak measurements to resolve the long standing paradox between the impossibility to exceed the speed of light and the seemingly ^\primesuperluminal^\prime behavior of the tunnelling particle in the barrier. We demonstrate that ^\primesuperluminality^\prime occurs when the value of the duration \tau spent in the barrier is uncertain, whereas when \tau is known accurately, no ^\primesuperluminal^\prime behavior is observed. In all cases only subluminal durations contribute to the transmission across the barrier.

^Supported by U.S. DOE, Basic Energy Sciences, Office of Science.

[P1.003] Realization of controlled-NOT gate and quantum entanglement with coupled SQUID flux qubits

We propose a scheme for implementation of quantum information processing using two coupled SQUID qubits. We show that two SQUIDs with realistic parameters and proper coupling can be used as a basic unit for two-bit quantum gate operations. We demonstrate, by exploring the bit-flip operation of the coupled qubits through highly accurate numerical solution of the time-dependent Schrödinger equation, that operation of the quantum controlled-NOT (C-NOT) gate and creation of the entangled states can be performed by applying resonant microwave pulses to the qubits. Since the coupling scheme can readily be extended to many qubits system our result illustrates that SQUID qubits are promising for scalable quantum information processing.

[P1.004] Quantum computing with magnetically interacting atoms.

A scalable quantum computing architecture is proposed based on magnetically interacting complex open-shell atoms confined to the nodes of an optical lattice. The lattice is placed in a high gradient magnetic field and the resultant Zeeman sublevels define qubit states. Microwave pulses tuned to space-dependent resonant frequencies are used for individual addressing. Nearest neighbor magnetic-dipolar atomic interactions allow for the implementation of a quantum controlled NOT gate. For certain atoms the resulting single-qubit gate operation times are on the order of microseconds, while the two-qubit operations require milliseconds. These times are much faster than the anticipated decoherence times. Specific to the proposed architecture is a potential loss of coherence due to an entanglement of the internal and motional degrees of freedom during gate operation. We demonstrate that the associated decoherence is negligible. For alkali-metal atoms short laser wavelengths on the order of 250 nm are required for the optical lattice. We argue that for complex open-shell atoms (such as metastable ^3\!P_2 alkaline-earth atoms) more practical wavelengths of 400 nm would suffice.

[P1.005] Stability of atomic clocks based on entangled atoms

We analyze the effect of realistic noise sources for an atomic clock consisting of a local oscillator that is actively locked to a spin-squeezed (entangled) ensemble of N atoms. We show that the use of entangled states can lead to an improvement of the long-term stability of the clock when the measurement is limited by decoherence associated with instability of the local oscillator combined with fluctuations in the atomic ensemble's Bloch vector. Atomic states with a moderate degree of entanglement yield the maximal clock stability, resulting in an improvement that scales as N^1/6 compared to the atomic shot noise level.

[P1.006] Shaping few-photon pulses via atomic memory

We present experimental progress towards generation, storage, and retrieval of few-photon electromagnetic pulses using two-photon Raman scattering and electromagnetically induced transparency in thermal Rb87 vapor. We investigate nonclassical photon correlations in such a process, and demonstrate our ability to control the pulse shape and bandwidth. In addition, we describe progress towards conditional generation of nonclassical few-photon states.

[P1.007] Mesoscopic Cavity Quantum Electrodynamics

We describe a technique for strong, coherent interactions between spatially separated quantum systems. Using a mechanism analogous to cavity quantum electrodynamics, the state of a isolated neutral atom or a quantum dot spin or charge can be transferred to long-lived modes of a superconducting transmission line. The small mode volume of the transmission line allows coherent interactions between atoms or quantum dots separated by millimeters. Potential applications include an on-chip double-dot microscopic maser, coupling between distant electron spin or neutral atom qubits, and a new interface to map quantum information between atoms and solid state devices.

[P1.008] Controlling a mesoscopic spin environment for quantum information processing

We present a unified description of cooling and manipulation of a mesoscopic bath of nuclear spins via coupling to a single quantum system of electronic spin (quantum bit). We show that a bath cooled by the quantum bit rapidly saturates. Although the resulting saturated states of the spin bath (``dark states'') generally have low degrees of polarization and purity, their symmetry properties make them a valuable resource for the coherent manipulation of quantum bits. Specifically, we demonstrate that the dark states of nuclear ensembles can be used to coherently control the system-bath interaction and to provide a robust, long-lived quantum memory for qubit states. Extensions of these techniques to implement quantum information protocols are considered.

[P1.009] Anisotropic Magnetic Nanodots As Qubits For Scalable Quantum Computing

Scalability of quantum computing devices is becoming a critical problem, and thus much attention has been directed recently to condensed matter systems. Magnetic nanodots have been proposed as promising candidates for realization of qubits due to their well-separated energy levels, which allow operation at relatively high temperatures. Here we examine the entanglement of a pair of magnetic nanodots, which is crucial for their use as qubits. We show that for the case of weak ferromagnetic coupling the entanglement depends resonantly upon the differences in properties of the nanodots. We specify the conditions under which maximal entanglement may be achieved. Our results thus provide guidance for fabrication of nanodots so that they may be used as qubits.

[P1.010] Encoding a physical qubit into a logical qubit

We propose two protocols to encode a physical qubit into a logical qubit relying on common types of qubit-qubit interactions in as simple forms as possible. We comment on its experimental implementation in several quantum computing architectures, e.g. with trapped atomic ion qubits, atomic qubits inside a high Q optical cavity, solid state Josephson junction qubits, and Bose-Einstein condensed atoms.

[P1.011] Coherent Population Transfer into the 85Rb 44D Rydberg State

In order to use Rydberg atoms as elements in fast neutral atom quantum gates, population must be coherently transferred into the Rydberg state. A robust method of coherent population transfer in a three-level system is stimulated Raman adiabatic passage (STIRAP), in which a ``counter-intuitive'' pulse sequence can theoretically transfer 100% of the population. We have studied the efficiency of Rydberg atom excitation in an experiment in which population is driven from the 5S ^85Rb ground state to the 44D Rydberg state through the 5P intermediate state. Both excitation pulses have durations of 500ns, rise times of about 100ns, and Rabi frequencies of order 10MHz. The signature of STIRAP is observed by scanning the delay of the 5P->44D laser pulse with respect to the 5S->5P laser pulse. Due to STIRAP, the population in the Rydberg state is observed to be greatest when the 5P->44D pulse precedes the 5S->5P pulse. We compare the data with theoretical results, which model the coherent population transfer to the 44D Rydberg state in the experimental system used and allow us to estimate the absolute excitation efficiency.

[P1.012] Teleportation with Dissipation Assisted Entanglement

We consider a single two-level atom inside an optical cavity, which also contains a material with a \chi^(2) nonlinearity.The atom and cavity are assumed to be resonant at ømega and the system is driven by light at 2ømega.For an initial trigger detection in the transmitted field, the appropriate collapsed state is given by

\begineqnarray |\psi_c^T\rangle&\equiv &a|\psi \rangle_SS/|a|\psi\rangle_SS|\nonumber &=&\sqrt2C_g,2^SS\mid g,1 \rangle+C_e,1^SS\mid e,0 \rangleøver\sqrt2\mid C_g,2^SS\mid^2+\mid C_e,1^SS\mid^2\nonumber &=&C_g,1^C\mid g,1 \rangle+C_e,0^C\mid e,0 \rangle \endeqnarray with \begineqnarray C_g,1^C&=&\kappa+\gamma/2øver\sqrt(\kappa+\gamma/2)^2+g^2 C_e,0^C&=&-gøver\sqrt(\kappa+\gamma/2)^2+g^2 \endeqnarray

Two such systems can be coupled via a beamsplitter to share entanglement, and to perform teleportation.

[P1.013] Quantum information protocols in a scalable multiplexed ion trap.

We describe experiments directed towards achieving scalable quantum information processing in an array of interconnected ion traps [1]. We study experimentally several protocols using ions in single and multiple trap zones that can be used as benchmarks in reaching this goal. These include superdense coding, quantum teleportation, entanglement-enhanced quantum state detection, and entangled-state spectroscopy. We describe a six-zone linear trap array in which two or more ions are first entangled in one trap, then distributed to separate trap zones, where further entangling operations and/or measurements are performed.

[1] D. Kielpinski, C. Monroe, and D. J. Wineland, \textitNature \textbf417, 709-711 (2002).

[P1.014] Creating Arbitrary Quantum Entanglement of Multi Fock States from A Single Photon

We propose a method using electromagnetically induced transparency (EIT) and fractional stimulated Raman adiabatic passage (f-STIRAP) to prepare a large class of superposition of Fock states from a single photon. In fractional STIRAP, both population and coherence can be continuously transferred between states. Here, the input photon can be stored in the medium using dark state polaritons, and then f-STIRAP pulses are used to coherently split the atomic Raman coherence into pairs. Then reading pulses are used to retrieve the quantum information in these coherence, and arbitrary Fock state superposition states (entangled states), which could be useful, e.g., for the use in quantum information are thus formed.

[P1.015] Entanglement with Classical Spinors

The spinor formulation of classical dynamics, which arises naturally in Clifford algebra approaches, describes particle dynamics in terms of spinor amplitudes and gives quantum mechanical, spin-1/2 form to many classical expressions for particles whose dynamics can be represented by single spinor fields. Here we use tensor products of the algebra of physical space (APS)[1] to explore the quantum/classical interface and provide insight into quantum properties and, in particular, entanglement in multiparticle spin-1/2 systems. Entanglement in mixed-state systems is seen as spinor (“quantum”) correlation beyond the maximum possible with classical frequencies or probabilities. The relevance to systems of qubits in a quantum computer is elaborated.

[1] W. E. Baylis, “Applications of Clifford Algebras in Physics”, in Lectures on Clifford (Geometric) Algebras and Applications, R. Ablamowicz and G. Sobczyk, eds., Birkhäuser Boston, 2004.

[P1.016] Atom-photon entanglement generation and distribution

We extend an earlier model by Law et al. for a cavity QED based single-photon-gun to atom-photon entanglement generation and distribution(C. K. Law and J. Kimble, J. Mod. Opt. 44), 2067 (1997).. We illuminate the importance of a small critical atom number on the fidelity of the proposed operation in the strong coupling limit. Our result points to a promisingly high purity and efficiency using currently available cavity QED parameters, and sheds new light on constructing quantum computing and communication devices with trapped atoms and high Q optical cavities.

[P1.017] Attosecond Phenomena

This abstract not available.

[P1.018] Sequential Ionization of D_2 Molecules in an Ultra-short

The released kinetic energy spectra of D^+ is simulated for the sequential double ionization of D_2 molecules in an ultra-short intense laser field. D_2 is first ionized at its equilibrium distance, followed later by the subsequent further ionization of D_2^+ at larger intenuclear separations. By comparing our simulated D^+ energy spectra with the measured one, we can tell the time duration between the two ionizations to sub-femtosecond accuracy and internuclear separation to sub-Å\ accuracy.

[P1.019] Laser-assisted Autoionization

A quantum mechanical model is developed to describe laser-assisted autoionization. Numerical simulation is performed for a two-channel model system under XUV and laser pulses. The laser-dressed electron spectra calculated with both methods are in good agreement justifying the validity of the theoretical model. The dynamics of the system is traced in time domain by varying the time delay between two the pulses and lifetime of the resonance is obtained from the time dependence of electron count within sidebands. The model is further applied to the case of two resonances. From the oscillation of the electron counts with the time delay, the energy separation between the two resonances, as well as the lifetime of each resonance, can be deduced.

[P1.020] Nonlinear Optics

This abstract not available.

[P1.021] Large enhancement of fully-resonant sum-frequency generation through quantum control via continuum states

A theory of quantum control of short-wavelength sum-frequency generation, which employs the continuum states, is developed. The proposed scheme is based on all-resonant coupling and trade-off optimization of the accompanying constructive and destructive quantum interference effects in the lower-order and higher-order polarizations controlled by the overlap of two laser-induced continuum structures. The scheme does not rely on adiabatic passage, coherent population trapping or maximum atomic coherence as a means to facilitate maximum output. The feasibility of creating frequency-tunable narrowband filters, polarization rotators, and dispersive elements for vacuum ultraviolet radiation is shown. The features specific for quantum interference in Doppler-broadened media are investigated. The possibility of almost complete conversion of fundamental radiation into generated short-wavelength radiation, and of a dramatic decrease in the intensity of required fundamental radiations, is shown.

[P1.022] Quantum interference in a lambda system driven by non-overlapping pulses with the same carrier frequency

A pulse with sufficient bandwidth can drive both dipole-allowed transitions in a lambda system, especially if the two lower levels are only slightly different in energy. Therefore a short pulse with one carrier frequency can drive a small amount of population from one lower state to the other lower state. When a second pulse arrives, its effect depends critically on its phase relations with the already oscillating dipole transitions. (Using pulses with the same carrier frequency makes these calculations different from Raman-Ramsey calculations.) I will explore these phase-dependent quantum interference effects first by using a low-inversion model, which can be pictured in a simple fashion in the time or frequency domain. I will then compare those results with solutions to the optical Bloch equations. The goal of this work is not high population transfer; rather, it is to investigate narrow features that result from these quantum interference effects.

[P1.023] Effect of Raman Detuning in High Order Anti-Stokes Generation in H_2

High order anti-Stokes emission (up to 9^th order) in H_2 under different conditions of pressure, laser intensity, pulse delay time, and detuning off the Q(1) Raman resonance have been studied systematically using two single-mode pulsed lasers at 589nm and 780nm respectively. For every order the highest conversion is observed to occur at a detuning away from the Raman resonance. The magnitude of the detuning decreases with the order of the anti-Stokes emission. This detuning phenomenon is interpreted by electromagnetic induced control on the refractive index of H_2 [1]. We observed a total energy conversion of 26% from the pump laser to the anti-Stokes. At the 9^th anti-Stokes, the conversions is 0.25%. Due to the large Raman shift (4155cm^-1) of H_2, it is a preferred medium to use for generating short wavelengths in the VUV. [1]S. E. Harris and A. V. Sokolov, Phys. Rev. A \textbf55, R4019 (1997)

[P1.024] Creation and doubling of vortices in intracavity second harmonic generation

Optical vortices are topological objects whose transformation properties under propagation in linear and nonlinear optical media have been the subject of much recent interest. In this work we demonstrate generation and frequency doubling of unit charge vortices in a linear astigmatic resonator. By appropriate alignment of a near confocal cavity we couple a fundamental laser beam at 860nm to a vortical resonator mode. With a nonlinear crystal in the resonator a doubly charged vortex at the second harmonic frequency is generated. Topological instability of the double charge harmonic vortices leads to well separated vortex cores that are shown to rotate and become anisotropic, as the resonator is tuned across resonance. A simple theory that accounts for crystal induced astigmatism agrees well with the experimental measurements.

[P1.025] The role of diffusion in Coherent Population Trapping linewidths

We report ongoing experimental studies of the effect of atomic diffusion on the lineshape of Coherent Population Trapping (CPT) resonances. Two optical fields in Raman resonance with the Rb-87 hyperfine sublevels of the electronic ground state optically pump Rb atoms into a non-interacting coherent superposition of the ground states. The characteristic width of this CPT resonance is determined by several effects, including Rb atom diffusion in and out of the laser beam. We study the effects of diffusion by applying a transverse gradient in the longitudinal magnetic field in the Rb vapor cell, which increases the decoherence of atoms both within and outside the laser beam. By comparing the linewidth of the CPT resonance with and without the magnetic gradient, we characterize Rb diffusion dynamics and the effects of CPT coherence outside the laser beam.

[P1.026] Optimizing the fidelity of stored light in atomic ensembles

We report ongoing experimental investigations to optimize the fidelity of stored light in ensembles of warm Rb atoms. In particular, we are studying: the role played by off-resonant interactions of the control and signal fields with various atomic sub-levels; the effect of atomic coherence diffusing out of (and back into) the laser beams; and the use of an optical cavity surrounding the vapor cell to increase the optical depth without increasing loss due to spin-exchange collisions.

[P1.027] Stationary pulses of light

We describe and experimentally demonstrate a method for controlled conversion of light pulses propagating in an atomic medium into excitations with localized stationary electromagnetic energy. We further study the guiding and localization of such stationary photonic pulses in three spatial dimensions using a variety of experimental techniques.

[P1.028] Self-Compression of High Power Laser Pulses in an Atomic Gas

We observe a new form of pulse compression that operates at ionizing laser intensities when an ultrashort pulse propagates through an atomic gas. Normally, when a laser pulse propagates through a gas-filled waveguide at intensities below the ionizing threshold, nonlinear effects such a self-phase modulation (SPM) broaden the spectrum of the pulse. However, these nonlinear effects do not change the pulse envelope - the pulse emerges from the fiber with the same pulse duration but with a broader spectrum. The pulse can then be compressed externally. In this work, we observe pulse compression of 28fs pulses down to 14fs, without the need for post-compression. The waveguide is filled with low pressure argon gas (2-9 torr). We use amplified 800nm pulses at an intensity of 10^15 W/cm^2, which doubly ionize Ar. The input and output pulses were measured using SHG FROG. This new compression scheme cannot be explained by 1-dimensional nonlinear propagation, but may be due to a spatial-temporal coupling. This compression technique can be used to advantage in experiments performed in waveguides, such as HHG or exciting molecular vibrations.

[P1.029] Atom Optics and Atom Interferometry

This abstract not available.

[P1.030] Measurement of atomic recoil using ground state atom interferometry

We have used a cloud of Laser cooled Rb atoms to extend the precision of a previous time domain measurement of atomic recoil by more than two orders of magnitude. An off-resonant, standing wave pulse is used to create a superposition of momentum states involving atoms in the same ground state. After a time T, a second standing wave pulse rephases the superposition resulting in a density grating in the vicinity of t=2T. The grating is detected by back scattering an off resonant traveling wave pulse and measuring the amplitude of the scattered light using a heterodyne technique. We have improved the precision by eliminating decoherence mechanisms due to collisions and stray light so that the signal lifetime is nearly the transit time of atoms through the region of interaction (T=10ms). The degree of precision is three orders of magnitude better than our previous measurement in the frequency domain. We are currently investigating systematic effects that may contribute to the measurement of the recoil frequency.

[P1.031] Aharonov-Casher is not a which-way experiment

Boyer^1 claimed that a sufficiently large Aharonov-Casher (A-C) phase will lead to Which-Path information in an atom interferometer, and hence a reduction in interference fringe contrast. He argues this because displacement of the de Broglie wave phase depends on which path is taken through the interferometer. We present a theoretical study of quantum dephasing of wave \emphpackets due to the A-C effect. In contradiction to Boyer, we predict contrast will be unaffected by the A-C effect, even when using a thermal atom beam interferometer. While we agree that displacement of any one velocity component of a wave packet depends on the interferometer branch, we find that the resulting wave packet envelope remains unshifted regardless of the magnitude of the A-C interaction. ^1T.H. Boyer, "Proposed Aharonov-Casher effect: Another example of and Aharonov-Bohm effect arrising from a classical lag", Phys. Rev. A 36 p. 5083 (1987)

[P1.032] Atom-Surface Interaction effects on Talbot Images

In atom optics, the Talbot effect causes periodic self-imaging of a grating structure as a consequence of Fresnel diffraction. We simulated how Talbot images get modified by van der Waals interaction between atoms and material gratings. We will also present progress towards observing Talbot images from a mechanical grating using atom lithography and an AFM.

[P1.033] Decoherence due to Scattering Atoms

Coherent manipulation of a quantum system is difficult because of uncontrolled interactions with the system's environment. The study of decoherence so introduced is important for progress in quantum mechanical engineering, and for understanding the transition from quantum to classical behavior. We have observed loss of fringe contrast in a Mach-Zhender atom interferometer due to scattering background gas atoms and propose that this might be interpreted as quantum decoherence. Progress will be reported on the use of a general model of decoherence incorporating a semi-classical picture of atom scattering to explain the contrast loss [1]. A formal analogy is made to decoherence due to scattering photons from atoms in an interferometer [2].

[1] S.M. Tan, D.F. Waals, ``Loss of coherence in interferometry", Phys. Rev. A 47 p.4663 (1993) [2] D.A. Kokorowski, A.D. Cronin, T.D. Roberts, and D.E. Pritchard, ``From single- to multiple-photon decoherence in an atom interferometer", Phys. Rev. Lett. 86 p. 2191 (2001)

[P1.034] Matter wave propagation through microstructured waveguide bends

The ability to manipulate ultracold atoms has seen significant progress in recent years. In particular, considerable work has been done on ``atom chips''. To further explore the wave nature of propagation through these microstructures, time-dependent quantum mechanical calculations were performed over a range of parameters close to those accessible by recent experiments. It was found that vortices can be generated --- even in the linear regime --- and can be understood to be a general consequence of wave interference. Here, we focussed on the generation and dynamics of vortices during wavepacket propagation through a simple microstructure: a 180^\circ circular waveguide bend with harmonic transverse confinement. In addition, we performed classical calculations based on Ehrenfest's theorem and compared them to our quantum mechanical results to determine whether classical mechanics can predict the amount of transverse excitation caused by a waveguide bend. This comparison elucidates some limits on the use of classical mechanics for predicting matter wave propagation through microstructures.

[P1.035] Beamsplitting of a Bose-Einstein Condensate in a Microtrap by a Standing Light Wave

We have developed an atom beamsplitter using lithographically patterned wires on an aluminum nitride substrate. Splitting is accomplished by a standing wave light field while the atoms are confined by trapping potentials along an atom waveguide structure. A Bose-Einstein Condensate (BEC) is formed in a ``microtrap'' region of the guide. The standing light field is enabled by a pair of prism-shaped mirrors mounted on the substrate along the waveguide. One mirror directs a laser beam along the waveguide while the second retro-reflects this beam to create a standing wave just above the substrate surface. Exposing the trapped BEC cloud to a pulse of the standing light field produces wave packets that propagated symmetrically in opposite directions along the waveguide. Two oppositely directed wave packets are then recombined after applying another light pulse that simultaneously reverses the momentum direction of both wave packets. As the splitting and recombination is done intra-waveguide, the technique may prove viable for atom-chip based interferometric devices.

[P1.036] An Asymmetric Grating for Large Quantum Particles

Inspired by current efforts to perform diffraction and interference experiments with objects of size that is equal or even larger than the diffraction structure, we develop an approach to investigate how the particle diameter influences the interference pattern in an asymmetric double slit interferometer. The approach\footnote D. Arsenovi\'c, M. Bo\vzi\'c, and L. Vu\vskovi\'c, J. Opt. B: Quantum Semiclass. Opt. 4, S358 (2002). is based on the use of the time dependent wave function of particle's transverse motion and the probability amplitude of transverse momentum. Similar functions were determined and applied by Dubetsky and Berman\footnote B. Dubetsky and P. A. Berman, in Atom Interferometry, edited by P. R. Berman (Academic Press, New York, 1997), p. 407. for infinite periodic gratings. For the asymmetric double slit grating we identify three characteristic cases for the ratio of slit widths \delta_1 and \delta_2 and the diameter D of the particle: a\/) D\ll\delta_1 and D\ll\delta_2, b\/) \delta_1>D>\delta_2, c\/) D> \delta_1>\delta_2. Taking into account the influence of both slits on the particle wave function, regardless through which slit the particle did passed, we treat the particle-wall interaction in the simple fashion, such that if the particle size is greater that the slit opening there is no transmission. The results show that the interference should be in cases a\/) and b\/), while it is absent in case c\/).

[P1.037] Wavepacket Dynamics and Coherent Control

This abstract not available.

[P1.038] Adiabatic and diabatic switching in qubits

Analytic expressions have been found for both slow (adiabatic) and fast (diabatic) switching of states in two-state quantum systems. In the adiabatic limit, the coupling interaction, V(t), is approximately independent of time, while in the diabatic limit V(t) is proportional to a series of instantaneous kicks , i.e. a series of delta functions in time. We discuss the conditions under which both the adiabatic and the diabatic approximations are applicable, and examine the way in which a general V(t) may be expanded around either one of these limiting cases.. In the limit where both states of the qubit have the same energy, the switching probabilities are simply proportional to sin or cos of the action integral (or phase area), namely the integral of the switching interaction, V(t), over time. Away from this limit, time correlation (or time ordering) contributions appear in the probabilities.

[P1.039] Generation and detection of high angular momentum states in Rydberg Stark atoms

We explore the generation and control of high angular momentum wave packets in Rydberg atoms by shaped ultrafast laser pulses. A simple shape consisting of two time-delayed ultrafast pulses combined with a static electric field is found to be effective in many cases. Time-resolved detection of the angular momentum of the wave packet is performed with a half-cycle pulse probe. The HCP maps the angular momentum distribution to an n-state population, which is measured by state-selective field ionization.

[P1.040] Interpreting Learning Control of Molecular Fragmentation

We present results from a series of experiments that examine the fragmentation of molecules using shaped, ultrafast laser pulses. A Genetic Algorithm (GA) is implemented to find optimal, tailored pulse shapes for the desired control. We have developed methods to help explore interesting regions of the pulse shape parameter space and to aid in the interpretation of the physical mechanisms responsible for the control. We also make use of pump-probe spectroscopy to help provide a time domain interpretation of our control results.

[P1.041] Molecular Dynamics in the Rescattering and Sequential Double-Ionization of H_2 in Ultra-Short laser Pulses.

We present a systematic study on the Coulomb explosion of H_2 when exposed to ultra short laser pulses. The relative contribution of rescattering versus sequential double- ionization is presented over a range of 8- 40 fs pulse duration and 1-12 X 10^1^4 watt/cm^2 laser peak intensity. The proton pairs produced in the Coulomb explosion of H_2 were measured in coincidence using a standard COLTRIMS arrangement. The kinetic energy released in these explosions was used to deduce information about the evolution of the molecular hydrogen when ionized by the laser field. A quantitative model is compared with the experimental data and accounts for the major features observed in the experiment.

[P1.042] Chaotic filtering with cold atoms in standing waves of light by control of Dynamical Localisation: properties of Floquet states.

Dynamical Localisation is the well-studied phenomenon of quantum suppression of chaotic diffusion. We have found previously that, for a simple quantum kicked rotor pulsed repeating cycles of unequal period spacing, Localisation lengths and 'break-times' are momentum dependent. A mechanism for a velocity-selective device was proposed by us (T. Jonckeere et al, Phys. Rev.Lett. 91,253003(2003)): packets of cold atoms travel in one direction through a pulsed periodic potential to pass undisturbed, while dispersing atoms travel in the opposite direction. It was implemented experimentally (as proof-of-principle) in P.H.Jones et al,. quant-ph/0309149.

We investigate here the properties of the Floquet states (as the system is time periodic) which underpin this mechanismand compare their properties with the 'Standard Map' implementation of the Quantum kicked rotor. We show that the 'break-times' (the time where the quantum behaviour diverges from the corresponding classical system ) oscillate with initial momentum with period of \pi/b, where b represents a small deviation from the average kicking period. This is also obtained from mean energy level spacing of the Floquet states.Hence we can suggest the best conditions to produce experimentally the best velocity-selective device.

[P1.043] Sensitivity of a cavityless opto-mechanical system

Optomechanical systems play a crucial role in a variety of precision measurement like gravitational wave detection and atomic force microscope. They are based on the interaction between a movable mirror, a meter experiencing tiny forces, and a radiation field, a probe reading out the mirror’s position. In these applications one needs a very high resolution measurement and a good control of the various noise sources, classical and quantum, because one has to detect the effect of a very weak force. As optomechanical system, it is usually considered a Fabry-Perot cavity with a movable mirror coupled to the external force and to the radiation probe. Instead, in our work, we consider a single perfectly reflecting mirror shined by an intense and quasi-monochromatic optical beam. The physical process is very similar to a stimulate Brillouin scattering, even though in this case the Stokes and anti-Stokes component are back scattered by the acoustic wave at reflection, and the optomechanical coupling is provided by the radiation pressure. An effective interaction Hamiltonian for that system has been derived; we further consider the action of a classical coherent force on the probe and its readout through radiation field. Since the Hamiltonian was written in a frame rotating at the frequency of the mirror, we obtain a new Hamiltonian whit new related Heisenberg equations, by assuming the force constant. The mirror is considered initially in a thermal state, and the meter modes in pure entangled state (two mode squeezed state). Then, supposing to perform the heterodyne detection on the reflected sidebands modes, the relevant quantities for the sensitivity of the system are determined to get the signal to noise ratio, from which the minimum detectable force is also obtained. The latter is compared with the standard quantum limit (SQL), showing the possibility to go beyond it by using nonclassical entangled state, (likewise to what happens in the model involving an optical cavity whit the squeezed light). The scaling of the sensitivity in terms of other parameters like laser power is investigated as well. It is to remark that the model is particularly suited to perform pulsed measurement on the probe, while the cavity model presuppose a stationary condition between meter and probe. In conclusion, a cavityless optomechanical model is studied to reveal weak coherent forces, showing that entanglement allows to beat the SQL greatly improving the sensitivity.

[P1.044] Pulse Shaping and Rotational Revivals

Periodic rephasing, or ``revivals'', of molecular rotational wave packets can be used to manipulate the phase and spectral content of ultrashort light pulses. This phenomenon is an integral part of a pulse compression scheme that has been demonstrated, experimentally, to achieve temporal compression ratios of a factor of nine. The technique is very general and can be applied over a broad spectral range. For this application, the rapid fluctuations in the optical properties of the gas that occur during the periodic revivals provide the bandwidth broadening necessary for further temporal compression. We have also demonstrated the feasibility of using the transient birefringence induced in the molecular gas to phase-match nonlinear optical frequency conversion processes. In this application, a high degree of molecular alignment during the periodic revivals provides the necessary birefringence. We are investigating the affects of pulse-shaping on the rotational wave packets and how these relate to the transient optical properties of the gas. For phase-matching using birefringence the degree to which the molecules become rotationally aligned should be maximized. For optical pulse compression it is the time-scale of the revivals that is more important.

[P1.045] Spectroscopy and Fundatmental Symmetries III

This abstract not available.

[P1.046] Measurements of L-shell ion line emission spectra for diagnostics of stellar atmospheres

Chandra and XMM-Newton observations have found many unidentified relatively weak emission lines in astrophysical spectra taken in the 20 -- 70 Å region, which may arise from L-shell ions of astrophysically abundant elements. Current line lists are insufficient for identifying these ions. We have conducted laboratory measurements employing the Livermore electron beam ion traps to record spectra of the relevant ions at densities similar to stellar atmospheres (\leq 10^12 cm^-1. We completed line lists of the nell \rightarrow 2ell transitions for Ar IX -- Ar XVI, S VII -- S XIV, and Si V -- Si XII. Our measurements are compared to calculations using the HULLAC set of atomic computer codes, which are used to confirm line identifications. Comparing our data to Chandra observations of Procyon, we confirm identifications of some smaller lines and correct others, misidentified to element or charge state.

This work was supported by NASA SARA grant W-19,878 and performed under auspices of DOE by UC-LLNL under Contract W-7405-Eng-48.

[P1.047] Exotic Nuclear Radii from Isotope Shifts

The goal of this research is to obtain the nuclear charge radii of short-lived isotopes of helium and lithium by combining high precision spectroscopic measurements of the isotope shift with atomic theory. Recent advances in theoretical techniques for calculating the isotope shift (especially the QED shift due to the Bethe logarithm) allow all contributions (other than the nuclear volume effect) to be calculated to sufficient precision that they can be subtracted from experiment. The nuclear charge radius is then determined from the residual nuclear volume contribution to the isotope shift. Recent progress in measuring the isotope shift for the neutron-rich isotopes ^6He, ^8Li, ^9Li, and ^11Li will be reviewed, along with a number of other high-precision comparisons between theory and experiment for transition frequencies and the ionization potential of lithium.

[P1.048] Experimental Studies of the NaK 3\,^3\Pi Double Minimum State

The double minimum of the NaK 3\,^3\Pi state arises from an avoided crossing with the 4\,^3\Pi state. Using the Doppler-free, perturbation-facilitated optical-optical double resonance (PFOODR) technique, we have investigated the vibrational, rotational, and hyperfine structure of this state. Many striking patterns in the data provide a sensitive probe of the electronic wave function in the various regions of the double well potential. A single-mode cw dye laser excites 2(A)^1\Sigma^+(v_A, J) \sim 1(b)^3\Pi_Ømega=0(v_b, J) mixed singlet-triplet levels from thermally populated ro-vibrational ground state levels, X\,^1\Sigma^+(v_X, J\pm1). Further excitation by a single-mode cw Ti:Sapphire laser selects various 3\,^3\Pi(v_\Pi, J_\Pi) ro-vibrational levels, which are detected by observing direct 3\,^3\Pi \rightarrow 1(a)^3\Sigma^+ fluorescence in the green spectral region. Using the IPA (Inverse Perturbation Approximation) and other methods, we have determined 3\,^3\Pi potential curves that reproduce the measured energies to \sim0.24 cm^-1. In addition, the 3\,^3\Pi state hyperfine and spin-orbit coupling constants (b_F and A_v, respectively) have been determined for each region of the well.

[P1.049] Theoretical Studies of the NaK 3\,^3\Pi Double Minimum State

The hyperfine structure of various ro-vibrational levels of several excited electronic states of the NaK molecule has been analyzed using a model based on diabatic electronic states. The patterns of the experimentally observed hyperfine levels exhibit considerable variation, which can be interpreted by associating different hyperfine coupling constants with each diabatic state contributing to a given adiabatic potential curve. The theoretical work is based on performing ab initio electronic structure calculations for several adiabatic states (using the GAMESS code) and then determining diabatic curves using the block diagonalization method. The ab initio calculations for the 3\,^3\Pi state clearly show that the double minimum arises from the crossing of diabatic states. Using the ab initio results as a guide to the correct form, we parametrized the diabatic potential curves and fitted the experimental data (adjacent poster) using parameterized, diabatic potential curves and coupling terms. Further calculations yield the hyperfine and spin-orbit coupling constants (b_F and A_v, respectively) for each region of the potential.

[P1.050] Measurement of the 6P_1/2,3/2 States of Cesium Using a Mode-Locked Laser

We extend our atomic lifetime measurement technique^1 to include both the 6P_1/2 and 6P_3/2 states of cesium. Briefly, a single pulse from a mode-locked Ti:Sapphire laser excites atoms in a thermal beam to the desired excited state. A subsequent laser pulse is frequency-doubled and used to ionize any atoms remaining in the excited state, which are collected using a charged particle detector. The measurement is repeated using excitation and detection pulses that are increasingly separated in time, allowing the decay from the excited state to be determined. We will discuss improvements to our apparatus to eliminate stray ions and other systematic effects observed in our earlier measurement.^1 The National Science Foundation (Grant No. 9988100) and the United States Air Force Academy provided financial support for this work. ^1B.M. Patterson, C.D. Lindstrom, T. Takekoshi, J.R. Lowell, C. Villarreal, and R.J. Knize, Opt. Lett. 28, 1814 (2003).

[P1.051] Generalized oscillator strengths for inner-shell electron transitioins

We derive a general formula to calculate the generalized oscillator strengths (GOS's) for an inner-shell electron transition between two open-shells of any atom and check it against our previously derived formula for a transition from an open-shell to an empty shell. The GOS of the sodium 2p^63s(^2S)\rightarrow 2p^53s^2(^2P) transition has been evaluated with correlation effects among the various subshells considered through the spin polarized technique of the random phase approximation with exchange and compared with measurement. The general formula has also been used to calculate for the first time ever the GOS for the nitrogen 2s^22p^3(^4S)\rightarrow 2s2p^4(^4P) transition. We urge experimentalists to confirm the predicted results.

[P1.052] Oscillator strengths from the ^87Rb excited state 5p(^2P)

Results from configuration-interaction (CI) and multiconfiguration Hartree-Fock (MCHF) calculations for the oscillator strengths of the ^87Rb 5p(^2P) \rightarrow 4d(^2D) transition have been obtained. In the CI calculation the orbital basis set includes orbitals: 1s,2s,2p,3s,3p,3d,4s,4p,4d,5s,5p,5d,6s, 6p,6d,7s,7p,4f,5f,5g. Final configurations for 5p(^2P) and 4d(^2D) involve transitions of one and two electrons from the 4s-5g orbitals. To reduce the computing time the coefficients whose value are less than 0.002 in the CI expansion have been deleted. A fine-tuning technique was used for the adjustment of the diagonal matrix elements to achieve accurate energy splittings. Both CI and MCHF calculations include some kind of core-valence and core-core correlations. The relativistic effects were included in both calculations through the Breit-Pauli approximation. Data will be presented and compared with measurements and other calculations.

Work supported by U.S. DOE, Office of Basic Energy Sciences, Office of Science.

[P1.053] Electrostatic Focusing of Cesium Atoms in a Fountain

We have used a three element electrostatic lens, based upon the design in Ref. 1, to transversely focus a fountain of neutral cesium atoms (strong-field seeking) launched from a magneto-optic trap. Each of the three lens elements focuses in one transverse direction and defocuses in the other. Combined, the elements generate a net focusing in both transverse directions. Observations are compared with calculations.

Collisional shifts in atomic fountain clocks could be significantly reduced, without loss of signal, by using electrostatic lenses and collimation. Focusing and collimation allows only atoms that will reach the detector to enter the interaction region, excluding atoms that contribute solely to collisional shifts.

[1] J.G. Kalnins, G. Lambertson, and H. Gould, Rev. Sci. Instr. 73, 2557 (2002)

[P1.054] Physicochemical principle to identify spherical symmetries in the genetic code

Based on the molecular structural regularity in nucleobases, upon analysing the atomic contents in amino acid side chains together with solid geometrically rearranging a Hamiltonian graph of the genetic code, hidden rotational symmetries inherent in the degeneracy of codons are unraveled. The internal relation of the 20 amino acids is identified to be in agreement with the spherical and polyhedral symmetry of a quasi-28-gon, i.e., icosikaioctagon, accompanied with two proposed evolutionary axes. Quasi-rotational symmetries in the distribution of both side-chain carbon atoms and side-chain skeleton atoms (carbon, nitrogen, oxygen and sulfur) within the amino acids are presented in the framework of this 28-gon organization. Additionally, we have identified that the sum of the side-chain skeleton atom (C, N, O and S) numbers from amino acids encoded by the 16 genetic code doublets is 100, which is equal to the sum of the backbone skeleton [C, N and O from NH2CHCOOH] atom numbers (5 for each amino acid) from 20 standard amino acids. All together, this study suggests that side chain carbon atomic numbers, side-chain skeleton atomic numbers and amino-acid backbone atomic numbers are balanced within the genetic code by an yet unknown physicochemical principle and non-physicochemical factors.

[P1.055] "Dressing" of lines and vertices in many-body diagrams of the coupled-cluster method

The linearized coupled cluster single-double (LCCSD) method has proven to be successful in high-accuracy calculations of various atomic properties. We are exploring new practical techniques aimed at improving the accuracy of this method. Such improvements are required, for example, in calculations of parity-violating effects in cesium and thallium. Here we suggest a new approach that takes into account so-called non-linear coupled-cluster contributions. In particular, these contributions arise in expressions for matrix elements, and are usually omitted in the traditional LCCSD approaches. We formulate an infinite summation scheme that accounts for the non-linear terms. Qualitatively, one subset of diagrams leads simply to "dressing" of the hole and particle lines of the LCCSD diagrams. The other subset of diagrams leads to RPA-like dressing of matrix elements. The details of this new technique as well as numerical results for univalent atoms will be reported at the conference.

[P1.056] New experiment to measure the electron electric dipole moment

We are building a new experiment to measure the electric dipole moment (edm) of the electron. The experiment will use laser-cooled Cs atoms trapped in two, side-by-side, standing wave, far-off resonance optical dipole force traps. High voltage electrodes will apply opposite polarity electric fields to the two traps. The signature of an edm would be a first-order electric field shift of the atomic Zeeman levels. The traps will be loaded inside a titanium vacuum chamber with atoms captured in optical molasses from a 2D MOT cold atom source. We have paid special attention to the magnetic noise generated by Johnson noise currents of conductors in the design of this apparatus. The apparatus is designed to be sensitive to an electron edm as small as 10^-29 e cm. In this presentation, we will discuss the design of our experiment and our experimental progress.

[P1.057] Progress towards a diode laser resonant with the 657 nm calcium intercombination line with Hertz-level stability.

We are developing a stable laser resonant with the 657 nm ^1 S_0 to ^3 P_1 transition in calcium for use in an optical frequency standard. Similar to lasers in other calcium frequency standards, the laser beam will be generated by an external-cavity grating stabilized diode laser locked to a high finesse optical cavity. The optical cavity is made of ultra-low expansion quartz and has a finesse near 300,000. It will be placed inside of a temperature-stabilized and mechanically isolated vacuum chamber. The external cavity diode laser uses a novel design developed in our lab. This design is similar to the Littman-Metcalf design, but it incorporates a Faraday-effect isolator in the laser cavity for improved power output. To find the position of the optical cavity resonances relative to the atomic transition frequency we will lock the laser to the cavity and beat it with a second laser locked to atomic absorption in a high temperature vapor cell.

[P1.058] Initial Results on an Approach for Creating Tunable UV Radiation for Spectroscopy at 243nm

Convenient tunable coherent UV radiation could be used in number of atomic physics applications. Our particular interest is in a 243nm laser that can be used to precisely measure the 1S to 2S interval in atomic tritium. An approach is being investigated which might ultimately be less cumbersome and expensive than current methods. A multi longitudinal mode “980nm” pump module is converted to a single longitudinal mode laser using costume fiber Bragg grating. Results for the short term frequency stability will be given. A first doubling stage using PPMgO:LN waveguide has been investigated and experimental results will be discussed. A second stage of doubling, using CLBO, which we calculated to have a better conversion efficiency than well known BBO crystal, is planned. Theoretical calculation for this stage and comparison with BBO will be presented.

[P1.059] Improvements in an Atomic Beam Apparatus for Use in Precision Spectroscopy of Helium

We present work done to investigate and implement various improvements to an atom beam apparatus used in high precision laser spectroscopy of helium. Efforts to improve experimental conditions include improving the signal to noise by constructing a UHV chamber to reduce background counts, implementing a modified Helmholtz coil geometry for a more uniform magnetic field, and installing a feedback controlled mirror to replace retroreflecting prism for more reliable Doppler cancellation. Also presented is the implementation of a cost effective method of efficient recirculation to minimize the consumption of He-3. Finally, investigations into future improvements are presented including calculations in the use of a high brightness lanthanum hexaboride source for electron emission, and the possibility of using a laser for initial state atom preparation.

[P1.060] Variational calculations of four-body molecular systems

Fully nonadiabatic calculations are performed for various four-body two-center molecular systems, using variational method in Hylleraas coordinates. The systems under study include H_2, HeH^+, MuH, and their isotopes. Our studies demonstrate that the traditional Hylleraas coordinates, which has been used widely for one-center atomic systems, can be equally well applied to two-center molecular systems. High-precision energy eigenvalues will be reported.

[P1.061] Theoretical study of dissociative recombination in H2D+ and HD2+

Recently, we have developed a method allowing a theoretical treatment of dissociative recombination (DR) in H3+. Using the method we could interpret DR experiments with H3+ and D3+. The method was successful also in interpretation of photoionization experiments. In this study we apply the developed method to an investigation of the DR process in mixed isotopomers of H3+: H2D+ and HD2+. One key finding of the study is that the broken D3h symmetry for H2D+ and HD2+ results in stronger nonadiabatic coupling in the hyperradius, compared to H3+ and D3+. Whereas an adiabatic hyperradial approximation was adequate in the equal mass systems, it will be far more important for to include nonadiabatic coupling in the calculation of the H2D+ and HD2+ ionic vibrational energy levels and eigenfunctions. The study of these molecules paves a road to treat DR in such small polyatomic ions as H2O+.

[P1.062] Dipole Polarizabilities of Excited Alkali-Metal Atoms and Long Range Interactions with Helium Atoms

The scalar and tensor dynamic polarizabilities of the ground ^2S and first excited ^2P states of the alkali metal atoms Na, K and Rb are calculated using many-body perturbation theory. Comparison with experimental measurements of the static polarizabilities suggests that the errors in the theoretical predictions do not exceed 1%. The dynamic polarizabilities at imaginary frequencies are employed to calculate the long range van der Waals coefficients for the interaction of helium atoms with the excited alkali metal atoms to a probable error of less than 2%.

[P1.063] Photodissociation and Photoassociation

This abstract not available.

[P1.064] Circularly-polarized H\alpha emission produced by photodissociation of H_2 with circularly-polarized light

We have bombarded hydrogen molecules with circularly-polarized light ranging in energy from 32 to 36 eV. Subsequent fluorescence of photodissociated H(n=3) atoms was observed at an angle of 30^o with respect to the incident photon beam, and the intensity and circular polarization of the H\alpha light was measured as a function of incident photon energy. The excitation function for H\alpha light is consistent with earlier measurements made using linearly-polarized incident light [1]. The circular polarization switches sign at about 32.5 eV, from negative to positive as incident photon energy is increased. This behavior is not understood.

[1] M. Glass-Maujean, J.Chem.Phys. \textbf89, 2839 (1988).

[P1.065] Dissociation of diatomic molecular ions in ultrafast intense laser fields probed by coincidence 3D momentum imaging

Laser induced dissociation of some diatomic molecular ions, including H_2^+, N_2^+ and O_2^+, has been investigated by coincidence 3D momentum imaging. The keV energy ion beam is crossed by an ultrafast intense laser beam, and the resultant fragments are recorded by a position-sensitive detector. The momentum vector of each fragment is evaluated, and the true coincidences are selected by momentum conservation. A vibrationally resolved kinetic energy distribution is obtained. The kinetic energy release is analyzed in a complete angular distribution, which reveals valuable information on the dissociation dynamics of molecular ions. Laser induced bond-softening and trapping effects (as well as other phenomena) have been observed. Dissociative ionization, the weaker channel, is studied simultaneously.

*Supported by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

[P1.066] Rovibrationally-resolved Photodissociation of LiCl

In cool brown dwarf atmospheres, LiCl appears to be the dominant Li-bearing gas for a large range of temperatures and pressures. Thus, accurate absorption oscillator strengths and photodissociation cross sections are needed for astronomers modeling the atmospheres of cool stars and extrasolar giant planets. Using recent ab initio configuration interaction calculations of the ground and low-lying excited states of LiCl, rovibrationally-resolved photodissociation cross sections of LiCl have been calculated for all the transitions from the ground electronic state, X~^1\Sigma^+, into the B~^1\Sigma^+ and A~^1\Pi states. These initial studies of the photodissociation of LiCl do not take account of predissociation induced by an avoided crossing in the singlet sigma channels.

[P1.067] Coherent Control of Product Branching in the Photodissociation of NaI

We present several schemes to actively manipulate the product branching and the production of polarized iodine atoms in the photodissociation of sodium iodide (NaI). The combination of novel matter-wave interferometric effects observed in recent studies of diatomic photodissociation and interferences induced by temporally separated laser pulses, open up the possibility to actively control the photodissociation dynamics. We choose a range of external parameters such as the optical phase and the intensity and the delay time between the laser pulses to control the product branching in the photodissociation process. Calculations employ the time-dependent quantum wave packet method with \emphab initio potential curves, spin-orbit coupling elements, and transition dipole moments.

[P1.068] Ionization and dissociative ionization through repulsive Rydberg states in Na_2

We have studied the ionization and dissociative ionization of Na_2 via two-color resonantly enhanced excitation plus absorption of one more photon. The maximum total energy is about 2000cm^-1 above the dissociative ionization threshold into Na (3s) and ground state Na^+. Based on kinetic energy analysis of Na^+ fragments, and the comparison of experiment and our model calculation for the branching ratio between Na^+ and Na^+_2, we believe that the repulsive Rydberg states converging to Na^+_2(1^2\Sigma_u) is mainly responsible for the dissociative ionization process, revealing a close connection between autoionization, electronic excitation of the core and fragmentation.

[P1.069] Photofragmentation of Cl_2 Following Photoexcitation near the Cl-L_2-3 Ionization Threshold

Decay processes following core-level excitation and ionization of molecules have been widely studied over the last decade. The advent of 3^rd generation synchrotron radiation sources has allowed the measurement of weaker channels with nearly the same resolution and statistics as that of total absorption measurements, resulting in new experimental insights on resonant and non-resonant core-level processes. In this work we present partial ion yields for Cl_2, obtained with high resolution over a range between 180 and 260eV. In addition to the sharp Rydberg series below the L_2-3 ionization thresholds, two broad structures were observed for each molecule. If we carefully examine the Cl_2^n+ spectra and compare them with the Cl^n+ spectra we see a definite enhancement for a number of peaks, all of which are related to n\textitd Rydberg orbitals from both series. In addition there are a few weak spectral lines which appear in the Cl^n+ specta but not in the Cl_2^n+ spectra.

[P1.070] Photofragment Imaging of Ultracold Collisions

We have constructed a photofragment imaging spectrometer to study nonadiabatic processes that take place during ultracold collisions. We show that information on the nature of the coupling mechanisms that lead to nonadiabatic events may be obtained from these types of measurements. Progress towards realizing the experiments will be described. Measurements of the high n Rydberg states needed to resolve small energy changes during the collisions will be presented.

[P1.071] Resonance Multiphoton Ionization and Dissociation of Dimethyl Ether via the C', C and B states

We have studied multiphoton ionization and dissociation of a jet supersonic of Dimethyl Ether (DME) through absorption of multiple photons at 1 nm intervals in the 450-550 nm region (visible range). In this region the multiphoton spectra is similar to the absorption spectra in 150-183 nm region and it is possible to observe three prominent bands corresponding to the three-photon transitions C'--X, C--X and B--X. Fragmentation of DME shows several dissociation channels for the visible region studied here: CH3+ and CHnO+ (n=1-3). However, CH3OCH3+ (parent ion) is the ion more abundant. Also we have obtained multiphoton ionization photoelectron spectrum of DME and measured the ionization potential to DME; 9.55 eV.

[P1.072] Multiphoton ionization and dissociation of Cyclopropane at 355 and 532 nm

We have studied multiphoton ionization and dissociation of a jet supersonic of cyclopropane using second and third harmonics of Nd:YAG laser (532 and 355 nm). At 532 nm the molecule of cyclopropane absorbed one or two photon to dissociate at C3H4 + H2 and C2H3 + CH3 and then each fragment absorbed more photons until reach its ionization potential. At 355 nm, we have observed the parent ion and ionized small fragments. In this situation, cyclopropane absorbed three photons to reach the ionization potential then cyclopropane cation dissociates to C3H5+, C2H3+, CH3+ y CH2+.

[P1.073] Bond rearrangement caused by sudden multiple ionization of water molecules

Bond rearrangement, namely the dissociation of water into H_2^+ + O^q+ following sudden ionization by swift highly charged ion impact, was investigated. Single ionization by fast proton impact exhibits a strong isotopic effect, the dissociation of H_2O^+ \to H_2^+ + O being about twice as likely as D_2O^+ \to D_2^+ + O, with HDO^+ \to HD^+ + O in between. This suggests that the bond-rearrangement does not happen during the slow dissociation, but rather during the very fast ionization, and thus H_2^+ should also be produced when the water molecule is multiply ionized. We observed that the H_2^+ + O^+ and H_2^+ + O^2+ production in 1 MeV/amu F^7+ + H_2O collisions are 0.209\pm 0.006% and 0.0665\pm 0.003%, respectively, of the main double-ionization dissociation product, H_2O^2+ \quad \to H^+ + OH^+. Similar dissociation channels in the heavier water isotopes, expected to be smaller, are under study.

*Supported by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

[P1.074] Intense Field Effects

This abstract not available.

[P1.075] Imaging molecular structures with few-cycle pulses

Recollision events govern intense laser interactions with matter. Advanced laser techniques produce intense, ultrashort pulses that can include a single strong laser cycle within the envelope. Such pulses can be used dynamically to image molecular structures by the means of electron diffraction. The first half-cycle laser field can extract a molecular electron wave packet, and the second half-cycle return it to scatter from the nuclei. From the interference patterns so generated, dynamical molecular structure information can be retrieved. By solving the 3D time-dependent Schrödinger equation, we demonstrated this effect for molecular ions of K2+.

[P1.076] Determination of the carrier-envelope phase of ultrashort laser pulses using metal surfaces

Many results of ultrashort-laser matter experiments strongly depend on the relative phase \varphi of the field oscillations with respect to the peak of the laser pulse. Until recently, determination of \varphi was limited by a \pm \pi ambiguity and restricted to high-energy (\gg 1 \muJ) pulses. Control mechanisms for pulses at moderate intensity levels were missing. Our simulations of ultrashort laser pulses interacting with metal surfaces based on time dependent density functional theory indicate that photoemission from surfaces, especially in the multiphoton regime (I<10^13 W/cm^2), might be a promising candidate for measuring \varphi for pulse durations \tau shorter than 10 fs. To better understand this surprising result we set up a classical trajectory Monte Carlo simulation of the process including photon absorption by conduction band electrons giving insight into the relative importance of underlying mechanisms. First experiments support out predictions. This work has been supported by Fonds zur Förderung der wissenschaftlichen Forschung under project no.\ FWF-SFB016.

[P1.077] Double Ionization of N_2 and O_2 in Intense Laser Field

Different ionization processes can be identified by measuring the full momentum vectors of Coulomb exploding N^+ or O^+ fragments in coincidence using cold target recoil ion momentum spectroscopy (COLTRIMS). We measured high resolution kinetic energy release spectra and showed angular dependences for doubly ionized N_2 and O_2 molecules with laser peak intensities between 1 and 20 X10^1^4 W/cm^2. We found that the process of double ionization proceeds through well defined electronic states of the excited molecular dications. Using linear and circular polarized light, we identified two mechanisms for the production of theses states, rescattering and sequential ionization. By using 8 fs pulses, we observed that the internuclear distance can be frozen during the pulse.

[P1.078] Time-dependent treatment of HD^+ in an intense laser field

The HD^+ molecular ion in the field of a strong, linearly polarized, short, infrared laser pulse is considered in the framework of the time-dependent Schrödinger equation. We consider a reduced dimensionality approximation to the system by assuming the nuclei are aligned with the field and cannot rotate. Thus, we include one nuclear and two electronic egrees of freedom. Beyond this reduction, our only approximations are due to the discretization of the problem. In particular, we use the full Coulomb potential, not the soft core often used in reduced dimensionality models. The calculations are performed for 10~fs Gaussian laser pulses with intensities in the range 10^14 to 10^15 W/cm^2. The dependence of the D/H dissociation branching ratio on the peak intensity is calculated along with the ionization probability.

[P1.079] Laser-induced Coulomb explosion imaging for studying fast molecular dynamics

Strong ultra-short (<10 fs) laser pulses cause multiple ionization of molecules followed by immediate dissociation (Coulomb explosion). Measuring momenta of all ion fragments allows to reconstruct the structure of molecular ionbefore the explosion. We demonstrate that for intense 8 fs pulses this structure approaches an equilibrium structure of a neutral molecule. Using two ultra-short laser pulses with variable delay one can observe fast dynamics of nuclear wave packets with sub-10 fs time resolution. We present pump-probe measurements of fast nuclear motion in D_2 and SO_2 molecules.

[P1.080] On the mechanism of anomalous ellipticity dependence of high-order harmonic generation in intense laser fields

Based on the weak field approximation, the high-order harmonic generation (HHG) yield should decrease monotonically as the ellipticity of a laser field increases. In the experiment, for certain HHG, the observed HHG yield may increase as the ellipticity of the laser field increases. Here we investigate the mechanism of this anomalous ellipticity dependence of the HHG spectra by solving the time-dependent Schrödinger equation. Two kinds of anomalous ellipticity dependence of the HHG spectra have been found. One appears near the ionization threshold and another appears in the cut-off regime. The near ionization threshold one is originated from the near-resonance due to the ac Stark shift and such an enhancement strongly depends on the laser intensity, wavelength as well as atomic structure. The one in the cut-off regime is due to that the higher energy photo-electron is confined by the circular component of the field and emits a HHG.

[P1.081] Nonperturbative study of high-order above-threshold multiphoton detachment of H^-: time-dependent non-Hermitian Floquet approach.

High-order above-threshold detachment of H^- in intense laser fields is studied non-perturbatively using a new time-dependent non-Hermitian Floquet approach. We present a detailed exploration of the electron energy and angular distributions for the laser field with the wavelength 10.6 \mum and intensities 10^10 -- 10^11 W/cm^2. Our results are in accordance with the qualitative semiclassical predictions: the electron energy spectrum exhibits a plateau region in the higher energy part. The electron angular distributions in this region show dramatic transformations. Our computational method makes use of the complex-scaling generalized pseudospectral spatial discretization and non-Hermitian time propagation of the time-evolution operator. The approach is designed for effective treatment of multiphoton processes in very intense and/or low-frequency laser fields, which are generally more difficult to treat using the conventional time-independent Floquet matrix techniques.

[P1.082] Applications of AMO Science

This abstract not available.

[P1.083] Theoretical Description of the Excited States of Extended Pi-Conjugated Molecules

Description of the excited states of large molecules is a computational challenge and time-dependent density-functional theory (TDDFT) is widely used for such systems. However, extended, pi-conjugated systems are challenging for TDDFT due to functionals that use the local-density approximation. Quantum-correlated methods, such as configuration interaction or coupled-clusters, have a large computation demand, and may only be applied presently to the smallest molecules of interest. We will present descriptions of the electronic structure of these extended pi-systems using a variety of semi-empirical and first-principles methods, e.g., time-dependent Hartree-Fock, TDDFT, and coupled-cluster theories. Emphasis will be placed on size-extensive methods, i.e., methods that maintain a degree of precision with increases in the size of the material system. Phenomena studied include the low-lying singlet excitations and emissions for individual oligimers and pi-pi stacked systems.

Research sponsored by the Division of Materials Sciences and Engineering, U. S. Department of Energy and by Advanced Research and Development Activity (ARDA), under Contract DE-AC05-00OR22725 with UT-Battelle, LLC.

[P1.084] Demonstration of human lung imaging in an open-access, low-field MRI system

NMR of laser-polarized noble gas (^129Xe and ^3He) has great utility as a probe of a wide variety of physical and biomedical problems. We have demonstrated human lung imaging as a function of subject orientation using an open access MRI system that operates at low applied magnetic field (approx. 50 gauss).

[P1.085] Imaging of brain magnetic fields with an atomic magnetometer

Measurements of the magnetic fields generated by the brain (Magnetoencephalography or MEG) are widely used for non-invasive studies of the brain. They typically use arrays of hundreds of SQUID detectors operating in liquid Helium. We are developing a new multi-channel atomic magnetometer suitable for mapping of magnetic fields from a human brain. The magnetometer uses high-density K vapor and operates in a very low magnetic field, eliminating the broadening due to spin-exchange collisions. We have previously demonstrated a 7-channel magnetometer with magnetic field sensitivity exceeding the sensitivity of SQUID detectors [1]. Currently we are constructing a 256-channel magnetometer system operating in a human-size magnetic shield. The magnetic fields will be measured on a two-dimensional grid in a cubical cell approximately 7 cm on the side located about 2 cm away from a human head. Numerical simulations indicate that spatial localization of the magnetic field sources within the brain should be improved by more than one order of magnitude compared with traditional SQUID systems.

[1] I. K. Kominis, T. W. Kornack, J. C. Allred and M. V. Romalis, Nature, \textbf422, 596 (2003).

[P1.086] Timing the Acetylene-Vinylidene Isomerization Using Ultra Short Laser Pulses

The isomerization of acetylene to vinylidene has been investigated for many years. Very recently, the upper limit for the time of the rearrangement in the dication has been deduced experimentally in the photo-ionization of the carbon K-shell from acetylene [1]. In this work, we used COLTRIMS and measured in coincidence the ion pairs produced in the fragmentation of acetylene after being doubly ionized by intense short laser pulses. Using the fragments' momentum spectra, the acetylene and vinylidene breakup channels are clearly isolated. Additionally, using two ultra-short laser pulses with variable delay in a pump-probe arrangement, important information about the isomerization time can be obtained. 1- T. Osipov, et. al., Phys. Rev. Lett.90,233002(2003).

[P1.087] Highly Excited Atoms/Rydberg States

This abstract not available.

[P1.088] Localized Hartree-Fock density-functional calculations of singly, doubly, and triply excited Rydberg states of He- and Li- like ions

An exact spin-dependent localized Hartree-Fock (LHF) exchange potential is derived for both close-shell and open-shell of atomic systems. The LHF exchange potential is free of the Coulomb self-interaction, has the correct long-range behavior, requires only the occupied orbitals, and thus implies the requirements for the investigation of the excited states. An effective procedure of the exact exchange density-functional theory (DFT), the spin-polarized LHF density-functional method, is presented based on the LHF exchange potential for the multiply excited states of the atomic systems. This method is applied to the calculations of singly, doubly, and especially triply excited Rydberg states of He- and Li- like ions. The exchange-only (X-only) results are found to be surprisingly close to those of the Hartree-Fock (HF) method. The correlation effects are considered by incorporating the Lee-Yang-Parr (LYP) correlation potential into the LHF exchange potential. The results are in overall agreement with the available theoretical and experimental data in light of the typical errors of the DFT calculations of the excited states.

[P1.089] Dynamic Polarizabilities of Rydberg States of Alkali Atoms and Inert Gases

For photon frequencies exceeding the ionization threshold of an atomic level, the contribution of virtual continuum states to its dynamic polarizability (DP) becomes important. We generalize the exact analytical results for DP of hydrogen-like excited states [1] to the case of alkali atoms and inert gases. The extension is based on the use of the generalized Sturmian expansion [1] for the Coulomb Green’s function having a non-integer angular momentum parameter. This expansion ensures the convergence of Sturmian series for DP at above-threshold frequencies, where the standard Sturmian expansion is divergent. The angular momentum parameter for a given l is connected with quantum defects of |nl>-states [2], so that the accuracy of our results for DP is comparable to that for quantum defect theory. We present numerical values for DP of excited states over wide interval of frequencies. These results may be used to estimate the Stark-shifts and widths of Rydberg levels in laser fields. [1] A. A. Krylovetsky, N. L. Manakov, and S. I. Marmo, Sov. Phys.-JETP 92, 37 (2001). [2] N. L. Manakov and V. D. Ovsiannikov, J. Phys. B 10, 569 (1977).

[P1.090] Microwave spectroscopy of Al Rydberg atoms: Quantum defect analysis of new measurements in S, P, D, F and G states

Microwave resonance techniques have been used with two-step pulsed-laser excitation and field-ionization of Rydberg states in an atomic beam to study one- and two-photon transitions in the normal configuration 3s^2 n\ell of neutral aluminum for n = 22 to 45 and \ell = 0 to 4. Line centers have been determined with accuracy approx.~1 MHz, and doublet fine-structure splittings have been measured in ^2P and ^2D terms. Two-photon transitions nP\rightarrow(n+1)P have allowed quantum-defect Ritz-expansion coefficients for the ^2 P_1/2 and ^2P_3/2 series to be determined. >From these together with P \rightarrowS and P\rightarrowD transitions, quantum defects for ^2 S_1/2, ^2D_3/2 and ^2D_5/2 were found. Based on D\rightarrowF and F\rightarrowG one-photon transitions out of laser-excited nf states, F- and G-series quantum defects could also be determined. The results, based on over 100 newly observed Rydberg microwave resonances together with earlier accurate results from optical spectroscopy, allow corresponding Al I levels and transitions \ell = 0 to 4 to be calculated with confidence for all n.

[P1.091] Suppression of Rydberg excitation in an ultracold atomic sample

Recently, the dipole blockade mechanism(M.D. Lukin et al.), Phys. Rev. Lett. 87, 037901 (2001). has been proposed to implement quantum information processing using Rydberg atoms. We report an advance toward this goal, a local excitation blockade in an ultracold sample containing 10^7 ^85Rb atoms. We illuminate the sample with narrowband (\sim 100 MHz) 297 nm UV pulses to excite atoms to np_3/2 states (n=30, 70, and 80). The resulting Rydberg atoms are detected by pulsed field ionization. We observe a dramatic suppression of excitation for n=70 and 80, whereas n=30 behaves as isolated atoms. Our local blockade arises, not from dipolie interactions, but from van der Waals interactions which scale very rapidly with n. We present results on the dependence of the blockade on both laser irradiance and atom density, and compare with a mean-field model. The model and experimental measurements agree well.

[P1.092] Manipulation of the Dipole-Dipole Interaction in a Magneto-Optical Trap

Ultra-cold highly-excited atoms in a magneto-optical trap are strongly coupled by the dipole-dipole interaction, which can be tuned into resonance with a static electric field. We have investigated controlling the complicated many-body interactions in this system. Software has been developed to produce a Stark map, find resonances, and calculate their interaction strengths. The calculations are shown to be in good agreement with experimental results.

[P1.093] Studies of Negative Ion Properties with a Penning Trap

A novel permanent-magnet Penning ion trap is being used to study the properties of a variety of negative ion species formed through Rydberg electron transfer in collisions with K(np) Rydberg atoms. Studies with valence-bound parent anions such as C_6H_5NO_2^- reveal the creation of a number of negative ion states that have different lifetimes, the relative numbers in each state changing with n. Surprisingly, dipole-bound anions injected into the trap are also observed to decay, with lifetimes in the range \tau \sim 60-100 \mus. This decay is attributed to photodetachment induced by background 300K thermal radiation. Negative ion collisional properties are also being examined by admitting target gas into the trap. The data show that the rate constants for collisional destruction of dipole-bound ions can be large, \tau \sim 10^-7 cm^3 s^-1, consistent with their weak binding. Other processes of interest include the formation of new negative ion species by charge transfer and the collisional stabilization of valence-bound anions. The lifetimes of negative ions formed by free electron attachment in the trap are also being examined. The free electrons are generated by the decay of very short-lived ion species that are initially introduced into the trap.

[P1.094] Dynamics of Rydberg Electron Transfer to CH3CN: Velocity Dependent Studies

The dynamics of free-ion production through electron transfer in K(np)/CH_3CN collisions are examined through measurements using velocity-selected Rydberg atoms. The data show that Rydberg electron transfer leads to the creation of two groups of dipole-bound CH_3CN^- ions, one long lived (\tau > 85 \mus), the other very short lived (\tau \ll 1 \mus). The velocity dependences associated with the production of both groups of ions are similar, the ion signal decreasing markedly with decreasing Rydberg atom velocity, principally as a result of post-attachment electrostatic interactions between the product ions. The results are in reasonable accord with the predictions of a model that considers the effect of crossings between the diabatic potential curves for the covalent K(np)/CH_3CN system and a K^+/CH_3CN^- ion pair. This model also accounts for the relatively small reaction rate constant, \sim 5 x 10^-9 cm^3 s^-1, associated with formation of long-lived ions. No velocity dependence in the lifetime of the CH_3CN^- ions is observed.

[P1.095] The Kicked Rydberg Atom: Effect of Noise and External Fields on Dynamical Stabilization

The dynamical stabilization of high-n (n\sim350) Rydberg atoms subject to a train of half-cycle pulses (HCPs) is examined. Data obtained using quasi one-dimensional atoms reveal pronounced differences in survival probabilities when the HCPs are directed parallel and anti-parallel to the atomic axis, indicating very different dynamical behaviors. Classical and quantum simulations show that for impulses anti-parallel to the atomic axis, the phase space for the system is mixed with large stable islands embedded in a chaotic sea, leading to dynamical stabilization. No similar islands are evident when the impulses are reversed, producing a globally chaotic system leading to rapid ionization. We explore how superposing noise and/or a dc field during the HCP train influences dynamical stabilization and show that pronounced effects are observed in the survival probability.

[P1.096] Engineering Atomic Wavefunctions Using Sequences Of Orthogonally-Directed Half-Cycle Pulses.

The use of a series of orthogonally-directed half-cycle pulses (HCPs) to generate targeted electronic states is explored. In this work, quasi one-dimensional potassium Rydberg atoms are created by selectively exciting, in a weak dc field, extreme red-shifted states in the n=350 Stark manifold. A HCP applied along the same axis as the dc field is then used to induce transient phase space localization, the electron probability density becoming strongly localized near the outer classical turning point. A second HCP, applied transverse to the initial pulse, transfers the electron into selected circular or elliptical orbits. The evolution of product states is analyzed by applying further HCPs, and their final state distribution is determined by selective field ionization. Near circular states provide an ideal starting point for further studies of the control and manipulation of atomic wavefunctions, and for investigating non-linear dynamics in the “kicked” atom.

[P1.097] Study of evolution of cold Rydberg Rb atoms to plasma

We report on studies of the evolution of dense, cold samples of Rydberg rubidium atoms to plasma. We excite cold Rb atoms to Rydberg states in the range 25 < n^\ast < 50 using a 10 ns pulsed Littman dye laser, achieving Rydberg densities of \sim 10^10 cm^-3. The Rydberg atoms are allowed to evolve on time scales of up to 50 \mus. After a specific time delay, the atoms are field ionized, and the electrons or ions detected using a microchannel plate detector. As has been found in a number of other studies, (see, for example M. P. Robinson et al.), Phys. Rev. Lett., 85, 4466 (2000) we observe the formation of a plasma from such a sample. We will report our findings on the behavior of such a sample.

[P1.098] Effect of Pulse Shape on Strongly Driven Two-Level Systems

We present an experimental study of the interaction between an effective two-level system and strong radiation pulses as a function of pulse shape. We have explored the qualitative behavior of the transition probability as a function of pulse area for five different intensity profiles: Lorentzian, Lorentzian squared, hyperbolic secant, hyperbolic secant squared, and Gaussian. The experimental system consists of fine-structure levels of Rydberg states in alkali atoms. Raman transitions are driven through far-off-resonance intermediate states. The pulses are in the microwave regime and have high fidelity, F \ge 0.995, and uniform intensity. Experiments were performed with pulses that are nearly impulsive (adiabatic evolution), intermediate, and nonimpulsive (nonadiabatic evolution) and show that despite the similarity in the pulse shapes, the character of the population transfer versus intensity depends strongly on the shape for all but impulsive transitions.

[P1.099] Electron and Positron Scattering

This abstract not available.

[P1.100] Double ionization of lithium near threshold by electron impact

The energy dependence of a multiple-ionization cross section near threshold is a many-body process whose theoretical description remains of current interest. We previously reported on use of ultracold, trapped lithium atoms as a target for measurements of single-, double-, and triple-ionization by electron impact far above the ionization thresholds. Here we describe measurements of the double ionization of lithium by electron impact from near threshold to 160 eV excess energy. The cross section near threshold is sensitive to electron correlations among the three slow continuum electrons and the ion core. Double ionization of neon near threshold was also measured to compare with other reported experiments. The experimental methods and the results obtained will be presented.

[P1.101] Neutral Dissociation of SiF4 by Electron Impact.

We report the results of experimental studies aimed at measuring the absolute cross section for the formation of Si atoms in the ^1S_o ground state following electron-impact neutral dissociation of SiF_4 molecules. We combine electron scattering techniques with the final-state specific laser-induced fluorescence (LIF) detection of the neutral ground-state Si atoms. We probe the Si(^1S_o) atoms by laser excitation at 390.550 nm to the ^1P_1 state and measure the subsequent emission at 288.2 nm corresponding to the ^1P_1=> ^1D_2 transition by a gated photon detection method. Absolute calibration of the cross section is made relative to the same cross section for the neutral dissociation of SiH_4 measured earlier (N. Abramzon et al., J. Chem. Phys. 113 (2000) 2250).

Work supported by the US Department of Energy and in part by NASA.

[P1.102] Electron Impact Ionization of Helium

Doubly-differential cross sections for the electron impact ionization of helium have been measured at low incident energies. The measurements were taken using the moveable nozzle technique recently developed in our lab.(M.\ Hughes, K.\ E.\ James, Jr., J.\ G.\ Childers, and M.\ A.\ Khakoo, Meas. Sci. Technol.) 14, 841 (2003) Data were taken at 26~eV, 28~eV, 30~eV, 32~eV, 34~eV, 36~eV, and 40~eV incident energies. The results are compared to the theoretical convergent close-coupling calculations of Bray et al.(Igor Bray, Dmitry V.\ Fursa, and Andris T.\ Stelbovics J.\ Phys.\ B) 36, 2211 (2003), and good agreement is observed. This work is funded by the National Science Foundation under grant # NSF-RUI-PHY-0096808.

[P1.103] Absolute Cross Section for Electron Impact Excitation of Metastable C^2+

Progress toward measurements of the absolute cross section for electron impact excitation (EIE) of C^2+ (2s2p ^3P^o - 2p^2 ^3P) for energies below threshold to 15 eV above is reported. These measurements will be used to determine the EIE rate coefficients required for astrophysical applications. Ions are produced in a 5 GHz Electron Cyclotron Resonance (ECR) ion source. A modulated beams technique with inclined electron and ion beams is being used. The radiation from the excited ions at \lambda 117.5 nm is detected using an absolutely calibrated optical system that subtends slightly over \pi steradians. The population of the C^2+ metastable state in the incident ion beam is determined experimentally. This work is supported by NASA Supporting Research and Technology grants NAG5-9516 and NAG5-12863 in Solar and Heliospheric Physics and by the Smithsonian Astrophysical Observatory.

[P1.104] (e,2e) experiments on the direct ionization of helium.

Conventional (e,2e) experiments on direct ionization measure the angular distribution of ejected electrons in coincidence with electrons scattered through a particular angle. We have begun a series of (e,2e) experiments on helium direct ionization where we measure the angular distribution of scattered electrons in coincidence with electrons ejected in a particular direction. For example, we have measured electrons scattered through a range of angles -15^\circ to +15^\circ and the ejected electron direction 90^\circ with respect to the 488eV incident beam. We present the data as the sum and difference of scattered electron angular distributions for \pm90^\circ ejected electron directions in order to separate the mainly dipole cross section and the odd parity interference cross terms. We find that the results are in puzzlingly good agreement with a model based on the plane wave Born approximation in the low momentum transfer limit (K\ll1), even for K>1.

[P1.105] Accurate r-ratios for the Electron Impact Excitation of Argon

The ratio of the differential cross sections for the electron impact excitation of the 4s[3/2]^o_2 and 4s'[1/2]^o_0 levels of the first excited 3p^54s configuration of argon, designated the r-ratio(M.\ A.\ Khakoo et al.), J.\ Phys.\ B 37, 247 (2004), has been more accurately measured at 15~eV, 17.5~eV, 20~eV, and 30~eV incident energies. The measurements were performed predominately at small scattering angles to look for the effects of second-order couplings during the electron impact excitation process. The measured values of the ratio are close to the LS-coupling limit of 5 indicating that second-order effects in the excitation of the target can be considered negligible. The results will be presented. This work is funded by the National Science Foundation under grant # NSF-RUI-PHY-0096808.

[P1.106] Positive and Negative Ion Formation Following Electron Impact on Uracil

We report absolute partial cross sections for the formation of selected positive and negative ions resulting from electron interactions with the biologically important molecule uracil. Absolute calibration of the measured partial cross sections for the formation of the three most intense positive ions, the parent C_4H_4N_2O_2^+ ion and the C_3H_2NO^+ and OCN^+ fragment ions, was achieved by normalization of the total single uracil ionization cross section to a calculated cross section based on the semi-classical Deutsch-Märk (DM) formalism at 100 eV. Subsequently, we used the OCN^+ cross section in conjunction with the known sensitivity ratio for positive and negative ion detection in our apparatus (obtained from the well-known cross sections for SF_4^+ and SF_4^- formation from SF_6) to determine the dissociative attachment cross section for OCN^- formation from uracil.

This work was partially supported by the FWF, ÖNB, and ÖAW, Wien, Austria and the EU Commission, Brussels. We acknowledge financial support from the US Department of Energy to KB.

[P1.107] Atmospheric behaviour as driven by electron impact

We report on some recent studies using our enhanced statistical equilibrium suite of programs. This code simulates atmospheric behaviour, including light emission from aurora and dayglow. Results from our work into N_ 2, NO and O_2 will be presented and compared with measured values. In addition, the importance of employing accurate electron impact cross sections in these sorts of investigations will be highlighted.

[P1.108] Electron impact coherence parameters for Ba 6^1 P_1

We have carried out relativistic distorted-wave (RDW) calculations for the excitation of the 6^1 P_1 state of barium by electron impact. The fine-structure target states were represented by Dirac-Fock wave functions and the scattering wave functions were calculated in a distorted-wave formulation of the Dirac equations. We will present results for the Stokes parameters P1, P2 and P3 at scattering energies below 20 eV and compare them with recent experimental measurements [1] and previous theoretical calculations [2,3]. Agreement between our results and the measurements is very good for all parameters except for P3. [1] P.V. Johnson, C. Spanu, Y. Li and P.W. Zetner, J. Phy. B 33 5367 (2000), P.V. Johnson, C. Spanu and P.W. Zetner, J. Phy. B 34 4311 (2001). [2] R.E.H. Clark, G. Csanak and J. Abdallah Jr., Phys. Rev A 40 2935 (1989). [3] D.V. Fursa and I. Bray, Phys. Rev. A 59 282 (1999).

[P1.109] Accurate theoretical calculation for electron impact excitation of resonance transitions in atomic oxygen

Electron collision excitation cross sections for the resonance 2p^4~^3P - 2p^33s~^3S^o, 2p^4~^3P - 2p^33d~^3D^o, 2p^4~^3P - 2p^33s~^3D^o, 2p^4~^3P - 2p^33s~^3P^o, and 2p^4~^3P - 2s2p^5~^3P^o transitions have been calculated by using the R matrix with pseudostates approach for incident electron energies from near-threshold to 100 eV. The excitation of these transitions gives rise to strong atomic oxygen emission features at 1304, 1027, 989, 878, and 792 Åin the spectra of several planetary atmospheres. We included 22 spectroscopic bound and autoionizing states and 30 pseudostates in the close-coupling expansion. The target wave functions are chosen to properly account for the important correlation and relaxation effects. The effect of coupling to the continuum is included through the use of pseudostates. The contribution of the ionization continuum is significant for resonance transitions. Measured absolute direct excitation cross sections of atomic oxygen are reported by experimental groups from the Jet Propulsion Laboratory and Johns Hopkins University. Excellent agreement is noted for the 2p^4~^3P - 2p^33s~^3S^o transition (\lambda1304 Åwith measured cross sections from both groups that agree very well with each other. There is disagreement between experiments for other transitions. Our results support the measured cross sections from the Johns Hopkins University for the 2p^4~^3P - 2p^33d~^3D^o and 2p^4~^3P - 2p^33s~^3D^o transitions, while for the 2p^4~^3P - 2p^33s~^3P^o transition the agreement is switched to the measured cross sections from the Jet Propulsion Laboratory.

[P1.110] Ortho- and Para-Positronium Formation Measurements for Positron Scattering by CO_2~^\ast

We are measuring cross sections for ortho- and para-positronium formation for positrons interacting with CO_2 in a gas scattering cell. These measurements involve the detection of two gamma rays in coincidence for energy windows (1) centered at 511 keV resulting from the decay of short-lived (0.1 ns) para-Ps and the destruction of longer-lived (0.1\mu s) ortho-Ps at the scattering cell walls, and (2) from 300 to 460 keV resulting from the three gamma decay of ortho-Ps. By taking the ratio of the 300 to 460 keV signal to the 511 keV signal (R_3g/2g) versus positron impact energy we find that near the Ps formation threshold this ratio has its largest value of about 1.5, which is where Ps has its lowest kinetic energy and ortho-Ps decays without breakup at the cell walls. For a positron energy of about 5 to 7 eV above the formation threshold we find that R_3g/2g reveals a secondary bump (not present in similar ratio measurements for other target gases) indicating another threshold for forming Ps, which is consistent with forming Ps with an inner orbital electron of CO_2. ^\astResearch supported by NSF Grant PHY 99-88093.

[P1.111] Measurements of cross sections for positrons scattered by Cs atoms^\ast

We report our most recent measurements of total and positronium (Ps) formation cross sections (Q_Ps's) for positrons scattered by Cs atoms. These results are found to be in reasonable agreement with the theoretical calculations by Kernoghan et al.^1 The total cross sections and the upper limit on the Q_Ps's are measured using a beam transmission technique. The lower limit on the Q_Ps's and an additional contribution from ortho-Ps decay are measured by detecting two coincident \gamma rays in different energy windows. We are also making first estimates of Cs excitation cross sections. These results are obtained from the analysis of the energy spectrum of positrons that have passed through the scattering region. We resolve the fraction of positrons that have lost energy due to the excitation of Cs atoms. ^\astResearch supported by NSF Grant PHY 99-88093. ^1 A.A. Kernoghan, M.T. McAlinden, H.R.J. Walters, J. Phys. B 29, 3971 (1996).

[P1.112] Progress Toward Triply Differential Cross Sections for Positron and Electron Impact Ionization

For intermediate energy positron and electron impact, total cross sections are identical for single ionization of light-medium weight targets. But electrons are more effective for double ionization. For heavy targets, electron impact is always more effective. Recently, [1] we have investigated these projectile charge differences as a function of energy loss and found qualitative agreement for argon. But for krypton the positron-electron impact differences disappeared with increasing energy loss. As a next step, we have modified the apparatus for triple coincidence studies between energy analyzed forward scattered projectiles, recoil ions, and electrons ejected between 30-140 degrees. Energy conservation will provide the energies of the ionized electrons with ion time-of-flight giving the degree of ionization. Thus, e,2e (e,3e-1) experiments will be performed for single (multiple) ionization for positron and electron impact and projectile charge differences will be investigated in even more detail. Experimental methods and details, plus preliminary results for electron impact will be presented.

1. A.C.F. Santos, et al., Phys. Rev. A 67, 052708 (2003), and Phys. Rev. A (in press).

[P1.113] Positronium Formation Measurements for Positron - Helium Scattering^\ast

We are making three different measurements in an attempt to obtain absolute positronium formation cross sections (Q_Ps's) for up to 100 eV positrons scattering from He atoms. Upper limit measurements of Q_Ps's are made by using a beam transmission experiment to monitor positrons lost from our beam under conditions where most have formed Ps. The other measurements involve the detection of two gamma rays in coincidence in energy windows (1) centered at 511 keV resulting from the decay of short-lived (0.1 ns) para-Ps and the destruction of longer-lived (0.1 \mus) ortho-Ps at the scattering cell walls, and (2) from 300 - 460 keV resulting from the three gamma decay of ortho-Ps. An analysis where we combine the coincidence measurements for the two different energy windows and compare this result with the change in the upper limit measurements as the positron energy is increased through the Ps formation threshold enables us to obtain estimates of Q_Ps. These results appear to be in remarkable agreement (in both shape and magnitude) with coupled-state calculations by Campbell et al.^1 ^\astResearch supported by NSF Grant PHY 99-88093. ^1C.P. Campbell et al., Nucl. Instr. Meth. B 143, 41 (1998).

[P1.114] Positronium Formation in the Noble Gas Atoms+

Results are presented for absolute positronium and direct ionization by positron impact on Ne, Ar, Kr and Xe at energies up to 90 eV. The experiments use a high-resolution, trap-based positron beam and exploit the properties of positron orbits in a magnetic field, with two distinct regions of field strength to separate inelastic scattering processes [1]. The results are compared with theoretical predictions and with measurements obtained using a complimentary technique [2]. There is generally excellent agreement between the two sets of measurements, providing an important benchmark for theoretical calculations. A discrepancy in the prominence of a feature observed in the previous measurements in Ar between 25 and 50 eV is discussed including phenomena relevant in this region and possible origins of the discrepancy. + This work is supported by NSF grant PHY 02-44653. * Present Address: Research School of Physical Sciences, Australian National University, Canberra, A.C.T., Australia [1] J. P. Sullivan et al., Phys. Rev. A. \textbf66, 042708 (2002) [2] G. Laricchia et al., J. Phys. B. \textbf35, 1-16 (2002)

[P1.115] Energy-resolved positron annihilation: the structure of positron-molecule complexes

The causes of the unusually large annihilation rates for some large molecules have been recently elucidated by energy-resolved measurements of the annihilation parameter, Z_\mathiteff [1,2]. These measurements, and their interpretation in terms of a recent model [3], provide the first direct evidence that positrons bind to molecules. Analysis of the position and shape of the observed Feshbach resonances gives information on the structure of these positron-molecule bound states and their population during scattering events. There are a number of substantial gaps in our understanding of these resonances including the rapid rise in annihilation rate with molecular size, the effect of chemical substitution on annihilation, and the behavior of the annihilation rate for positrons at very low energies (i.e. \leq 50 meV). Progress toward answers to these and other outstanding questions will be discussed. \ [1] S. J. Gilbert \emphet al., Physical Review Letters \textbf88, 43201 (2002). \ [2] L. D. Barnes, \emphet al. , Physical Review A \textbf67, 032706 (2003). \ [3] G. Gribakin, Physical Review A 61, 022720 (2000).

[P1.116] Positron scattering and annihilation from hydrogen-like ions

The past few years has seen the Configuration Interaction (CI) method applied to study the interactions of positrons with various one- and two-electron atoms. Here the Kohn-variational method is used with a CI type trial wave function and applied to the scattering and annihilation of positrons and hydrogenic ions. The resultant J = 0 and J = 1 phase shifts are within 1-2% of the best previous calculations, while the values of the annihilation parameter (Z_eff) are small and do not exceed unity for any of the momenta considered. In addition, analytic expressions within the Coulomb Wave Born Approximation are derived and used to help elucidate the dynamics of positron collisions with positive ions. Of interest is that annihilation enhancement due to electron-positron cluster formation is significant even for strong Couloumb fields. At thermal energies Z_eff is minute with a value of order 10^-50 occurring for He^+ at k = 0.05 a_0^-1. Essentially this means that positron cooling schemes using cations can neglect losses due to annihilation.

[P1.117] Positron Impact Ionization of Diatomic Molecules

We have carried out distorted wave calculations of positron ionization of molecular hydrogen, nitrogen and oxygen. In this work the target molecule was represented by Gaussian wave functions. We find that the use of our CPE model in a two-center formalism produces results which are in good agreement with the measurements for all molecular targets.

[P1.118] Study of systematic effects pertaining to an atom interferometric measurement of atomic recoil

We have recently utilized both time domain and frequency domain techniques to measure the atomic recoil frequency in cold Rb atoms. These experiments involve manipulation of atoms in a single hyperfine ground state using echo experiments. For both techniques, it has become necessary to understand systematic effects on the signal shape at level of 1 ppm. These include the effect of spontaneous emission, the strength of the atom field coupling, effect of optically pumping atoms into a single magnetic sublevel, angle between interferometer pulses, sample density, magnetic fields, and spatial profiles of excitation beams. We present evidence for these systematic effects and show that it is possible to make an atom interferometric measurement of the radiative rate of the F=3 to F=4 transition.

[P1.119] Post-deadline

This abstract not available.

[P1.120] Lattice Calculations of the Photoionization of Li

Calculations are presented for the double photoionization (with excitation) and triple photoionization of the Li atom. The motion of all three electrons is treated equally by solving the time-dependent Schrödinger equation in nine dimensions. A radial lattice is used to represent three of the nine dimensions, while a coupled channels expansion is used to represent the other six dimensions. Probabilities for photoionization are obtained by t\rightarrow\infty projection onto fully antisymmetric spatial and spin functions, with care as to orthogonality of different representations. Double photoionization cross sections for lithium leaving the ion in the 1s, 2s, and 2p states are presented. The total double photoionization cross section is found to be in excellent agreement with the measurements of Huang et al (Phys. Rev. A 59, 3397 (1999)), and the triple photoionization cross section for lithium is found to be in good agreement with the experimental measurements of Wehlitz et al (Phys. Rev. Lett. 81, 1813 (1998)).

[P1.121] Decoupling the refractive index from the material thickness for optical characterization of materials

Theoretical models of the passage of laser light through a flat-parallel optical material commonly have the refractive index, \textitn, coupled to the physical thickness, \textitd, of the medium in the phase term of the laser's electric field. Interferometric experiments measuring \textitn for flat-parallel optical materials assume that \textitd is already known to a high degree of accuracy, and vice versa for experiments optically measuring \textitd. Results of these experiments are limited to approximations for different temperature environments where both \textitn and \textitd are changing. We will present a simple experimental interferometric technique that can accurately and independently measure both the physical thickness and the refractive index of flat-parallel infrared materials using a carbon dioxide laser source. Initial ``guesses'' for the values of \textitn and \textitd are required, but can be upwards of 50% off of their actual values. Experimental results for Si, Ge, GaAs, and ZnSe yield refractive index values to within 0.1% of their accepted values, and thickness measurements with uncertainties of less than 10 microns. Measurements can be performed for optical samples at either room temperature or cryogenic temperatures.

[P1.122] Electron-Nuclear Dynamics of atomic and molecular collisions: Charge exchange and energy loss

Processes like electron exchange (capture and loss), bond breaking, and chemical reactions are difficult to visualize and treat in a time-independent approach. In this work, we present the Electron-Nuclear Dynamics (END) method for the study of time-dependent scattering processes. The END is a general approach for treating time-dependent problems which includes the dynamics of electrons and nuclei simultaneously by considering the full electron-nuclear coupling in the system and thus eliminates the necessity of constructing potential-energy surfaces. The theory approximates the time dependent Schrö\-din\-ger equation starting from the time dependent variational principle (TDVP) by deriving a Hamiltonian dynamical system for time dependent nuclear and electronic wave function parameters. The wave function is described in a coherent state manifold, which leads to a system of Hamilton's equations of motion. The resulting system of coupled, first order, ordinary differential equations approximates the Schrödinger equation. A detailed analysis of the END equations is given for the case of a single-determinantal state for the electrons and a classical treatment of the nuclei. Emphasis is put on electron exchange, differential cross section and energy loss (stopping cross section) of collision of ions, atoms and molecules involving H, He, C, N, O, and Ne atoms. We compare our results to available experimental data.

[P1.123] Measuring Nonadiabatic Interactions in Cold Gases: The Atomic Hot Potato

A relevant question in atom trapping is the validity of the Born-Oppenheimer (BO) approximation, i.e., determining the relative time scales at which the nuclear and electronic degrees of freedom evolve. We propose a scenario in which one can examine this question.

Trapping potentials typically depend on an atom's internal state. A single two-level atom in its ground state might feel a trapping potential, while the same atom in its excited state would feel an anti-trapping potential. Suppose we have many such atoms, coupled by van der Waals interactions. If all the atoms are trapped initially, what happens when a single atom suddenly becomes excited?

One might imagine two possible limits: (1) the excited atom leaves the trap, or (2) the atoms share the excitation so rapidly that they all remain trapped--an effective ``hot potato!" Asking how well the BO approximation holds means determining which limit applies in a real cold atom gas. We begin with a time-dependent quantum mechanical model for the simplest possible case, two atoms confined to lines. The results suggest that the real physical situation, millions of atoms in three dimensions, may be amenable to mixed quantum-classical treatment. We present our initial attempts to develop and refine such a model.

[P1.124] Fabrication of Subwavewave-length size Aperture for Possible Nearfield Optical Trapping

There have been tremendous interests about nearfield optical probe and the optical trapping of the biological objects. In order to trap the particle smaller than 1 micrometer, the aperture diameter has to be larger than 100 nm due to insufficient radiation force from light. Though, the traditional fiber-tapered nearfield optical probe has disadvantage of low thoughput intensity. Recent development of the surface plasmon enhanced nearfield optical probe has provided high throughput of the nearfield optical probe, especially for semiconductor batch fabricated subwavelnegth size nearfield probe. It is well known that even single subwavelength size metal- aperture with proper fabrication condition, either textured or periodic surface, can significantly enhance thoughput of the light intensity In this abstract, we will report the fabrication of the surface plasmon enhanced nearfield optical probe which can be performed for possible submicron size objects trapping.

[P1.125] Quantum Control with the Non-resonant Dynamic Stark Effect

New Quantum Control scenarios involving non-perturbative but non-ionizing near-infrared laser fields are investigated. These lie between the well known perturbative interference control techniques and the strong field ionization-fragmentation control schemes. Using exclusively the non-resonant Dynamic Stark Effect, applied to a molecular non-adiabatic (avoided) crossing, we show that the photodissociation branching ratio and resonance lifetimes may be controlled. Decay channels are selected by using control pulses to effect motion during photo-excitation of a wavepacket and during traversal of the avoided crossing. The resonance 'lifetimes' are controlled by using properly timed short control pulses that modify the relative phase differences between the wavepackets on each diabatic electronic surface.

[P1.126] Preparation and characterization of photo catalytic thin films TiO2 on glass deposited by spray pyrolysis

Transparent TiO2 thin films were deposited on soda lime glass by spray pyrolysis method from precursor solutions of peroxo-titanium complex, it was prepared varying the substrate temperature at 230, 280, 330, 380 and 430º C, all films had thickness of 400 nm, these samples was called Series 1. Series 2 was created by heat-treatment in air at 500º C for 3 hours and cooling for 15 hours. All films were characterized by Profilometric technique, AFM, SEM, EDS, TEM, XRD as well as UV-Vis spectroscopy, the photo catalytic activity was carried out by a photo catalytic reactor using degradation of methylene-blue solution. The main characteristics of Series 1 were its predominant amorphous structure, low porosity in the surface structure and grains agglomerates. Series 2 were characterized by a increase in the polycrystalline structure in both anatase and brookite phases, By the surface roughness and the crystal phases presented in our films, we can say that spraying coating method might be found applicable in the syntheses of other metal oxide and mixed metal-oxide ceramics. The TiO2/glass obtained by this method shows photo catalytic activity, the efficiency for de degradation of methylene-blue is also reported in this work.

[P1.127] Atom Optics for Bose-Einstein Condensates

The creation of integrated atom optics for a Bose-Einstein condensate and the demonstration of an atom interferometer is the primary goal of the experiment. The atom optics are derived from magnetic potentials generated by current carrying wires lithographically deposited onto a small chip. Methods for the reduction of size and complexity of the apparatus for real world applications are also explored.

[P1.128] Long-range interactions for hydrogen molecular ions

There is an increasing interest in studying ultra-cold physics, such as ultra-cold spectroscopy of purely long-range molecules. A general formalism for calculating long-range interaction energies between two ground-state atomic or molecular systems is presented. Static polarizabilities alpha1, alpha2, alpha3, and alpha4, as well as the dispersion coefficients C6, C8, C10 are evaluated to high precision for the ground-state hydrogen molecular ions H2+, D2+, T2+, HD+, HT+, T2+ and DT+ using variational wavefunctions in Hylleraas coordinates.

[P1.129] Beam-gas Spectroscopy of Sextet transitions in O IV, F V and Ne VI

We present observations of VUV transitions between doubly excited sextet states of O IV. Spectra were produced by collisions of an oxygen, fluorine and neon beam with nitrogen gas jet target. Some observed lines were assigned to the 1s2s2p^3 ^6S-1s2p^33s, 3d ^6P electric-dipole transitions in O IV, F V and Ne VI, and are in good agreement with our accurate MCHF (with QED and higher-order corrections) and MCDF calculations. Four lines have been reassigned.

[P1.130] Capture of antiprotons by some radioactive atoms and ions

Cross sections for antiproton capture are calculated using the fermion molecular dynamics method for ions of current interest in experiments determining nuclear structure of the radioactive nuclei ^8He, ^11Li, ^11Be, and ^21Mg. The cross sections for the corresponding neutral atoms are also calculated. It is found that, except for helium, the cross sections for the ion and neutral atom at usual capture energies are similar, i.e., neither the enhanced trajectory curvature nor the absence of the most weakly bound electron have great effect. The behavior of the cross sections is also analyzed at very low collision energies, where the ion cross sections go as 1/E and the neutral cross sections as 1/\sqrtE.

[P1.131] Theoretical energy levels of highly-exicted hydrogen and deuterium

Updated energy levels of hydrogen and deuterium atoms are presented. They provide frequencies of transitions between highly-excited states with principal quantum number n up to 200. The fundamental constants necessary for the calculation are taken from the latest CODATA 2002 least-squares adjustment. Up-to-date QED and all relativistic corrections are included in the results. The uncertainties take into account uncertainties in the fundamental constants and theory as well as the covariances between the various contributions. The data will be available on the Physics Laboratory WEB site at NIST.

[P1.132] HYDROGEN AS AN ATOMIC CONDENSER

Bohr radius, aB and the de Broglie wavelength, ldB,H are given by,

aB = ldB,H = e2/2kEH = 2(mN - mB)/eac = (lC,e + lC,p)/2pa = h/2pmredac (1) where EH is the ground state energy of hydrogen (H), and all other symbols have their standard significance. The last three terms in eq.1 show that aB has sections pertaining to the electron, e- and proton, p+. Since EH = eIH, where IH is the ionization potential, it also has two terms,

EH = eIH = e2/2kaB = e(Ip + Ie)/2 = (e2/2k)[(1/ap) – (1/ae)] (2)

where Ip = e/kap, Ie = -e/kae and aB = ap + ae. It follows from eq. (2) that ae/ap = f, the Golden ratio, and that EH is the difference between two terms. In a Golden ellipse with aB as the major axis and e = 1/f as the eccentricity, the inter-focal distance, aB/f = eaB (= ae) = 0.0327 nm, which is the reported atomic radius of hydrogen. Since kae = Ce and kap = Cp are capacities, kaB = CB is their effective Golden mean. Thus, EH = (1/2)(e2/CB) is the electromagnetic energy of the simplest atomic condenser.

[P1.133] THE DECISIVE ROLE OF THE GOLDEN RATIO IN ATOMIC DIMENSIONS

It has been found that the golden ratio, f plays a quantitative role in establishing the atomic/ionic radii: d(A) = d(AA)/2, d(A-) = d(AA)/f, d(A+) = d(AA)/f2 and d(AA) = d(A+) + d(A-) for many elements. For example, the inter-ionic distances d(MX) in alkali halide crystals are given by,

d(MX) = d(M+) + d(X-) = d(MM)/f2 + d(XX)/f (1)

where d(MM) = L(M) is the lattice constant for the metals, d(M+) = L(M)/f2 = d(MH) – d(HH)/f2 is the metal ionic radius, H stands for hydrogen, d(X-) = d(XX)/f is the halogen ionic radius and d(XX) is the inter-atomic distance for tetrahedral coordination in crystals (except for fluorides where d(F) = d(FF)/2 holds). Eq. 1 holds quantitatively for all alkali halides.

[P1.134] Direct Measurement of Atom-Surface Induced Phase Shifts with an Atom Interferometer

Atom-surface interactions over small distances will grow in importance as the field of integrated atom optics progresses. In principle these interactions can cause decoherence or limit the usefulness of matter-wave interferometry on a chip because any force the atoms experience will result in a matter-wave phase shift. There are at least two mechanisms for atom-surface induced phase shifts: static fields and van der Waals interactions. Here an atom interferometer is used to probe the interaction of Na atoms with the walls of a 50 nm wide cavity. To our knowledge this is the first report concerning a direct measurement of the coherent phase shift caused by atom-surface interactions. The magnitude of the phase shift is in fair agreement with that predicted by QED for a non-retarded van der Waals interaction. This puts an upper limit on the contribution of static fields caused by surface charge effects in our experiment. Our experiment also demonstrates that matter-waves can retain their phase coherence even when atom-surface distances are on the order of 10 nm.

[P1.135] Measured Hyperfine structure of the A-state of CaH

We report the first measurements of hyperfine structure within the A~^2\Sigma ^+(v~=~0) state of CaH. In the experiments, a molecular beam of CaH was crossed by a cw laser beam that excited low-lying rotational transitions within the A\leftarrow X(0,0) band of CaH. Excitation spectra of \sim 1~MHz resolution were recorded by measuring the subsequent A\to X fluorescence versus laser frequency. Knowledge of this hyperfine structure is necessary for executing proposed schemes for laser-cooling CaH.

[P1.136] Cesium Isotopic Ratio Measurements in a Magneto-Optical Trap

Magneto-optical trapping of radioactive cesium isotopes poses a promising approach towards high sensitivity and high selectivity detection of trace amounts of cesium for applications in environmental and nuclear non-proliferation studies. A high-efficiency MOT is coupled to a mass separator using mass-separated ion implantation into a zirconium foil and release as neutral atoms upon foil heating. The fluorescence light from the trapped atoms is detected using an APD/lock-in amplification scheme. A sensitivity of 10^6 atoms per sample has been demonstrated [1]. We are currently working on several improvements to increase the sensitivity and trapping efficiency and to reduce a 'memory effect' resulting from cesium implanted in the foil in previus experimental cycles. We expect to push our detection limit significantly below 10^6 atoms (200 attograms) per sample, while maintaining the excellent selectivity (>10^12 suppression of ^133Cs) measured earlier. Isotopic ratio measurements of ^135Cs/^137Cs as well as ^134Cs/^137Cs in selected samples are underway. References: [1] M.D. Di Rosa et al., Appl. Phys. B 76 (2003) 45-55.

Part P of program listing