Session D1: Poster Session I (4:00 pm - 6:00 pm)

Bethe-Salpeter equation applied to Energy Levels of Kaonic Hydrogen

We apply, for the first time, the spin-1/2 - scalar formalism derived by Owen (Phys. Rev. D42, 3534(1990);Found. of Phys. 24, 273(1994)) to the kaonic hydrogen. We generalized the previously derived formalism to include both the finite size of the kaon and proton and calculate the energy level including all recoil corrections. The developed formalism can be extended to all orders in $\alpha$ and to the case in which renormalization is required.   

Microwave/RESIS technique for measurement of heavy ion properties

The subtle but distinctive patterns of binding energies of high-L Rydberg electrons bound to heavy positive ions reveal the ion properties, such as polarizabilities and permanent moments, that control the long-range interactions between ion and the Rydberg electron. A specialized experimental technique, Resonant Excitation Stark Ionization Spectroscopy (RESIS), facilitates study of these fine structure patterns in a wide variety of Rydberg systems. The simplest RESIS measurements use a Doppler-tuned CO$_{2}$ laser to selectively detect individual high-L Rydberg states in a fast Rydberg beam by resonant excitation to a much higher level, followed by Stark ionization and collection of the resulting ion. Much more precise studies use the selective RESIS excitation to detect direct microwave transitions between Rydberg levels of the same n. Recent microwave/RESIS studies of this type have determined many properties of the ions Th$^{4+}$[1], Th$^{3+}$[2], and Ni$^{+}$[3]. Details of this method will be described, with particular attention to studies of multiply-charged Rydberg ions.\\[4pt] [1] Chris S. Smith et. al., DAMOP 2012\\[0pt] [2] Julie A. Keele, et. al., DAMOP 2012\\[0pt] [3] Shannon L. Woods, et. al. DAMOP 2012   

Current Status of Atomic Spectroscopy Databases at NIST

NIST's Atomic Spectroscopy Data Center maintains several online databases on atomic spectroscopy. These databases can be accessed via the http://physics.nist.gov/PhysRefData web page. Our main database, Atomic Spectra Database (ASD) has recently been upgraded to v. 4.1.1, which contains critically evaluated data for about 174,000 spectral lines and 92,000 energy levels of almost all elements in the periodic table. A new version 5.0 is to be released this year. It will be extended to include the ground states and ionization energies of all elements up to Ds ($Z$=110) in all ionization stages with a new Web interface for displaying them. We continue maintaining and regularly updating our bibliography databases, ensuring comprehensive coverage of current literature on atomic spectra, including energy levels, spectral lines, transition probabilities, hyperfine structure, isotope shifts, Zeeman and Stark effects. We continue maintaining other popular databases such as the Handbook of Basic Atomic Spectroscopy Data, searchable atlases of spectra of Pt-Ne and Th-Ne lamps, and non-LTE plasma-kinetics code comparisons.   

EIT Noise Resonance Power Broadening: a probe for coherence dynamics

EIT noise correlation spectroscopy holds promise as a simple, robust method for performing high resolution spectroscopy used in devices as diverse as magnetometers and clocks. One useful feature of these noise correlation resonances is that they do not power broaden with the EIT window. We report on measurements of the eventual power broadening (at higher optical powers) of these resonances and a simple, quantitative theoretical model that relates the observed power broadening slope with processes such as two-photon detuning gradients and coherence diffusion. These processes reduce the ground state coherence relative to that of a homogeneous system, and thus the power broadening slope of the EIT noise correlation resonance may be a simple, useful probe for coherence dynamics.   

Properties of rotationally excited H$_{2}^{+}$ from fine structure measurements of high-L Rydberg states of H$_{2}$

Measurement of the fine structure pattern of high-angular momentum Rydberg states provides information about the basic properties of the ion core, such as the Quadrupole moment and polarizability. Resonant Excitation Stark Ionization Spectroscopy (RESIS) uses a Doppler-tuned CO$_{2}$ laser to resonantly excite transitions in a fast molecular beam, which are detected by Stark ionization. Reported here is the analysis of the fine structure measurements of the high-L Rydberg states of the rotationally excited (R=2) ground vibrational level of molecular hydrogen. This determines the Quadrupole moment and scalar and tensor dipole polarizabilities of H$_{2}^{+}$. The experimental progress made using a novel approach to the detection techniques of RESIS which will allow the first measurements of the higher rotational levels of H$_{2}$ that were previously unattainable due to their fast autoionization rates will also be discussed.   

Quantum Assisted Sensing Using Rydberg Atom Electromagnetically Induced Transparency

We present a method to probe AC electric fields with high sensitivity based on dark resonances in electromagnetically induced transparency (EIT) spectroscopy. The basic mechanism is to couple the electric field to a ladder-type Rydberg atom EIT system. Data from experiments using Cs and Rb will be shown to illustrate the method. The experiments take place in small (mm-$\mu $m) vapor cells. We discuss our experiments to push the electric field sensitivity of the method below 1$\mu $V/cm.   

Evolution of Xe spectrum and ion charge under sudden incoming radiation

Experiments [1] and simulations of Xe at high temperature were recently reported, due to the possible scaling of astrophysical radiative shocks [2]. We used the newest version of HULLAC [3] to compute energy levels, radiative and collisional transition rates and level populations in a Coronal Radiative Model for the ions Xe9+ to Xe44+ (36263 configurations), at electron temperature of 100 eV and electron density of 10$^{19}$ -- 10$^{21}$ e/cm$^3$, in the presence of an external Planckian radiation field. Static and time dependent influence of the radiation on ion charge and spectrum is described. We show an effect of shell structure on relaxation of ion charge when the radiation field is suddenly turn on.\\[4pt] [1] Busquet, M., Thais, F., Gonzalez, M.\textit{, et al.}, J. App. Phys. \textbf{107}, 083302 (2010).\\[0pt] [2] Ryutov, D., Drake, R. P., Kane, J.\textit{, et al.}, Astrophys. J. \textbf{518}, 821 (1999).\\[0pt] [3] Klapisch, M. and Busquet, M., High Ener. Dens. Phys. \textbf{7}, 98 (2011).   

Lifetime Measurements of Trapped $^{232}$Th$^{3+}$

In recent years, there has been considerable interest in the low lying nuclear isomer state of $^{229}$Th which is only several eV above the nuclear ground state [1]. To date, several groups are taking a variety of approaches to finding and exciting this unique state [2], including the use of trapped Th$^{3+}$ ions. Despite this attention, few precise measurements have been made of atomic lifetimes. In this work we present experiments to measure the $6D_{3/2}$ and $6D_{5/2}$ states using laser cooled $^{232}$Th$^{3+}$ confined in a linear Paul trap.\\[4pt] [1] E.~Peik and Chr.~Tamm, \textit{Europhys. Lett.} \textbf{61}, 181 (2003); V.~V.~Flambaum, \textit{Phys. Rev. Lett.} \textbf{97}, 092502 (2006); B.~R.~Beck \textit{et al.}, \textit{Phys. Rev. Lett.} \textbf{98}, 142501 (2007).\\[0pt] [2] W.~G.~Rellergert \textit{et al.}, \textit{Phys. Rev. Lett.} \textbf{104}, 200802 (2010); S.~G.~Porsev \textit{et al.}, \textit{Phys. Rev. Lett.} \textbf{105}, 182501 (2010); C.~J.~Campbell \textit{et al.}, \textit{Phys. Rev. Let.} \textbf{106}, 223001 (2011).   

Lifetime Measurements of the 2$^{1}\Sigma _{u}^{+}$ and 4$^{1}\Sigma _{g}^{+}$ states of Na$_{2}$

We have measured lifetimes of individual ro-vibrational levels in the excited states of Na$_{2}$ using pump-probe resonant ionization. For the double well 2$^{1}\Sigma _{u}^{+}$ state, we use a 2-photon scheme. Ground state Na$_{2}$ produced in a molecular beam is excited resonantly by the doubled output of a suitably tuned dye laser and then ionized by a photon (532 nm) from a delayed Nd:YAG laser. By adjusting the delay of the second laser, the population decay of the excited state was observed and its lifetime can be extracted. Moreover, by tuning the first laser to different ro-vibrational level, we were able to measure the lifetime as a function of vibrational quantum number. Initial data show a noticeable and systematic variation especially near the potential barrier. The overall magnitude of our results is consistent with the average value of 52.5 ns reported for states below the barrier.\footnote{Mehdizadeh, E., et. al., Appl. Phys. B, 509-515 (1994)} For the 4$^{1}\Sigma _{g}^{+}$ state, we employed a double resonance technique via the A$^{1}\Sigma _{u}^{+}$ (v=19, J=20) state followed by one-photon (1064 nm) delayed ionization from a third laser. Our experimental method, analysis and results, showing vibrational state dependence here as well, will be presented.   

Long Range Rydberg Molecules

A pair of Rydberg atoms can interact through the long range dipole-dipole interaction, leading to both attractive and repulsive potential curves at long range. Since there are many Rydberg levels, there are at shorter range avoided crossings between potentials of the same symmetry, forming potential wells. The depths and locations of the wells are dictated by the spacings of the atomic levels. Here we describe how the application of a static (or off resonant) rf field can be used to create such wells. Consider a pair of stationary atoms in the \textit{ns}$_{1/2}$ and \textit{np}$_{3/2}$ states. A weak electric field lifts the degeneracy of the \textit{np}$_{3/2} m_{j}$ levels, splitting them by $\Delta $. Choosing the field direction as the quantization axis, there are four states of total $M_{Z}$=1. Two of the states connect to R=$\infty $ states containing $m_{j}$=1/2, and two to states containing $m_{j}$=3/2. The latter two states have no dipole-dipole interaction with each other, only with the states connected to $m_{j}$=1/2 at R=$\infty $. Thus, for large R their potential curves are flat, and if the R=$\infty \quad m_{j}=3/2$ level lies above the $m_{j}$=1/2 level a potential well is formed by the intersection of the $M_{Z}$ =1 curves. Its depth and the location of its minimum are controlled by the Stark shift. Calculations show that the well is quite broad in $\theta $, the angle between the quantization axis and the internuclear axis. Other examples of wells will be given.   

Photodissociation-Photoionization of Bromomethanes

Molecular photodissociation -- photoionization of bromomethanes were measured employing the laser-time of flight technique. By using molecular beams of different bromomethanes produced by adiabatic expansion (CH$_{2}$Br$_{2}$, CHBr$_{3}$, CBr$_{4})$, interacting with laser radiation of 266 and 355 nm from a Nd:YAG, pulse widths of 3.5-4.5 and 5.5-6.5 ns, respectively; and intensities of the order of 109 to 1010 Wcm$^{-2}$. Ions resulting of the interaction molecule-photon processes were analyzed using an R-ToF mass spectrometer. At the intensities of radiation used in the experiments, multiphoton processes are possible. From experimental data, was observed that the bromomethanes fast dissociate previous to the ionization, and molecular parents ions were no detected at the used wavelengths. The main detected ions correspond to H$^{+}$. C$^{+}$, CH$^{+}$, Br$^{+}$, CBr$^{+}$, CHBr$^{+}$, and Br$_{2}^{+}$. These are the result of molecular dissociation when the original molecules absorb one photon forming neutral radicals, absorption of additional photons produces the ionization. From experimental data, we could calculate the number of absorbed photons needed to the ionization processes, being it of the order of two and three photons at 266 nm, three, and four at 355 nm. Detected ions and the precursors play an important role in the chemistry and physics of the atmosphere; they can interact with water and ozone molecules, evolving in the deterioration of the air quality.   

Radiation Damping in the Photoionization of Fe$^{14+}$

We have completed a new theoretical investigation of photoabsorption and photoionization processes in Fe$^{14+}$, extending beyond an earlier frame transformation R-matrix implementation by performing fully-correlated, Breit-Pauli R-matrix calculations, to include both fine-structure splitting of the strongly-bound resonances and radiation damping effects. We find that radiation damping of $2p\rightarrow nd$ resonances is important, giving rise to a resonant photoionization cross section that is significantly lower than the total photoabsorption cross section. Furthermore, our radiation-damped photoionization cross section is found to be in excellent agreement with recent EBIT measurements once a global shift in energy of $\approx -3.5$ eV is applied. These findings have important implications. Firstly, the use of EBIT experimental data is applicable only to photoionization processes and not to photoabsorption; the latter is required in opacity calculations. Secondly, our computed cross section shows a series of $2p\rightarrow nd$ Rydberg resonances that are about 3.5 eV higher in energy than the corresponding experimental profiles, indicating that those threshold L-edge energy values currently recommended by NIST are likely in error by more than one eV.   

Temperature Dependence of Rb 5P Fine-Structure Transfer Induced by $^{4}$He Collisions

Employing ultrafast laser excitation and time-correlated single-photon counting, we have measured the fine-structure transfer between Rb 5P states induced by collisions with $^{4}$He buffer gas at temperatures up to 150$^{o}$C. The temperature dependence of the binary cross-section agrees with earlier measurements while having almost an order of magnitude smaller uncertainty. Our data show that the temperature dependence of the three-body rate is about the same as that of the binary rate. The three-body rate can be described as arising from the reduction of the rubidium fine-structure splitting due to nearby helium atoms. Our fine-structure transfer studies are relevant for understanding alkali-inert gas atomic interactions as well as for practical applications in alkali laser development.   

Velocity-Map Imaging Spectroscopy of the Ge$^{-}$, Sn$^{-}$, and Pb$^{-}$ Negative Ions

Photoelectrons ejected from collisions between laser-produced photons and fast-moving beams of negaitve ions have been studied using the technique of Velocity-Map Imaging (VMI) spectroscopy. Digital images produced by the VMI spectrometer have been used to determine photoelectron kinetic energy spectra, as well as photoelectron angular distributions for select isoelectronic Group 14 anions. Analysis of these data are helping to clarify detailed structural properties of these ions with increasing $Z$ and is providing dynamical information on the photon-ion collision systems.   

Computational analysis of population transfer via STIRAP in sodium vapor

We present a theoretical and computational analysis of STIRAP and SEP population transfer in sodium vapor as measured by fluorescence emission imaged onto a spectrometer. Calculations include 1) a careful analysis of the fraction of measured fluorescence output over all spatial positions in the incident beams and due to experimental geometry, 2) calculations of an unexpectedly strong effect on the STIRAP transfer efficiency with beams detuned between the D1 and D2 Fraunhofer lines, 3) a study of the relative efficiency of STIRAP and SEP on resonance at the D1 and D2 transitions, 4) the effects of varying pulse parameters (such as spatial shape, energy, focus) on transfer efficiencies, and 5) explorations of population transfer in sodium as a function of the pump-Stokes energy landscape. The system states are calculated utilizing a Hamiltonian which includes fine and hyperfine structure (two nine-state and four five-state transitions) of the 3s, 3p and 5s levels in sodium. The findings are compared to experimental results obtained using a picosecond laser system with linewidth very near the transform-limit ($\pm 15\%$).   

Laser Interactions with Atomic and Molecular Positronium

Positronium (Ps), the bound state between an electron and its antiparticle, the positron, may be efficiently created by bombarding certain porous materials with intense bursts of positrons obtained from a positron accumulator. Using a Surko-type buffer gas trap we have produced a high-density pulsed positron beam makes it possible to study interactions between Ps atoms, allowing for measurements of molecular Ps$_{2}$ formation and Ps-Ps scattering. Moreover, even at a low spatial density the $\sim $ 1 ns wide pulses are well suited to laser spectroscopy of Ps atoms; numerous experiments are possible, including measurements of atomic energy intervals (e.g., the hyperfine interval), the effects of confinement on transition wavelengths, Ps cooling and the production of long-lived Rydberg Ps atoms. High density pulses used with lasers have also been used to perform optical spectroscopy on the Ps$_{2}$ system.   

Photoabsorption spectrum of the Xe@C$_{60}$ endohedral fullerene

Photoabsorption spectrum of the Xe@C$_{60}$ endohedral fullerene has been studied using the time-dependent-density-functional-theory (TDDFT), which represents the dynamical polarizability of an interacting electron system by an off-diagonal matrix element of the resolvent of the Liouvilliam superoperator and solves the problem with the Lanczos algorithm. The method has been tested with the photoabsorption cross sections of the free Xe atom and C$_{60}$ fullerene. The result for the Xe@C$_{60}$ confirms the three main peaks observed in the recent measurement in the energy region of the Xe 4$d$ giant resonance [1] and shows the possibility that the Auger decay of the Xe$^+$ has been greatly suppressed if the ion is encapuslated inside C$_{60}$. It is suggested to perform the same measurement around 22 eV to check this possibility. \\[4pt] [1] A L D Kilcoyne et al, Phys. Rev. Lett. 105 213001 (2010).   

Photoionization of confined noble gas atoms: Hybridization and interchannel coupling effects

A theoretical study of the photoionization of the noble gas atoms Ne, Ar, Kr and Xe confined endrohedrally with a C$_{60}$ fullerene molecule is presented. The fullerene shell is represented by a jellium potential of 60 smeared out C$^{4+}$ ions and the wave functions 240 delocalized valence electrons plus the atomic electrons move in the field generated by the atomic potential plus the shell potential. The photoionization is calculated within the framework of the time-dependent local-density approximation (TDLDA) [1] which includes significant aspects of correlation. The results show that in all four cases, the valence photoionization channel cross sections of the entrapped atoms are dramatically increased by interchannel coupling with the C$_{60}$ plasmons. In addition, hybridization, the mixing of initial-state wave functions of atom and shell, occurs in a number of cases, a phenomenon which substantially alters the cross sections of both the atomic and the shell states. Confinement resonances are also in evidence for all cases. The evolution of these effects along the noble gas sequence is discussed.\\[4pt] [1] M.E. Madjet et al., \textit{Phys. Rev. A} \textbf{81}, 013202 (2010).   

Single photoionization with excitation and double photoionization of He endofullerenes

Recently, using a non-perturbative time-dependent close-coupling (TDCC) method we investigated and confirmed the existence of these resonances in the double photoionization cross section of He@C$_{60}$ [1, 2]. Here, we extend our previous studies to examine confinement resonances not only in the double photoionization process, but in the process of single photoionization with~excitation for various He endofullerenes, namely He@C$_{36}$, He@C$_{60}$ and He@C$_{82}$. We found He@C$_{82}$ also displays confinement resonances in the double~photoionization cross sections; while for He@C$_{36}$ the confinement resonances are suppressed. For single photoionization leaving the He$^{+}$ ion in its ground state, we found the magnitude of the cross sections for the endofullerenes is comparable to that of helium. For single photoionization with excitation to the n=2 shell, the endofullerene cross sections showed a~reduction as compared to bare He atoms; while for photoionization with excitation to the n=3 shell, the cross sections for the endofullerenes showed an enhancement. In addition, we also found confinement resonances in the single photoionization with excitation cross sections.\\[4pt] [1] J A Ludlow, T-G Lee, and M S Pindzola, Phys. Rev. A 81, 023407 (2010)\\[0pt] [2] J A Ludlow, T-G Lee and M S Pindzola, J. Phys. B: At. Mol. Opt. Phys. 43 235202 (2010)   

Time delay in photoionization near Cooper minima

The connection between the energy dependence of the scattering phase shift and time delay is known [1]. With the developments of techniques in attosecond physics, it has become possible to measure the time delay between photoemission from different subshells [2, 3]. There have been several nonrelativistic calculations of the time delay between photoelectrons from different subshells [4, 5] that confirmed the need to include many-electron correlations. In the present work, the RRPA [6], which includes both relativity and many of the important electron correlation effects, is employed to calculate the time delay between photoelectrons from the valance ns, np$_{3/2}$ and np$_{1/2}$ subshells of noble gas atoms in the dipole approximation, and particularly dramatic variations occur in the vicinity of Cooper minimum [7] owing to the rapid variation of the scattering phase shift in the vicinity of Cooper minima, including effects that occur only due to relativistic splittings. These effects appear to be amenable to experimental investigation.\\[4pt] [1] E. P. Wigner, Phys. Rev. \textbf{98}, 145 (1955). [2] M. Schultze \textit{et al}, Science \textbf{328}, 1658 (2010). [3] K. Klunder \textit{et al}, Phys. Rev. Lett. \textbf{106}, 143002 (2011). [4] A. S. Kheifets and I. A. Ivanov, Phys. Rev. Lett.\textbf{ 105}, 233002 (2010). [5] C. H. Zhang and U. Thumm, Phys. Rev. A \textbf{82}, 043405 (2010). [6] W. R. Johnson and C. D. Lin, Phys. Rev. A \textbf{20}, 964 (1979). [7] J. W. Cooper, Phys. Rev. \textbf{128}, 681 (1962).   

2s $\to $ np Autoionizing Resonances of the Neon Isoelectronic Sequence using RRPA and RMQDT

Extensive theoretical and experimental studies of the photoionization of various atoms and ions have been carried out over long period of time [1, 2] owing both to the fundamental importance of the process and to the many applications, e.g., astrophysical and atmospheric modeling, plasma dynamics, etc. In the present work, we report our studies of the 2$s \quad \to $ n$p$ autoionizing resonances in the Ne isoelectronic sequence, of significance due to the cosmic abundance of these systems [2-4]. In particular, Ne, Na$^{+}$, Mg$^{2+}$, Al$^{3+}$ and Sc$^{11+}$ have been studied. The study has been performed within the framework of the relativistic random-phase approximation (RRPA) [5] and relativistic multichannel quantum defect theory (RMQDT) [6]. The resonances have been characterized in terms of position, width and shape, i.e., Fano profiles [7, 8], and the evolution of the parameters of the resonances along the sequence has been investigated.\\[4pt] [1] A. Neogi \textit{et al}, Phys. Rev. A \textbf{67}, 042707 (2003). [2] H. S. Chakraborty \textit{et al}, Phys. Rev. Lett. \textbf{83}, 2151 (1999). [3] H. S. Chakraborty \textit{et al}, Ap. J. \textbf{595}, 1307 (2003). [4] G. Nasreen Haque, Ph.D. thesis (unpublished), Georgia State University, Atlanta, USA (1991). [5] W.R. Johnson et al, Phys. Scr. \textbf{21}, 409 (1980). [6] C. M. Lee and W.R. Johnson, Phys. Rev. A \textbf{22}, 979 (1980). [7] U. Fano and J. W. Cooper, Phys. Rev. A \textbf{40}, 441 (1968). [8] W.R. Johnson, et al, Phys. Rev. A \textbf{22}, 989 (1980).   

Theoretical Electronic Structure of Fluoromethanes and dissociation pathways

Fluoromethanes (CH$_{n}$F$_{4-n}$, n=0-3) are compounds characterized by a high reactivity. They are liberated into the atmosphere as consequence of anthropogenic activity. In the higher atmosphere, they can dissociate by the interaction with UV photons and other energetic particles. From experiments in our laboratory we had observe that these compounds dissociate when they interact with high density of photons. In this work we attempt to explain the main dissociation mechanisms involved when these molecules interact with photons of 255 and 355 nm, and the resulting products are neutral fragments with one and two atoms. The first electronic states, $S_{0}$ to $S_{8}$ and $T_{1}$ to $T_{8}$, of above mentioned compounds were calculated using time dependent density functional theory along the C-F and C-F$_{2}$ coordinates. From theoretical results we observe that C-F dissociation channel can be easy reached by the absorption of one photon of 266 or 355 nm, leading the formation neutral F and CH$_{n}$F$_{3-n}$ (n=1-3). Another mechanism is a two step processes mediated by stable transition structures, the molecule can dissociate as F$_{2}$ and CH$_{n}$F$_{2-n}$ (n=1,2).   

Plasmon-plasmon coupling in buckyonion fullerenes: Photoexcitation of interlayer plasmonic cross modes

Considering the photoionization of a two-layer fullerene-onion system, C$_{60}$@C$_{240}$, strong plasmonic couplings between the nested fullerenes are predicted [1]. The resulting hybridization produces four cross-over plasmons generated from the bonding and antibonding mixing of excited charge clouds of individual fullerenes. The properties of these hybrid plasmons are also greatly different from the plasmons that exist in isolated C$_{60}$ and C$_{240}$. This suggests the possibility of designing buckyonions exhibiting plasmon resonances with specified properties as candidates for nanomaterial plasmonics. The results can further motivate future research to modify the resonances by encaging atoms, molecules or clusters in multi-layered fullerenes.\\[4pt] [1] M.A. McCune, R. De, M.E. Madjet, H.S. Chakraborty, and S.T. Manson, \textit{J. Phys.} B Fast Track Comm. \textbf{44}, 241002 (2011).   

Kinetic Energy Release dependence in the Photo Double Ionization of H$_{2}$

In the Photo Double Ionization (PDI) of hydrogen molecules with photon energies of 150eV we were able to probe the electronic two particle density as a function of the bond length, i.e. the Kinetic Energy Release (KER) of the ions, and the orientation of the molecular axis with respect to the polarization vector of the incoming ligh. We applied the COLTRIMS technique and measured two electrons and two protons in coincidence. We found a shift in the KER for $\sigma $ and $\pi $ transitions. While the KER is lower when the molecular axis is aligned parallel to the linear polarization vector ($\sigma -\sigma )$, the KER for a perpendicular orientation ($\sigma -\pi )$ is clearly higher by a little more than 1eV. Quantum mechanical ab initio calculations are able to quantify the shift in KER and the ratio for the two different transitions ($\beta $-parameter) for a broad range of photon energies (75 to 240eV). These results reflect the dependence of the $\sigma $ and $\pi $ amplitudes to the bond length. This shows that a simple KER measurement for horizontal and vertical polarization can be used to extract this information; it makes measuring the $\beta $-parameter as a function of KER obsolete.   

Photofragmentation of Fullerene Molecular Ions

Experimental results are reported for single ionization and ionization with fragmentation of the fullerene molecular ions C$_{60}^{+}$ and C$_{70}^{+}$ after excitation by monochromatized vacuum ultraviolet synchrotron radiation at different photon energies: 22 eV, 35 eV, 65 eV, 105 eV and 140 eV. Since fullerenes are composed of even numbers of carbon atoms, the fragmentation occurs by the loss of differing numbers of carbon atom pairs. The energy dependences of relative cross sections for direct photoionization yielding C$_{60}^{2+}$ and C$_{70}^{2+}$ are compared with those for forming different doubly charged fullerene fragment ions. This research was supported by the Division of Chemical Sciences, Geosciences and Biosciences of the U.S. Department of Energy.   

Theoretical study of the vibration-dependent electron anisotropy in O$_2^-$ photodetachment

Recent experimental work [1] reports observation of a significant vibrational dependence of the photoelectron angular distributions (PADs) recorded for the O$_2$(X$^3\Sigma_g^?$) $\leftarrow$ O$_2^-$(X$^2\Pi_g$) band. It is the aim of the theoretical model presented here to reproduce the experimental results, allow for a deeper insight into the mechanism of this process and explain the sensitivity of the PAD to vibronic coupling in the anion ground electronic state. The vibrational dynamics is treated using the vibrational frame transformation [2], the K-matrices in the fixed-nuclei approximation are obtained from the \textit{ab initio} molecular \textsl{R}-matrix calculations. \\[4pt] [1] R. Mabbs \textit{et al.}, Phys. Rev. A 82 011401(R) (2010).\\[0pt] [2] H. Gao and C.H. Greene, Phys. Rev. A 42, 6946 (1990).   

Acceleration of proton bunches by petawatt chirped radially-polarized laser pulses

Results from theoretical investigations will be presented which show that protons can be accelerated from rest to a few hundred MeV by a 1 PW chirped radially-polarized laser pulse of several hundred femtosecond duration and focused to a waist radius comparable to the radiation wavelength. Single-particle calculations are supported by many-particle and particle-in-cell simulations. Compared with laser acceleration by a similar linearly-polarized pulse, the gained energies are less, but have better beam quality. For a suitable initial phase, a particle bunch gets accelerated by the axial component $E_z$ of the laser pulse and, initially focused by the transverse electric field component $E_r$. Beam diffraction finally sets in due to the particle-particle Coulomb repulsion, after interaction with the pulse ceases to exist.   

High-order harmonic generation enhanced by x rays from free-electron lasers

We theoretically examine high-order harmonic generation (HHG), by an intense near-infrared~(\textsc{nir}) laser, in the light of the emerging, intense x-ray free electron lasers (FELs) which have started to revolutionize x-ray science. We present two theories based on modified three-step models of HHG. Once, we combine HHG with resonant x-ray excitation of a core electron into the transient valence vacancy that is created in the course of the HHG process via tunnel ionization (first step of HHG) by the \textsc{nir}~light. When the continuum electron is driven back to the parent ion, a recombination with the valence and the core hole may occur. Modified HHG spectra are determined and analyzed for krypton on the $3d \rightarrow 4p$~resonance and for neon on the $1s \rightarrow 2p$~resonance. Another time, we examine HHG where tunnel ionization by the \textsc{nir}~light is replaced by direct x-ray ionization of a core electron. We use the boosted HHG radiation from $1s$~electrons of neon to predict single attosecond pulses in the kiloelectronvolt regime. For both presented schemes, we find substantial HHG yield from the recombination of the continuum electron with the core hole. Our research brings the capabilities of HHG-based sources to FELs.   

Development of a High Harmonic Beamline for Time-Resolved XUV Spectroscopy

In order to better understand bond breaking and other photochemical processes it is critical to determine the valence electron dynamics occurring during such phenomena. Extreme ultraviolet (XUV) light induces transitions between narrowly confined core electronic states and valence states. Thus ultrafast XUV absorption provides a route to determine electron distributions during chemical change. We present the design of our new femtoseconds XUV absorption spectrometer. The XUV pulses are generated in a rare gas cell in a high harmonic generation (HHG) process. Strong laser field HHG yields a promising probe source in the 10-100 eV spectral range, making it an ideal tool for XUV absorption spectroscopy of molecules containing 3d transition metals with M$_{2,3}$ edges between 40-70 eV. The femtosecond duration pulses intrinsically produced by HHG allow for the necessary temporal resolution. We plan to study organometallic molecules such as the transition metal carbonyls which undergo ligand dissociation under the influence of ultraviolet light. After UV excitation a radiationless non-Born-Oppenheimer processes occur before dissociation. The understanding of these non-Born-Oppenheimer dynamics is important to the general field of photocatalysis. This work is supported by the Office of Science Early Career Research Program.   

Probing the Sub-cycle AC Stark Shift by means of Attosecond Pulses: An \emph{ab initio} Study of Transient Absorption

We report a first fully \emph{ab initio} theoretical exploration of the sub-cycle dynamical AC Stark shift and broadening of He atoms driven by an attosecond pulse and IR pulse. Since the duration of the UV pulse is much shorter than that of the optical cycle of the IR dressing laser field, the sub-cycle dynamics of the dressed atoms can be unfolded by applying the attosecond pulse at different time delay. A nonperturbative method is developed to calculate the transient absorption spectrum without weak-field limitation. By solving the time-dependent Schr\"{o}dinger equation accurately by means of the time-dependent generalized pseudospectral method, we predict novel sub-cycle laser-induced time-dependent AC Stark shift and power broadening of He atoms whose dynamical features are in good agreement with the latest ongoing experiments at UCF. Detailed results will be presented. This work is partially supported by DOE and NSF.   

Revisiting molecular ionization: Does a molecule like to share?

The ever-increasing detail obtained in strong-field experiments calls for a deeper understanding of the laser-molecule interaction. For instance, recent measurements reported in PRL {\bf 107}, 143004 (2011) reveal a limitation in understanding strong-field ionization dynamics in terms of the strong-field approximation. We have addressed the question of how the electron and the nuclei share the energy when H$_2^+$ breaks up in the presence of an intense IR field via the process: H$_2^++n\hbar\omega\to p+p+e^-$. Solving the time-dependent Schr\"{o}dinger equation and calculating the ionization probability resolved as a function of the asymptotic electron energy and the nuclear kinetic energy release (KER) allow us to give an answer. The energy sharing is non-trivial and plays an important role in the prediction of, for instance, the KER. We also address the limitations of current understanding of molecular ionization by comparing to models like the strong-field approximation and the Floquet picture. Such benchmarking may be facilitated by XUV+IR pump-probe schemes and carrier-envelope-phase control that allow for time-resolved and spatial probing of the dynamics.   

Dissociation dynamics of O$_{2}^{+}$ in intense laser fields

We studied the nuclear dynamics of diatomic molecular ions in intense infrared laser fields by analyzing their fragment kinetic energy release (KER) spectra as a function of time [1]. We found that, in general, ionization of the neutral parent molecule by an ultra-short pump pulse populates several intermediate electronic states of the molecular ion that contribute to the same KER. Within the Born-Oppenheimer (BO) approximation, we calculated \textit{ab--initio} adiabatic potential energy curves for the molecular ions and their electric dipole-couplings, using the quantum chemistry code GAMESS [2]. By comparing KER spectra that result from the nuclear dynamics on individual and on dipole coupled BO potential curves with that measured for O$_{2}$ molecules, we developed a scheme for identifying intermediate states of the molecular ions that are relevant during the dissociation dynamics. \\[4pt] [1] S. De \textit{et al}., PRA \textbf{80}, 011404 (2009); S. De \textit{et al}, PRA \textbf{84}, 043410 (2011) \\[0pt] [2] M. W. Schmidt \textit{et al}, J. Comput. Chem., \textbf{14}, 1347 (1993).   

An assessment of tunneling-multiphoton dichotomy in atomic photo-ionization: Keldysh parameter versus scaled frequency

It is common practice in strong-laser physics community that dynamical regime of atomic ionization is described by the Keldysh parameter, $\gamma$. Two distinct cases where $\gamma\ll 1$ and $\gamma\gg 1$ are associated with ionization mechanisms that are predominantly in tunneling and in multi-photon regimes, respectively. We report on our fully three-dimensional {\it ab initio} quantum simulations of ionization of hydrogen atoms in laser fields described in terms of the Keldysh parameter by solving the corresponding time-dependent Schr\"odinger equation. We find that the Keldysh parameter is useful in inferring the dynamical ionization regime only when coupled with the scaled laser frequency, $\Omega$, when a large range of laser frequencies and peak intensities are considered. The additional parameter $\Omega$ relates the laser frequency $\omega$ to the classical Kepler frequency $\omega_K$ of the electron, and together with the Keldysh parameter, they can be used to refer to an ionization regime.   

Size dependent ionization dynamics of argon clusters in intense x-ray pulses

Free Electron Lasers open the door for novel experiments in many science areas ranging from ultrafast chemical dynamics to single shot imaging of molecules. For the success of virtually all experiments with free electron lasers a detailed understanding of the light - matter interaction in the x-ray regime is pivotal. The Linac Coherent Light Source (LCLS) free electron laser in Stanford allows for the first time to study innershell ionization dynamics of intense x-ray pulses on a femtosecond time scale. We performed experiments on the ionization dynamics of Argon clusters at different pulse length using the slotted spoiler foil in the second LCLS bunch compressor [1]. The Auger rate of argon clusters is predicted to be size dependent and lower than in atoms due to delocalization of the valence electrons [2]. We observe a dependence of the ionization dynamics on pulse length and cluster size. The results are discussed and also compared to recent atomic and molecular data from LCLS.\\[4pt] [1] P. Emma et al. PRL 92, 074801 (2004)\\[0pt] [2] U. Saalmann, JM Rost PRL 89, 14 (2002)   

Quantum dynamics in strong fields with Fermion Coupled Coherent States

We present a new version of the Coupled Coherent State method, specifically adapted for solving the time-dependent Schr{\"{o}}dinger equation for multi-electron dynamics in atoms and molecules. This new theory takes explicit account of the exchange symmetry of fermion particles, and uses fermion molecular dynamics to propagate trajectories. As a demonstration, calculations in the He atom are performed using the full Hamiltonian and accurate experimental parameters. Single and double ionization yields by 160 fs and 780 nm laser pulses are calculated as a function of field intensity in the range 10$^{14}$ - 10$^{16}$ W/cm$^{2}$ and good agreement with experiments by Walker {\it{et al}}.\ is obtained. Since this method is trajectory based, mechanistic analysis of the dynamics is straightforward. We also calculate semiclassical momentum distributions for double ionization following 25 fs and 795 nm pulses at 1.5 10$^{15}$ W/cm$^{2}$, in order to compare to the detailed experiments by Rudenko {\it{et al}}. For this more challenging task, full convergence is not achieved, but however major effects such as the finger-like structures in the momentum distribution are reproduced.   

Strong-field control over the product branching ratios in molecular dissociation

We present a theoretical and experimental study of strong-field control over the fragmentation channel in molecular dissociation by intense, single-color laser fields with emphasis on the effect of chirped pulses. In particular, the branching ratio between H+D$^+$ and H$^+$+D from an HD$^+$ target is examined as a function of kinetic energy release for 790 nm pulses with intensities on the order of $10^{14}$ W/cm$^2$ and pulse lengths ranging from 25 to 65 fs. Theoretical calculations based on numerical solutions of the time-dependent Schr\"odinger equation in the Born-Oppenheimer approximation are compared to measurements using a coincidence 3-D momentum imaging technique. Both demonstrate that control is indeed possible and depends, as expected, on details of the laser pulse such as its chirp.   

Quantum resonances in selective rotational excitation of molecules with a sequence of ultrashort laser pulses

The periodically kicked rotor is a paradigm system for studying classical and quantum chaos. In the quantum regime, the dynamics of the kicked rotor exhibit such phenomena as suppression of classical chaos, Anderson localization in angular momentum and quantum resonances in the accumulation of rotational energy. Even though these effects have been studied with ultracold atoms in optical fields and Rydberg atoms in microwave fields, they have never been observed in a real rotational system. In this work we study the effect of quantum resonance in the rotational excitation of a diatomic molecule. By using femtosecond pulse shaping and rotational state-resolved detection, we measure the rotational distribution of molecules interacting with a train of pulses. We show enhancement of population transfer from the ground to the excited rotational states at resonance, and demonstrate selective rotational excitation of two nitrogen isotopes. We utilize fractional quantum resonances for separating para- and ortho-nitrogen, paving the way to novel methods of coherent control of molecular rotation.   

Molecular Ionization at High Intensities: Characterizing OPA Laser Pulses

Ultrashort laser pulses have long been the primary instruments of probing and analyzing intense-field molecular dynamics on femtosecond timescales. In particular, processes involving resonance-enhanced multiphoton ionization (REMPI) have provided insight into ionization and dissociation dynamics. Typically the scope of REMPI is limited by the laser properties; namely, REMPI is limited by the transition energies accessible by an integer number of photons. However, the ability to tune the energies of these photons adds flexibility to the available resonances and, for longer wavelengths, makes tunneling the dominant ionization process. Optical parametric amplification (OPA) provides these changes, but the nonlinear processes required for OPA could have complicating effects on pulse duration and focusability, distorting beam quality and compromising experiments. We present the parametric amplification of 800-nm, 50-fs laser pulses in a TOPAS-C system: we use autocorrelation, power measurements, and knife-edging techniques to determine output pulse duration, intensity, and focal characteristics as a function of wavelength. We also report on the effects such changes will have on the practicality of various techniques requiring high-intensity processes.   

High Resolution X-ray Spectroscopy of Charge Exchange Collisions of Astrophysical Interest

Soft X-ray emission following charge exchange (CX) by fully stripped and hydrogen-like ions of carbon, nitrogen, and oxygen on H, H$_{2}$ and He were measured in a collision energy range of 0.5 keV/u -- 30.0 keV/u. CX experiments were performed using the ORNL Multicharged Ion Research Facility ion-atom merged-beams apparatus with a high resolution X-ray quantum calorimeter (XQC) from the University of Wisconsin. First recorded X-ray spectra were made with He and H$_{2}$ gases introduced into the beam line and with ion beams decelerated from a high voltage platform to simulate a range of solar wind ion velocities. Current results are compared with the previous experimental and theoretical studies, and presented along with the status of CX measurements with atomic hydrogen using a merged-beams technique.   

Progress in development of public three-body code

We report our progress in development of public software for fast and accurate quantum mechanical three-body calculations. This tool allows general users to perform bound state and low energy scattering calculations for general three-body below the break-up threshold. We describe the basics of the numerical scheme, the procedure of automatic grid construction and report results for elastic and reactive scattering in atom-dimer collisions.   

Anisotropy induced Feshbach resonances in quantum dipolar gas of magnetic atoms

The best atoms to search for effects of anisotropy on collisions are submerged-shell atoms, which have an electronic configuration with an unfilled inner shell shielded by a closed outer shell. In particular, we are interested in the $^5{\rm I}_8$ ground-state rare-earth dysprosium (Dy) atom with total atomic angular momentum $j=8$ and a large magnetic moment of $\approx 10\mu_B$, for which the 4$f^{14}$ electrons in the inner shell are aligned in such a way that the orbital moment is largely unquenched. As a result, Dy magnetic and electrostatic properties are highly anisotropic. Here we introduce a new coupled-channel model allowing us to calculate the anisotropy-induced magnetically-tunable Feshbach resonance spectrum of bosonic Dy atoms. The model treats the Zeeman interaction of the Dy atoms due to an external magnetic field and the magnetic dipole-dipole, (isotropic and anisotropic) electrostatic dispersion, and electric quadrupole-quadrupole interactions on equal footing. Our detailed quantum mechanical calculation describes a novel anisotropic nature of Feshbach resonances in interactions between magnetic Dy atoms and reveals a striking correlation between anisotropy in magnetic and electrostatic interactions and the Feshbach spectrum.   

Study of collisional dynamics in highly excited Li$_{2}$

Energy transfer during molecular collisions is a fundamental process in astronomy and chemistry. As Li$_{2}$ is a relatively simple molecule, it has been possible to model collisions of its low-lying excited state with ground state atoms for some years. We now intend to experimentally measure collisions involving much higher energy levels: studying the vibrational inelastic collisions and dissociation for molecules starting in the A (1 $^{1}\Sigma _{u}^{+}$,$\nu $' $>$45) states, and working towards studies of V-R coupling in the ``shelf'' region of the E (3 $^{1}\Sigma _{g}^{+})$ state. To carry out these experiments, we are using a dual pulsed dye laser system. We have recently demonstrated that we can measure equivalent rate constants using either pulsed or cw excitation.   

Rotationally inelastic collisions of He and Ar with NaK: Experiment and theory

We are investigating collisions of the ground ($X^1\Sigma^+$) and first excited ($A^1\Sigma^+$) electronic states of NaK using both experimental and theoretical methods. Potential surfaces for HeNaK (fixed NaK bond length) are used for coupled channel calculations of cross sections for rotational energy transfer and also for collisional transfer of orientation and alignment. Additional calculations use the MCTDH wavepacket method. The measurements of the $A$ state collisions involve a pump--probe excitation scheme using polarization labeling and laser-induced fluorescence spectroscopy. The pump excites a particular ro-vibrational level $(v,J)$ of the $A$ state from the $X$ state, and the probe laser is scanned over various transitions to the $3^1\Pi$ state. In addition to strong direct transitions, weak satellite lines are observed that arise from collisionally-induced transitions from the $(v,J)$ level to $(v,J'=J+\Delta J)$. This method provides information about the cross sections for transfer of population and orientation for $A$ state levels, and it can be adapted to transitions starting in the $X$ state. For the $A$ state we observe a strong $\Delta J=\mathrm{even}$ propensity for both He and Ar perturbers. Preliminary results for the $X$ state do not show this propensity.   

Experimental Studies of High Lying Electronic State of NaCs

We present new results from experimental studies of high-lying electronic states of the NaCs molecule that are currently underway in our laboratory. The optical-optical double resonance method is used to obtain Doppler-free excitation spectra for several excited states. Selected data from the $5^3\Pi_0$, $4^3\Pi_0$ and other high lying electronic states are used to obtain Rydberg-Klein-Rees (RKR) and Inverse Perturbation Approach (IPA) potential curves. Small oscillations in the other wall of the $5^3\Pi_0$ potential suggest strong interactions with other electronic states. A modified version of Le~Roy's BCONT program was used to simulate NaCs $5^3\Pi_0 \rightarrow 1(a)^3\Sigma^+$ bound-free emission spectra. These simulations were used to fit the experimental spectra with a parameterized $1(a)^3\Sigma^+$ repulsive wall and the $5^3\Pi_0 \rightarrow 1(a)^3\Sigma^+$ transition dipole moment function, $\mu(R)$. The fitted $\mu(R)$ is in good agreement with the theoretical transition dipole moment function of Aymar and Dulieu [Mol.Phys. \textbf{105}, 1733 (2007)]. In related work, we have identified additional electronic states which we have tentatively assigned as the $4^3\Pi_0$ and $5^3\Pi_1$ (and possibly the $5^3\Pi_2$) electronic states of NaCs.   

Free-free transitions in the presence of laser fields and Debye potential at very low incident electron energies

We study the free-free transition in electron-helium ion in the ground state and embedded in a Debye potential in the presence of an external laser field at very low incident electron energies. The laser field is treated classically while the collision dynamics is treated quantum mechanically. The laser field is chosen as monochromatic, linearly polarized and homogeneous. The incident electron is considered to be dressed by the laser field in a nonperturbative manner by choosing Volkov wave function for it. The scattering wave function for the incident electron on the target embedded in a Debye potential is solved numerically by taking into account the effect of electron exchange. We calculate the laser-assisted differential and total cross sections for free-free transition for absorption/emission of a single photon or no photon exchange. The results will be presented at the conference.   

Electron scattering from silicon

The $B$-spline $R$-matrix method~[1] is used to study electron collisions with neutral silicon over an energy range from threshold to 100~eV. The multi\-configuration Hartree-Fock method with non-orthogonal orbitals is employed for an accurate representation of the target wave functions. The close-coupling expansion includes 34 bound states of neutral silicon derived from the [Ne]$3s^23p^2$, $3s3p^3$, $3s^23p4s$, $3s^23p5s$, $3s^23p4p$, $3s^23p5p$, $3s^23p3d$, and $3s^23p4d$ configurations, plus seven pseudo\-states to fully account for the dipole polarizability of the ground state and the lowest three excited states. Results are presented for transitions from the $3s^23p^2~^3P$ ground state and the metastable $3s^23p^2~^1D$ and $3s^23p^2~^1S$ states. Both correlation and polarization effects are found to be important for accurate calculations. The sensitivity of the results was checked by comparing data obtained in different approximations. The current predictions represent an extensive set of electron scattering data for neutral silicon. The results are compared with those obtained earlier for e-C collisions~[2].\\[4pt] [1] O. Zatsarinny, Comp. Phys. Commun. {\bf 174} (2006) 273.\\[0pt] [2] O. Zatsarinny, K. Bartschat, L. Bandurina, and V. Gedeon, Phys. Rev. A~{bf 71} (2005) 042702.   

B-Spline R-Matrix with Pseudo-States Treatment of Electron Collisions with Neon

We have further developed the $B$-Spline $R$-matrix (BSR) code~[1] to allow for a large number of pseudo-states in the close-coupling expansion. In the present work, the BSRMPS approach~[2] was employed to perform semi-relativistic (Breit-Pauli) close-coupling calculations for elastic scattering, excitation, and ionization of neon from both the ground state and the metastable excited states. Coupling to the ionization continuum through the pseudo-states is important for low-energy elastic scattering (to represent polarizability effects), for excitation in the ``intermediate'' energy regime of about 1-3 times the ionization potential, and to allow for the calculation of ionization processes by transforming the results obtained for excitation of the positive-energy pseudo-states. The current results represent a significant extension of our earlier near-threshold work~[3] and previous RMPS calculations~[4,5].\\[4pt] [1] O.~Zatsarinny, Comp. Phys. Commun.~{\bf 174} (2006) 273.\\[0pt] [2] O.~Zatsarinny and K.~Bartschat, Phys.~Rev.~Lett.~{\bf 107} (2011) 023203.\\[0pt] [3] O.~Zatsarinny and K.~Bartschat, J.~Phys.~B~{\bf 37} (2004) 2173.\\[0pt] [4] C.~P.~Ballance and D.~C.~Griffin, J.~Phys.~B~{\bf 37} (2004) 2943.\\[0pt] [5] C.~P.~Ballance {\it et al.}, J.~Phys.~B~{\bf 37} (2004) 4779.   

Electron-impact excitation of Cl$^{2+}$

We present calculation results for electron-impart excitation of Cl$^{2+}$ ions. The collision strengths are calculated in the close-coupling approximation using the B-spline Breit-Pauli R-matrix method. The multi-configuration Hartree-Fock method with term-dependant non-orthogonal orbitals is employed for an accurate description of the target wave functions. The 68 fine-structure levels belonging to the 32 \textit{LS} states of 3s$^{2}$3$p^{3}$, 3$s$3$p^{4}$, 3$s^{2}$3$p^{2}$3$d$, 3$s^{2}$3$p^{2}$4$s$ and 3$s^{2}$3$p^{2}$4$p$ configurations are included in the close-coupling approximation; this leads to 2278 possible fine-structure transitions. The effective collision strengths are obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities, and these are tabulated for all fine-structure transitions at electron temperatures in the range 5,000 to 1,000,000 K. Our results are compared with previous theoretical results and available experimental data. This work is supported by NASA grant NNG09AB63G from the Planetary Atmospheres Program.   

Electron-impact ionization of Li$_{2}$

Electron-impact ionization cross sections are calculated for Li$_{2}$. A two active electron time-dependent close -coupling method is used to calculate cross sections for Li$_{2}$ at the equilibrium internuclear distance for incident energies of 10 eV, 15 eV, and 20 eV. The nonperturbative close-coupling cross sections are found to be lower than perturbative distorted-wave cross sections due to electron correlation effects between the two outgoing continuum electrons.   

Momentum Imaging of Dissociative Electron Attachment to Molecules

Dissociative electron attachment (DEA) to diatomic and polyatomic molecules, including O$_2$, C$_2$H$_2$, and CO$_2$, is studied using a COLTRIMS apparatus which is capable of imaging 3D dissociation dynamics upon impact from a low energy ($\sim$10eV) electron. A pulsed electric field is used to extract and distinguish ion fragments in a time-of-flight mass spectrometer, from which a complete picture of the reaction dynamics may be constructed. Through the axial recoil approximation, dependence of the attachment probability on a molecule's orientation with respect to the incoming electron's momentum is revealed.   

Metastable Decay of Molecular Ions

Metastable dissociation of singly and multiply ionized molecules has been observed in two-dimensional coincidence mass spectra of molecules caused by electron impact dissociative ionization. These molecules include ethane, propane, butane, carbonyl sulphide and isocyanic acid. The decay of the molecular ions occurs either in the ion acceleration region or in the drift tube of a Wiley-McLaren type mass spectrometer, which exhibits two distinctly featured traces on the coincidence mass spectrum if the life time of the molecular ions is comparable with the time-of-flight of the ions. These traces generally start from a coincidence island, which indicates the species of the daughter ions, and ends at a point on the diagonal of the spectrum, which indicates the species of the parent ion. The intensity distribution and the geometric properties of the decay traces can be used to retrieve valuable information on the decay lifetime and dissociation dynamics of the molecular ions. Some new decay channels have been discovered. Asymmetric charge distribution and orientation of the molecular ions in the mass spectrometer has also been observed. Project supported by the WIU-URC grant.   

Dissociative recombination of HCl$^+$

Recently, the molecular ion HCl$^+$ has been observed in the interstellar medium. There is little information available about the cross sections for creation and destruction of this ion. Therefore, we have begun calculations to predict the dissociative recombination cross section and the final state distribution of atomic states produced in the dissociation. The relevant electronic states are calculated \textit{ab initio} by combining electron scattering calculations using complex Kohn variational method to obtain resonance positions and autoionization widths and multi-reference configuration interaction calculations to construct the ion and Rydberg states. The direct dissociation recombination cross section is obtained by using wave packets propagating on the resonant states.   

Theory of dissociative recombination of highly-symmetric polyatomic ions

A general first-principles theory of dissociative recombination is developed for highly-symmetric molecular ions and applied to H$_3$O$^{+}$ and CH$_3^+$, which play an important role in astrophysical, combustion, and laboratory plasma environments. The theoretical cross-sections obtained for the dissociative recombination of the two ions are in good agreement with existing experimental data from storage ring experiments.   

Rotating wall compression of positron swarm in a harmonic potential: a Monte Carlo simulation

Several experiments have demonstrated successful application of rotating wall technique for compressing positron beams in a single particle regime. While the basic mechanism of compression is understood, the role of the cooling gases which have to be used is poorly explained. Thus, we have simulated behavior of a swarm of particles (electrons or positrons) in an antisymmetric dipole rotating field inside a buffer gas trap. We have used our existing Monte Carlo code for the simulation, as the single particle conditions are inherently assumed. Varying mixtures of CF$_{4}$ and N$_{2}$ are used as the buffer gas in order to mimic the operating conditions of Surko trap, and to pinpoint the collisions responsible for compression. For a given parameter range, the simulation shows significant compression and axialization of positron swarm. We have investigated the change of swarm behavior by varying the applied rotating wall potential and frequency, strength of axial magnetic field, and background gas composition and pressure. The results show fast initial heating of the swarm, and subsequent cooling to the thermal temperature, as the radius of the cloud compresses, demonstrating that it is possible to compress the beam of charged particles in a single particle regime.   

Low energy positron beam studies

Measurements of positrons interacting with atoms and surfaces indicate surface structure and scattering dynamics. The positron beam has an energy range from about 1 to 900 eV, an expected polarization of about 20{\%} and intensity of 1000 counts/sec in a 10 mm radius on a microchannel plate detector used in retarding potential mode. A W(100) single crystal at 10 $^{-10}$ mbar supports the growth of Fe thin films. Results indicate the elastic and inelastic scattering of positrons, generation of secondary electrons, re-emission of thermalized positrons normal to different surfaces and various scattering mechanisms.   

Radiative double electron capture (RDEC) in collisions of bare fluorine ions with carbon foils

Radiative double electron capture (RDEC) is a charge exchange process involving the capture of two target electrons into a bound state of the projectile simultaneously with the emission of a single photon. RDEC is the time reversed process of double photoionization if the target electrons are loosely bound. This approach provides us with a clean tool to explore the problems involved with electron-electron correlations and a proper description of a two-electron-continuum wave function in various atomic systems. In this work, we investigate both radiative electron capture (REC) and RDEC in collisions of 42 MeV singly- and doubly-charge changed fluorine ions with carbon targets. The experiment was performed at the tandem Van de Graaff accelerator of Western Michigan University in which emitted x rays were measured at 90\r{ } to the beam line in coincidence with projectile charge-changing of bare and H-like fluorine. The first evidence to see the RDEC process in O$^{8+}$ + C collisions\footnote{A. Simon \textit{et al}., Phys. Rev. Lett. \textbf{104} (12), 123001 (2010)} was the motivation to conduct the current work for the sake of the comparison between both observations and with recent theoretical calculations.\footnote{A. I. Mikhailov \textit{et al}., Phys. Lett. A \textbf{328}, 350 (2004)}$^,$\footnote{A. I. Mikhailov \textit{et al}., Phys. Rev. A \textbf{69}, 032703 (2004)}$^,$\footnote{A. Nefiodov \textit{et al}., Phys. Lett. A \textbf{346}, 158 (2005).}   

Importance of post collision interactions for charge transfer process

Recently experimental fully differential cross sections (FDCS) have been reported for double capture, single capture and transfer excitation in proton helium collisions. In case of double capture, the proton captures both of the electrons from helium and leaves the collision as a H- ion. For single capture, the proton captures one electron from helium and leaves the other electron in the ground state. Transfer excitation is similar to single capture except the target is excited to an excited state. Recently experiments performed for proton energies ranging from 25keV to 300keV. We introduce here a theoretical model for charge transfer processes which is fully quantum mechanical and takes all post collision interactions (PCI) between the particles into account exactly. Numerically, this requires a full nine-dimensional integral which is computationally expensive. The theoretical results will be compared with absolute experimental measurements.   

Robust and Efficient Population Transfer in Ultracold Rubidium Using A Single Linearly Chirped Laser Pulse With a Novel Pulse Envelope

The ability to manipulate the state of a quantum system is the at very heart of the field of quantum control. As quantum control is an essential aspect of the emerging field of quantum computing, it is necessary to find techniques for manipulating quantum systems that are both robust and efficient to implement industrially. In this work the population dynamics of the valence electron of Rubidium, interacting with a single linearly chirped laser pulse, are studied. The pulse envelope is constructed from overlapping Gaussian waveforms and is described analytically by the formula: $E_{0}\sum_{\beta=-n}^{n}Exp\{\frac{-[t-(T-n*\epsilon)]^{2}}{2\tau_{0}^{2}}\}$ with the parameter $\epsilon$ being the separation in time between each peak with the oscillating electric field is phase locked to the central peak. The response of the quantum yield obtained at the end of the pulse to changes in the parameters of the oscillating electric field and pulse envelope are studied. For certain values of these parameters, achievement of a transfer of over $99\%$ of the population to a desired quantum state within the hyperfine structure of the $5S$ shell via adiabatic passage using beam intensities which are on the order of $100W/cm^{2}$ is demonstrated. Results are robust in the adiabatic regime.   

Single chirped pulse control of hyperfine states population in Rb atom in the framework of the four-level system

Electron population dynamics within the hyperfine structure in the Rb atom induced by a single ns pulse is theoretically investigated. The aim is to develop a methodology of the implementation of linearly chirped laser pulses for the desired excitations in the Rb atoms resulting in the creation of predetermined non-equilibrium states. A semi-classical model of laser pulse interaction with a four-level system representing the hyperfine energy levels of the Rb atom involved into dynamics has been developed. The equations for the probability amplitudes were obtained from the Schrodinger equation with the Hamiltonian that described the time evolution of the population of the four states in the field interaction representation. A code was written in Fortran for a numerical analysis of the time evolution of probability amplitudes as a function of the field parameters. The dependence of the quantum yield on the pulse duration, the linear chirp parameter and the Rabi frequency was studied to reveal the conditions for the entire population transfer to the upper hyperfine state of the 5S$_{1/2}$ electronic level. The results may provide a robust tool for quantum operations in the alkali atoms.   

Image based adaptive femtosecond control of ethylene fragmentation

Using an adaptive femtosecond control scheme, ethylene is ionized by a shaped ultrafast laser pulse, leading to isomerization to the ethylidene (HC-CH3)$^{q+}$ configuration, from which CH$_{3}^{+}$ fragments are generated. Feedback for the control process is obtained by rapidly inverting velocity map images of the CH$_{3}^{+}$ and competing CH$_{2}^{+}$ fragments, allowing identification of dissociation channels and subsequent control of the CH$_{3}^{+}$/CH$_{2}^{+}$ ratio. Additionally, we have identified the C$_{2}$H$_{4}^{+} \quad \to $ C$_{2}$H$_{3}^{+}$ + H and C$_{2}$H$_{4}^{+} \quad \to $ C$_{2}$H$_{2}^{+}$ + H$_{2}$ channels as creating ion images with rich structure that offer possible routes to investigate control via conical intersections on the C$_{2}$H$_{4}^{+}$ potential energy surface.   

Electromagnetically induced transparency and absorption in warm Rb vapor via the Hanle effect: Analysis of observed spectra

We have observed electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) in room temperature Rubidium vapor, by coherent population trapping on the Zeeman substates formed by a magnetic field co-linear with a laser beam passing through the vapor. We have observed EIA on $F_{g} = 3 \rightarrow F'$ transitions in ${}^{85}$Rb and on $F_{g} = 2 \rightarrow F'$ transitions in ${}^{87}$ Rb. We have observed with good signal-to-noise ratio EIT on $F_{g} = 2 \rightarrow F'$ transitions in ${}^{85}$Rb and, for the first time, on $F_{g} = 1 \rightarrow F'$ transitions in ${}^{87}$ Rb. However, certain unexpected features are revealed in the observed spectra, the origins for which remain unclear. We report on our progress toward modelling and understanding the observed EIT and EIA spectra.   

Superluminal squeezed light propagation with Rb atoms

We present an all atomic method for the generation and manipulation of broadband squeezed states of light ranging in frequency from a few hundred Hz to several MHz and matching an atomic transition of Rb atoms. Our squeezer is based on the polarization self-rotation (PSR) effect in an atomic medium. We have developed a method allowing us to cast an arbitrary temporal pulse shape of the squeezed state by applying a longitudinal magnetic field to the squeezing Rb cell. Such a modulated squeezed state can then serve as a quantum probe to an atomic ensemble of hot Rb vapor. We show that under certain conditions, the squeezed light shows a superluminal propagation speed through the Rb vapor. Also, the application of an additional optical field to the atomic ensemble allows us to control and selectively filter the squeezed state of light. These techniques are of potential interest for precision metrology and the quantum information community.   

Controlling emission of nitrogen-vacancy centers in diamond with nanoscale photonic interfaces

Nitrogen-vacancy (NV) centers are a promising candidate for quantum information processing. They act as artifical atoms in the solid state that can be addressed optically, exhibit spin-dependent fluorescence, and can have transform-limited linewidths at the zero phonon line (ZPL). However, most ($>$95{\%}) of the emission is into a broad, incoherent phonon side band, limiting quantum applications. We will present recent progress toward coupling NV centers in bulk diamond to photonic crystals and waveguides, with the goal of directing emission into the ZPL and realizing the strong coupling regime for applications such as entanglement of distant NV centers and single photon transistors.   

3D Raman sideband cooling of single atoms in an optical tweezer trap

We have cooled a single atom in an optical tweezer trap very close to its three-dimensional ground state. An atom loaded with an initial temperature of around 110 uK has radial and axial occupation numbers of $n_r = 23$ and $n_a = 170$; after cooling, we achieve final occupation numbers of $n_r < 0.1$ and $n_a=7.5$. The principal technical challenge we encountered was effective magnetic field gradients arising from distortions of the dipole trap polarization in the optical tweezer focus, which we will discuss in some detail. Additionally, we will present ongoing work on two fronts: using the tightly localized atom to sense optical fields on the nanometer-scale, and bringing the atom close to nanoscale optical waveguides and can ities with the goal of achieving strong atom-photon interactions.   

Progress towards building lattice atom interferometer using $^{7}$Li

We are building an atom interferometer using $^{7}$Li atoms for the ultimate goal to test the universality of free fall. To deal with light mass of lithium and its large recoil velocity, we will develop a new technique using an optical lattice. The lattice will act as a waveguide to prevent atom losses due to the high thermal velocity of Li, and as large momentum transfer beam splitters in analogy to the Bloch-Bragg-Bloch beam splitters already developed by us~[2,3]. We discuss investigations of novel all-optical cooling of lithium using degenerate Raman sideband cooling as well as recent progress towards a demonstration of the first ultracold lithium interferometer. \\[4pt] [1] H. M\"{u}ller et al., Phys. Rev. Lett. {\bf 100}, 180405 (2008) \\[0pt] [2] H. M\"{u}ller et al., Phys. Rev. Lett. {\bf 102}, 240403 (2009)   

Atom Interferometry: A Matter Wave Clock and a Measurement of $\alpha$

Developments in large-momentum transfer beamsplitters (eg. Bragg diffraction) and conjugate Ramsey-Bord\'{e} interferometers have enabled atom interferometers with unparalleled size and sensitivity. The atomic wave packet separation is large enough that the Coriolis force due to the earth's rotation reduces interferometer contrast. We compensate for this effect using a tip-tilt mirror, improving our contrast by up to a factor of 3.5, allowing pulse separations of up to 250 ms with $10\hbar k$ beamsplitters. This interferometer can be used to make a precise measurement of the recoil frequency ($\propto h/m$) and thus the fine structure constant. The interferometer also gives us indirect access to the Compton frequency ($\nu_C\equiv mc^2/h$) oscillations of the matter wave, since $h/m$ is simply $c^2/\nu_C$. Using an optical frequency comb we reference the interferometer's laser frequency to a multiple of a cesium atom's recoil frequency. This self-referenced interferometer thus locks a local oscillator to a specified fraction of the cesium Compton frequency, with a fractional stability of 2 pbb over several hours. This has potential application in redefining the kilogram in terms of the second. We also present a preliminary measurement of the fine structure constant.   

Condensate Interferometry in a Magnetic Guide

We present recent progress on experiments on atom interferometry using Bose-Einstein condensates confined in a magnetic guide. Several sources of decoherence can be avoided by using a harmonic trap potential to control the motion of the the atoms, and common-mode noise sources such as vibrations can be controlled using simultaneous dual interferometers in the same trap. Important limitations that remain include anharmonicity in the trap potential and residual motion of the condensate in the trap. We will also describe a new apparatus featuring a cylindrically symmetric potential that is optimized for gyroscopic measurements.   

Generation of single frequency blue light by highly efficient harmonic generation of IR laser diodes in resonance build-up cavities using nonlinear crystals

Blue and UV lasers have a wide variety of applications, including atomic spectroscopy. We are particularly interested in 486 nm and 243 nm for hydrogen spectroscopy. Blue and UV laser diodes are at the early stages of development. At this time, harmonic generations (HG) is a viable technique to produce blue and UV light with well developed fiber coupled IR laser diodes. We recently reported a polarization maintaining (PM) fiber to fiber conversion efficiency of 71 percent overall. We used a PPKTP (Periodically Poled Potassium Titanyl Phosphate) crystal in an external build-up cavity. The 600 mW of blue at 486 nm was generated from second HG of a 972 nm PM fiber coupled laser diode [1]. PPKTP presents blue absorption (BA) and blue light induced IR absorption (BLIIRA) which cause thermal instability and inefficiency in the buildup cavity. Another crystal, PPSLT (Periodically Poled Lithium Tantalite) promises less BA and less BLIIRA. Our latest results for producing 486 nm using PPSLT and comparison with PPKTP will be presented. \\[4pt] [1] Koustrubh Danekar, Ali Khademian, and David Shiner, Opt. Lett. 36, 294 (2011)   

Microscopic and Macroscopic Descriptions of Nonlinear Electromagnetic Interactions in Atomic Ensembles

Microscopic and macroscopic descriptions of nonlinear electromagnetic interactions relevant to resonant pump-probe optical phenomena in quantized many-electron systems are formulated within the framework of a general reduced-density-matrix approach. Time-domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations are developed in a unified and self-consistent manner. A semiclassical perturbation treatment of the electromagnetic interaction is adopted, in which the electromagnetic field is described as a classical field satisfying either the microscopic form or the macroscopic form of the Maxwell equations. A quantized-field approach is essential for a fully self-consistent quantum-mechanical formulation. Compact Liouville-space operator expressions are obtained for the general (n'th order) non-linear electromagnetic-response tensors for moving atomic systems. Environmental interactions can be treated in terms of the Liouville-space self-energy operator.   

Quantum interference of single photons from two remote nitrogen-vacancy centers in diamond

The interference of two identical photons impinging on a beam splitter leads to perfect photon coalescence where both photons leave through the same output port. This effect, known as Hong-Ou-Mandel (HOM) interference, can be used to characterize the properties of quantum emitters with high accuracy. This is a particularly useful tool for quantum emitters embedded in a solid state matrix because their internal properties, unlike those of atoms in free space, differ substantially from emitter to emitter due to strong interactions with the environment. HOM interference can also be used to generate optically mediated entanglement between two remote quantum emitters, a crucial step toward the development of long-distance quantum communication and scalable quantum computation architectures. Here, we demonstrate this interference effect with single photons emitted from two single Nitrogen-Vacancy (NV) centers in diamond samples that are spatially separated by 2 meters [1]. The detuning of the photons can be tuned by applying a DC electric field to one NV center. We discuss current efforts toward optical entanglement of the two NV centers. \\[4pt] [1] A. Sipahigil, M. L. Goldman, E. Togan, Y. Chu, M. Markham, D. J. Twitchen, A. S. Zibrov, A. Kubanek, and M. D. Lukin, arXiv:1112.3975v1.   

Discrimination of one and two-photon effects in electromagnetically induced transparency for ladder-type three-level atoms

We present a theoretical study of complete discrimination of the effects of one-photon, two-photon, and their combination in electromagnetically induced transparency for a ladder-type three-level noncycling (or cycling) atomic system. By considering the interaction routes of the coupling and probe photons, we are able to completely discriminate the pure one-photon and pure two-photon effects. We show that the narrow EIT spectrum results from the pure two-photon effect, whereas the relatively broad spectrum results from the terms of pure one-photon and combination effects.   

Control of Spectrally-Manifested Decoherence in Giant Rabi Sidebands

We study the broadband Rabi oscillations supported by excited states of oxygen atoms in a laser-generated microplasma. The dynamic Rabi sidebands show characteristic fringe patterns of spatial-spectral interference. The variable contrast of these patterns is determined by decoherence phenomena in the nonequilibrium underdense microplasma channel, with corresponding decoherence times in the range of 750 fs to 3 ps. We have determined the decoherence rate as a function of the pump pulse intensity and the pump-probe delay time. The rate increases with the pump laser intensity and decreases with the delay, in good agreement with model calculations, revealing that electron scattering dominates the dynamics for the subnanosecond relaxation processes. The results provide insight into both the behavior of the transient effective two-state systems and the evolution of the characteristics of the laser-generated microplasma.   

A single-atom quantum memory

A prerequisite for the realization of quantum networks is a coherent and reversible interface between flying and stationary qubits. So far, most experiments have been based on the exchange of information between photons and collective atomic excitations. A promising alternative is the development of an interface between single photons and a single atom, employing an optical cavity to achieve sufficient coupling strength. This approach has fundamental advantages, as it allows for the individual manipulation of the atomic qubit and the implementation of a nondestructive heralding scheme based on a measurement of the atomic hyperfine state. In our experiment, a single rubidium atom is trapped inside a cavity in the intermediate coupling regime of cavity QED. The storage of a photon impinging onto the system is achieved by a stimulated Raman adiabatic passage mediated by an appropriate control laser pulse driving the atom. The polarization state of the photon is unambiguously mapped onto the internal Zeeman state of the atom. After a variable storage time, the atomic state is read out by producing a single photon, thereby recreating the initial polarization state.   

Quantum information processing between different atomic ions

There is increasing interest in utilizing and combining the advantages of different quantum systems. Here, we discuss the experimental generation of entanglement between the quantum states of different atomic ions through the Coulomb interaction at the same linear radio-frequency trap. This scheme would be extended to implement the teleportation of quantum information from one kind of atom to the other. Moreover, the hybrid system of trapped ions is expected to play an essential role in the realization of a large quantum system, where a quantum state of one species is used for quantum operation and that of the other is for the cooling and stabilization of the whole ion chain. Finally, we will report the experimental progress on building the hybrid trapped ion system.   

Improved ion addressing in surface electrode traps using compensating sequences

Several proposed quantum processor architectures require precise control over the intensity, duration, and spatial alignment of laser pulses. In particular, single-ion laser addressing in quantum registers composed of tightly-spaced ion chains is sensitive to errors introduced by pointing instabilities and by the finite beam waist. Compensating pulse sequences may relax these precision requirements by producing accurate gates in the presence of unknown systematic errors. Here we report on experimental progress in the suppression of systematic errors in the control of $^{40}$Ca$^{+}$ ions in a microfabricated surface electrode trap. Further, we discuss other systems where compensating sequences may be used to produce accurate gates in the presence of control errors.   

2D Holographic optical lattices for single atoms manipulation

Two-dimensional lattices of single atoms are a promising environment allowing fine control of the atomic interactions in a mesoscopic ensemble. We propose an experiment to study the long range dipole-dipole interactions in the system working in the Rydberg blockade regime. The versatility of holographically generated 2D arrays of single atoms should allow us to achieve arbitrary geometries as well as site-to-site addressability, thus enabling the tunability of the interactions within the system.   

Spectroscopy and Thermometry of Drumhead Modes in a Mesoscopic Trapped-Ion Crystal using Entanglement

Studies of quantum mechanics at intermediate scales between microscopic and mesoscopic regimes have recently focused on the observation of quantum coherent phenomena in optomechanical systems. We demonstrate spectroscopy and thermometry of individual motional modes in a mesoscopic 2D ion array using entanglement-induced decoherence as a method of transduction. Our system is a $\sim $400 $\mu $m-diameter planar crystal of several hundred $^{9}$Be$^{+}$ ions exhibiting complex drumhead modes in the confining potential of a Penning trap. Exploiting precise control over the $^{9}$Be$^{+}$ valence electron spins, we apply a homogeneous spin-dependent optical dipole force to excite arbitrary transverse modes with an effective wavelength approaching the interparticle spacing ($\sim $20 $\mu $m). Center-of-mass displacements of $\sim $120 pm are detected via entanglement of spin and motional degrees of freedom.   

Quantum entanglement in helium-like ions

Recently, there have been considerable interests to investigate quantum entanglement in two-electron atoms [1-3]. Here we investigate quantum entanglement for the ground and excited states of helium-like ions using correlated wave functions, concentrating on the particle-particle entanglement coming from the continuous spatial degrees of freedom. We use the two-electron wave functions constructed by employing $B$-spline basis to calculate the linear entropy of the reduced density matrix $L=1-Tr_A (\rho _A^2 )$ as a measure of the spatial entanglement. Here$\rho _A =Tr_B (\left| \varphi \right\rangle _{AB} { }_{AB}\left\langle \varphi \right|)$ is the one-electron reduced density matrix obtained after tracing the two-electron density matrix over the degrees of freedom of the other electron. We have investigated the spatial entanglement for the helium-like systems with $Z$=1 to $Z$=10. For the helium atoms (Z=2), we have calculated the linear entropy for the ground state and the 1$s$n$s ^{1}S^{e}$ (n=2-10) excited states. Results are compared with other calculations [1-3]. \\[4pt] [1] J. P. Coe and I. D'Amico, \textit{J. Phys.: Conf. Ser.} \textbf{254}, 012010 (2010) \\[0pt] [2] D. Manzano \textit{et. al.}, \textit{J. Phys. A: Math. Theor.} \textbf{43}, 275301 (2010) \\[0pt] [3] J. S. Dehesa \textit{et. al.}, \textit{J. Phys. B}\textbf{ 45}, 015504 (2012)   

Ion traps for quantum information and simulation at ETH

We are developing two new experimental setups for quantum information processing, simulation and state engineering with trapped atomic ions. The systems are designed to simultaneously trap both beryllium and calcium ions. The first system comprises a segmented linear Paul trap which will be run at room temperature. The second consists of a micro-fabricated surface trap which will operate at 4 Kelvin.   

Using optical pulse shaping to entangle individual ions in a chain by coupling to multiple motional modes

We present progress in an anharmonic linear trap that produces a uniformly-spaced chain of $^{171}$Yb$^{+}$ ions that allows for individual optical addressing. When 355 nm laser beams are directed to the target ions, Raman transitions can be driven to couple ion qubit states through their collective transverse motional modes [1]. By optimizing the parameters of the applied laser pulse sequences, simultaneous coupling to multiple modes of motion may allow for high gate fidelity while increasing the gate speed [2]. Here, we show simulations that optimize the intensities, duration, and detuning of the laser pulses as well as our preliminary results for implementing this scheme. \\[4pt] [1] G.-D. Lin, et al., \textit{Europhys. Lett.} \textbf{86}, 60004 (2009)\\[0pt] [2] S-L. Zhu, et al., \textit{Europhys. Lett.} \textbf{73}, 485491 (2006)   

BEC magnetometry as a probe of hybrid quantum systems

We describe our progress towards realization of a hybrid quantum system consisting of a Bose Condensate magnetically coupled to a micromechanical oscillator. Due to the presence of a magnetic domain on the oscillator, the micromotion of the oscillator results in a periodically varying Zeeman shift that we measure using non-destructive imaging [1]. We estimate the sensitivity of the position readout to be comparable to the zero-point motion of the oscillator. We also outline prospects of achieving the strong-coupling limit of this BEC-membrane system to enable sympathetic cooling and the creation of non-classical states of this mechanical device [2]. In order to achieve this strong-coupling limit, we are investigating both cavity-enhanced schemes as well as coupling the BEC to a graphene membrane whose mass is comparable to that of the atomic gas. \\[4pt] [1] M. Vengalattore {\em et al}, Phys. Rev. Lett. \textbf{98}, 200801 (2007);\\[0pt] [2] S. Singh {\em et al}, ``Quantifying measurement back-action on a macroscopic object: BEC magnetometry on mechanical oscillators.'' Phys. Rev. A {\bf 84}, 023841 (2011).   

Electrically guided continuous supersonic beams of polar molecules from a cryogenic buffer-gas source

In order to obtain dense samples of internally and translationally cold polar molecules, we use the method of buffer-gas cooling [1], combined with supersonic expansion. We have demonstrated that when the cryogenic buffer-gas cell is operated in a supersonic regime, molecular fluxes are hydrodynamically enhanced by up to two orders of magnitude. Meanwhile, the translational velocity profile of the output molecular beam is cooled to beyond Mach number 6 via supersonic expansion. Due to the cryogenic cell temperature, the forward velocity of the supersonic molecular beam is below $190\,$m/s. The low-field-seeking molecules in the so-produced continuous supersonic beam are selected via quadrupole electric guiding [2] and transfered to further experiments. Such high-flux guided continuous supersonic beams from a cryogenic reservoir provide a promising source of polar molecules amenable to deceleration and further cooling.\\[4pt] [1] L.D. van Buuren {\sl et al.}, Phys. Rev. Lett. \textbf{102}, 033001 (2009)\\[0pt] [2] S.A. Rangwala {\sl et al.}, Phys. Rev. A \textbf{67}, 043406 (2003)   

Long lived dipolar molecules in optical lattices

Ultracold polar molecules in the quantum degenerate regime allow for the realization of quantum systems with long-range, spatially anisotropic interactions. Ultracold fermionic ground-state KRb molecules are created in a three-dimensional optical lattice, where the molecules are shielded from chemically reactive collisions. Lifetimes of around 25 seconds are observed, limited by off-resonant light scattering from the lattice laser. With polar molecules confined in a 3D lattice, we can remove all remaining atoms using resonant light. By reversing the STIRAP process, we recreate Feshbach molecules in a purified 3D lattice, resulting in long lifetimes of up to 20 seconds for Feshbach molecules, limited also by only light scattering. In order to create a colder, denser molecular gas, we have recently implemented a species selective dipole trap that allows us to tune the relative size and position of the K and Rb clouds.   

Cold Rydberg atoms in a CO$_{2}$ optical dipole trap

There has been increasing interest in cold Rydberg atoms over the last several years. The primary reason for this attention is that interactions between Rydberg atoms are strong and lead to many interesting and useful phenomena, which require high atomic density samples. In this work, we have built an experimental setup to investigate cold Rydberg atom collision in a CO$_{2}$ optical dipole trap. Briefly, we have loaded a Rb standard magneto-optical trap from an atomic vapor provided by a dispenser. Then we turn on 100W CO$_{2}$ dipole trap and we apply a loading phase, in which the repumper light intensity is reduced and the trapping frequency is detuned to the red. After this phase, the trapping and repumper laser beams are turned off and we wait 100ms for the atoms, that were not trapped, to fall off the dipole trap region due to gravity. Finally, we turn off the dipole trap and excite the Rydberg state using a two photon transition. The Rydberg atoms are detected using pulsed field ionization technique. During the presentation we shall present preliminary results involving collisions between nD states.   

Cold Rydberg atoms in circular states

Circular-state Rydberg atoms are interesting in that they exhibit a unique combination of extraordinary properties; long lifetimes ($\sim$$n^{5}$), large magnetic moments ($l=|m|=n-1$) and no first order Stark shift. Circular states have found applications in cavity quantum electrodynamics and precision measurements [1,2], among other studies. In this work we present the production of circular states in an atom trapping apparatus using an adiabatic state-switching method (the crossed-field method [3]). To date, we have observed lifetimes of adiabatically prepared states of several milliseconds. Their relatively large ionization electric fields have been verified by time-of-flight signatures of ion trajectories. We intend to explore the magnetic trapping of circular state Rydberg atoms, as well as their production and interaction properties in ultra-cold and degenerate samples.\\[4pt] [1] P. Bertet et al., Phys. Rev. Lett., \textbf{88}, 14 (2002)\\[0pt] [2] M. Brune et al., Phys. Rev. Lett., \textbf{72}, 21 (1994)\\[0pt] [3] D. Delande and J.C. Gay, Europhys. Lett., \textbf{5}, 303-308 (1988).   

Electron temperature dependence on DC applied electric fields in ultracold plasmas

One of the features that make ultracold neutral plasmas interesting to study is the ability to create these plasmas at very low initial electron temperatures as compared to other laboratory plasma systems. In this poster, we report on our measurements of initial electron temperatures as a function of applied DC electric field. Our observations indicate that the application of such a field can raise the initial electron temperature, limiting the temperature range over which experiments can be performed unless care is taken to null the DC electric field strength in the region of space where the plasma is created.   

Redistribution of atomic population among nearly degenerate Rydberg states through dipole-dipole interactions

Ultra-cold highly-excited atoms in a magneto-optical trap are strongly coupled by the dipole-dipole interaction. Rubidium atoms that have been excited to the 32d$_{5/2}$, $|m_{j}|$ = 1/2 sublevel can exchange energy when an applied static electric field tunes the Stark states into resonance. They do so via the densely packed set of resonant interactions 32d+32d$\rightarrow$34p+30g near 0.3 V/cm. Atoms that have exchanged energy and are now in the final p and manifold states can be coupled to a resonance involving 32d$_{5/2}$, $|m_{j}|$ = 3/2 and 1/2 states, which redistributes population among the $|m_{j}|$ sublevels. We present experimental and computational studies that investigate this redistribution.   

Vibrational ground state cooling of a neutral atom in a tightly focused optical dipole trap

Recent experiments have shown that an efficient interaction between a single trapped atom and light can be established by concentrating light field at the location of the atom by focusing [1-3]. However, to fully exploit the benefits of strong focusing one has to localize the atom at the maximum of the field strength [4]. The position uncertainty due to residual kinetic energy of the atom in the dipole trap (depth $\sim 1\mathrm{mK}$) after molasses cooling is significant (few 100 nm). It limits the interaction between a focused light mode and an atom already for moderate focusing strength [2]. To address this problem we implement a Raman Sideband cooling technique, similar to the one commonly used in ion traps [5], to cool a single $^{\mathrm{87}}$Rb atom to the ground state of the trap. We have cooled the atom along the transverse trap axis (trap frequency $\nu_{\tau}=55\,\mathrm{kHz}$), to a mean vibrational state $\bar{n_{\tau}}=0.55$ and investigate the impact on atom-light interfaces.\\[4pt] [1] M. K. Tey, et al., Nature Physics {\bf 4} 924 (2008)\\[0pt] [2] M. K. Tey et. al., New J. Phys. {\bf 11}, 043011 (2009)\\[0pt] [3] S.A. Aljunid et al., PRL {\bf 103}, 153601 (2009)\\[0pt] [4] C. Teo and V. Scarani Opt. Comm. {\bf 284} 4485-4490 (2011)\\[0pt] [5] C. Monroe et al., PRL {\bf 75}, 4011 (1995)   

Occupation numbers of the harmonically trapped few-boson system

We consider a harmonically trapped dilute $N$-boson system with pairwise interactions, which are characterized by the two-body $s$-wave scattering length $a_{s}$ and the effective range $r_{e}$. We construct the one-body density matrix of the weakly-interacting $N$-boson system and calculate the condensate fraction, defined as the largest occupation number, by employing a perturbative treatment within the framework of second quantization. The condensate fraction for the harmonically trapped $N$-boson system, calculated within first order perturbation theory, is $1-(N-1)0.420004a_{s}^{2}$. Corrections of order $a_s^{3}$ and $a_s^{3}r_{e}$ are also considered. The condensate depletion induced by effective three-body interactions is identified to occur at order $a_s^{3}$. Our expression for $N=2$ is confirmed by comparing with the expansion of the exact solution [1]. Our results for $N=3$ and $4$ are compared with high precision $ab$ $initio$ calculations for Bose gases that interact through finite-range two-body model potentials. \\[4pt] [1] T. Busch, B.-G. Englert, K. Rzazewski, and M. Wilkens, Foundations of Phys. \textbf{28}, 549 (1998).   

Josephson Junctions for a BEC in a Toroidal Trap

The Josephson Effect is one of the most important consequences of superconductivity and superfluidity. It also plays a crucial role in many technological innovations, including the SQUID. Previous experimental work on creating Josephson Junctions and studying the Josephson Effect with a BEC has mostly relied on somewhat inflexible methods to create the junctions, limiting possible geometries. Here we report our work towards creating arbitrary Josephson Junction arrays based on our ``painted potential'' method for manipulating BECs. In the previous work, arbitrary potentials for a BEC, including a toroidal trap, were created by using the time averaged optical dipole potential of a 2D scanning laser beam. To implement tunneling junctions, a high resolution long distance objective was installed, allowing painting of arbitrary potentials with a resolution of 1.5 micron. One particularly interesting Josephson Junction geometry is that of a BEC in a toroidal trap with tunneling junctions, which would be analogous to a SQUID. This configuration can be used to sense rotation and create a Schr\"{o}dinger cat state of different flow states. Towards this goal, we painted two symmetric Josephson Junctions for a BEC in a toroidal trap and studied Josephson effects in this set up. In this poster we will report progress on this experiment.   

Preparation of a mixture of ultracold Cs-133 and Li-6 atoms for the study of inter- species collisions

We report experimental progress toward a Bose-Fermi mixture of Cs-133 (Boson) and Li-6 (Fermion) atoms. Based on a dual-species magneto-optical trap, we trap $10^8$ Cs atoms and $10^9$ Li atoms at temperatures of $\sim$30 $\mu$K and $\sim$300 $\mu$K, respectively. Further optical cooling, including optical molasses and degenerate Raman sideband cooling, also have been implemented to cool Cs atoms down to a temperature of 2 $\mu$K. The cooling allows us to load 2*$10^7$ Cs atoms into a crossed dipole trap. We plan to load Li atoms into a second dipole trap, which spatially separates Li atoms from Cs atoms. After evaporative cooling Li atoms down to a temperature of few $\mu$K in the second dipole trap, we will merge the two samples to study collisional properties between the two species. The collisional properties will provide essential knowledge for us to work toward achieving a degenerate quantum gas of cesium and lithium mixture. Furthermore, the result will give important information to identify Li-Cs molecular states below the continuum, from which a scalable quantum information processing can be implemented.   

Experiments with Non-Equilibrium Co- and Counter-circulating Vortices

We present an experimental study of real-time dynamics of small clusters of vortices in a trapped Bose-Einstein condensate. These dynamics have been typically understood in terms of vortex-vortex interactions and interactions between each vortex and the condensate background. We demonstrate that thermal atoms can also play an important role, and a rotating thermal cloud can be used in conjunction with established techniques to create and manipulate vortex clusters. The effect of co- and counter-rotating a thermal cloud is to move the vortices in towards or away from the center of the condensate, respectively. With this technique different configurations of vortices in the cluster can be readily achieved.   

Spinor dynamics in a $^{23}$Na Bose-Einstein condensate

Spinor Bose-Einstein condensates (BECs) are characterized by an additional internal degree of freedom, which results in a vector order parameter. In particular, this system may be used to produce an internal state matter-wave amplifier, as well as spin-squeezcd states. In order to pursue these goals it is critical to have an accurate measurement of the spin-dependent interaction energy c$_2$, which is proportional to the difference in scattering lengths a$_{F=2} $ and a$_{F=0}$. The spin-dependent interaction energy determines the ground-state structure as well as the dynamical properties of spinor condensates. A recent result used Feshbach resonance measurements in a BEC to create realistic atomic potentials for sodium and yielded a value which is approximately a factor of two larger than the only measurement in a sodium spinor condensate. Here we discuss the difficulties associated with measuring c$_2$ in sodium, as well as a revised measurement from spinor dynamics. In addition we will discuss our experiments on microwave-dressed spinor states, seeded, and unseeded matter-wave amplification.   

Atom Interferometric Holography and Arbitrary Pattern Nanolithography Using Bose-Einstein Condensates

We describe a technique where atomic interferometry along with light-shift induced, two dimensional phase imprinting with optical pulses are used to produced three dimensional holographic patterns of atoms, using a Bose-Einstein Condensate as a source. We also show how a variation of this technique can be used to realize arbitrary pattern nanolithography with a feature size as small as 2 nm. We have used the Gross-Pitaevskii equations to model the evolution of the condensate order parameter through free space as well as during interaction with the optical fields, using typical values of scattering lengths, in the absence of Feshbach resonances. In our scheme, the condensate is first split into two components in different hyperfine states, using a Raman pulse. Detuned optical pulses are then used to imprint desired phase pofiles on one or both parts of the split components. For proper choice of pulses and phase patterns, the atoms form a three-dimensional hologram or a two-dimensional pattern, upon recombination of the two parts using additional Raman pulses. These techniques could be used for nanolithography by transfering the pattern to coinage metals, or to produce various topological patterns of condensates for fundamental studies.   

Quantum degenerate Fermi and Bose gases of dysprosium

Advances in the quantum manipulation of ultracold atomic gases are opening a new frontier in the quest to better understand strongly correlated matter. By exploiting the long-range and anisotropic character of the dipole-dipole interaction, we hope to create novel forms of quantum mesophases, states of quantum soft matter intermediate between canonical states of order and disorder. Our group has recently created quantum degenerate gases of both bosonic and fermionic isotopes of dysprosium, the most magnetic atom. With this most dipolar degenerate Fermi gas yet created, we intend to investigate quantum liquid crystals, mesophases thought to exist in, e.g., high Tc cuprate superconductors.   

Universal Thermodynamics and Dimensional Crossover of a Strongly Interacting Fermi Gas

We have measured with high precision the universal thermodynamics of a unitary Fermi gas of $^6$Li atoms using a novel method that requires no fit or external thermometer. This has allowed us to observe the first direct thermodynamic signature of the superfluid transition, revealed in the compressibility, the chemical potential, the entropy, and the heat capacity. Our precision measurement of the thermodynamics provide a benchmark for many-body theories on strongly interacting fermions, relevant for problems ranging from high-$T_c$ superconductivity to the equation of state of neutron stars. In a separate experiment, we follow the evolution of fermionic pairing from three dimensions to two dimensions. Using a 1D optical lattice, we confine $^6$Li atoms into stacks of two-dimensional pancakes. The reduced dimensionality leads to a 2-body bound state even on the BCS side of a Feshbach resonance. We have measured the binding energy of such pairs across the dimensional crossover using RF spectroscopy. Surprisingly, the binding energy closely follows the theoretical prediction for two particles in vacuum.   

Inter-band dynamics in a tunable hexagonal lattice

Hexagonal lattices have recently attracted a lot of attention in the condensed matter community and beyond. Upon other intriguing features, their unique band structure exhibits Dirac cones at the corners of the Brillouin zone of the two lowest energy bands. Here, we report on the experimental observation of momentum-resolved inter-band dynamics of ultracold bosons between the two lowest Bloch bands (s- and p-band) of a hexagonal optical lattice with tunable band structure. Due to the spin-dependency of the lattice potential [1,2], a rotation of the magnetic quantization axis and the choice of the atomic spin state allow for an in-situ manipulation of the lattice structure from hexagonal to triangular geometry. It is thus possible to modify the band structure and open a gap at the Dirac cones. The loading of atoms into the excited band is achieved by a microwave transition between different spin states which in certain cases is only allowed as a result of interaction effects. We observe the time-dependent population of quasi momenta, revealing a striking influence of the existence of Dirac cones on the dynamics of atoms in the first two energy bands.\\[4pt] [1] P. Soltan-Panahi et al., Nature Physics 7, 43 (2011)\\[0pt] [2] P. Soltan-Panahi et al., Nature Physics 8, 71 (2012)   

Probing many-body physics with an optical lattice clock

Advances in ultra-stable lasers now permit sub-Hz resolution of optical atomic transitions. At this level, interactions can dominate dynamics of the interrogated atoms, even for ultracold spin-polarized fermions. Density dependent frequency shifts of the $^1S_0$ to $^3P_0$ clock transition were first observed in $^{87}$Sr [1]. Originally, this effect was attributed to s-wave interactions enabled by inhomogeneous excitations [2,3]. More recently, evidence for p-wave interactions was reported in $^{171}$Yb [4]. Understanding interactions in theses systems is necessary to improve clock accuracy and stability. Moreover, such an understanding will enable optical lattice clock systems to serve as quantum simulators for open, driven, strongly-interacting quantum systems at the mesoscopic scale. We present a comprehensive evaluation and understanding of the interactions present in a $^{87}$Sr optical lattice clock system under various conditions using a mean-field theory. The regime in which only a genuine many-body treatment can properly describe our system is within immediate experimental reach.\\[4pt] [1] G. Campbell et al., Science 324, 360 (2009). [2] A. M. Rey et al., PRL 103, 260402 (2009). [3] K. Gibble, PRL 103, 113202 (2009). [4] N. D. Lemke et al., PRL 107, 103902 (2011).   

Dynamics of interacting fermions in optical lattices

Quantum gases in optical lattices offer a wide range of applications for quantum simulation due to fully tunable lattice and atomic interaction parameters. In particular fermions are of high interest due to their resemblance with conventional solid state systems. In this poster, we present results on ultracold fermionic quantum gases of $^{40}$K in optical lattices. We investigate the excitation spectrum with full momentum resolution and resolve an interaction-induced shift of the band structure. The excited particle-hole pairs show confinement-induced higher orbital dynamics in good agreement with a single particle model. To tune the interaction between the fermions, we explore Feshbach resonances in different binary mixtures. We study stable or unstable mixtures and observe a variety of resonances in good agreement with calculations. Our results open new perspectives to study dynamical properties of interacting Fermi spin-mixtures in lattice systems.   

Superfluidity of Bosons in Optical lattices with Spin-Orbit coupling

Recent experimental and theoretical work has explored artificial spin-orbit coupling induced among two species of boson. Here we examine superfluidity of a cold gas of bosons with spin-orbit coupling in a periodic optical lattice, in the presence of additional short-range interactions. We compute the density distribution after free expansion from the lattice as a probe of superfluidity, and phase transitions, of the trapped gas.   

Probing the 1D-3D Crossover of a Spin-Imbalanced Fermi Gas

We have previously mapped the phase diagram of a 1D spin-imbalanced Fermi gas by confining the atoms in an array of tubes using a 2D optical lattice.\footnote{Y.A. Liao et al., Nature 467, 567 (2010).} Within each tube we observed separation of the atoms into a partially polarized superfluid core and fully paired or fully polarized wings (depending on the spin polarization). In 3D, the phase separation is inverted, such that the cloud center is fully paired.\footnote{G. B. Partridge et al., Science 311, 503 (2006); Y. Shin et al., Phys. Rev. Lett. 97, 030401 (2006).} We investigate the transition from a 1D to 3D gas by smoothly varying the lattice depth which changes the tunneling between the tubes. This allows us to study how the spin density changes as a function of inter-tube coupling. By varying the lattice depth quickly, we can measure the spin transport properties in a strongly interacting system. Progress will be reported.   

The realization of a tunable optical kagome lattice using ultracold atoms

We report the realization of a two-dimensional kagome lattice for ultracold $^{87}$Rb atoms by overlaying two commensurate triangular optical lattices generated by light at the wavelengths of 532 and 1064 nm. Stabilizing and tuning the relative position of the two triangular lattices, different lattice geometries including a kagome, a one-dimensional stripe, and a decorated triangular lattice are explored. We characterize these geometries using Kapitza-Dirac diffraction and by analyzing the Bloch-state composition of a superfluid released suddenly from the lattice. The tunable optical superlaatice implemented in this work offers a new way to investigate a possible superfluid (SF) to Mott insulator (MI) phase transition by tuning the lattice geometries with different number of nearest neighbors. In this poster, we report the experimental progress on the geometry-induced SF-MI phase transition between triangular and kagome lattice geometries.   

Li-7 Machine for Quantum Magnetism Experiments

A new Li-7 Bose-Einstein condensate experiment (currently under construction) will realize and probe novel magnetic phases of matter. Because of the small mass of the Li atom and tight lattice spacing, we expect to achieve a 100-fold increase in tunneling rate between lattice sites over comparable Rb-87 optical lattice emulator experiments. These improvements will allow us to access new regimes in quantum magnetic phase transitions and spin dynamics.   

Progress toward the installation of a two-dimensional accordion lattice for ultra-cold atoms

One of the benefits of using ultra-cold atoms in optical lattices to perform traditional condensed matter style experiments is the opportunity to continuously change the lattice periodicity by as much as one order of magnitude in each dimension. We have constructed a wide-range two-dimensional accordion optical lattice by steering four paraxial laser beams onto an atom cloud using a single large annular lens.\footnote{L. Fallani et al., Opt. Express 13, 4303-4313 (2005).}$^,$\footnote{T.C. Li et al., Opt. Express 16, 5465-5470 (2008).}$^,$\footnote{R.A. Williams et al., Opt. Express 16, 16977-16983.} The device has been aligned and bench tested without atoms. It is now being installed in an apparatus for producing $^{87}$Rb Bose-Einstein condensates and artificial magnetic fields. We present preliminary data on the performance of the device with atoms.   

The impact of spatial correlation on the tunneling dynamics of few-boson mixtures in a combined triple well and harmonic trap

We investigate the tunneling properties of a two-species few-boson mixture in a one-dimensional triple well and harmonic trap. The mixture is prepared in an initial state with a strong spatial correlation for one species and a complete localization for the other species. We observe a correlation-induced tunneling process in the weak interspecies interaction regime. The onset of the interspecies interaction disturbes the spatial correlation of one species and induces tunneling among the correlated wells. The corresponding tunneling properties can be controlled by the spatial correlations with an underlying mechanism which is inherently different from the well known resonant tunneling process. We also observe the correlated tunneling of both species in the intermediate interspecies interaction regime and the tunneling via higher band states for strong interactions.   

Nonequilibrium Dynamics of Interacting Two Particle in Driven Cold Atomic System

We investigate the nonequilibrium fluctuational dynamics in the dynamic bistable state which is based on the parametrically modulated cold atomic system. In the absence of interaction between atoms, each atom consider as a single nonlinear oscillator and its dynamics is described by the activation energy and most probable escape path. But if the interaction exit, system exhibit complicate cooperative dynamics which is hard to deal with. We simulate the interacting two particle system for the model system of the interacting many atom system. In our work, the interaction has the form $f_{ij}=-f_{sh}{\rm sgn}[z_i-z_j]$ which describe the effective attractive interaction called ``shadow force'' in magneto-optical trap. The simulation results show clear evidence that two particle correlation grows as the interaction strength increases below the certain value. This is closely related to the spontaneous symmetry breaking transition in the parametrically modulated cold atomic system.   

Fractional Quantum Hall Effect of lossy Rydberg Dark-State Polaritons

Dark-state-polaritons (DSP) are bosonic quasiparticles arising in the interaction of light with 3-level atoms under conditions of electromagnetically induced transparency (EIT). When exposed to a strong artificial magnetic field, they can enter the lowest Landau level regime. With additional long range interactions, as realized e.g. when the 3-level atom contains a Rydberg-excited state, DSPs are natural candidates for a realization of the bosonic fractional quantum Hall effect. Besides their high controllability, they offer the possibility to examine open quantum Hall systems. We show how highly-correlated quantum Hall states of DSPs can be prepared, making use of nonlinear polariton losses. The possibility of realizing these states as stationary states of open systems is investigated. We propose a realistic quantum-optical setup, and show that different fractional quantum Hall states can be prepared, manipulated and observed. Numerical and analytical results for the excitation gaps of the $\nu=1/2p$ Laughlin states are presented.   

Detecting FFLO Pairs in a 1D Spin-Polarized Fermi Gas by Time-of-Flight Expansion

We previously reported the experimental phase diagram of a 1D spin-imbalanced Fermi gas consisting of ultracold $^6$Li atoms prepared in two unequally-populated hyperfine sublevels \footnote{Y. A. Liao \textit{et al}., Nature \textbf{467}, 567 (2010).}. This system exhibits three phases: a uniformly paired phase, a fully-polarized phase consisting of only spin-up atoms, and a partially-polarized phase that is predicted to be the elusive FFLO superfluid. The FFLO state accommodates the mismatched Fermi surfaces by forming atom pairs with nonzero center-of-mass momentum, which we aim to directly characterize via time-of-flight expansion imaging. We confine the atoms in an array of 1D tubes formed from a 2D optical lattice. A blue-detuned anti-trapping laser beam will be applied to exactly cancel the axial harmonic confinement, allowing the atoms to freely expand in 1D. We will report the progress of our experiment.   

Quantum Calculations of Ultracold Molecule Formation by Nanosecond-Timescale Frequency-Chirped Pulses

We report on the results of quantum calculations of $^{87}$Rb$_{2}$ formation from ultracold atoms by pulses of frequency-chirped light on the nanosecond timescale. This time-dependent photoassociation is modeled by following the dynamics of the collisional wave functions on both ground-state and excited-state potentials in the presence of the chirped light. Because of the relatively long time scales involved, spontaneous emission from the excited state must be accounted for. Results of the calculations are compared to recent measurements made with 40 ns FWHM Gaussian pulses and chirps that sweep 1 GHz in 100 ns. Dependencies on pulse intensity and chirp direction will be presented. This work is supported by DOE.   

Towards Photoassociation and Ultracold Collisions in Cs/K trap

We present our setup and recent results in simultaneous trapping of potassium and cesium atoms in a mixed MOT. Our setup is based on diode lasers and a tapered amplifier for producing all trapping and repumping beam frequencies. The beam geometry allows for optimal overlap of two ultracold atom clouds, necessary for studying ultracold collisions and photoassociation. Fluorescence and trap-loss detection is used for both studies. We outline mechanism for creating and detecting deeply bound $X^{1}\Sigma^{+}$ ground state $KCs$ molecules, and discuss particular characteristic of ultracold $KCs$.   

Cold and ultracold H$_2$-H$_2$ collisions on high accuracy ab initio potentials

We report quantum calculations of rovibrational transitions in H$_2$ + H$_2$ collisions on different ab initio potential surfaces (PESs). The PESs employed include the six-dimensional interaction potential of Hinde [1] and a hybrid potential constructed from the Hinde potential and the high accuracy 4-dimensional PES of Patkowski et al. [2]. Results show that vibrational relaxation cross sections are sensitive to details of the potentials at low energies but the sensitivity is significantly suppressed for quasiresonant transitions that involve small energy gaps and that conserve the total rotational angular momentum of the colliding molecules. Additionally, we present results for H$_2(v=2)$ + H$_2(v = 0)$ collisions and explore competition between vibration-vibration (VV) transfer leading to H$_2(v=1)$ +H$_2(v=1)$ products and vibration-translation (VT) transfer yielding H$_2(v=1)$ + H$_2(v=0)$ products. Results show that the VV process dominates over the VT process, in agreement with available experimental data. [1] Robert J. Hinde, J. Chem. Phys. {\bf 128}, 154308 (2008). [2] K. Patkowski, W. Cencek, P.Jankowski, K. Szalewicz, J. B. Mehl, G. Garberoglio, and A. H. Harvey, J. Chem. Phys. {\bf 129}, 094304 (2008).   

Analytic coupled channel calculation of ultracold three-body collision rates

We analyze three-body recombination for positive two-body $s$-wave scattering lengths. Using the adiabatic hyperspherical representation as a starting point, we introduce coupling between the three-body continuum and the weakly bound diatom plus atom channel in the vicinity of $R\sim a$---the location where rigorous calculations have shown the coupling to peak~[1]. In order to model loss to deeply bound diatom channels, we introduce a complex short-range $K$-matrix. Analytic expressions for the loss rates are derived and we recover the behavior found previously~[2], including the overall $a^4$ scaling for identical bosons as well as the log-periodic modulation due to Efimov physics. Our formulation permits straightforward extensions to other symmetries and higher energies. \\[4pt] [1] J.~P.~D'Incao and B.~D.~Esry, Phys.~Rev.~A 72, 032710 (2005) \newline [2] B.~D.~Esry, C.~H.~Greene, and J.~P.~Burke, Jr., Phys.~Rev.~Lett. 83, 1751 (1999).   

Theoretical and Experimental evidence for the observation of trilobite states in Cs

A novel binding mechanism arises from the attractive, low-energy scattering of a Rydberg electron from a neighboring ground state atom. The states formed by this binding mechanism are referred to as trilobite or trilobite-like states. A primary difference between the trilobite and trilobite-like states is the angular momentum of the Rydberg atom, which is dominated by an s-wave Rydberg orbit. The larger angular momentum of trilobite states can change the properties of the molecules that form. For example, large $l$ trilobite molecules are predicted to have giant, body-fixed permanent dipole moments ($\sim 1 $kD). Trilobite-like states were observed in 2009 in Rb [1]. We present experimental evidence for trilobite molecules formed as a result of state mixing between the $nS$ and $(n-4)\ge F$ states in Cs, due to the small non-integer quantum defects in the Cs s state, and compare the observation with theoretical results. \\[4pt] [1] V. Bendkowsky et al. Nature 458, 1005 (2009)   

Universal relations in ultracold three-body observables associated with Efimov physics

We explore universal aspects in homonuclear and heteronuclear three-body systems displaying the Efimov effect using the adiabatic hyperspherical representation. The existence of repulsive barrier in the three-body adiabatic potentials prevent atoms to approach small distances and, consequently, to access the region where the details of the interactions are important. As a result many of the properties of the system becomes universal. Here, we study the universal relation between the position of Efimov resonances for positive and negative scattering lengths with the goal of understanding current discrepancies between theory and experiment.   

Ultracold collisions properties of two dipoles in a Fermi sea

We investigate the low-energy scattering properties of two bosonic dipoles in the presence of a Fermi sea. The interaction between each dipole and the Fermi sea gives rise to an induced potential between the dipoles which is oscillatory, isotropic, and (approximately) bounded by $1/r^3$. We numerically investigate the momentum dependence of the low-energy s-wave phase shift. The presence of the Fermi sea adds a potential experimental control in few-body phenomena.   

Atom trapping laboratory for upper level undergraduate students

We present an overview of experiments covered in two semester-length laboratory courses dedicated to laser spectroscopy and atom trapping. These courses constitute a powerful approach for teaching experimental physics in a manner that is both contemporary and capable of providing the background and skills relevant to a variety of research laboratories. The courses are designed to be accessible for all undergraduate streams in physics and applied physics as well as incoming graduate students. In the introductory course, students carry out several experiments in atomic and laser physics. In a follow up course, students trap atoms in a magneto-optical trap and carry out preliminary investigations of the properties of laser cooled atoms based on the expertise acquired in the first course. We discuss details of experiments, impact, possible course formats, budgetary requirements, and challenges related to long-term maintenance. The experiments described here have operated reliably for over five years.   

Polarization Effects in STIRAP Between Triplet He States

We studied the effect of laser polarization on the excitation of helium atoms from the metastable 2$^3$S state to Rydberg $n$S states via the intermediate 3$^3$P states. For STIRAP, an infrared laser connects the $3^3$P$_{2,1,0}$ and $n$S levels, and then $389$ nm uv light drives the $2^3$S$_1$ to $3^3$P$_{2,1,0}$ transition. The light polarizations determine the nature of the couplings between the different Zeeman sublevels, and interference may arise in those different excitation paths. Rydberg atoms are suitable for this experiment because of their relatively long life times so the $n$S populations are readily measured. The correspondence between polarizations and $n$S level populations have been studied both theoretically and experimentally, and the interference patterns are revealed.   

Saturated absorption spectroscopy of Ho atoms for laser cooling experiments

We present spectroscopy measurements of the 410.5 nm cooling transition in Ho using a source based on a frequency doubled diode laser. The laser is locked to the Ho $F=11 - F'=12$ transition between resolved hyperfine states using saturated absorption spectroscopy in a hollow cathode cell. Progress towards using the 410.5 nm source for laser cooling and trapping of Ho atoms generated in an effusion cell will be presented.   

Experimental apparatus for ultracold Rb-K mixture

We describe our experimental apparatus for producing ultracold 87Rb and 40K mixture. Double MOT(Magneto-Optical trap) system consisting of 2-dimensional MOT, and 3-dimensional MOT is employed in our system. The 2-dimensional MOT produces an intense cold atomic beam utilizing a two-color pushing laser beam that could adjust the mean velocity of the atomic beam. The Rb atoms from 2D MOT are collected in the 3D MOT for production of BEC(Bose-Einstein Condensate). After MOT compression and polarization gradient cooling, atoms are captured in the QUIC(Quadrupole Ioffe Configuration) magnetic trap for the rf induced evaporative cooling. Our system produces pure condensates with the atoms number of 10$^5$ range.   

Toward Laser Cooling without Spontaneous Emission

The bichromatic force (BF) can be used for laser cooling in the absence of closed cycling transitions because it can cool without spontaneous emission\footnote{H. Metcalf, \textit{Phys. Rev. A} \textbf{77}, 061401 (2008).} (SE). Previous BF experiments have used transitions with long characteristic cooling times \mbox{$\tau_c = \Delta p/F \sim \pi /4 \omega_r$} thereby allowing many SE events. We are building an experiment using the $2^3S_1 \rightarrow 3^3P_2$ transition at $\lambda$ = 389 nm in He because its large recoil frequency $\omega_r = 2 \pi \times 330$ kHz makes $\tau_c$ comparable to the $3^3P_2$ lifetime $\sim$100 ns so that there would be minimal SE events during $\tau_c$. We will describe our experiment as well as studies of the density matrix solutions for the force integrated over short interaction times accounting for atomic velocity changes. These solutions are used for Monte Carlo simulations of experimental conditions incorporating He beam trajectories and velocity distributions.   

Spin Exchange Cooling in an Ultracold $^{85/87}$Rb Mixture

Through the combination of the application of a magnetic field and using optical pumping for spin polarization, it is possible to use spin-exchange collisions to cool a mixture of ultracold $^{85}$Rb and $^{87}$Rb atoms trapped in an optical trap. This cooling can be accomplished without requiring the intrinsic loss of atoms from the gas. The use of two isotopes is also advantageous in mitigating reabsorption of the optical pumping light in the gas, a significant limitation in non-evaporative cooling. We report on our most recent implementation of this cooling technique and discuss the cooling performance with improved initial atom density, optical trap confinement, microwave coupling for optical pumping, and optical pumping scheme.   

Magic wavelengths and other properties of Li for optical cooling and trapping

Using first-principles calculations, we identify magic wavelengths $\lambda$ for the $2s-2p_{1/2}$, $2s-2p_{3/2}$, $2s-3p_{1/2}$, and $2s-2p_{3/2}$ transitions in Li. The $ns$ and $np_j$ atomic levels have the same ac Stark shifts at the corresponding magic wavelength, which facilitates state-insensitive optical cooling and trapping. Possible differences between the positions of magic wavelengths in $^6$Li and $^7$Li are investigated. Our approach uses high-precision, relativistic all-order method in which all single, double, and partial triple excitations of the Dirac-Fock wave functions are included to all orders of perturbation theory. Recommended values are provided for a large number of Li electric-dipole matrix elements. Trends of dynamic polarizabilities of the ground and $2p_j$, $3s$, and $3p_j$ states are investigated. Uncertainties of all recommended values are estimated. Implications of our results for optical cooling and trapping of Li are discussed.   

Simulations of streamers in N$_{2}$:O$_{2}$ and N$_{2}$:CO$_{2}$ mixtures using highly accurate transport data

Streamers are growing filaments of weakly-ionized non-stationary plasma produced by an ionization front that moves through non-ionized matter. They can emerge in a wide variety of gases and pressures. Previous experiments and numerical simulations have shown that streamer properties such as velocity and diameter are remarkably insensitive to changes in gas composition. In our numerical simulations, we use a fluid model to compute the densities of charged particles, obeying drift-diffusion-reaction equations. Previously, we have used a constant, empirical value for the diffusion and mobility coefficients in these simulations. Using a multi term theory for solving the Boltzmann equation, we now have highly accurate transport data, which we have used to simulate streamers in N$_{2}$:O$_{2}$ and N$_{2}$:CO$_{2}$ mixtures to compare with our previous results. It is found that the simulated streamers are more sensitive to the transport data than they are to the gas composition.   

Precise determination of atomic g-factor ratios from a dual isotope magneto-optical trap

We demonstrate a technique, for carrying out precise measurements of atomic g-factor ratios, which relies on measurements of Larmor oscillations from coherences between magnetic sublevels in the ground states of $^{85}$Rb and $^{87}$Rb atoms confined in a dual isotope magneto-optical trap. We show that a measurement of $g^{(87)}_{F} /g^{(85)}_{F}$ with a resolution of 0.69 parts per $10^6$ is possible by recording the ratio of Larmor frequencies in the presence of a constant magnetic field. This represents the most precise single measurement of $g^{(87)}_{F} /g^{(85)}_{F}$ without correcting for systematic effects (I. Chan et al., Phys. Rev. A \textbf{84}, 032509 (2011)).   

A Search for Nonstandard Neutron Spin Interactions using Dual Species Xenon Nuclear Magnetic Resonance

NMR measurements using polarized noble gases can constrain possible exotic spin-dependent interactions involving nucleons. A differential measurement insensitive to magnetic field fluctuations can be performed using a mixture of two polarized species with different ratios of nucleon spin to magnetic moment. We used the NMR cell test station at Northrop Grumman Corporation (NGC) (developed to evaluate dual species xenon vapor cells for the Nuclear Magnetic Resonance Gyroscope) to search for NMR frequency shifts of xenon-129 and xenon-131 when a non-magnetic zirconia rod is modulated near the NMR cell. We simultaneously excited both Xe isotopes and detected free-induction-decay transients.~In combination with theoretical calculations of the neutron spin contribution to the nuclear angular momentum, the measurements put a new upper bound on possible monopole-dipole interactions of the neutron for ranges around 1mm. This work is supported by the NGC Internal Research and Development (IRAD) funding, the Department of Energy, and the NSF.   

Precise measurement of the scalar polarizability of $^{115}$In in an indium atomic beam

In recent years, we have pursued a series of precise atomic structure measurements in Group III elements thallium and indium in order to test recent \emph{ab initio} theory calculations in these three-valance-electron systems. We are currently completing a precision measurement of the indium scalar polarizability within the 410 nm 5P$_{1/2} \rightarrow 6S_{1/2}$ transition using a GaN semiconductor laser interacting transversely with a collimated indium atomic beam in the presence of precisely calibrated high voltage electric field. We use 100 MHz laser frequency modulation and RF lock-in detection to obtain a high-resolution absorption signal despite indium beam optical depths of $< 10^{-3}$. An in-vacuum chopper wheel modulates the atomic beam and provides further noise and background reduction. Our current level of precision produces $1\%$ statistical measurement of the Stark Shift in less than one hour of data collection. Our preliminary results for the scalar polarizability within this transition agree with a previous result,\footnote{T.R. Fowler and J. Yellin, Phys. Rev. A 1, 1006 (1970)} and we expect an eventual tenfold improvement in accuracy, providing a challenge to ongoing atomic theory calculations. Current results will be presented.   

Current Work to Improve Precision in Measurements of Helium Fine Structure

Measurements on the fine structure of the 2P state of the helium atom show good agreement, 0.22(30) kHz, between the most recent theory (complete m$\alpha ^{7}$ evaluation with 0.02 kHz numerical uncertainty) and experiment. Among other things, this result could be used to give a value for the fine structure constant alpha with a 5 ppb uncertainty. However, some of the uncalculated m$\alpha ^{8}$ terms (those with large Z scaling), might contribute as much as 1.2 kHz, limiting the precision and thus calling for further theoretical work. For application to a precision alpha determination, an order of magnitude experimental improvement is desirable, given the electron g factor (0.4 ppb) and photon recoil (0.7 ppb) uncertainties. To this end we are currently addressing a major source of experimental uncertainty in our previous measurements by incorporating a convenient and reliable tunable laser frequency selector.\footnote{Marc Smiciklas and David Shiner, Phys. Rev. Lett. 105, 123001 (2010) } An approach using a fiber grating and fiber circulator will be discussed.   

Progress towards a new microwave measurement of the hydrogen n=2 Lamb shift: a measurement of the proton charge radius

We propose to make a more precise measurement of the atomic hydrogen n=2 Lamb shift using the Ramsey method of separated oscillatory fields. This new measurement (with an anticipated uncertainty of 2 kHz -- 5 times more accurate than the 1981 measurement of Lundeen and Pipkin), along with existing precise atomic theory calculations, will allow for a new determination of the proton charge radius to an accuracy of 0.6 percent. The measurement will shed light on the 5$\sigma$ discrepancy between proton radius recently obtained from muonic hydrogen [Pohl, et al, Nature 466, 213 (2010)] and the CODATA value.   

Atomic properties of Ra for a future EDM measurement

Searches for non-zero permanent electric-dipole moments (EDM) of particles, atoms, and molecules represent remarkable opportunity to probe new physics beyond the standard model. The EDMs arise from the violations of both parity and time-reversal invariance. Atomic EDMs caused by the nuclear parity and time invariance violating effects are enhanced in certain diamagnetic atoms, such as $^{199}$Hg and $^{225}$Ra. For the latter, there is additional enhancement due to close states of opposite parity and the large nuclear charge Z [Dzuba et al., PRA 61, 062509 (2000)]. The search for EDM in $^{225}$Ra is presently underway [Holt et al., Nucl. Phys. A 844, 53c (2010)]. Few atomic properties of Ra are experimentally known. In this work, we carry out a systematic study of Ra atomic properties of interest to the EDM search using recently developed relativistic \textit{ab initio} method [Safronova at. al, PRA 80, 012516 (2009)] that allows to accurately treat correlation corrections in atoms with a few valence electrons. This method combines the coupled-cluster method, that yielded excellent results for monovalent systems, with the configuration-interaction approach. We have calculated energy levels, electric-dipole matrix elements, lifetimes, hyperfine constants, and polarizabilities.   

Development of 171Yb optical lattice clock at KRISS

We measured the absolute frequency of the optical clock transition 1S0 (F = 1/2) - 3P0 (F = 1/2) of 171Yb atoms confined in a one-dimensional optical lattice and it was determined to be 518 295 836 590 865.7 (9.2) Hz. The measured frequency was calibrated to the Coordinated Universal Time (UTC) by using an optical frequency comb of which frequency was phase-locked to a hydrogen maser as a flywheel oscillator traceable to the UTC. The magic wavelength was also measured as 394 798.48 (79) GHz. The results are in good agreement with two previous measurements of other institutes within the specified uncertainty of this work.   

Molecular Spectroscopy by Coherent Motion Detection

We are currently constructing an experiment to perform spectroscopy on single trapped molecular ions. A silicon monoxide molecular ion (SiO$^{+}$) will be co-trapped with a barium ion in a linear Paul trap. The barium ion is laser-cooled and sympathetically cools the molecular ion; rotational cooling of SiO$^{+}$ will be accomplished by P-branch optical pumping on the B-X electronic transition. The spectroscopy result of the molecular ion is mapped to the barium ion through a state-dependent coherent motional state excitation. We are particularly interested in probing rotational (microwave) or vibrational (infrared) transitions sensitive to a time-varying electron-to-proton mass ratio.   

Michelson-Morley with a Birefringent Cavity

We report on the progress of a birefringent cavity test of the isotropy of the speed of light. Previous experimental tests have constrained anisotropies in the speed of light at the level of parts in $10^{17}$ [1-2]. These experiments search for frame-dependent variations in the resonant frequencies of two orthogonally mounted optical cavities. Uncorrelated fluctuations in the cavity lengths are a significant challenge for such experiments. Our experiment uses a single dielectric-filled cavity, and measures the difference in the resonant frequency of two orthogonally polarized modes. Anisotropies in the speed of light will manifest as a frame-dependent strain on the dielectric [3-4], giving rise to a frame-dependent variation in the cavity birefringence. By making the length of each cavity mode identical, we expect that our experiment will be less sensitive to thermal cavity fluctuations. \\[4pt] [1] S. Herrmann, A. Senger, K. M\"ohle, M. Nagel, E.V. Kovalchuk and A. Peters, PRD {\bf 80,} 105011 (2009).\newline [2] Ch. Eisel, A. Yu. Nevsky, and S. Schiller, PRL {\bf 103,} 090401 (2009).\newline [3] H. M\"uller, PRD {\bf 71,} 045004 (2005).\newline [4] V.A. Kosteleck\'y and M. Mewes, PRD {\bf 80,} 015020 (2009).   

Magnetic Shield Design and Processing

Magnetic shielding is a necessary component of many sensitive instruments including those required for a wide array of atomic and molecular physics experiments and inertial instruments, but what are the critical parameters influencing the performance of the shields? How can one achieve the greatest shielding factor in a limited physical space? What are the limits to shield performance? Shield thickness, size, number of layers, distance between layers, material, and so on all have influence on the performance. Magnetic permeability alone depends on incident magnetic flux density, magnetostriction effects, shield material impurities, material microstructure, crystalline grain size, mechanical strain, skin depth effects, and shield size and thickness. Magnetic noise produced by the shields is a function of magnetic permeability, temperature, and shield thickness, electrical resistivity, and size. These phenomena and the ability to control the influence of these parameters for a given instrument will be discussed. A set of design and processing guidelines and generalized equations will be presented for the purposes of optimizing the magnetic shielding design and thereby achieving the highest possible performance from a magnetically shielded instrument.   

There is no speed barrier in the universe

In a 1972 paper we have advanced the hypothesis that there is no speed barrier in the universe and one can construct any speed from zero to infinity. We considered that the superluminal speeds do not violate the causality principle, do not produce time traveling and it is not needed infinite energy in order for a particle to travel at a speed greater than the speed of light. On September 22, 2011, Dr. Antonio Ereditato and his team at CERN has experimentally found the neutrino particles traveling at a speed greater than c, partially confirming this hypothesis.   

Economical Nanoactuator Alternatives to Lead Zirconium Titanate

This paper describes using inexpensive commercially available ceramic capacitors as a substitute for the lead containing and relatively expensive PZT based nano actuators. A sample PZT actuator is compared with actuators made from both X5R and Y5V type ceramic dielectric capacitors using white light interferometry and a spectrometer. This work is useful in that it can provide nano-motion capability to budget constrained undergraduate and graduate level research laboratories. Additionally, unlike the PZT material the alternative ceramic materials do not contain lead which is needed to create products compliant with the European Rohs (Restriction On Hazardous Substances) initiative.   

Multi-Beam Shuttering, Pulsing, and Intensity Control Using Liquid Crystals

To date, most experiments involving lasers have required space-consuming acousto-optic modulators and mechanical shutters to control the intensity of laser beams used in cold-atom experiments. To support emerging cold-atom sensors such as atomic clocks, inertial navigation units, and magnetometers these complex electro optics must be replaced with compact components that can operate in a field environment. Using liquid-crystal spatial light modulators we have demonstrated an optical component that separates a single laser source into multiple beam paths that can be independently controlled. Each beam can be shuttered with 70 dB of contrast, pulsed down to 12 us, and intensity stabilized with 150 kHz loop bandwidth. These devices operate in the wavelength range of 630-1000 nm. We will present current designs and results of the liquid crystal multi-beam shutter and how it enables complete and compact cold-atom laser systems the size of a paperback novel.   

Refractive index sensing of turbid media by differentiation of the reflectance profile: Analysis of error

Refractive index detection typically consists of a measurement of the reflectance of light from the sample surface for various angles of incidence, and determining the critical angle for total internal reflection (TIR). A commonly used technique for locating the critical angle is to differentiate the angular reflectance profile with respect to the incidence angle, and look for the point of maximum change of slope. For turbid media this differentiation technique leads to errors in refractive index measurement, which need to be accurately estimated. We show that previous attempts by other workers to calculate the error using traditional Fresnel theory yield an expression that is impossible to physically justify, and hence must be incorrect. We calculate the error using a recent model of TIR in turbid media by Calhoun, et al. (Opt. Lett. {\bf{35}}, 1224 (2010)) which departs from traditional Fresnel theory, and show that this error varies with turbidity in an expected manner. Important differences from previous work relying on traditional Fresnel theory are revealed with regard to the size of error as a function of turbidity, and the choice of polarization for minimizing error.   

Theoretical description of transverse measurements of polarization in optically-pumped Rb vapor cells

In optical pumping of alkali-metal vapors, the polarization of the atoms is typically determined by probing along the entire length of the pumping beam, resulting in an averaged value of polarization over the length of the cell. Such measurements do not give any information about spatial variations of the polarization along the pump beam axis. Using a D1 probe beam oriented perpendicular to the pumping beam, we have demonstrated a heuristic method for determining the polarization along the pump beam's axis. Adapting a previously developed theory [1], we provide an analysis of the experiment which explains why this method works. The model includes the effects of Rb density, buffer gas pressure, and pump detuning. \\[4pt] [1] E.B. Norrgard, D. Tupa, J.M. Dreiling, and T.J. Gay, Phys. Rev. A 82, 033408 (2010).   

A focused CO$_{2}$ laser beam for phase contrast electron microscopy

Phase contrast electron microscopy, in analogy to the Zernike microscopy, enables imaging of previously elusive organic or nonorganic specimens [1]. While existing physical phase plates degrade due to electron charging effects, a laser phase plate (LPP) utilizes the pondermotive potential to shift the electron phase and should offer reusability and improved longevity. The un-diffracted electrons travel through the laser beam (150 W, Apollo 150 CO$_{2}$ laser), which produces the ponderomotive potential. To increase the phase shift with the same amount of laser power, we use axicon lenses to generate Laguerre-Gaussian mode, which can be optimally focused by the parabolic mirror. To further enhance the focal intensity, we place a partial reflector at the opening of the parabolic mirror to form an optical resonator. This scheme will offer $\pi $/2 electron phase shift [1], and will enable phase contrast imaging. We present experimental demonstration of the parabolic-mirror cavity (the LPP) and the resulting electron phase shift. \\[4pt] [1] Mueller et al., New J. Phys. 12 (2010) 073011.   

Worldline Method for Electromagnetic Casimir Energies

We present our work on the generalization of the worldline method for calculating electromagnetic Casimir energies. Previously, this method has been restricted to calculations for a scalar field. Our work calculates the Casimir energy due to dispersionless, dielectric bodies with arbitrary geometries. The worldline method calculates the energy by generating an ensemble of closed space-time paths via a Monte-Carlo algorithm, and then summing up the contributions from the dielectric along each path. We will present our work on handling the convergence issues associated with the path integral, and some preliminary results comparing the method with other algorithms and known test cases.   

Characterization of a green astro-comb using a Fourier Transform Spectrometer

Searches for Earth-like exoplanets using precision stellar radial velocity (PRV) measurements require a precision and accuracy below 10 cm/s over several years. An astro-comb, the combination of a laser frequency comb with a coherent wavelength shifting mechanism (such as a doubling crystal or photonic crystal fiber) and a mode-filtering Fabry-Perot cavity (FPC), produces evenly spaced frequency markers with broad spectral coverage and is a promising approach to improved wavelength calibration for astrophysical spectrographs. The accuracy of an astro-comb relies on high-quality suppression of undesired comb lines by the FPC. Here we present a characterization of a green astro-comb using a high-resolution Fourier Transform Spectrometer (FTS) constructed in our laboratory. The FTS has an unapodized resolution of 125 MHz, which enables high resolution measurements of our 1 GHz repetition rate laser frequency comb after it has been filtered into a 20 GHz astro-comb. FTS measurements of the green astro-comb will reveal any systematic defects in our filtering process and help determine the ultimate accuracy of the astro-comb as a wavelength reference.   

Evaluation of the Sensitivity Limits of Chip-scale Atomic Magnetometers

Despite the fact that atomic DC magnetometers have reached impressive sensitivities,\footnote{J. C. Allred et al, \emph{Phys. Rev. Lett.} \textbf{89} 130801 (2002)} the fundamental limits predicted by atom and photon shot noise have not been reached. In a 1$mm^{3}$ micro fabricated vapor cell, the theoretically predicted sensitivity is about 0.7$\frac{fT}{\sqrt{Hz}}$, while about 5$\frac{fT}{\sqrt{Hz}}$ is measured experimentally.\footnote{W.C.Griffith et al, \emph{Opt. Express}, \textbf{18}, (26) 27167 (2010)} We investigate the magnetometer sensitivity by measuring the optical rotation of a linearly polarized light beam induced by a polarized hot rubidium atomic vapor. The magnetometer operates near zero magnetic field with high atomic density to suppress the spin-exchange collisions. In this poster, we discuss the noise introduced by both the pump and probe lasers, the atoms, and external sources, specifically metallic elements in the experiment. Our measurements suggest that the rubidium droplets condensed on the vapor-cell windows contribute largely to the overall noise. This study of the sensitivity limits is not only significant for the fundamental understanding of atomic magnetometry in small vapor cells but also for future applications of miniaturized atomic devices.   

A compact fiberized alkali-vapor atomic magnetometer

Alkali-vapor atomic magnetometers are among the world's most sensitive magnetic-field measuring devices, with demonstrated precisions [1] better than $1 \textrm{fT}/\sqrt{\textrm{Hz}}$ when operated in the SERF regime. All-optical magnetometers operating at finite fields require synchronous optical pumping to reinforce the precessing atomic spin polarization. Here describe a synchronously pumped magnetometer in which the vapor cell is coupled to the pump and probe optics solely by optical fibers. Tests of this device at finite field ($\sim$10 mG) and at Earth's field will be presented.\\[4pt] [1] H.~B.~Dang, A.~C.~Maloof, and M.~V.~Romalis, Appl. Phys. Lett. \textbf{97}(15), 151110.   

Powerful low-cost laser lab instrumentation using 32-bit microcontrollers and an Android tablet interface

Recently, our laboratory has developed several homemade instruments based on 16-bit microcontrollers.\footnote{E.E. Eyler, Rev. Sci. Instrum. \textbf{82}, 013105 (2011).} Since then, powerful 32-bit microcontrollers have become available, often including host-mode USB interfaces. Concurrently, Android-based tablets with high-resolution graphical displays have become commonplace. With appropriate programming, some tablets can communicate via USB, allowing them to serve as bidirectional touch-screen interfaces. I will describe ramp and timing sequence generators with resolution up to 12.5 ns that can be constructed with very little cost or effort, by making minor additions to commercial development boards. With these instruments, a graphical tablet interface is used mainly for parameter entry, but it is even more useful as a data display for applications such as laser frequency locking or signal monitoring. To minimize programming for the Android devices, my approach is to develop just a few general-purpose ``apps'' that can operate a wide range of instruments. When the USB interface is connected, the microcontroller informs the tablet of its display requirements. This arrangement can eliminate the need for dedicated computers, custom data entry units, or oscilloscopes.